Universal Serial Bus 3.0 Specification

Universal Serial Bus 3.0 Specification
Universal Serial Bus 3.0
Specification
Hewlett-Packard Company
Intel Corporation
Microsoft Corporation
NEC Corporation
ST-NXP Wireless
Texas Instruments
Revision 1.0
November 12, 2008
Universal Serial Bus 3.0 Specification, Revision 1.0
Revision History
Revision
Comments
Issue Date
1.0
Initial release.
November 12, 2008
INTELLECTUAL PROPERTY DISCLAIMER
THIS SPECIFICATION IS PROVIDED TO YOU “AS IS” WITH NO WARRANTIES WHATSOEVER, INCLUDING ANY
WARRANTY OF MERCHANTABILITY, NON-INFRINGEMENT, OR FITNESS FOR ANY PARTICULAR PURPOSE. THE
AUTHORS OF THIS SPECIFICATION DISCLAIM ALL LIABILITY, INCLUDING LIABILITY FOR INFRINGEMENT OF ANY
PROPRIETARY RIGHTS, RELATING TO USE OR IMPLEMENTATION OF INFORMATION IN THIS SPECIFICATION. THE
PROVISION OF THIS SPECIFICATION TO YOU DOES NOT PROVIDE YOU WITH ANY LICENSE, EXPRESS OR
IMPLIED, BY ESTOPPEL OR OTHERWISE, TO ANY INTELLECTUAL PROPERTY RIGHTS.
Please send comments to [email protected]
For industry information, refer to the USB Implementers Forum web page at http://www.usb.org
All product names are trademarks, registered trademarks, or servicemarks of their respective owners.
Copyright © 2007-2008, Hewlett-Packard Company, Intel Corporation, Microsoft Corporation, NEC Corporation, ST-NXP
Wireless, and Texas Instruments.
All rights reserved.
ii
Acknowledgement of USB 3.0 Technical
Contribution
Dedication
Dedicated to the memory of Brad Hosler, the impact of whose
accomplishments made the Universal Serial Bus one of the most
successful technology innovations of the Personal Computer era.
The authors of this specification would like to recognize the following people who participated in the
USB 3.0 Bus Specification technical workgroups. We would also like to acknowledge the many others
throughout the industry who provided feedback and contributed to the development of this specification.
Promoter Company Employees
Alan Berkema
Hewlett-Packard Company
Walter Fry
Hewlett-Packard Company
Anthony Hudson
Hewlett-Packard Company
David Roderick
Hewlett-Packard Company
Kok Hong Chan
Intel Corporation
Huimin Chen
Intel Corporation
Bob Dunstan
Intel Corporation
Dan Froelich
Intel Corporation
Howard Heck
Intel Corporation
Brad Hosler
Intel Corporation
John Howard
Intel Corporation
Rahman Ismail
Intel Corporation
John Keys
Intel Corporation
Yun Ling
Intel Corporation
Andy Martwick
Intel Corporation
Steve McGowan
Intel Corporation
Ramin Neshati
Intel Corporation
Duane Quiet
Intel Corporation
Jeff Ravencraft
Intel Corporation
Brad Saunders
Intel Corporation
Joe Schaefer
Intel Corporation
Sarah Sharp
Intel Corporation
Micah Sheller
Intel Corporation
Gary Solomon
Intel Corporation
Karthi Vadivelu
Intel Corporation
Clint Walker
Intel Corporation
Jim Walsh
Intel Corporation
Randy Aull
Microsoft Corporation
Fred Bhesania
Microsoft Corporation
Martin Borve
Microsoft Corporation
Jim Bovee
Microsoft Corporation
Stephen Cooper
Microsoft Corporation
Lars Giusti
Microsoft Corporation
Robbie Harris
Microsoft Corporation
iii
Universal Serial Bus 3.0 Specification, Revision 1.0
Allen Marshall
Microsoft Corporation
Kiran Muthabatulla
Microsoft Corporation
Tomas Perez-Rodriguez
Microsoft Corporation
Mukund Sankaranarayan
Microsoft Corporation
Nathan Sherman
Microsoft Corporation
Glen Slick
Microsoft Corporation
David Wooten
Microsoft Corporation
Rob Young
Microsoft Corporation
Nobuo Furuya
NEC Corporation
Hiroshi Kariya
NEC Corporation
Masami Katagiri
NEC Corporation
Yuichi Mizoguchi
NEC Corporation
Kats Nakazawa
NEC Corporation
Nobuyuki Mizukoshi
NEC Corporation
Yutaka Noguchi
NEC Corporation
Hajime Nozaki
NEC Corporation
Kenji Oguma
NEC Corporation
Satoshi Ohtani
NEC Corporation
Takanori Saeki
NEC Corporation
Eiji Sakai
NEC Corporation
Hiro Sakamoto
NEC Corporation
Hajime Sakuma
NEC Corporation
Makoto Sato
NEC Corporation
Hock Seow
NEC Corporation
"Peter" Chu Tin Teng
NEC Corporation
Yoshiyuki Tomoda
NEC Corporation
Satomi Yamauchi
NEC Corporation
Yoshiyuki Yamada
NEC Corporation
Susumu Yasuda
NEC Corporation
Alan Chang
ST-NXP Wireless
Wing Yan Chung
ST-NXP Wireless
Socol Constantin
ST-NXP Wireless
Knud Holtvoeth
NXP Semiconductors, B.V.
Linus Kerk
ST-NXP Wireless
Martin Klein
NXP Semiconductors, B.V.
Geert Knapen
NXP Semiconductors, B.V.
Chee Ee Lee
ST-NXP Wireless
Christian Paquet
NXP Semiconductors, B.V.
Veerappan Rajaram
ST-NXP Wireless
Shaun Reemeyer
ST-NXP Wireless
Dave Sroka
ST-NXP Wireless
Chee-Yen TEE
ST-NXP Wireless
Jerome Tjia
ST-NXP Wireless
Bart Vertenten
NXP Semiconductors, B.V.
Hock Meng Yeo
ST-NXP Wireless
Olivier Alavoine
Texas Instruments.
David Arciniega
Texas Instruments
Richard Baker
Texas Instruments
Sujoy Chakravarty
Texas Instruments
T. Y. Chan
Texas Instruments
iv
Romit Dasgupta
Texas Instruments.
Alex Davidson
Texas Instruments
Eric Desmarchelier
Texas Instruments
Christophe Gautier
Texas Instruments
Dan Harmon
Texas Instruments
Will Harris
Texas Instruments
Richard Hubbard
Texas Instruments
Ivo Huber
Texas Instruments
Scott Kim
Texas Instruments
Grant Ley
Texas Instruments
Karl Muth
Texas Instruments
Lee Myers
Texas Instruments
Julie Nirchi
Texas Instruments
Wes Ray
Texas Instruments
Matthew Rowley
Texas Instruments
Bill Sherry
Texas Instruments
Mitsuru Shimada
Texas Instruments
James Skidmore
Texas Instruments
Yoram Solomon
Texas Instruments.
Sue Vining
Texas Instruments
Jin-sheng Wang
Texas Instruments
Roy Wojciechowski
Texas Instruments
Contributor Company Employees
Glen Chandler
John Chen
Roger Hou
Charles Wang
Norman Wu
Steven Yang
George Yee
George Olear
Sophia Liu
William Northey
Tom Sultzer
Garry Biddle
Kuan-Yu Chen
Jason Chou
Gustavo Duenas
Bob Hall
Jiayong He
Jim Koser
Joe Ortega
Ash Raheja
James Sabo
Pei Tsao
Kevin Walker
Tsuneki Watanabe
Chong Yi
Taro Hishinuma
Kaz Ichikawa
Ryozo Koyama
Karl Kwiat
Tadashi Sakaizawa
Shinya Tono
Acon
Acon
Acon
Acon
Acon
Acon
Acon
Contech Research
Electronics Testing Center, Taiwan (ETC)
FCI
FCI
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Foxconn
Hirose Electric
Hirose Electric
Hirose Electric
Hirose Electric
Hirose Electric
Hirose Electric
v
Universal Serial Bus 3.0 Specification, Revision 1.0
Eiji Wakatsuki
Takashi Ehara
Ron Muir
Kazuhiro Saito
Hitoshi Kawamura
Takashi Kawasaki
Atsushi Nishio
Yasuhiko Shinohara
Tom Lu
Edmund Poh
Scott Sommers
Jason Squire
Dat Ba Nguyen
Jan Fahllund
Richard Petrie
Panu Ylihaavisto
Martin Furuhjelm
Julian Gorfajn
Marc Hildebrant
Tony Priborsky
Harold To
Robert Lefferts
Saleem Mohammad
Matthew Myers
Daniel Weinlader
Mike Engbretson
Thomas Grzysiewicz
Masaaki Iwasaki
Kazukiyo Osada
Hiroshi Shirai
Scott Shuey
Masaru Ueno
vi
Hirose Electric
Japan Aviation Electronics Industry Ltd. (JAE)
Japan Aviation Electronics Industry Ltd. (JAE)
Japan Aviation Electronics Industry Ltd. (JAE)
Mitsumi
Mitsumi
Mitsumi
Mitsumi
Molex Inc.
Molex Inc.
Molex Inc.
Molex Inc.
NTS/National Technical System
Nokia
Nokia
Nokia
Seagate Technology LLC
Seagate Technology LLC
Seagate Technology LLC
Seagate Technology LLC
Seagate Technology LLC
Synopsys, Inc.
Synopsys, Inc.
Synopsys, Inc.
Synopsys, Inc.
Tektronix, Inc.
Tyco Electronics
Tyco Electronics
Tyco Electronics
Tyco Electronics
Tyco Electronics
Tyco Electronics
Contents
1 Introduction ................................................................................................. 1-1
1.1
1.2
1.3
1.4
1.5
1.6
1.7
Motivation .................................................................................................................1-1
Objective of the Specification ...................................................................................1-2
Scope of the Document............................................................................................1-2
USB Product Compliance.........................................................................................1-2
Document Organization............................................................................................1-3
Design Goals............................................................................................................1-3
Related Documents..................................................................................................1-3
2 Terms and Abbreviations ........................................................................... 2-1
3 USB 3.0 Architectural Overview................................................................. 3-1
3.1
3.2
USB 3.0 System Description ....................................................................................3-1
3.1.1
USB 3.0 Physical Interface .....................................................................3-2
3.1.1.1
USB 3.0 Mechanical........................................................3-2
3.1.2
USB 3.0 Power .......................................................................................3-3
3.1.3
USB 3.0 System Configuration ...............................................................3-3
3.1.4
USB 3.0 Architecture Summary..............................................................3-3
SuperSpeed Architecture .........................................................................................3-4
3.2.1
Physical Layer ........................................................................................3-5
3.2.2
Link Layer ...............................................................................................3-6
3.2.3
Protocol Layer.........................................................................................3-7
3.2.4
Robustness.............................................................................................3-8
3.2.4.1
Error Detection ................................................................3-8
3.2.4.2
Error Handling .................................................................3-9
3.2.5
SuperSpeed Power Management...........................................................3-9
3.2.6
Devices .................................................................................................3-10
3.2.6.1
Peripheral Devices ........................................................3-10
3.2.6.2
Hubs..............................................................................3-11
3.2.7
Hosts ....................................................................................................3-12
3.2.8
Data Flow Models .................................................................................3-12
4. SuperSpeed Data Flow Model .................................................................... 4-1
4.1
4.2
4.3
4.4
Implementer Viewpoints ...........................................................................................4-1
SuperSpeed Communication Flow...........................................................................4-1
4.2.1
Pipes.......................................................................................................4-2
SuperSpeed Protocol Overview ...............................................................................4-2
4.3.1
Differences from USB 2.0 .......................................................................4-2
4.3.1.1
Comparing USB 2.0 and SuperSpeed Transactions.......4-3
4.3.1.2
Introduction to SuperSpeed Packets...............................4-4
Generalized Transfer Description.............................................................................4-4
4.4.1
Data Bursting ..........................................................................................4-5
4.4.2
IN Transfers ............................................................................................4-5
4.4.3
OUT Transfers ........................................................................................4-6
4.4.4
Power Management and Performance ...................................................4-7
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Universal Serial Bus 3.0 Specification, Revision 1.0
4.4.5
4.4.6
4.4.7
4.4.8
4.4.9
4.4.10
4.4.11
Control Transfers ....................................................................................4-8
4.4.5.1
Control Transfer Packet Size ..........................................4-8
4.4.5.2
Control Transfer Bandwidth Requirements .....................4-8
4.4.5.3
Control Transfer Data Sequences...................................4-9
Bulk Transfers.........................................................................................4-9
4.4.6.1
Bulk Transfer Data Packet Size ......................................4-9
4.4.6.2
Bulk Transfer Bandwidth Requirements........................4-10
4.4.6.3
Bulk Transfer Data Sequences .....................................4-10
4.4.6.4
Bulk Streams.................................................................4-11
Interrupt Transfers ................................................................................4-12
4.4.7.1
Interrupt Transfer Packet Size ......................................4-13
4.4.7.2
Interrupt Transfer Bandwidth Requirements .................4-13
4.4.7.3
Interrupt Transfer Data Sequences...............................4-14
Isochronous Transfers ..........................................................................4-14
4.4.8.1
Isochronous Transfer Packet Size ................................4-15
4.4.8.2
Isochronous Transfer Bandwidth Requirements ...........4-15
4.4.8.3
Isochronous Transfer Data Sequences.........................4-16
Device Notifications ..............................................................................4-16
Reliability ..............................................................................................4-16
4.4.10.1
Physical Layer...............................................................4-16
4.4.10.2
Link Layer......................................................................4-16
4.4.10.3
Protocol Layer ...............................................................4-17
Efficiency ..............................................................................................4-17
5 Mechanical ................................................................................................... 5-1
5.1
5.2
5.3
viii
Objective ..................................................................................................................5-1
Significant Features..................................................................................................5-1
5.2.1
Connectors .............................................................................................5-1
5.2.1.1
USB 3.0 Standard-A Connector ......................................5-2
5.2.1.2
USB 3.0 Standard-B Connector ......................................5-2
5.2.1.3
USB 3.0 Powered-B Connector ......................................5-2
5.2.1.4
USB 3.0 Micro-B Connector............................................5-2
5.2.1.5
USB 3.0 Micro-AB and USB 3.0 Micro-A Connectors.....5-3
5.2.2
Compliant Cable Assemblies..................................................................5-3
5.2.3
Raw Cables ............................................................................................5-3
Connector Mating Interfaces ....................................................................................5-4
5.3.1
USB 3.0 Standard-A Connector..............................................................5-4
5.3.1.1
Interface Definition ..........................................................5-4
5.3.1.2
Pin Assignments and Description .................................5-14
5.3.1.3
USB 3.0 Standard-A Connector Color Coding ..............5-14
5.3.2
USB 3.0 Standard-B Connector............................................................5-15
5.3.2.1
Interface Definition ........................................................5-15
5.3.2.2
Pin Assignments and Description .................................5-20
5.3.3
USB 3.0 Powered-B Connector ............................................................5-20
5.3.3.1
Interface Definition ........................................................5-20
5.3.3.2
Pin Assignments and Descriptions................................5-25
5.3.4
USB 3.0 Micro Connector Family .........................................................5-25
5.3.4.1
Interfaces Definition ......................................................5-25
5.3.4.2
Pin Assignments and Description .................................5-33
Contents
5.4
5.5
5.6
5.7
Cable Construction and Wire Assignments............................................................5-35
5.4.1
Cable Construction ...............................................................................5-35
5.4.2
Wire Assignments.................................................................................5-36
5.4.3
Wire Gauges and Cable Diameters ......................................................5-36
Cable Assemblies...................................................................................................5-37
5.5.1
USB 3.0 Standard-A to USB 3.0 Standard-B Cable Assembly.............5-37
5.5.2
USB 3.0 Standard-A to USB 3.0 Standard-A Cable Assembly.............5-38
5.5.3
USB 3.0 Standard-A to USB 3.0 Micro-B Cable Assembly ..................5-39
5.5.4
USB 3.0 Micro-A to USB 3.0 Micro-B Cable Assembly ........................5-41
5.5.5
USB 3.0 Micro-A to USB 3.0 Standard-B Cable Assembly ..................5-43
5.5.6
USB 3.0 Icon Location ..........................................................................5-44
5.5.7
Cable Assembly Length........................................................................5-45
Electrical Requirements .........................................................................................5-46
5.6.1
SuperSpeed Electrical Requirements...................................................5-46
5.6.1.1
Raw Cable.....................................................................5-46
5.6.1.1.1
Characteristic Impedance.........................................5-46
5.6.1.1.2
Intra-Pair Skew .........................................................5-46
5.6.1.1.3
Differential Insertion Loss .........................................5-47
5.6.1.2
Mated Connector...........................................................5-47
5.6.1.3
Mated Cable Assemblies ..............................................5-48
5.6.1.3.1
Differential Insertion Loss (EIA-360-101) .................5-49
5.6.1.3.2
Differential Near-End Crosstalk between
SuperSpeed Pairs (EIA-360-90)........................5-50
5.6.1.3.3
Differential Crosstalk between D+/D- and
SuperSpeed Pairs (EIA-360-90)........................5-51
5.6.1.3.4
Differential-to-Common-Mode Conversion ...............5-52
5.6.2
DC Electrical Requirements..................................................................5-52
5.6.2.1
Low Level Contact Resistance (EIA 364-23B) ..............5-52
5.6.2.2
Dielectric Strength (EIA 364-20) ...................................5-52
5.6.2.3
Insulation Resistance (EIA 364-21)...............................5-53
5.6.2.4
Contact Current Rating (EIA 364-70, Method 2) ...........5-53
Mechanical and Environmental Requirements.......................................................5-53
5.7.1
Mechanical Requirements ....................................................................5-53
5.7.1.1
Insertion Force (EIA 364-13).........................................5-53
5.7.1.2
Extraction Force (EIA 364-13).......................................5-53
5.7.1.3
Durability or Insertion/Extraction Cycles (EIA 364-09) ..5-53
5.7.1.4
Cable Flexing (EIA 364-41, Condition I)........................5-54
5.7.1.5
Cable Pull-Out (EIA 364-38, Condition A).....................5-54
5.7.1.6
Peel Strength (USB 3.0 Micro Connector
Family Only) ..................................................................5-54
5.7.1.7
4-Axes Continuity Test (USB 3.0 Micro Connector
Family Only) ..................................................................5-54
5.7.1.8
Wrenching Strength (Reference, USB 3.0 Micro
Connector Family Only) ................................................5-56
5.7.1.9
Lead Co-Planarity .........................................................5-56
5.7.1.10
Solderability...................................................................5-56
5.7.1.11
Restriction of Hazardous Substances (RoHS)
Compliance ...................................................................5-56
5.7.2
Environmental Requirements ...............................................................5-56
ix
Universal Serial Bus 3.0 Specification, Revision 1.0
5.8
5.7.3
Materials ...............................................................................................5-57
Implementation Notes and Design Guides.............................................................5-57
5.8.1
Mated Connector Dimensions ..............................................................5-57
5.8.2
EMI Management .................................................................................5-60
5.8.3
Stacked Connectors .............................................................................5-60
6 Physical Layer ............................................................................................. 6-1
6.1
6.2
6.3
6.4
6.5
6.6
6.7
6.8
6.9
x
Physical Layer Overview ..........................................................................................6-1
Physical Layer Functions .........................................................................................6-1
6.2.1
Measurement Overview..........................................................................6-4
6.2.2
Channel Overview ..................................................................................6-5
Symbol Encoding .....................................................................................................6-5
6.3.1
Serialization and Deserialization of Data ................................................6-6
6.3.2
Normative 8b/10b Decode Rules............................................................6-6
6.3.3
Data Scrambling .....................................................................................6-6
6.3.4
8b/10b Decode Errors.............................................................................6-7
6.3.5
Special Symbols for Framing and Link Management .............................6-8
Link Initialization and Training ..................................................................................6-8
6.4.1
Normative Training Sequence Rules ......................................................6-9
6.4.1.1
Training Control Bits........................................................6-9
6.4.1.2
Training Sequence Values ..............................................6-9
6.4.2
Lane Polarity Inversion .........................................................................6-11
6.4.3
Elasticity Buffer and SKP Ordered Set .................................................6-11
6.4.4
Compliance Pattern ..............................................................................6-12
Clock and Jitter.......................................................................................................6-13
6.5.1
Informative Jitter Budgeting ..................................................................6-13
6.5.2
Normative Clock Recovery Function ....................................................6-14
6.5.3
Normative Spread Spectrum Clocking (SSC).......................................6-16
6.5.4
Normative Slew Rate Limit ...................................................................6-16
Signaling.................................................................................................................6-17
6.6.1
Eye Diagrams .......................................................................................6-17
6.6.2
Voltage Level Definitions ......................................................................6-18
6.6.3
Tx and Rx Input Parasitics....................................................................6-19
Transmitter Specifications ......................................................................................6-20
6.7.1
Transmitter Electrical Parameters ........................................................6-20
6.7.2
Low Power Transmitter.........................................................................6-21
6.7.3
Transmitter Eye ....................................................................................6-22
6.7.4
Tx Compliance Reference Receiver Equalize Function .......................6-22
6.7.5
Informative Transmitter De-emphasis...................................................6-23
6.7.6
Entry into Electrical Idle, U1..................................................................6-23
Receiver Specifications ..........................................................................................6-24
6.8.1
Receiver Equalization Training .............................................................6-24
6.8.2
Informative Receiver CTLE Function....................................................6-24
6.8.3
Receiver Electrical Parameters ............................................................6-26
6.8.4
Receiver Loopback ...............................................................................6-27
6.8.4.1
Loopback BERT ............................................................6-27
6.8.5
Normative Receiver Tolerance Compliance Test .................................6-29
Low Frequency Periodic Signaling (LFPS).............................................................6-30
6.9.1
LFPS Signal Definition..........................................................................6-30
Contents
6.9.2
6.10
6.11
Example LFPS Handshake for U1/U2 Exit, Loopback Exit, and U3
Wakeup ................................................................................................6-33
6.9.3
Warm Reset..........................................................................................6-34
Transmitter and Receiver DC Specifications..........................................................6-35
6.10.1
Informative ESD Protection ..................................................................6-35
6.10.2
Informative Short Circuit Requirements................................................6-35
6.10.3
Normative High Impedance Reflections ...............................................6-35
Receiver Detection .................................................................................................6-36
6.11.1
Rx Detect Overview ..............................................................................6-36
6.11.2
Rx Detect Sequence.............................................................................6-37
6.11.3
Upper Limit on Channel Capacitance ...................................................6-37
7 Link Layer .................................................................................................... 7-1
7.1
7.2
Byte Ordering ...........................................................................................................7-2
Link Management and Flow Control.........................................................................7-3
7.2.1
Packets and Packet Framing..................................................................7-3
7.2.1.1
Header Packet Structure.................................................7-3
7.2.1.1.1
Header Packet Framing .............................................7-3
7.2.1.1.2
Packet Header............................................................7-4
7.2.1.1.3
Link Control Word.......................................................7-6
7.2.1.2
Data Packet Payload Structure .......................................7-7
7.2.1.2.1
Data Packet Payload Framing....................................7-7
7.2.1.2.2
Data Packet Payload ..................................................7-8
7.2.1.2.3
Spacing Between Data Packet Header and
Data Packet Payload.........................................7-10
7.2.2
Link Commands....................................................................................7-10
7.2.2.1
Link Command Structure ..............................................7-10
7.2.2.2
Link Command Word Definition ....................................7-11
7.2.2.3
Link Command Placement ............................................7-14
7.2.3
Logical Idle............................................................................................7-14
7.2.4
Link Command Usage for Flow Control, Error Recovery, and Power
Management.........................................................................................7-15
7.2.4.1
Header Packet Flow Control and Error Recovery .........7-15
7.2.4.1.1
Initialization...............................................................7-15
7.2.4.1.2
General Rules of LGOOD_n and LCRD_x Usage....7-18
7.2.4.1.3
Transmitting Header Packets ...................................7-18
7.2.4.1.4
Receiving Header Packets .......................................7-18
7.2.4.1.5
Rx Header Buffer Credit ...........................................7-19
7.2.4.1.6
Receiving Data Packet Payload ...............................7-19
7.2.4.1.7
Receiving LGOOD_n................................................7-20
7.2.4.1.8
Receiving LCRD_x ...................................................7-20
7.2.4.1.9
Receiving LBAD .......................................................7-20
7.2.4.1.10
Transmitter Timers ...................................................7-21
7.2.4.2
Link Power Management and Flow...............................7-22
7.2.4.2.1
Power Management Link Timers..............................7-22
7.2.4.2.2
Low Power Link State Initiation ................................7-23
7.2.4.2.3
U1/U2 Entry Flow .....................................................7-24
7.2.4.2.4
U3 Entry Flow ...........................................................7-25
7.2.4.2.5
Concurrent Low Power Link Management Flow.......7-25
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Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.4.2.6
7.3
7.4
7.5
xii
Concurrent Low Power Link Management
and Recovery Flow............................................7-26
7.2.4.2.7
Low Power Link State Exit Flow ...............................7-26
Link Error Rules/Recovery .....................................................................................7-26
7.3.1
Overview of SuperSpeed Bit Errors......................................................7-26
7.3.2
Link Error Types, Detection, and Recovery ..........................................7-27
7.3.3
Header Packet Errors ...........................................................................7-27
7.3.3.1
Packet Framing Error ....................................................7-27
7.3.3.2
Header Packet Error .....................................................7-28
7.3.3.3
Rx Header Sequence Number Error .............................7-28
7.3.4
Link Command Errors...........................................................................7-28
7.3.5
ACK Tx Header Sequence Number Error.............................................7-30
7.3.6
Header Sequence Number Advertisement Error ..................................7-30
7.3.7
Rx Header Buffer Credit Advertisement Error ......................................7-30
7.3.8
Training Sequence Error.......................................................................7-31
7.3.9
8b/10b Errors ........................................................................................7-31
7.3.10
Summary of Error Types and Recovery ...............................................7-31
PowerOn Reset and Inband Reset.........................................................................7-33
7.4.1
PowerOn Reset ....................................................................................7-33
7.4.2
Inband Reset ........................................................................................7-33
Link Training and Status State Machine (LTSSM) .................................................7-35
7.5.1
SS.Disabled ..........................................................................................7-38
7.5.1.1
SS.Disabled Requirements ...........................................7-38
7.5.1.2
Exit from SS.Disabled ...................................................7-38
7.5.2
SS.Inactive............................................................................................7-38
7.5.2.1
SS.Inactive Substate Machines ....................................7-38
7.5.2.2
SS.Inactive Requirements.............................................7-38
7.5.2.3
SS.Inactive.Quiet ..........................................................7-39
7.5.2.3.1
SS.Inactive.Quiet Requirements ..............................7-39
7.5.2.3.2
Exit from SS.Inactive.Quiet ......................................7-39
7.5.2.4
SS.Inactive.Disconnect.Detect......................................7-39
7.5.2.4.1
SS.Inactive.Disconnect.Detect Requirements..........7-39
7.5.2.4.2
Exit from SS.Inactive.Disconnect.Detect ..................7-39
7.5.3
Rx.Detect ..............................................................................................7-40
7.5.3.1
Rx.Detect Substate Machines.......................................7-40
7.5.3.2
Rx.Detect Requirements ...............................................7-40
7.5.3.3
Rx.Detect.Reset ............................................................7-41
7.5.3.3.1
Rx.Detect.Reset Requirements ................................7-41
7.5.3.3.2
Exit from Rx.Detect.Reset ........................................7-41
7.5.3.4
Rx.Detect.Active............................................................7-41
7.5.3.5
Rx.Detect.Active Requirements ....................................7-41
7.5.3.6
Exit from Rx.Detect.Active ............................................7-41
7.5.3.7
Rx.Detect.Quiet.............................................................7-42
7.5.3.7.1
Rx.Detect.Quiet Requirements.................................7-42
7.5.3.7.2
Exit from Rx.Detect.Quiet .........................................7-42
7.5.4
Polling ...................................................................................................7-43
7.5.4.1
Polling Substate Machines............................................7-43
7.5.4.2
Polling Requirements ....................................................7-43
7.5.4.3
Polling.LFPS .................................................................7-43
Contents
7.5.5
7.5.6
7.5.7
7.5.8
7.5.9
7.5.10
7.5.11
7.5.4.3.1
Polling.LFPS Requirements .....................................7-43
7.5.4.3.2
Exit from Polling.LFPS .............................................7-43
7.5.4.4
Polling.RxEQ.................................................................7-44
7.5.4.4.1
Polling.RxEQ Requirements.....................................7-44
7.5.4.4.2
Exit from Polling.RxEQ .............................................7-44
7.5.4.5
Polling.Active.................................................................7-44
7.5.4.5.1
Polling.Active Requirements ....................................7-45
7.5.4.5.2
Exit from Polling.Active.............................................7-45
7.5.4.6
Polling.Configuration .....................................................7-45
7.5.4.6.1
Polling.Configuration Requirements .........................7-45
7.5.4.6.2
Exit from Polling.Configuration .................................7-45
7.5.4.7
Polling.Idle.....................................................................7-46
7.5.4.7.1
Polling.Idle Requirements ........................................7-46
7.5.4.7.2
Exit from Polling.Idle.................................................7-46
Compliance Mode.................................................................................7-47
7.5.5.1
Compliance Mode Requirements..................................7-48
7.5.5.2
Exit from Compliance Mode ..........................................7-48
U0 .........................................................................................................7-48
7.5.6.1
U0 Requirements ..........................................................7-48
7.5.6.2
Exit from U0 ..................................................................7-48
U1 .........................................................................................................7-49
7.5.7.1
U1 Requirements ..........................................................7-49
7.5.7.2
Exit from U1 ..................................................................7-50
U2 .........................................................................................................7-50
7.5.8.1
U2 Requirements ..........................................................7-50
7.5.8.2
Exit from U2 ..................................................................7-51
U3 .........................................................................................................7-51
7.5.9.1
U3 Requirements ..........................................................7-51
7.5.9.2
Exit from U3 ..................................................................7-52
Recovery...............................................................................................7-52
7.5.10.1
Recovery Substate Machines .......................................7-53
7.5.10.2
Recovery Requirements................................................7-53
7.5.10.3
Recovery.Active ............................................................7-53
7.5.10.3.1
Recovery.Active Requirements ................................7-53
7.5.10.3.2
Exit from Recovery.Active ........................................7-53
7.5.10.4
Recovery.Configuration.................................................7-53
7.5.10.4.1
Recovery.Configuration Requirements ....................7-54
7.5.10.4.2
Exit from Recovery.Configuration.............................7-54
7.5.10.5
Recovery.Idle ................................................................7-54
7.5.10.5.1
Recovery.Idle Requirements ....................................7-54
7.5.10.5.2
Exit from Recovery.Idle ............................................7-55
Loopback ..............................................................................................7-56
7.5.11.1
Loopback Substate Machines .......................................7-56
7.5.11.2
Loopback Requirements ...............................................7-56
7.5.11.3
Loopback.Active............................................................7-56
7.5.11.3.1
Loopback.Active Requirements................................7-56
7.5.11.3.2
Exit from Loopback.Active ........................................7-56
7.5.11.4
Loopback.Exit................................................................7-57
7.5.11.4.1
Loopback.Exit Requirements....................................7-57
xiii
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.12
7.5.11.4.2
Exit from Loopback.Exit............................................7-57
Hot Reset..............................................................................................7-58
7.5.12.1
Hot Reset Substate Machines.......................................7-58
7.5.12.2
Hot Reset Requirements...............................................7-58
7.5.12.3
Hot Reset.Active ...........................................................7-58
7.5.12.3.1
Hot Reset.Active Requirements ...............................7-58
7.5.12.3.2
Exit from Hot Reset.Active........................................7-59
7.5.12.4
Hot Reset.Exit ...............................................................7-59
7.5.12.4.1
Hot Reset.Exit Requirements ...................................7-59
7.5.12.4.2
Exit from Hot Reset.Exit ...........................................7-60
8 Protocol Layer ............................................................................................. 8-1
8.1
8.2
8.3
8.4
8.5
8.6
8.7
8.8
xiv
SuperSpeed Transactions........................................................................................8-2
Packet Types............................................................................................................8-2
Packet Formats ........................................................................................................8-4
8.3.1
Fields Common to all Headers ...............................................................8-4
8.3.1.1
Reserved Values and Reserved Field Handling .............8-4
8.3.1.2
Type Field .......................................................................8-4
8.3.1.3
CRC-16 ...........................................................................8-4
8.3.1.4
Link Control Word ...........................................................8-5
Link Management Packet (LMP) ..............................................................................8-5
8.4.1
Subtype Field..........................................................................................8-6
8.4.2
Set Link Function ....................................................................................8-6
8.4.3
U2 Inactivity Timeout ..............................................................................8-7
8.4.4
Vendor Device Test ................................................................................8-8
8.4.5
Port Capabilities......................................................................................8-8
8.4.6
Port Configuration.................................................................................8-10
8.4.7
Port Configuration Response................................................................8-11
Transaction Packet (TP).........................................................................................8-12
8.5.1
Acknowledgement (ACK) Transaction Packet......................................8-12
8.5.2
Not Ready (NRDY) Transaction Packet ...............................................8-14
8.5.3
Endpoint Ready (ERDY) Transaction Packet .......................................8-14
8.5.4
STATUS Transaction Packet................................................................8-15
8.5.5
STALL Transaction Packet ...................................................................8-16
8.5.6
Device Notification (DEV_NOTIFICATION) Transaction Packet ..........8-16
8.5.6.1
Function Wake Device Notification ...............................8-17
8.5.6.2
Latency Tolerance Message (LTM) Device
Notification ....................................................................8-18
8.5.6.3
Bus Interval Adjustment Message Device
Notification ....................................................................8-19
8.5.6.4
Function Wake Notification ...........................................8-19
8.5.6.5
Latency Tolerance Messaging ......................................8-19
8.5.6.5.1
Optional Normative LTM and BELT Requirements ..8-20
8.5.6.6
Bus Interval Adjustment Message.................................8-20
8.5.7
PING Transaction Packet .....................................................................8-22
8.5.8
PING_RESPONSE Transaction Packet ...............................................8-22
Data Packet (DP) ...................................................................................................8-23
Isochronous Timestamp Packet (ITP) ....................................................................8-24
Addressing Triple ...................................................................................................8-25
Contents
8.9
8.10
8.11
8.12
8.13
Route String Field...................................................................................................8-26
8.9.1
Route String Port Field .........................................................................8-26
8.9.2
Route String Port Field Width ...............................................................8-26
8.9.3
Port Number .........................................................................................8-26
Transaction Packet Usages ...................................................................................8-26
8.10.1
Flow Control Conditions........................................................................8-27
8.10.2
Burst Transactions................................................................................8-27
8.10.3
Short Packets .......................................................................................8-28
TP or DP Responses..............................................................................................8-29
8.11.1
Device Response to TP Requesting Data ............................................8-29
8.11.2
Host Response to Data Received from a Device .................................8-30
8.11.3
Device Response to Data Received from the Host ..............................8-31
8.11.4
Device Response to a SETUP DP........................................................8-32
TP Sequences........................................................................................................8-33
8.12.1
Bulk Transactions .................................................................................8-33
8.12.1.1
State Machine Notation Information..............................8-33
8.12.1.2
Bulk IN Transactions .....................................................8-34
8.12.1.3
Bulk OUT Transactions .................................................8-35
8.12.1.4
Bulk Streaming Protocol................................................8-38
8.12.1.4.1
Stream IDs ...............................................................8-39
8.12.1.4.2
Bulk IN Stream Protocol ...........................................8-40
8.12.1.4.3
Bulk OUT Stream Protocol .......................................8-44
8.12.2
Control Transfers ..................................................................................8-48
8.12.2.1
Reporting Status Results ..............................................8-50
8.12.2.2
Variable-length Data Stage ...........................................8-51
8.12.2.3
STALL TPs Returned by Control Pipes.........................8-51
8.12.3
Bus Interval and Service Interval ..........................................................8-51
8.12.4
Interrupt Transactions...........................................................................8-52
8.12.4.1
Interrupt IN Transactions...............................................8-52
8.12.4.2
Interrupt OUT Transactions...........................................8-55
8.12.5
Host Timing Information........................................................................8-58
8.12.6
Isochronous Transactions.....................................................................8-60
8.12.6.1
Host Flexibility in Performing Isochronous
Transactions..................................................................8-66
8.12.6.2
Device Response to Isochronous IN Transactions .......8-66
8.12.6.3
Host Processing of Isochronous IN Transactions .........8-66
8.12.6.4
Device Response to an Isochronous OUT
Data Packet...................................................................8-67
Timing Parameters .................................................................................................8-68
9 Device Framework....................................................................................... 9-1
9.1
USB Device States...................................................................................................9-1
9.1.1
Visible Device States ..............................................................................9-1
9.1.1.1
Attached ..........................................................................9-5
9.1.1.2
Powered ..........................................................................9-5
9.1.1.3
Default.............................................................................9-5
9.1.1.4
Address ...........................................................................9-6
9.1.1.5
Configured.......................................................................9-6
9.1.1.6
Suspended ......................................................................9-6
xv
Universal Serial Bus 3.0 Specification, Revision 1.0
9.2
9.3
9.4
9.5
9.6
xvi
9.1.2
Bus Enumeration ....................................................................................9-6
Generic Device Operations ......................................................................................9-7
9.2.1
Dynamic Attachment and Removal ........................................................9-7
9.2.2
Address Assignment...............................................................................9-8
9.2.3
Configuration ..........................................................................................9-8
9.2.4
Data Transfer..........................................................................................9-9
9.2.5
Power Management................................................................................9-9
9.2.5.1
Power Budgeting.............................................................9-9
9.2.5.2
Changing Device Suspend State ....................................9-9
9.2.5.3
Function Suspend .........................................................9-10
9.2.5.4
Changing Function Suspend State ...............................9-10
9.2.6
Request Processing..............................................................................9-10
9.2.6.1
Request Processing Timing ..........................................9-11
9.2.6.2
Reset/Resume Recovery Time .....................................9-11
9.2.6.3
Set Address Processing................................................9-11
9.2.6.4
Standard Device Requests ...........................................9-11
9.2.6.5
Class-specific Requests................................................9-12
9.2.6.6
Speed Dependent Descriptors ......................................9-12
9.2.7
Request Error .......................................................................................9-12
USB Device Requests............................................................................................9-13
9.3.1
bmRequestType ...................................................................................9-13
9.3.2
bRequest ..............................................................................................9-14
9.3.3
wValue ..................................................................................................9-14
9.3.4
wIndex ..................................................................................................9-14
9.3.5
wLength ................................................................................................9-15
Standard Device Requests.....................................................................................9-15
9.4.1
Clear Feature........................................................................................9-18
9.4.2
Get Configuration..................................................................................9-19
9.4.3
Get Descriptor.......................................................................................9-19
9.4.4
Get Interface .........................................................................................9-20
9.4.5
Get Status.............................................................................................9-21
9.4.6
Set Address ..........................................................................................9-23
9.4.7
Set Configuration ..................................................................................9-24
9.4.8
Set Descriptor .......................................................................................9-24
9.4.9
Set Feature ...........................................................................................9-25
9.4.10
Set Interface .........................................................................................9-27
9.4.11
Set Isochronous Delay..........................................................................9-27
9.4.12
Set SEL ................................................................................................9-28
9.4.13
Synch Frame ........................................................................................9-29
Descriptors .............................................................................................................9-29
Standard USB Descriptor Definitions .....................................................................9-30
9.6.1
Device...................................................................................................9-30
9.6.2
Binary Device Object Store (BOS)........................................................9-32
9.6.2.1
USB 2.0 Extension ........................................................9-33
9.6.2.2
SuperSpeed USB Device Capability .............................9-34
9.6.2.3
Container ID ..................................................................9-36
9.6.3
Configuration ........................................................................................9-36
9.6.4
Interface Association ............................................................................9-38
9.6.5
Interface................................................................................................9-39
Contents
9.7
9.6.6
Endpoint ...............................................................................................9-41
9.6.7
SuperSpeed Endpoint Companion .......................................................9-45
9.6.8
String ....................................................................................................9-47
Device Class Definitions.........................................................................................9-48
9.7.1
Descriptors............................................................................................9-48
9.7.2
Interface(s)............................................................................................9-48
9.7.3
Requests...............................................................................................9-48
10 Hub, Host Downstream Port, and Device Upstream
Port Specification...................................................................................... 10-1
10.1
10.2
10.3
10.4
10.5
Hub Feature Summary ...........................................................................................10-1
10.1.1
SuperSpeed Capable Host with SuperSpeed Capable Software .........10-4
10.1.2
USB 2.0 Host ........................................................................................10-4
10.1.3
Hub Connectivity...................................................................................10-5
10.1.3.1
Packet Signaling Connectivity.......................................10-5
10.1.3.2
Routing Information.......................................................10-6
10.1.4
Resume Connectivity............................................................................10-8
10.1.5
Hub Fault Recovery Mechanisms.........................................................10-8
10.1.6
Hub Header Packet Buffer Architecture................................................10-9
10.1.6.1
Hub Data Buffer Architecture ........................................10-9
Hub Power Management......................................................................................10-10
10.2.1
Link States ..........................................................................................10-10
10.2.2
Hub Downstream Port U1/U2 Timers .................................................10-10
10.2.3
Downstream/Upstream Port Link State Transitions............................10-11
Hub Downstream Facing Ports ............................................................................10-11
10.3.1
Hub Downstream Facing Port State Descriptions ..............................10-13
10.3.1.1
DSPORT.Powered-off.................................................10-13
10.3.1.2
DSPORT.Disconnected (Waiting for SS Connect)......10-14
10.3.1.3
DSPORT.Training .......................................................10-14
10.3.1.4
DSPORT.ERROR .......................................................10-15
10.3.1.5
DSPORT.Enabled .......................................................10-15
10.3.1.6
DSPORT.Resetting .....................................................10-15
10.3.1.7
DSPORT.Compliance .................................................10-16
10.3.1.8
DSPORT.Loopback.....................................................10-16
10.3.1.9
DSPORT.Disabled ......................................................10-16
10.3.2
Disconnect Detect Mechanism ...........................................................10-16
10.3.3
Labeling ..............................................................................................10-16
Hub Downstream Facing Port Power Management .............................................10-16
10.4.1
Downstream Facing Port PM Timers..................................................10-17
10.4.2
Hub Downstream Facing Port State Descriptions ..............................10-19
10.4.2.1
Enabled U0 States ......................................................10-19
10.4.2.2
Attempt U0 – U1 Transition.........................................10-20
10.4.2.3
Attempt U0 – U2 Transition.........................................10-20
10.4.2.4
Link in U1 ....................................................................10-21
10.4.2.5
Link in U2 ....................................................................10-21
10.4.2.6
Link in U3 ....................................................................10-21
Hub Upstream Facing Port...................................................................................10-22
10.5.1
Upstream Facing Port State Descriptions...........................................10-23
10.5.1.1
USPORT.Powered-off.................................................10-23
xvii
Universal Serial Bus 3.0 Specification, Revision 1.0
10.6
10.7
xviii
10.5.1.2
USPORT.Powered-on.................................................10-24
10.5.1.3
USPORT.Training .......................................................10-24
10.5.1.4
USPORT.Connected...................................................10-24
10.5.1.5
USPORT.Error ............................................................10-24
10.5.1.6
USPORT.Enabled .......................................................10-24
10.5.2
Hub Connect State Machine...............................................................10-25
10.5.2.1
Hub Connect State Descriptions .................................10-25
10.5.2.2
HCONNECT.Powered-off ...........................................10-25
10.5.2.3
HCONNECT.Attempt SS Connect ..............................10-25
10.5.2.4
HCONNECT.Connected on SS...................................10-25
Upstream Facing Port Power Management .........................................................10-26
10.6.1
Upstream Facing Port PM Timer ........................................................10-28
10.6.2
Hub Upstream Facing Port State Descriptions ...................................10-28
10.6.2.1
Enabled U0 States ......................................................10-28
10.6.2.2
Attempt U0 – U1 Transition.........................................10-29
10.6.2.3
Attempt U0 – U2 Transition.........................................10-30
10.6.2.4
Link in U1 ....................................................................10-30
10.6.2.5
Link in U2 ....................................................................10-30
10.6.2.6
Link in U3 ....................................................................10-30
Hub Header Packet Forwarding and Data Repeater............................................10-31
10.7.1
Hub Elasticity Buffer ...........................................................................10-31
10.7.2
SKP Ordered Sets ..............................................................................10-31
10.7.3
Interpacket Spacing ............................................................................10-31
10.7.4
Header Packet Buffer Architecture .....................................................10-31
10.7.5
Upstream Facing Port Tx....................................................................10-34
10.7.6
Upstream Facing Port Tx State Descriptions......................................10-35
10.7.6.1
Tx IDLE .......................................................................10-35
10.7.6.2
Tx Header ...................................................................10-35
10.7.6.3
Tx Data........................................................................10-35
10.7.6.4
Tx Data Abort ..............................................................10-36
10.7.6.5
Tx Link Command .......................................................10-36
10.7.7
Upstream Facing Port Rx ...................................................................10-37
10.7.8
Upstream Facing Port Rx State Descriptions .....................................10-37
10.7.8.1
Rx Default ...................................................................10-37
10.7.8.2
Rx Data .......................................................................10-38
10.7.8.3
Rx Header ...................................................................10-38
10.7.8.4
Process Header Packet ..............................................10-38
10.7.8.5
Rx Link Command.......................................................10-40
10.7.8.6
Process Link Command ..............................................10-40
10.7.9
Downstream Facing Port Tx ...............................................................10-41
10.7.10
Downstream Facing Port Tx State Descriptions .................................10-42
10.7.10.1
Tx IDLE .......................................................................10-42
10.7.10.2
Tx Header ...................................................................10-42
10.7.10.3
Tx Data........................................................................10-42
10.7.10.4
Tx Data Abort ..............................................................10-43
10.7.10.5
Tx Link Command .......................................................10-43
10.7.11
Downstream Facing Port Rx...............................................................10-44
10.7.12
Downstream Facing Port Rx State Descriptions.................................10-45
10.7.12.1
Rx Default ...................................................................10-45
Contents
10.8
10.9
10.10
10.11
10.12
10.13
10.14
10.7.12.2
Rx Data .......................................................................10-45
10.7.12.3
Rx Header ...................................................................10-45
10.7.12.4
Process Header ..........................................................10-46
10.7.12.5
Rx Link Command.......................................................10-46
10.7.12.6
Process Link Command ..............................................10-47
10.7.13
SuperSpeed Packet Connectivity .......................................................10-47
Suspend and Resume..........................................................................................10-47
Hub Upstream Port Reset Behavior .....................................................................10-47
Hub Port Power Control .......................................................................................10-48
10.10.1
Multiple Gangs....................................................................................10-48
Hub Controller ......................................................................................................10-49
10.11.1
Endpoint Organization ........................................................................10-49
10.11.2
Hub Information Architecture and Operation ......................................10-50
10.11.3
Port Change Information Processing..................................................10-51
10.11.4
Hub and Port Status Change Bitmap..................................................10-52
10.11.5
Over-current Reporting and Recovery................................................10-53
10.11.6
Enumeration Handling ........................................................................10-54
Hub Configuration ................................................................................................10-54
Descriptors ...........................................................................................................10-56
10.13.1
Standard Descriptors for Hub Class ...................................................10-56
10.13.2
Class-specific Descriptors ..................................................................10-59
10.13.2.1
Hub Descriptor ............................................................10-59
Requests ..............................................................................................................10-61
10.14.1
Standard Requests .............................................................................10-61
10.14.2
Class-specific Requests .....................................................................10-62
10.14.2.1
Clear Hub Feature.......................................................10-64
10.14.2.2
Clear Port Feature.......................................................10-64
10.14.2.3
Get Hub Descriptor .....................................................10-65
10.14.2.4
Get Hub Status............................................................10-65
10.14.2.5
Get Port Error Count ...................................................10-67
10.14.2.6
Get Port Status............................................................10-67
10.14.2.6.1 Port Status Bits.......................................................10-68
PORT_CONNECTION.........................................................10-69
PORT_ENABLE...................................................................10-69
PORT_OVER_CURRENT ...................................................10-69
PORT_RESET .....................................................................10-70
PORT_LINK_STATE ...........................................................10-70
PORT_POWER ...................................................................10-70
PORT_SPEED.....................................................................10-70
10.14.2.6.2 Port Status Change Bits .........................................10-70
C_PORT_CONNECTION ....................................................10-72
C_PORT_OVER_CURRENT...............................................10-72
C_PORT_RESET ................................................................10-72
C_PORT_BH_RESET .........................................................10-72
C_PORT_LINK_STATE.......................................................10-72
C_PORT_CONFIG_ERROR ...............................................10-72
10.14.2.7
Set Hub Descriptor......................................................10-73
10.14.2.8
Set Hub Feature..........................................................10-73
10.14.2.9
Set Hub Depth.............................................................10-73
xix
Universal Serial Bus 3.0 Specification, Revision 1.0
10.14.2.10
Set Port Feature..........................................................10-74
10.15 Host Root (Downstream) Ports ............................................................................10-77
10.16 Peripheral Device Upstream Ports .......................................................................10-78
10.16.1
Peripheral Device Upstream Ports .....................................................10-78
10.16.2
Peripheral Device Connect State Machine .........................................10-78
10.16.2.1
PCONNECT.Powered-off............................................10-79
10.16.2.2
PCONNECT.Attempt SS Connect ..............................10-79
10.16.2.3
PCONNECT.Connected on SS...................................10-79
10.16.2.4
PCONNECT.Connected on USB 2.0 ..........................10-80
10.16.2.5
PCONNECT.Connected on USB 2.0 and
Attempting SS Connection ..........................................10-80
10.17 Hub Chapter Parameters .....................................................................................10-81
11 Interoperability and Power Delivery ........................................................ 11-1
11.1
11.2
11.3
11.4
USB 3.0 Host Support for USB 2.0 ........................................................................11-1
USB 3.0 Hub Support for USB 2.0 .........................................................................11-2
USB 3.0 Device Support for USB 2.0.....................................................................11-2
Power Distribution ..................................................................................................11-2
11.4.1
Classes of Devices and Connections ...................................................11-3
11.4.1.1
Self-powered Hubs........................................................11-4
11.4.1.1.1
Over-current Protection ............................................11-4
11.4.1.2
Low-power Bus-powered Devices.................................11-5
11.4.1.3
High-power Bus-powered Devices................................11-5
11.4.1.4
Self-powered Devices ...................................................11-6
11.4.2
Steady-State Voltage Drop Budget.......................................................11-6
11.4.3
Power Control During Suspend/Resume..............................................11-8
11.4.4
Dynamic Attach and Detach .................................................................11-9
11.4.4.1
Inrush Current Limiting..................................................11-9
11.4.4.2
Dynamic Detach..........................................................11-10
11.4.5
VBUS Electrical Characteristics ...........................................................11-10
11.4.6
Powered-B Connector ........................................................................11-10
11.4.7
Wire Gauge Table...............................................................................11-11
A Symbol Encoding ........................................................................................A-1
B Symbol Scrambling.....................................................................................B-1
B.1
Data Scrambling...................................................................................................... B-1
C Power Management.....................................................................................C-1
C.1
xx
SuperSpeed Power Management Overview ........................................................... C-1
C.1.1
Link Power Management ....................................................................... C-1
C.1.1.1
Summary of Link States ................................................. C-2
C.1.1.2
U0 – Link Active ............................................................. C-2
C.1.1.3
U1 – Link Idle with Fast Exit........................................... C-2
C.1.1.3.1
U1 Entry .................................................................... C-2
C.1.1.3.2
Exiting the U1 State................................................... C-3
C.1.1.4
U2 – Link Idle with Slow Exit .......................................... C-4
C.1.1.5
U3 – Link Suspend......................................................... C-5
C.1.2
Link Power Management for Downstream Ports ................................... C-6
C.1.2.1
Link State Coordination and Management..................... C-6
Contents
C.2
C.3
C.4
C.5
C.1.2.2
Packet Deferring ............................................................ C-7
C.1.2.3
Software Interface .......................................................... C-7
C.1.3
Other Link Power Management Support Mechanisms .......................... C-8
C.1.3.1
Packets Pending Flag .................................................... C-8
C.1.3.2
Support for Isochronous Transfers................................. C-9
C.1.3.3
Support for Interrupt Transfers....................................... C-9
C.1.4
Device Power Management................................................................... C-9
C.1.4.1
Function Suspend .......................................................... C-9
C.1.4.2
Device Suspend ........................................................... C-10
C.1.4.3
Host Initiated Suspend ................................................. C-10
C.1.4.4
Host Initiated Wake from Suspend............................... C-11
C.1.4.5
Device Initiated Wake from Suspend ........................... C-11
C.1.5
Platform Power Management Support................................................. C-12
C.1.5.1
System Exit Latency and BELT.................................... C-12
Calculating U1 and U2 End to End Exit Latencies ................................................ C-14
C.2.1
Device Connected Directly to Host ...................................................... C-15
C.2.1.1
Host Initiated Transition ............................................... C-15
C.2.1.2
Device Initiated Transition............................................ C-16
C.2.2
Device Connected Through a Hub ...................................................... C-17
C.2.2.1
Host Initiated Transition ............................................... C-17
C.2.2.2
Device Initiated Transition............................................ C-19
Device-Initiated Link Power Management Policies ............................................... C-20
C.3.1
Overview and Background Information................................................ C-20
C.3.2
Entry Conditions for U1 and U2 ........................................................... C-21
C.3.2.1
Control Endpoints......................................................... C-21
C.3.2.2
Bulk Endpoints ............................................................. C-21
C.3.2.3
Interrupt Endpoints....................................................... C-22
C.3.2.4
Isochronous Endpoints................................................. C-22
C.3.2.5
Devices That Need Timestamp Packets ...................... C-22
Latency Tolerance Message (LTM) Implementation Example .............................. C-22
C.4.1
Device State Machine Implementation Example ................................. C-23
C.4.1.1
LTM-Idle State BELT.................................................... C-23
C.4.1.2
LTM-Active State BELT................................................ C-23
C.4.1.3
Transitioning Between LT-States ................................. C-24
C.4.1.3.1
Transitioning From LT-idle to LT-active................... C-24
C.4.1.3.2
Transitioning From LT-active to LT-idle................... C-24
C.4.2
Other Considerations........................................................................... C-25
SuperSpeed vs. High Speed Power Management Considerations....................... C-25
D Example Packets .........................................................................................D-1
xxi
Universal Serial Bus 3.0 Specification, Revision 1.0
Figures
3-1.
3-2.
3-3.
3-4.
4-1.
4-2.
4-3.
5-1.
5-2.
5-3.
5-4.
5-5.
5-6.
5-7.
5-8.
5-9.
5-10.
5-11.
5-12.
5-13.
5-14.
5-15.
5-16.
5-17.
5-18.
5-19.
5-20.
5-21.
5-22.
5-23.
5-24.
5-25.
5-26.
5-27.
5-28.
5-29.
5-30.
6-1.
6-2.
6-3.
6-4.
6-5.
6-6.
6-7.
6-8.
6-9.
xxii
USB 3.0 Dual Bus Architecture ................................................................................3-1
USB 3.0 Cable..........................................................................................................3-2
SuperSpeed Bus Communications Layers and Power Management Elements ......3-5
Examples of Supported SuperSpeed USB Physical Device Topologies................3-11
SuperSpeed IN Transaction Protocol.......................................................................4-6
SuperSpeed OUT Transaction Protocol...................................................................4-7
USB SuperSpeed IN Stream Example...................................................................4-11
USB 3.0 Standard-A Receptacle Interface Dimensions ...........................................5-8
USB 3.0 Standard-A Plug Interface Dimensions....................................................5-11
Reference Footprint for the USB 3.0 Standard-A Receptacle................................5-12
Reference Footprint for the USB 3.0 Double-Stacked Standard-A Receptacle .....5-13
Illustration of Color Coding Recommendation for USB 3.0 Standard-A
Connector ......................................................................................................5-15
USB 3.0 Standard-B Receptacle Interface Dimensions .........................................5-17
USB 3.0 Standard-B Plug Interface Dimensions....................................................5-18
Reference Footprint for the USB 3.0 Standard-B Receptacle................................5-19
USB 3.0 Powered-B Receptacle Interface Dimensions .........................................5-22
USB 3.0 Powered-B Plug Interface Dimensions ....................................................5-23
Reference Footprint for USB 3.0 Powered-B Receptacle ......................................5-24
USB 3.0 Micro-B and-AB Receptacles Interface Dimensions ................................5-27
USB 3.0 Micro-B and Micro-A Plug Interface Dimensions .....................................5-30
Reference Footprint for the USB 3.0 Micro-B or Micro-AB Receptacle..................5-32
Illustration of a USB 3.0 Cable Cross-Section........................................................5-35
USB 3.0 Standard-A to USB 3.0 Standard-B Cable Assembly ..............................5-37
USB 3.0 Micro-B Plug Cable Overmold Dimensions..............................................5-39
USB 3.0 Micro-A Cable Overmold Dimensions......................................................5-41
USB 3.0 Icon ..........................................................................................................5-44
Typical Plug Orientation .........................................................................................5-45
Impedance Limits of a Mated Connector................................................................5-47
Illustration of Test Points for a Mated Cable Assembly..........................................5-48
Differential Insertion Loss Requirement .................................................................5-49
Differential Near-End Crosstalk Requirement between SuperSpeed Pairs ...........5-50
Differential Near-End and Far-End Crosstalk Requirement between
D+/D- Pair and SuperSpeed Pairs ................................................................5-51
Differential-to-Common-Mode Conversion Requirement .......................................5-52
4-Axes Continuity Test ...........................................................................................5-55
Mated USB 3.0 Standard-A Connector ..................................................................5-58
Mated USB 3.0 Standard-B Connector ..................................................................5-58
Mated USB 3.0 Micro-B Connector ........................................................................5-59
SuperSpeed Physical Layer .....................................................................................6-1
Transmitter Block Diagram.......................................................................................6-2
Receiver Block Diagram...........................................................................................6-3
Channel Models without a Cable (Top) and with a Cable (Bottom) .........................6-4
Character to Symbol Mapping..................................................................................6-5
Bit Transmission Order.............................................................................................6-6
LFSR with Scrambling Polynomial ...........................................................................6-7
Jitter Filtering – “Golden PLL” and Jitter Transfer Functions..................................6-14
“Golden PLL” and Jitter Transfer Functions ...........................................................6-15
Contents
6-10.
6-11.
6-12.
6-13.
6-14.
6-15.
6-16.
6-17.
6-18.
6-19.
6-20.
6-21.
6-22.
6-23.
7-1.
7-2.
7-3.
7-4.
7-5.
7-6.
7-7.
7-8.
7-9.
7-10.
7-11.
7-12.
7-13.
7-14.
7-15.
7-16.
7-17.
7-18.
7-19.
7-20.
7-21.
7-22.
8-1.
8-2.
8-3.
8-4.
8-5.
8-6.
8-7.
8-8.
8-9.
8-10.
8-11.
8-12.
8-13.
Period Modulation from Triangular SSC.................................................................6-16
Generic Eye Mask ..................................................................................................6-17
Single-ended and Differential Voltage Levels ........................................................6-18
Device Termination Schematic...............................................................................6-19
Tx Normative Setup with Reference Channel ........................................................6-22
De-Emphasis Waveform ........................................................................................6-23
Frequency Spectrum of TSEQ ...............................................................................6-24
Tx Compliance Rx EQ Transfer Function...............................................................6-25
Rx Tolerance Setup................................................................................................6-29
Jitter Tolerance Curve ............................................................................................6-29
LFPS Signaling.......................................................................................................6-31
U1 Exit, U2 Exit, and U3 Wakeup LFPS Handshake Timing Diagram...................6-33
Example of Warm Reset Out of U3 ........................................................................6-35
Rx Detect Schematic..............................................................................................6-36
Link Layer.................................................................................................................7-1
SuperSpeed Byte Ordering ......................................................................................7-2
Header Packet with HPSTART, Packet Header, and Link Control Word.................7-3
Packet Header..........................................................................................................7-4
CRC-16 Remainder Generation ...............................................................................7-5
Link Control Word.....................................................................................................7-6
CRC-5 Remainder Generation .................................................................................7-7
Data Packet Payload with CRC-32 and Framing .....................................................7-7
CRC-32 Remainder Generation ...............................................................................7-8
Data Packet with Data Packet Header Followed by Data Packet Payload ............7-10
Link Command Structure........................................................................................7-11
Link Command Word Structure ..............................................................................7-11
State Diagram of the Link Training and Status State Machine...............................7-37
SS.Inactive Substate Machine ...............................................................................7-40
Rx.Detect Substate Machine..................................................................................7-42
Polling Substate Machine.......................................................................................7-47
U1...........................................................................................................................7-50
U2...........................................................................................................................7-51
U3...........................................................................................................................7-52
Recovery Substate Machine ..................................................................................7-55
Loopback Substate Machine ..................................................................................7-57
Hot Reset Substate Machine..................................................................................7-60
Protocol Layer Highlighted .......................................................................................8-1
Example Transaction Packet....................................................................................8-3
Link Control Word Detail ..........................................................................................8-5
Link Management Packet Structure .........................................................................8-5
Set Link Function LMP .............................................................................................8-6
U2 Inactivity Timeout LMP .......................................................................................8-7
Vendor Device Test LMP .........................................................................................8-8
Port Capability LMP..................................................................................................8-8
Port Configuration LMP ..........................................................................................8-10
Port Configuration Response LMP.........................................................................8-11
ACK Transaction Packet ........................................................................................8-12
NRDY Transaction Packet .....................................................................................8-14
ERDY Transaction Packet......................................................................................8-14
xxiii
Universal Serial Bus 3.0 Specification, Revision 1.0
8-14.
8-15.
8-16.
8-17.
8-18.
8-19.
8-20.
8-21.
8-22.
8-23.
8-24.
8-25.
8-26.
8-27.
8-28.
8-29.
8-30.
8-31.
8-32.
8-33.
8-34.
8-35.
8-36.
8-37.
8-38.
8-39.
8-40.
8-41.
8-42.
8-43.
8-44.
8-45.
8-46.
8-47.
8-48.
8-49.
8-50.
8-51.
9-1.
9-2.
9-3.
9-4.
9-5.
9-6.
9-7.
9-8.
10-1.
10-2.
xxiv
STATUS Transaction Packet .................................................................................8-15
STALL Transaction Packet.....................................................................................8-16
Device Notification Transaction Packet..................................................................8-16
Function Wake Device Notification.........................................................................8-17
Latency Tolerance Message Device Notification ...................................................8-18
Bus Interval Adjustment Message Device Notification ...........................................8-19
PING Transaction Packet.......................................................................................8-22
PING_RESPONSE Transaction Packet.................................................................8-22
Example Data Packet.............................................................................................8-23
Isochronous Timestamp Packet .............................................................................8-25
Route String Detail .................................................................................................8-26
Legend for State Machines ....................................................................................8-34
Sample BULK IN Sequence ...................................................................................8-36
Sample BULK OUT Sequence ...............................................................................8-37
General Stream Protocol State Machine (SPSM) ..................................................8-38
Bulk IN Stream Protocol State Machine (ISPSM) ..................................................8-40
IN Move Data State Machine (IMDSM) ..................................................................8-42
OUT Stream Protocol State Machine (OSPSM).....................................................8-44
OUT Move Data State Machine (OMDSM) ............................................................8-46
Control Read Sequence .........................................................................................8-49
Control Write Sequence .........................................................................................8-50
Host Sends Interrupt IN Transaction in Each Service Interval ...............................8-53
Host Stops Servicing Interrupt IN Transaction Once NRDY is Received...............8-54
Host Resumes IN Transaction after Device Sent ERDY........................................8-54
Endpoint Sends STALL TP ....................................................................................8-54
Host Detects Error in Data and Device Resends Data...........................................8-55
Host Sends Interrupt OUT Transaction in Each Service Interval ...........................8-56
Host Stops Servicing Interrupt OUT Transaction Once NRDY is Received...........8-57
Host Resumes Sending Interrupt OUT Transaction After Device Sent ERDY.......8-57
Device Detects Error in Data and Host Resends Data...........................................8-58
Endpoint Sends STALL TP ....................................................................................8-58
Multiple Active Isochronous Endpoints with Aligned Service Interval
Boundaries ....................................................................................................8-59
Isochronous IN Transaction Format .......................................................................8-60
Isochronous OUT Transaction Format ...................................................................8-61
Sample Isochronous IN Transaction ......................................................................8-62
Sample Isochronous OUT Transaction ..................................................................8-63
Isochronous IN Transaction Example ....................................................................8-64
Isochronous OUT Transaction Example ................................................................8-65
Peripheral Device State Diagram .............................................................................9-2
Hub State Diagram (SuperSpeed Portion Only).......................................................9-3
wIndex Format when Specifying an Endpoint ........................................................9-14
wIndex Format when Specifying an Interface ........................................................9-14
Information Returned by a GetStatus() Request to a Device .................................9-21
Information Returned by a GetStatus() Request to an Interface ............................9-22
Information Returned by a GetStatus() Request to an Endpoint............................9-22
Example of Feedback Endpoint Relationships.......................................................9-44
Hub Architecture.....................................................................................................10-2
SuperSpeed Portion of the Hub Architecture .........................................................10-3
Contents
10-3.
10-4.
10-5.
10-6.
10-7.
10-8.
10-9.
10-10.
10-11.
10-12.
10-13.
10-14.
10-15.
10-16.
10-17.
10-18.
10-19.
10-20.
10-21.
10-22.
10-23.
10-24.
10-25.
11-1.
11-2.
11-3.
11-4.
11-5.
11-6.
11-7.
C-1.
C-2.
C-3.
C-4.
C-5.
C-6.
C-7.
C-8.
C-9.
D-1.
D-2.
Simple USB 3.0 Topology ......................................................................................10-4
Hub Signaling Connectivity ....................................................................................10-5
Route String Example ............................................................................................10-7
Resume Connectivity .............................................................................................10-8
Typical Hub Header Packet Buffer Architecture.....................................................10-9
Hub Data Buffer Traffic (Header Packet Buffer Only Shown for DS Port 1)...........10-9
Downstream Facing Hub Port State Machine ......................................................10-12
Downstream Facing Hub Port Power Management State Machine .....................10-18
Upstream Facing Hub Port State Machine...........................................................10-23
Hub Connect State Machine ................................................................................10-25
Upstream Facing Hub Port Power Management State Machine..........................10-27
Example Hub Header Packet Buffer Architecture - Downstream Traffic ..............10-32
Example Hub Header Packet Buffer Architecture - Upstream Traffic ..................10-32
Upstream Facing Port Tx State Machine .............................................................10-34
Upstream Facing Port Rx State Machine .............................................................10-37
Downstream Facing Port Tx State Machine.........................................................10-41
Downstream Facing Port Rx State Machine ........................................................10-44
Example Hub Controller Organization..................................................................10-49
Relationship of Status, Status Change, and Control Information to
Device States ..............................................................................................10-50
Port Status Handling Method ...............................................................................10-51
Hub and Port Status Change Bitmap ...................................................................10-52
Example Hub and Port Change Bit Sampling ......................................................10-53
Peripheral Device Connect State Machine...........................................................10-79
Compound Self-powered Hub ................................................................................11-4
Low-power Bus-powered Function.........................................................................11-5
High-power Bus-powered Function ........................................................................11-5
Self-powered Function ...........................................................................................11-6
Worst-case Voltage Drop Topology (Steady State) ...............................................11-7
Worst-case Voltage Drop Analysis Using Equivalent Resistance ..........................11-7
Typical Suspend Current Averaging Profile ...........................................................11-8
Flow Diagram for Host Initiated Wakeup............................................................... C-11
Device Total Intrinsic Latency Tolerance .............................................................. C-13
Host to Device Path Exit Latency Calculation Examples ...................................... C-14
Device Connected Directly to a Host..................................................................... C-15
Device Connected Through a Hub ........................................................................ C-17
Downstream Host to Device Path Exit Latency with Hub...................................... C-18
Upstream Device to Host Path Exit Latency with Hub .......................................... C-19
LT State Diagram .................................................................................................. C-23
System Power during SuperSpeed and High Speed Device Data Transfers........ C-26
Sample ERDY Transaction Packet ......................................................................... D-1
Sample Data Packet................................................................................................ D-1
xxv
Universal Serial Bus 3.0 Specification, Revision 1.0
Tables
3-1.
5-1.
5-2.
5-3.
5-4.
5-5.
5-7.
5-8.
5-9.
5-10.
5-11.
5-12.
5-13.
5-14.
5-15.
5-16.
5-17.
6-1.
6-2.
6-3.
6-4.
6-5.
6-6.
6-7.
6-8.
6-9.
6-10.
6-11.
6-12.
6-13.
6-14.
6-15.
6-16.
6-17.
6-18.
6-19.
6-20.
6-21.
6-22.
7-1.
7-2.
7-3.
7-4.
7-5.
7-6.
7-7.
7-8.
xxvi
Comparing SuperSpeed to USB 2.0 ........................................................................3-3
Plugs Accepted By Receptacles ..............................................................................5-2
USB 3.0 Standard-A Connector Pin Assignments .................................................5-14
USB 3.0 Standard-B Connector Pin Assignments .................................................5-20
USB 3.0 Powered-B Connector Pin Assignments..................................................5-25
USB 3.0 Micro-B Connector Pin Assignments .......................................................5-33
Cable Wire Assignments ........................................................................................5-36
Reference Wire Gauges.........................................................................................5-36
USB 3.0 Standard-A to USB 3.0 Standard-B Cable Assembly Wiring ...................5-38
USB 3.0 Standard-A to USB 3.0 Standard-A Cable Assembly Wiring ...................5-38
USB 3.0 Standard-A to USB 3.0 Micro-B Cable Assembly Wiring.........................5-40
USB 3.0 Micro-A to USB 3.0 Micro-B Cable Assembly Wiring...............................5-42
USB 3.0 Micro-A to USB 3.0 Standard-B Cable Assembly Wiring.........................5-43
SDP Differential Insertion Loss Examples..............................................................5-47
Durability Ratings ...................................................................................................5-54
Environmental Test Conditions ..............................................................................5-56
Reference Materials1,2 ............................................................................................5-57
Special Symbols.......................................................................................................6-8
TSEQ Ordered Set ...................................................................................................6-9
TS1 Ordered Set ....................................................................................................6-10
TS2 Ordered Set ....................................................................................................6-10
Link Configuration Field..........................................................................................6-10
SKP Ordered Set Structure ....................................................................................6-11
Compliance Pattern Sequences.............................................................................6-12
Informative Jitter Budgeting at the Silicon Pads.....................................................6-13
SSC Parameters ....................................................................................................6-16
Transmitter Normative Electrical Parameters.........................................................6-20
Transmitter Informative Electrical Parameters at Silicon Pads ..............................6-21
Normative Transmitter Eye Mask at Test Point TP1 ..............................................6-22
Receiver Normative Electrical Parameters.............................................................6-26
Receiver Informative Electrical Parameters ...........................................................6-26
BRST......................................................................................................................6-28
BDAT......................................................................................................................6-28
BERC .....................................................................................................................6-28
BCNT......................................................................................................................6-28
Input Jitter Requirements for Rx Tolerance Testing...............................................6-30
Normative LFPS Electrical Specification ................................................................6-31
LFPS Transmitter Timing1 .....................................................................................6-32
LFPS Handshake Timing for U1/U2 Exit, Loopback Exit, and U3 Wakeup............6-34
CRC-16 Mapping......................................................................................................7-5
CRC-32 Mapping......................................................................................................7-9
Link Command Ordered Set Structure ...................................................................7-10
Link Command Bit Definitions ................................................................................7-12
Link Command Definitions .....................................................................................7-13
Logical Idle Definition .............................................................................................7-14
Transmitter Timers Summary.................................................................................7-22
Link Flow Control Timers Summary .......................................................................7-23
Contents
7-9.
7-10.
7-11.
7-12.
8-1.
8-2.
8-3.
8-4.
8-5.
8-6.
8-7.
8-8.
8-9.
8-10.
8-11.
8-12.
8-13.
8-14.
8-15.
8-16.
8-17.
8-18.
8-19.
8-20.
8-21.
8-22.
8-23.
8-24.
8-25.
8-26.
8-27.
8-28.
8-29.
8-30.
8-31.
8-32.
8-33.
9-1.
9-2.
9-3.
9-4.
9-5.
9-6.
9-7.
Valid Packet Framing K-Symbol Order (K is one of SHP, SDP,
END or EDB) .................................................................................................7-28
Valid Link Command K-Symbol Order ...................................................................7-29
Error Types and Recovery .....................................................................................7-32
LTSSM State Transition Timeouts .........................................................................7-36
Type Field Description..............................................................................................8-4
Link Control Word Format ........................................................................................8-5
Link Management Packet Subtype Field..................................................................8-6
Set Link Function......................................................................................................8-7
U2 Inactivity Timer Functionality ..............................................................................8-7
Vendor-specific Device Test Function......................................................................8-8
Port Capability LMP Format .....................................................................................8-9
Port Type Selection Matrix .......................................................................................8-9
Port Configuration LMP Format (differences with Port Capability LMP) ................8-10
Port Configuration Response LMP Format (differences with Port
Capability LMP) .............................................................................................8-11
Transaction Packet Subtype Field..........................................................................8-12
ACK TP Format ......................................................................................................8-13
NRDY TP Format (differences with ACK TP).........................................................8-14
ERDY TP Format (differences with ACK TP) .........................................................8-15
STATUS TP Format (differences with ACK TP).....................................................8-15
STALL TP Format (differences with ACK TP) ........................................................8-16
Device Notification TP Format (differences with ACK TP) .....................................8-17
Function Wake Device Notification.........................................................................8-17
Latency Tolerance Message Device Notification ...................................................8-18
Bus Interval Adjustment Message Device Notification ...........................................8-19
PING TP Format (differences with ACK TP) ..........................................................8-22
PING_RESPONSE TP Format (differences with ACK TP) ....................................8-23
Data Packet Format (differences with ACK TP) .....................................................8-24
Isochronous Timestamp Packet Format.................................................................8-25
Device Responses to TP Requesting Data (bulk, control, and
interrupt endpoints)........................................................................................8-29
Host Responses to Data Received from a Device (bulk, control, and
interrupt endpoints)........................................................................................8-30
Device Responses to OUT Transactions (bulk, control, and interrupt
endpoints)......................................................................................................8-31
Device Responses to SETUP Transactions (only for control endpoints) ...............8-32
Status Stage Responses........................................................................................8-51
Device Responses to Isochronous IN Transactions...............................................8-66
Host Responses to IN Transactions.......................................................................8-67
Device Responses to OUT Data Packets ..............................................................8-67
Timing Parameters .................................................................................................8-68
Visible SuperSpeed Device States...........................................................................9-4
Format of Setup Data .............................................................................................9-13
Standard Device Requests.....................................................................................9-15
Standard Request Codes .......................................................................................9-16
Descriptor Types ....................................................................................................9-17
Standard Feature Selectors ...................................................................................9-17
Suspend Options....................................................................................................9-26
xxvii
Universal Serial Bus 3.0 Specification, Revision 1.0
9-8.
9-9.
9-10.
9-11.
9-12.
9-13.
9-14.
9-15.
9-16.
9-17.
9-18.
9-20.
9-21.
9-22.
10-1.
10-2.
10-3.
10-4.
10-5.
10-6.
10-7.
10-8.
10-9.
10-10.
10-11.
10-12.
10-13.
10-14.
10-15.
11-1.
11-2.
11-3.
A-1.
C-1.
xxviii
Standard Device Descriptor ...................................................................................9-31
BOS Descriptor ......................................................................................................9-32
Format of a Device Capability Descriptor...............................................................9-32
Device Capability Type Codes ...............................................................................9-33
USB 2.0 Extension Descriptor................................................................................9-33
SuperSpeed Device Capabilities Descriptor ..........................................................9-34
Container ID Descriptor..........................................................................................9-36
Standard Configuration Descriptor .........................................................................9-37
Standard Interface Association Descriptor .............................................................9-38
Standard Interface Descriptor ................................................................................9-40
Standard Endpoint Descriptor ................................................................................9-41
SuperSpeed Endpoint Companion Descriptor .......................................................9-45
String Descriptor Zero, Specifying Languages Supported by the Device ..............9-47
UNICODE String Descriptor ...................................................................................9-47
Downstream Port VBUS Requirements.................................................................10-14
Hub Power Operating Mode Summary ................................................................10-54
SuperSpeed Hub Descriptor ................................................................................10-59
Hub Responses to Standard Device Requests ....................................................10-61
Hub Class Requests.............................................................................................10-62
Hub Class Request Codes ...................................................................................10-63
Hub Class Feature Selectors ...............................................................................10-63
Hub Status Field, wHubStatus .............................................................................10-66
Hub Change Field, wHubChange.........................................................................10-66
Port Status Field, wPortStatus .............................................................................10-68
Port Change Field, wPortChange.........................................................................10-71
U1 Timeout Value Encoding.................................................................................10-75
U2 Timeout Value Encoding.................................................................................10-75
Downstream Port Remote Wake Mask Encoding ................................................10-76
Hub Parameters ...................................................................................................10-81
USB 3.0 and USB 2.0 Interoperability ....................................................................11-1
DC Electrical Characteristics................................................................................11-10
VBUS/Gnd Wire Gauge vs. Maximum Length.......................................................11-11
8b/10b Data Symbol Codes .................................................................................... A-1
Link States and Characteristics Summary .............................................................. C-2
1
Introduction
1.1
Motivation
The original motivation for the Universal Serial Bus (USB) came from several considerations, two
of the most important being:
•
•
Ease-of-use
The lack of flexibility in reconfiguring the PC had been acknowledged as the Achilles’ heel to
its further deployment. The combination of user-friendly graphical interfaces and the hardware
and software mechanisms associated with new-generation bus architectures have made
computers less confrontational and easier to reconfigure. However, from the end user’s point
of view, the PC’s I/O interfaces, such as serial/parallel ports, keyboard/mouse/joystick
interfaces, etc., did not have the attributes of plug-and-play.
Port Expansion
The addition of external peripherals continued to be constrained by port availability. The lack
of a bidirectional, low-cost, low-to-mid speed peripheral bus held back the creative
proliferation of peripherals such as storage devices, answering machines, scanners, PDA’s,
keyboards, and mice. Existing interconnects were optimized for one or two point products. As
each new function or capability was added to the PC, a new interface had been defined to
address this need.
Initially, USB provided two speeds (12 Mb/s and 1.5 Mb/s) that peripherals could use. As PCs
became increasingly powerful and able to process larger amounts of data, users needed to get more
and more data into and out of their PCs. This led to the definition of the USB 2.0 specification in
2000 to provide a third transfer rate of 480 Mb/s while retaining backward compatibility. In 2005,
with wireless technologies becoming more and more capable, Wireless USB was introduced to
provide a new cable free capability to USB.
USB is the most successful PC peripheral interconnect ever defined and it has migrated heavily into
the CE and Mobile segments. In 2006 alone over 2 billion USB devices were shipped and there are
over 6 billion USB products in the installed base today. End users “know” what USB is. Product
developers understand the infrastructure and interfaces necessary to build a successful product.
USB has gone beyond just being a way to connect peripherals to PCs. Printers use USB to
interface directly to cameras. PDAs use USB connected keyboards and mice. The USB On-TheGo definition provides a way for two dual role capable devices to be connected and negotiate which
one will operate as the “host.” USB, as a protocol, is also being picked up and used in many
nontraditional applications such as industrial automation.
Now, as technology innovation marches forward, new kinds of devices, media formats, and large
inexpensive storage are converging. They require significantly more bus bandwidth to maintain the
interactive experience users have come to expect. HD Camcorders will have tens of gigabytes of
storage that the user will want to move to their PC for editing, viewing, and archiving. Furthermore
existing devices like still image cameras continue to evolve and are increasing their storage
capacity to hold even more uncompressed images. Downloading hundreds or even thousands of
10 MB, or larger, raw images from a digital camera will be a time consuming process unless the
1-1
Universal Serial Bus 3.0 Specification, Revision 1.0
transfer rate is increased. In addition, user applications demand a higher performance connection
between the PC and these increasingly sophisticated peripherals. USB 3.0 addresses this need by
adding an even higher transfer rate to match these new usages and devices.
Thus, USB (wired or wireless) continues to be the answer to connectivity for PC, Consumer
Electronics, and Mobile architectures. It is a fast, bidirectional, low-cost, dynamically attachable
interface that is consistent with the requirements of the PC platforms of today and tomorrow.
1.2
Objective of the Specification
This document defines the next generation USB industry-standard, USB 3.0. The specification
describes the protocol definition, types of transactions, bus management, and the programming
interface required to design and build systems and peripherals that are compliant with this
specification.
USB 3.0’s goal remains to enable devices from different vendors to interoperate in an open
architecture, while maintaining and leveraging the existing USB infrastructure (device drivers,
software interfaces, etc.). The specification is intended as an enhancement to the PC architecture,
spanning portable, business desktop, and home environments, as well as simple device-to-device
communications. It is intended that the specification allow system OEMs and peripheral
developers adequate room for product versatility and market differentiation without the burden of
carrying obsolete interfaces or losing compatibility.
1.3
Scope of the Document
The specification is primarily targeted at peripheral developers and platform/adapter developers,
but provides valuable information for platform operating system/ BIOS/ device driver, adapter
IHVs/ISVs, and system OEMs. This specification can be used for developing new products and
associated software.
Product developers using this specification are expected to know and understand the USB 2.0
Specification. Specifically, USB 3.0 devices must implement device framework commands and
descriptors as defined in the USB 2.0 Specification.
1.4
USB Product Compliance
Adopters of the USB 3.0 specification have signed the USB 3.0 Adopters Agreement, which
provides them access to a reasonable and nondiscriminatory (RANDZ) license from the Promoters
and other Adopters to certain intellectual property contained in products that are compliant with the
USB 3.0 specification. Adopters can demonstrate compliance with the specification through the
testing program as defined by the USB Implementers Forum. Products that demonstrate
compliance with the specification will be granted certain rights to use the USB Implementers
Forum logos as defined in the logo license.
1-2
Introduction
1.5
Document Organization
Chapters 1 through 4 provide an overview for all readers, while Chapters 5 through 11 contain
detailed technical information defining USB 3.0.
Readers should contact operating system vendors for operating system bindings specific to
USB 3.0.
1.6
Design Goals
USB 3.0 is the next evolutionary step for wired USB. The goal is that end users view it as the same
as USB 2.0, just faster. Several key design areas to meet this goal are listed below:
• Preserve the USB model of smart host and simple device.
• Leverage the existing USB infrastructure. There are a vast number of USB products in use
today. A large part of their success can be traced to the existence of stable software interfaces,
easily developed software device drivers, and a number of generic standard device class drivers
(HID, mass storage, audio, etc.). SuperSpeed USB devices are designed to keep this software
infrastructure intact so that developers of peripherals can continue to use the same interfaces
and leverage all of their existing development work.
• Significantly improve power management. Reduce the active power when sending data and
reduce idle power by providing a richer set of power management mechanisms to allow devices
to drive the bus into lower power states.
• Ease of use has always been and remains a key design goal for all varieties of USB.
• Preserve the investment. There are a large number of PCs in use that support only USB 2.0.
There are a larger number of USB 2.0 peripherals in use. Retaining backward compatibility at
the Type-A connector to allow SuperSpeed devices to be used, albeit at a lower speed, with
USB 2.0 PCs and allow high speed devices with their existing cables to be connected to the
USB 3.0 SuperSpeed Type-A connectors.
1.7
Related Documents
Universal Serial Bus Specification, Revision 2.0
USB On-the-Go Supplement to the USB 2.0 Specification, Revision 1.3
Universal Serial Bus Micro-USB Cables and Connectors Specification, Revision 1.01
EIA-364-1000.01: Environmental Test Methodology for Assessing the Performance of Electrical
Connectors and Sockets Used in Business Office Applications
USB 3.0 Connectors and Cable Assemblies Compliance Document
USB SuperSpeed Electrical Test Methodology white paper
USB 3.0 Jitter Budgeting white paper
INCITS TR-35-2004, INCITS Technical Report for Information Technology – Fibre Channel –
Methodologies for Jitter and Signal Quality Specification (FC-MJSQ)
1-3
Universal Serial Bus 3.0 Specification, Revision 1.0
1-4
2
Terms and Abbreviations
This chapter lists and defines terms and abbreviations used throughout this specification.
Term/Abbreviation
Definition
ACK
Handshake packet indicating a positive acknowledgment.
ACK Tx Header Sequence
Number
The expected header sequence number in the link control word to be acknowledged.
active device
A device that is powered and is not in the Suspend state.
asynchronous data
Data transferred at irregular intervals with relaxed latency requirements.
attached
A downstream device is attached to an upstream device when there is a physical
connection between the two.
AWG#
The measurement of a wire’s cross section, as defined by the American Wire Gauge
standard.
bandwidth
The amount of data transmitted per unit of time, typically bits per second (bps) or bytes
per second (Bps).
big endian
A method of storing data that places the most significant byte of multiple-byte values at a
lower storage address. For example, a 16-bit integer stored in big endian format places
the least significant byte at the higher address and the most significant byte at the lower
address. See also little endian.
bit
A unit of information used by digital computers. Represents the smallest piece of
addressable memory within a computer. A bit expresses the choice between two
possibilities and is typically represented by a logical one (1) or zero (0).
bps
Transmission rate expressed in bits per second.
Bps
Transmission rate expressed in bytes per second.
buffer
Storage used to compensate for a difference in data rates or time of occurrence of events,
when transmitting data from one device to another.
bulk transfer
One of the four USB transfer types. Bulk transfers are non-periodic, large bursty
communication typically used for a transfer that can use any available bandwidth and can
also be delayed until bandwidth is available. See also transfer type.
bus enumeration
Detecting, identifying, and configuring USB devices.
bus interval
A 125 μs period that establishes the integral boundary of service intervals.
byte
A data element that is 8 bits in size.
cable
Raw cable with no plugs attached.
cable assembly
Cable attached with plugs.
captive cable
Cable assembly that has a Type-A plug on one end and that is either permanently
attached or has a vendor specific connector on the other end.
capabilities
Those attributes of a USB device that are administrated by the host.
CDR
Circuit that performs the Clock and Data Recovery function.
characteristics
Those qualities of a USB device that are unchangeable; for example, the device class is a
device characteristic.
client
Software resident on the host that interacts with the USB system software to arrange data
transfer between a function and the host. The client is often the data provider and
consumer for transferred data.
component
A physical chip or circuit that contains a port.
2-1
Universal Serial Bus 3.0 Specification, Revision 1.0
Term/Abbreviation
Definition
configuring software
Software resident on the host that is responsible for configuring a USB device.
control endpoint
A pair of device endpoints with the same endpoint number that are used by a control pipe.
Control endpoints transfer data in both directions and, therefore, use both endpoint
directions of a device address and endpoint number combination. Thus, each control
endpoint consumes two endpoint addresses.
control pipe
Same as a message pipe.
connected
A downstream device is connected to an upstream device when it is attached to the
upstream device, and when the downstream device has asserted Rx terminations for
SuperSpeed signaling or has asserted the D+ or D- data line in order to enter low-speed,
full-speed, or high-speed signaling.
control transfer
One of the four USB transfer types. Control transfers support
configuration/command/status type communications between client and function. See
also transfer type.
Controlling Hub
A controlling hub is any hub whose upstream link is not in U3.
CRC
CRC-5, CRC-16, CRC-32. See Cyclic Redundancy Check.
Cyclic Redundancy Check
(CRC)
A check performed on data to see if an error has occurred in transmitting, reading, or
writing the data. The result of a CRC is typically stored or transmitted with the checked
data. The stored or transmitted result is compared to a CRC calculated from the data to
determine if an error has occurred.
D codes
The data type codes used in 8b/10b encoding.
D+ and D-
Differential pair defined in the USB 2.0 specification.
default address
An address defined by the USB Specification and used by a USB device when it is first
powered or reset. The default address is 00H.
default pipe
The message pipe created by the USB system software to pass control and status
information between the host and a USB device’s endpoint zero.
descrambling
Restoring the pseudo-random 8-bit character to the original state. See scrambling.
detached
A downstream device is detached from an upstream device when the physical cable
between the two is removed.
device
A logical or physical entity that performs one or more functions. The actual entity
described depends on the context of the reference. At the lowest level, device may refer
to a single hardware component, as in a memory device. At a higher level, it may refer to
a collection of hardware components that perform a particular function, such as a USB
interface device. At an even higher level, device may refer to the function performed by
an entity attached to the USB. Devices may be physical, electrical, addressable, and
logical.
When used as a non-specific reference, a USB device is either a hub or a peripheral
device.
2-2
device address
A 7-bit value representing the address of a device on the USB. The device address is the
default address (00H) when the USB device is first powered or the device is reset.
Devices are assigned a unique device address by the USB system software.
device endpoint
A uniquely addressable portion of a USB device that is the source or sink of information in
a communication flow between the host and device. See also endpoint address.
device software
Software that is responsible for using a USB device. This software may or may not also
be responsible for configuring the device for use.
disconnected
(unconnected)
A downstream device is disconnected from an upstream device when it is attached to the
upstream device, and when the downstream device has not asserted Rx terminations for
SuperSpeed signaling or has not asserted either the D+ or D- data line in order to enter
low-speed, full-speed, or high-speed signaling.
Terms and Abbreviations
Term/Abbreviation
Definition
downstream
The direction of data flow from the host or away from the host. A downstream port is the
port on a hub electrically farthest from the host that generates downstream data traffic
from the hub. Downstream ports receive upstream data traffic.
downstream facing port
See downstream port.
downstream port
The port on a host or a hub to which a device is connected. For example, a system’s root
ports are downstream ports.
DP
Data Packet which consists of a Data Packet Header followed by a Data Packet Payload.
DPH
Data Packet Header. Contains the data packet’s address, route string, length, and other
information about the packet.
DPP
Data Packet Payload. Contains the data packet’s data and a 32-bit CRC.
DPPABORT
Frame ordered set used to abort a data packet payload.
DPPEND
Frame ordered set used to denote the end of a data packet payload.
DPPSTART
Frame ordered set used to denote the start of a data packet payload.
driver
When referring to hardware, an I/O pad that drives an external load. When referring to
software, a program responsible for interfacing to a hardware device, that is, a device
driver.
dual simplex
Two data paths that independently carry traffic in each direction.
DWORD
Double word. A data element that is two words (i.e., 4 bytes or 32 bits) in size.
dynamic insertion and
removal
The ability to attach and remove devices while the host is in operation.
endpoint
See device endpoint.
endpoint address
The combination of an endpoint number and an endpoint direction on a USB device.
Each endpoint address supports data transfer in one direction.
endpoint direction
The direction of data transfer on the USB. The direction can be either IN or OUT. IN
refers to transfers to the host; OUT refers to transfers from the host.
endpoint number
A four-bit value between 0H and FH, inclusive, associated with an endpoint on a USB
device.
external port
See port.
frame number
The bus interval counter value within the ITP divided by 8 (integer division).
full-duplex
Computer data transmission occurring in both directions simultaneously.
full-speed
USB operation at 12 Mbps. See also low-speed and high-speed.
function
A set of one or more related interfaces on a USB device that exposes a capability to a
software client.
Gbps
Transmission rate expressed in gigabits per second (1,000,000,000 bits per second).
handshake packet
A packet that acknowledges or rejects a specific condition. For examples, see ACK,
NRDY, or ERDY.
header
Packet header. For example, DPH, LMP, and TP are all headers.
Header Sequence Number
Advertisement
The exchange of the ACK Tx Header Sequence Numbers between the link partners upon
entry to U0.
high-speed
USB operation at 480 Mbps. See also low-speed and full-speed.
host
The host computer system where the USB host controller is installed. This includes the
host hardware platform (CPU, bus, etc.) and the operating system in use.
host controller
The interface provided to the system to support devices on the USB.
Hot Reset
Reset mechanism using TS1/TS2 ordered sets.
HPSTART
Frame ordered set used to denote the start of a header packet.
2-3
Universal Serial Bus 3.0 Specification, Revision 1.0
Term/Abbreviation
Definition
hub
A USB device that provides additional connections to the USB.
hub tier
One plus the number of USB links in a communication path between the host and a
peripheral device.
ID pin
Denotes the pin on the USB 3.0 Micro connector family that is used to differentiate a USB
3.0 Micro-A plug from a USB 3.0 Micro-B plug.
Inband Reset
Mechanism that relies on SuperSpeed and/or LFPS signaling to propagate the reset
across the link.
informative
Information given for illustrative purposes only and contains no requirements. See
normative.
interrupt transfer
One of the four USB transfer types. Interrupt transfers have a bounded latency and are
typically used to handle service needs. See also transfer type.
isochronous data
A stream of data whose timing is implied by its delivery rate.
isochronous device
An entity with isochronous endpoints, as defined in the USB Specification, that sources or
sinks sampled analog streams or synchronous data streams.
isochronous sink endpoint
An endpoint that is capable of consuming an isochronous data stream that is sent by the
host.
isochronous source endpoint
An endpoint that is capable of producing an isochronous data stream and sending it to the
host.
isochronous transfer
One of the four USB transfer types. Isochronous transfers are used when working with
isochronous data. Isochronous transfers provide periodic, continuous communication
between host and device. See also transfer type.
ITP
Isochronous Timestamp Packet, sent periodically by a host to inform devices on the USB
of the current bus time.
jitter
A tendency toward lack of synchronization caused by mechanical or electrical changes.
More specifically, the phase shift of digital pulses over a transmission medium.
KB
Kilobyte or 1,024 bytes.
K codes
The control type codes used in 8b/10b encoding.
SHP – start header packet
SDP – start data packet
END – end header or data packet
EDB – end of nullified (bad) packet
SLC – start link command
COM – comma
SKP – skip
EPF – end packet framing
2-4
LCSTART
Frame ordered set used to denote the start of a link command.
LFPS
Low frequency periodic signal. Used to communicate information across a link without
using SuperSpeed signaling.
LFSR
Linear feedback shift register. Used to create pseudo-random characters for scrambling.
link command
An eight-symbol sequence used for link-level flow control, retries, power management,
and device removal.
Link Control Word
Two bytes with 11 bits to define the link level flow control and a 5-bit CRC5 to ensure data
integrity.
Terms and Abbreviations
Term/Abbreviation
Definition
little endian
Method of storing data that places the least significant byte of multiple-byte values at
lower storage addresses. For example, a 16-bit integer stored in little endian format
places the least significant byte at the lower address and the most significant byte at the
next address. See also big endian.
LMP
Link Management Packet. A type of header packet used to communicate information
between a pair of links.
Local Rx Header Buffer
Credit
The availability of a single free Rx Header Buffer of a port itself.
Logical Idle
Period of one or more symbol times when no information (packets or link commands) is
being transmitted when link is in U0.
low-speed
USB operation at 1.5 Mbps. See also full-speed and high-speed.
LSb
Least significant bit.
LSB
Least significant byte.
LTSSM
Link Training and Status State Machine.
message pipe
A bi-directional pipe that transfers data using a request/data/status paradigm. The data
has an imposed structure that allows requests to be reliably identified and communicated.
MSb
Most significant bit.
MSB
Most significant byte.
normative
Required by the specification. See also informative.
NRDY
Handshake packet indicating a negative acknowledgment.
packet
A bundle of data organized in a group for transmission. Packets typically contain three
elements: control information (e.g., source, destination, and length), the data to be
transferred and error detection and correction bits.
peripheral
A physical entity that is attached to a USB cable and is currently operating as a “device”
as defined in this specification.
peripheral device
A non-hub USB device that provides one or more functions to the host, such as a mass
storage device.
persistent
State information (e.g., a descriptor field) that is retained and persistent through entry into
and exit from D3.
Phase Locked Loop
A circuit that acts as a phase detector to keep an oscillator in phase with an incoming
frequency.
physical device
A device that has a physical implementation; e.g., speakers, microphones, and CD
players.
pipe
A logical abstraction representing the association between an endpoint on a device and
software on the host. A pipe has several attributes; for example, a pipe may transfer data
as streams (stream pipe) or messages (message pipe). See also stream pipe and
message pipe.
PLL
See Phase Locked Loop.
plug
Connector attached to the cable, to be mated with the receptacle
port
Point of access to or from a system or circuit. For the USB, the point where a USB device
is attached.
PowerOn Reset (POR)
An event to restore a device to its initial state.
PPM
Parts Per Million.
PRBS
Pseudo-Random Bit Stream.
protocol
A specific set of rules, procedures, or conventions relating to format and timing of data
transmission between two devices.
2-5
Universal Serial Bus 3.0 Specification, Revision 1.0
Term/Abbreviation
Definition
receptacle
Connector mounted on the host or device, to be mated with the plug.
Remote Rx Header Buffer
Credit
The availability of a single free Rx Header Buffer from a link partner.
request
A request made to a USB device contained within the data portion of a SETUP packet.
root hub
A USB hub directly attached to or integrated into the host controller.
root port
The downstream port on a root hub.
Rx Header Buffer Credit
Advertisement
The exchange of the Remote Rx Header Buffer Credits between the link partners upon
entry to U0.
Rx Header Sequence
Number
The expected header sequence number of a header packet received from a link partner.
scrambling
The process of changing an eight-bit character in a pseudo-random way. See
descrambling.
SDP
Shielded Differential Pair.
service interval
An integral multiple of bus intervals within which a periodic endpoint must be serviced.
service jitter
The deviation of service delivery from its scheduled delivery time.
SSC
Spread Spectrum Clock.
stage
One part of the sequence composing a control transfer; stages include the Setup stage,
the Data stage, and the Status stage.
stream pipe
A pipe that transfers data as a stream of samples with no defined USB structure.
SuperSpeed
USB operation at 5 Gbps.
synchronization type
A classification that characterizes an isochronous endpoint’s capability to connect to other
isochronous endpoints.
termination
Passive components attached at the end of the connections to prevent signals from being
reflected or echoed.
timeout
A time interval within which an expected event shall occur.
TP
Transaction Packet. A type of header packet used to communicate information between a
device and the host.
training sequences
Ordered sets for initializing bit and symbol alignment and receiver equalization. Examples
are TS1, TS2, and TSEQ.
transaction
The delivery of service to an endpoint:
• The IN consists of an ACK TP with a response of NRDY TP, DP, or STALL TP.
• The OUT consists of a DP with a response of NRDY TP, an ACK TP, or STALL TP.
2-6
transfer
One or more bus transactions to move information between a software client and its
function.
transfer type
Determines the characteristics of the data flow between a software client and its function.
Four standard transfer types are defined: control, interrupt, bulk, and isochronous.
Type-A connector
The standard-A connector defined in this specification.
Tx Header Sequence
Number
The header sequence number to be added to a header packet to be transmitted.
upstream
The direction of data flow towards the host. An upstream port is the port on a device
electrically closest to the host. Upstream ports receive downstream data traffic.
upstream port
A port that a device uses to connect to a host or a hub. The port on all devices is an
upstream port.
upstream facing port
See upstream port.
Terms and Abbreviations
Term/Abbreviation
Definition
USB 3.0 Standard-A
connector
USB 3.0 host connector, supporting SuperSpeed mode.
USB 3.0 Powered-B
connector
The standard Type-B device connector, supporting USB 3.0 SuperSpeed mode with
additional pins for power delivery from the device.
USB 3.0 Standard-B
connector
The standard Type-B device connector, supporting USB 3.0 SuperSpeed mode.
USB 3.0 Micro-A plug
Part of the USB 3.0 Micro connector family for OTG use; it can be plugged into a USB 3.0
Micro-AB receptacle; it differs from the USB 3.0 Micro-B plug only in keying and ID pin
connection.
USB 3.0 Micro-AB receptacle
Part of the USB 3.0 Micro connector family; it accepts either a USB 3.0 Micro-B plug or a
USB 3.0 Micro-A plug.
USB 3.0 Micro-B connector
USB 3.0 device connector, supporting SuperSpeed mode.
USB 3.0 Micro connector
family
All the receptacles and plugs that are used on devices, including the USB 3.0 Micro-B,
USB 3.0 Micro-AB, and USB 3.0 Micro-A connectors.
USB 2.0 Standard-A
connector
The Type-A connector defined by the USB 2.0 specification.
USB 2.0 Standard-B
connector
The standard Type-B connector defined by the USB 2.0 specification.
USB-IF
USB Implementers Forum, Inc. is a nonprofit corporation formed to facilitate the
development of USB compliant products and promote the technology.
UTP
Unshielded Twisted Pair.
Warm Reset
Reset mechanism using LFPS.
WORD
A data element that is 2 bytes (16 bits) in size.
2-7
Universal Serial Bus 3.0 Specification, Revision 1.0
2-8
3
USB 3.0 Architectural Overview
This chapter presents an overview of Universal Serial Bus 3.0 architecture and key concepts.
USB 3.0 is similar to earlier versions of USB in that it is a cable bus supporting data exchange
between a host computer and a wide range of simultaneously accessible peripherals. The attached
peripherals share bandwidth through a host-scheduled protocol. The bus allows peripherals to be
attached, configured, used, and detached while the host and other peripherals are in operation.
USB 3.0 utilizes a dual-bus architecture that provides backward compatibility with USB 2.0. It
provides for simultaneous operation of SuperSpeed and non-SuperSpeed (USB 2.0 speeds)
information exchanges. This chapter is organized into two focus areas. The first focuses on
architecture and concepts related to elements which span the dual buses. The second focuses on
SuperSpeed specific architecture and concepts.
Later chapters describe the various components and specific requirements of SuperSpeed USB in
greater detail. The reader is expected to have a fundamental understanding of the architectural
concepts of USB 2.0. Refer to the Universal Serial Bus Specification, Revision 2.0 for complete
details.
3.1
USB 3.0 System Description
USB 3.0 is a physical SuperSpeed bus combined in parallel with a physical USB 2.0 bus (see
Figure 3-1). It has similar architectural components as USB 2.0, namely:
Non-SuperSpeed
Super
Speed
HighSpeed
FullSpeed
LowSpeed
USB 3.0 Host
Extended
Connector(s)
SuperSpeed
Extended
Connector(s)
Non-SuperSpeed
(USB 2.0)
Composite Cable
SuperSpeed
Hub
USB 2.0
Hub
USB 3.0 Hub
•
USB 3.0 interconnect
•
USB 3.0 devices
•
USB 3.0 host
The USB 3.0 interconnect is the manner in
which USB 3.0 and USB 2.0 devices
connect to and communicate with the
USB 3.0 host. The USB 3.0 interconnect
inherits core architectural elements from
USB 2.0, although several are augmented to
accommodate the dual bus architecture.
The baseline structural topology is the same
as USB 2.0. It consists of a tiered star
topology with a single host at tier 1 and
hubs at lower tiers to provide bus
connectivity to devices.
SuperSpeed
Function
NonSuperSpeed
Function
USB 3.0 Peripheral Device
Note: Simultaneous operation of SuperSpeed and non-SuperSpeed
modes is not allowed for peripheral devices.
U-087
Figure 3-1. USB 3.0 Dual Bus Architecture
The USB 3.0 connection model
accommodates backwards and forward
compatibility for connecting USB 3.0 or
USB 2.0 devices into a USB 3.0 bus.
Similarly, USB 3.0 devices can be attached
to a USB 2.0 bus. The mechanical and
electrical backward/forwards compatibility
3-1
Universal Serial Bus 3.0 Specification, Revision 1.0
for USB 3.0 is accomplished via a composite cable and associated connector assemblies that form
the dual-bus architecture. USB 3.0 devices accomplish backward compatibility by including both
SuperSpeed and non-SuperSpeed bus interfaces. USB 3.0 hosts also include both SuperSpeed and
non-SuperSpeed bus interfaces, which are essentially parallel buses that may be active
simultaneously.
The USB 3.0 connection model allows for the discovery and configuration of USB devices at the
highest signaling speed supported by the device, the highest signaling speed supported by all hubs
between the host and device, and the current host capability and configuration.
USB 3.0 hubs are a specific class of USB device whose purpose is to provide additional connection
points to the bus beyond those provided by the host. In this specification, non-hub devices are
referred to as peripheral devices in order to differentiate them from hub devices. In addition, in
USB 2.0 the term “function” was sometimes used interchangeably with device. In this specification
a function is a logical entity within a device, see Figure 3-3.
The architectural implications of SuperSpeed on hosts and devices are described in detail in
Section 3.2.
3.1.1
USB 3.0 Physical Interface
The physical interface of USB 3.0 is comprised of USB 2.0 electrical (Chapter 7 of the USB 2.0
specification), mechanical (Chapter 5), and SuperSpeed physical (Chapter 6) specifications for the
buses. The SuperSpeed physical layer is described in Section 3.2.1.
3.1.1.1
USB 3.0 Mechanical
The mechanical specifications for USB 3.0 cables and connector assemblies are provided in
Chapter 5. All USB devices have an upstream connection. Hosts and hubs (defined below) have
one or more downstream connections. Upstream and downstream connectors are not mechanically
interchangeable, thus eliminating illegal loopback connections at hubs.
USB 3.0 cables have eight primary conductors: three twisted signal pairs for USB data paths and a
power pair. Figure 3-2 illustrates the basic signal arrangement for the USB 3.0 cable. In addition
to the twisted signal pair for USB 2.0 data path, two twisted signal pairs are used to provide the
SuperSpeed data path, one for the transmit path and one for the receive path.
VBUS
VBUS
D+
D-
D+
D-
SSTX+
SSTXSSRX+
SSRX-
SSRX+
SSRXSSTX+
SSTX-
GND
GND
U-088
Figure 3-2. USB 3.0 Cable
3-2
USB 3.0 Architectural Overview
USB 3.0 receptacles (both upstream and downstream) are backward compatible with USB 2.0
connector plugs. USB 3.0 cables and plugs are not intended to be compatible with USB 2.0
upstream receptacles. As an aid to users, USB 3.0 mandates standard coloring for plastic portions
of USB 3.0 plugs and receptacles.
Electrical (insertion loss, return loss, crosstalk, etc.) performance for USB 3.0 is defined with
regard to raw cables, mated connectors, and mated cable assemblies, with compliance requirements
using industry test specifications established for the latter two categories. Similarly, mechanical
(insertion/extraction forces, durability, etc.) and environmental (temperature life, mixed flowing
gas, etc.) requirements are defined and compliance established via recognized industry test
specifications.
3.1.2
USB 3.0 Power
The specification covers two aspects of power:
• Power distribution over the USB deals with the issues of how USB devices consume power
provided by the downstream ports to which they are connected. USB 3.0 power distribution is
similar to USB 2.0, with increased supply budgets for devices operating at SuperSpeed.
• Power management deals with how hosts, devices, hubs, and the USB system software interact
to provide power efficient operation of the bus. The power management of the USB 2.0 bus
portion is unchanged. The use model for power management of the SuperSpeed bus is
described in Appendix C.
3.1.3
USB 3.0 System Configuration
USB 3.0 supports USB devices (all speeds) attaching and detaching from the USB 3.0 at any time.
Consequently, system software must accommodate dynamic changes in the physical bus topology.
The architectural elements for the discovery of attachment and removal of devices on USB 3.0 are
identical to those in USB 2.0. There are enhancements provided to manage the specifics of the
SuperSpeed bus for configuration and power management.
The independent, dual-bus architecture allows for activation of each of the buses independently and
provides for the attachment of USB devices to the highest speed bus available for the device.
3.1.4
USB 3.0 Architecture Summary
USB 3.0 is a dual-bus architecture that incorporates USB 2.0 and a SuperSpeed bus. Table 3-1
summarizes the key architectural differences between SuperSpeed USB and USB 2.0.
Table 3-1. Comparing SuperSpeed to USB 2.0
Characteristic
SuperSpeed USB
USB 2.0
Data Rate
SuperSpeed (5.0 Gbps)
low-speed (1.5 Mbps), full-speed (12 Mbps),
and high-speed (480 Mbps)
Data Interface
Dual-simplex, four-wire differential signaling
separate from USB 2.0 signaling
Simultaneous bi-directional data flows
Half-duplex two-wire differential signaling
Unidirectional data flow with negotiated
directional bus transitions
Cable signal count
Six:
Two:
Bus transaction
protocol
Host directed, asynchronous traffic flow
Packet traffic is explicitly routed
Four for SuperSpeed data path
Two for non-SuperSpeed data path
Two for low-speed/full-speed/highspeed data path
Host directed, polled traffic flow
Packet traffic is broadcast to all devices.
3-3
Universal Serial Bus 3.0 Specification, Revision 1.0
3.2
Characteristic
SuperSpeed USB
USB 2.0
Power
management
Multi-level link power management supporting
idle, sleep, and suspend states. Link-, Device-,
and Function-level power management.
Port-level suspend with two levels of entry/exit
latency
Device-level power management
Bus power
Same as for USB 2.0 with a 50% increase for
unconfigured power and an 80% increase for
configured power
Support for low/high bus-powered devices with
lower power limits for un-configured and
suspended devices
Port State
Port hardware detects connect events and
brings the port into operational state ready for
SuperSpeed data communication.
Port hardware detects connect events. System
software uses port commands to transition the
port into an enabled state (i.e., can do USB
data communication flows).
Data transfer
types
USB 2.0 types with SuperSpeed constraints.
Bulk has streams capability (refer to
Section 3.2.8)
Four data transfer types: control, bulk,
Interrupt, and Isochronous
SuperSpeed Architecture
The SuperSpeed bus is a layered communications architecture that is comprised of the following
elements:
• SuperSpeed Interconnect. The SuperSpeed interconnect is the manner in which devices are
connected to and communicate with the host over the SuperSpeed bus. This includes the
topology of devices connected to the bus, the communications layers, the relationships between
them and how they interact to accomplish information exchanges between the host and devices.
• Devices. SuperSpeed devices are sources or sinks of information exchanges. They implement
the required device-end, SuperSpeed communications layers to accomplish information
exchanges between a driver on the host and a logical function on the device.
• Host. A SuperSpeed host is a source or sink of information. It implements the required hostend, SuperSpeed communications layers to accomplish information exchanges over the bus. It
owns the SuperSpeed data activity schedule and management of the SuperSpeed bus and all
devices connected to it.
Figure 3-3 illustrates a reference diagram of the SuperSpeed interconnect represented as
communications layers through a topology of host, zero to five levels of hubs, and devices.
3-4
Host
Hub
Device
Device Driver/Application
Pipe Bundle (per Function Interface)
Function
USB System Software
Default Control Pipe
Device
Notifications
Transactions
Transaction
Packets
Notifications
Data
Packets
Port-to-Port
Chip to Chip
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Localized
Link Power
Management
PHYSICAL
8b/10b
encode/
decode
Data
Packets
LINK
Link Cmds
USB Device
Power
Management
(Suspend)
Link Management Packets
Link Control/Mgmt
Pkt
Delims
Transactions
Transaction
Packets
Link Management Packets
USB Function
Power
Management
Device or Host PROTOCOL
End-to-End
USB 3.0 Architectural Overview
U-089
Figure 3-3. SuperSpeed Bus Communications Layers and
Power Management Elements
The rows (device or host, protocol, link, physical) realize the communications layers of the
SuperSpeed interconnect. Sections 3.2.1 through 3.2.3 provide architectural overviews of each of
the communications layers. The three, left-most columns (host, hub, and device) illustrate the
topological relationships between devices connected to the SuperSpeed bus; refer to the overview
in Sections 3.2.6 through 3.2.7. The right-most column illustrates the influence of power
management mechanisms over the communications layers; refer to the overview in Section 3.2.5.
3.2.1
Physical Layer
The physical layer specifications for SuperSpeed are detailed in Chapter 6. The physical layer
defines the PHY portion of a port and the physical connection between a downstream facing port
(on a host or hub) and the upstream facing port on a device. The SuperSpeed physical connection
is comprised of two differential data pairs, one transmit path and one receive path (see Figure 3-2).
The nominal signaling data rate is 5 Gbps.
The electrical aspects of each path are characterized as a transmitter, channel, and receiver; these
collectively represent a unidirectional differential link. Each differential link is AC-coupled with
capacitors located on the transmitter side of the differential link. The channel includes the electrical
characteristics of the cables and connectors.
At an electrical level, each differential link is initialized by enabling its receiver termination. The
transmitter is responsible for detecting the far end receiver termination as an indication of a bus
connection and informing the link layer so the connect status can be factored into link operation and
management.
3-5
Universal Serial Bus 3.0 Specification, Revision 1.0
When receiver termination is present but no signaling is occurring on the differential link, it is
considered to be in the electrical idle state. When in this state, low frequency periodic signaling
(LFPS) is used to signal initialization and power management information. The LFPS is relatively
simple to generate and detect and uses very little power.
Each PHY has its own clock domain with Spread Spectrum Clocking (SSC) modulation. The
USB 3.0 cable does not include a reference clock so the clock domains on each end of the physical
connection are not explicitly connected. Bit-level timing synchronization relies on the local receiver
aligning its bit recovery clock to the remote transmitter’s clock by phase-locking to the signal
transitions in the received bit stream.
The receiver needs enough transitions to reliably recover clock and data from the bit stream. To
assure that adequate transitions occur in the bit stream independent of the data content being
transmitted, the transmitter encodes data and control characters into symbols using an 8b/10b code.
Control symbols are used to achieve byte alignment and are used for framing data and managing
the link. Special characteristics make control symbols uniquely identifiable from data symbols.
A number of techniques are employed to improve channel performance. For example, to avoid
overdriving and improve eye margin at the receiver, transmitter de-emphasis may be applied when
multiple bits of the same polarity are sent. Also, equalization may be used in the receiver with the
characteristics of the equalization profile being established adaptively as part of link training.
Signal (timing, jitter tolerance, etc.) and electrical (DC characteristics, channel capacitance, etc.)
performance of SuperSpeed links are defined with compliance requirements specified in terms of
transmit and receive signaling eyes.
The physical layer receives 8-bit data from the link layer and scrambles the data to reduce EMI
emissions. It then encodes the scrambled 8-bit data into 10-bit symbols for transmission over the
physical connection. The resultant data are sent at a rate that includes spread spectrum to further
lower the EMI emissions. The bit stream is recovered from the differential link by the receiver,
assembled into 10-bit symbols, decoded and descrambled, producing 8-bit data that are then sent to
the link layer for further processing.
3.2.2
Link Layer
The link layer specifications for SuperSpeed are detailed in Chapter 7. A SuperSpeed link is a
logical and physical connection of two ports. The connected ports are called link partners. A port
has a physical part (refer to Section 3.2.1) and a logical part. The link layer defines the logical
portion of a port and the communications between link partners.
The logical portion of a port has:
• State machines for managing its end of the physical connection. These include physical layer
initialization and event management, i.e., connect, removal, and power management.
• State machines and buffering for managing information exchanges with the link partner. It
implements protocols for flow control, reliable delivery (port to port) of packet headers, and
link power management. The different packet types are defined in Chapter 7.
• Buffering for data and protocol layer information elements.
The logical portion of a port also:
• Provides correct framing of sequences of bytes into packets during transmission; e.g., insertion
of packet delimiters
3-6
USB 3.0 Architectural Overview
•
•
Detects received packets, including packet delimiters and error checks of received header
packets (for reliable delivery)
Provides an appropriate interface to the protocol layer for pass-through of protocol-layer packet
information exchanges
The physical layer provides the logical port an interface through which it is able to:
• Manage the state of its PHY (i.e., its end of the physical connection), including power
management and events (connection, removal, and wake).
• Transmit and receive byte streams, with additional signals that qualify the byte stream as
control sequences or data. The physical layer includes discrete transmit and receive physical
links, therefore, a port is able to simultaneously transmit and receive control and data
information.
The protocol between link partners uses specific encoded control sequences. Note that control
sequences are encoded to be tolerant to a single bit error. Control sequences are used for port-toport command protocol, framing of packet data (packet delimiters), etc. There is a link-partner
protocol for power management that uses packet headers.
3.2.3
Protocol Layer
The protocol layer specifications for SuperSpeed are detailed in Chapter 8. This protocol layer
defines the “end-to-end” communications rules between a host and device (see Figure 3-3).
The SuperSpeed protocol provides for application data information exchanges between a host and a
device endpoint. This communications relationship is called a pipe. It is a host-directed protocol,
which means the host determines when application data is transferred between the host and device.
SuperSpeed is not a polled protocol, as a device is able to asynchronously request service from the
host on behalf of a particular endpoint.
All protocol layer communications are accomplished via the exchange of packets. Packets are
sequences of data bytes with specific control sequences which serve as delimiters managed by the
link layer. Host transmitted protocol packets are routed through intervening hubs directly to a
peripheral device. They do not traverse bus paths that are not part of the direct path between the
host and the target peripheral device. A peripheral device expects it has been targeted by any
protocol layer packet it receives. Device transmitted protocol packets simply flow upstream through
hubs to the host.
Packet headers are the building block of the protocol layer. They are fixed size packets with type
and subtype field encodings for specific purposes. A small record within a packet header is utilized
by the link layer (port-to-port) to manage the flow of the packet from port to port. Packet headers
are delivered through the link layer (port-to-port) reliably. The remaining fields are utilized by the
end-to-end protocol.
Application data is transmitted within data packet payloads. Data packet payloads are preceded (in
the protocol) by a specifically encoded data packet headers. Data packet payloads are not delivered
reliably through the link layer (however, the accompanying data packet headers are delivered
reliably). The protocol layer supports reliable delivery of data packets via explicit
acknowledgement (header) packets and retransmission of lost or corrupt data. Not all data
information exchanges utilize data acknowledgements.
Data may be transmitted in bursts of back-to-back sequences of data packets (depending on the
scheduling by the host). The protocol allows efficient bus utilization by concurrently transmitting
and receiving over the link. For example, a transmitter (host or device) can burst multiple packets
3-7
Universal Serial Bus 3.0 Specification, Revision 1.0
of data back-to-back while the receiver can transmit data acknowledgements without interrupting
the burst of data packets. The number of data packets in a specific burst is scheduled by the host.
Furthermore, a host may simultaneously schedule multiple OUT bursts to be active at the same time
as an IN burst.
The protocol provides flow control support for some transfer types. A device-initiated flow control
is signaled by a device via a defined protocol packet. A host-initiated flow control event is realized
via the host schedule (host will simply not schedule information flows for a pipe unless it has data
or buffering available). On reception of a flow control event, the host will remove the pipe from its
schedule. Resumption of scheduling information flows for a pipe may be initiated by the host or
device. A device endpoint will notify a host of its readiness (to source or sink data) via an
asynchronously transmitted “ready” packet. On reception of the “ready” notification, the host will
add the pipe to its schedule, assuming that it still has data or buffering available.
Independent information streams can be explicitly delineated and multiplexed on the bulk transfer
type. This means through a single pipe instance, more than one data stream can be tagged by the
source and identified by the sink. The protocol provides for the device to direct which data stream
is active on the pipe.
Devices may asynchronously transmit notifications to the host. These notifications are used to
convey a change in the device or function state.
A host transmits a special packet header to the bus that includes the host’s timestamp. The value in
this packet is used to keep devices (that need to) in synchronization with the host. In contrast to
other packet types, the timestamp packet is forwarded down all paths not in a low power state. The
timestamp packet transmission is scheduled by the host at a specification determined period.
3.2.4
Robustness
There are several attributes of SuperSpeed USB that contribute to its robustness:
• Signal integrity using differential drivers, receivers, and shielding
• CRC protection for header and data packets
• Link level header packet retries to ensure their reliable delivery
• End-to-end protocol retries of data packets to ensure their reliable delivery
• Detection of attach and detach and system-level configuration of resources
• Data and control pipe constructs for ensuring independence from adverse interactions between
functions
3.2.4.1
Error Detection
The USB SuperSpeed physical layer bit error rate is expected to be less than one in 1012 bits. To
provide protection against occasional bit errors, packet framing and link commands have sufficient
redundancy to tolerate single-bit errors. Each packet includes a CRC to provide error detection of
multiple bit errors. When data integrity is required an error recovery procedure may be invoked in
hardware or software.
The protocol includes separate CRCs for headers and data packet payloads. Additionally, the link
control word (in each packet header) has its own CRC. A failed CRC in the header or link control
word is considered a serious error which will result in a link level retry to recover from the error. A
failed CRC in a data packet payload is considered to indicate corrupted data and can be handled by
the protocol layer with a request to resend the data packet.
3-8
USB 3.0 Architectural Overview
The link and physical layers work together to provide reliable packet header transmission. The
physical layer provides an error rate that does not exceed (on average) one bit error in every
1012 bits. The link layer uses error checking to catch errors and retransmission of the packet header
further reducing the packet header error rate.
3.2.4.2
Error Handling
Errors may be handled in hardware or software. Hardware error handling includes reporting and
retrying of failed header packets. A USB host controller will try a transmission that encounters
errors up to three times before informing the client software of the failure. The client software can
recover in an implementation-specific way.
3.2.5
SuperSpeed Power Management
SuperSpeed provides power management at distinct areas in the bus architecture, link, device, and
function (refer to Figure 3-3). These power management areas are not tightly coupled but do have
dependencies; these mostly deal with allowable power state transitions based on dependencies with
power states of links, devices, and functions.
Link power management occurs asynchronously on every link (i.e., locally) in the connected
hierarchy. The link power management policy may be driven by the device, the host or a
combination of both. The link power state may be driven by the device or by the downstream port
inactivity timers that are programmable by host software. The link power states are propagated
upwards by hubs (e.g., when all downstream ports are in a low power state, the hub is required to
transition its upstream port to a low power state). The decisions to change link power states are
made locally. The host does not directly track the individual link power states. Since only those
links between the host and device are involved in a given data exchange, links that are not being
utilized for data communications can be placed in a lower power state.
The host does not directly control or have visibility of the individual links’ power states. This
implies that one or more links in the path between the host and device can be in reduced power
state when the host initiates a communication on the bus. There are in-band protocol mechanisms
that force these links to transition to the operational power state and notify the host that a transition
has occurred. The host knows (can calculate) the worst-case transition time to bring a path to any
specific device to an active, or ready state, using these mechanisms. Similarly, a device initiating a
communication on the bus with its upstream link in a reduced power state, will first transition its
link into an operational state which will cause all links between it and the host to transition to the
operational state.
The key points of link power management include:
• Devices send asynchronous ready notifications to the host.
• Packets are routed, allowing links that are not involved in data communications to transition to
and/or remain in a low power state.
• Packets that encounter ports in low power states cause those ports to transition out of the low
power state with indications of the transition event.
• Multiple host or device driven link states with progressively lower power at increased exit
latencies.
As with the USB 2.0 bus, devices can be explicitly suspended via a similar port-suspend
mechanism. This sets the link to the lowest link power state and sets a limit on the power draw
requirement of the device.
3-9
Universal Serial Bus 3.0 Specification, Revision 1.0
SuperSpeed provides support for function power management in addition to device power
management. For multi-function (composite) devices, each function can be independently placed
into a lower power state. Note that a device will transition into the suspended state when directed
by the host via a port command. The device will not automatically transition into the suspended
state when all the individual functions within it are suspended.
Functions on devices may be capable of being remote wake sources. The remote-wake feature on a
function must be explicitly enabled by the host. Likewise, a protocol notification is available for a
function to signal a remote wake event that can be associated with the source function. All remotewake notifications are functional across all possible combinations of individual link power states on
the path between the device and host.
3.2.6
Devices
All SuperSpeed devices share their base architecture with USB 2.0. They are required to carry
information for self-identification and generic configuration. They are also required to demonstrate
behavior consistent with the defined SuperSpeed Device States.
All devices are assigned a USB address when enumerated by the host. Each device supports one or
more pipes through which the host may communicate with the device. All devices must support a
designated pipe at endpoint zero to which the device’s Default Control Pipe is attached. All
devices support a common access mechanism for accessing information through this control pipe.
Refer to Chapter 9 for a complete definition of a control pipe.
SuperSpeed inherits the categories of information that are supported on the default control pipe
from USB 2.0.
The USB 3.0 specification defines two sets of USB devices that can be connected to a SuperSpeed
host. These are described briefly below.
3.2.6.1
Peripheral Devices
A USB 3.0 peripheral device must provide support for both SuperSpeed and at least one other nonSuperSpeed speed. The minimal requirement for non-SuperSpeed is for a device to be detected on
a USB 2.0 host and allow system software to direct the user to attach the device to a SuperSpeed
capable port. A device implementation may provide appropriate full functionality when operating
in non-SuperSpeed mode. Simultaneous operation of SuperSpeed and non-SuperSpeed modes is
not allowed for peripheral devices.
USB 3.0 devices within a single physical package (i.e., a single peripheral) can consist of a number
of functional topologies including single function, multiple functions on a single peripheral device
(composite device), and permanently attached peripheral devices behind an integrated hub
(compound device) (see Figure 3-4).
3-10
USB 3.0 Architectural Overview
Peripheral Device
Single Function (single interface)
USB 3.0
Function
Peripheral Device
Multiple Function (multiple interfaces)
(Composite Device)
USB 3.0
USB
3.0
Function
Function
USB 3.0
Device
USB 3.0
Hub
USB 3.0
Device
USB 3.0
Hub
USB 2.0
Device
Compound Device
(combinations)
USB 3.0
Device
U-090
Figure 3-4. Examples of Supported SuperSpeed USB Physical Device Topologies
3.2.6.2
Hubs
The specifications for the SuperSpeed portion of a USB 3.0 hub are detailed in Chapter 10. Hubs
have always been a key element in the plug-and-play architecture of the USB. Hosts provide an
implementation-specific number of downstream ports to which devices can be attached. Hubs
provide additional downstream ports so they provide users with a simple connectivity expansion
mechanism for the attachment of additional devices to the USB.
In order to support the dual-bus architecture of USB 3.0, a USB 3.0 hub is the logical combination
of two hubs: a USB 2.0 hub and a SuperSpeed hub (see the hub in Figure 3-1). The power and
ground from the cable connected to the upstream port are shared across both units within the
USB 3.0 hub. The USB 2.0 hub unit is connected to the USB 2.0 data lines and the SuperSpeed
hub is connected to the SuperSpeed data lines. A USB 3.0 hub connects upstream as two devices; a
SuperSpeed hub on the SuperSpeed bus and a USB 2.0 hub on the USB 2.0 bus.
The SuperSpeed hub manages the SuperSpeed portions of the downstream ports and the USB 2.0
hub manages the USB 2.0 portions of the downstream ports. Each physical port has bus-specific
control/status registers. Refer to the Universal Serial Bus Specification, Revision 2.0 for details on
the USB 2.0 hub. Hubs detect device attach, removal, and remote-wake events on downstream ports
and enable the distribution of power to downstream devices.
A SuperSpeed hub consists of two logical components: a SuperSpeed hub controller and a
SuperSpeed repeater/forwarder. The hub repeater/forwarder is a protocol-controlled router between
the SuperSpeed upstream port and downstream ports. It also has hardware support for reset and
suspend/resume signaling. The SuperSpeed controller responds to standard, hub-specific
status/control commands that are used by a host to configure the hub and to monitor and control its
ports.
SuperSpeed hubs actively participate in the (end-to-end) protocol in several ways, including:
• Routes out-bound packets to explicit downstream ports.
• Aggregates in-bound packets to the upstream port.
• Propagates the timestamp packet to all downstream ports not in a low-power state.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
3.2.7
Detects when packets encounter a port that is in a low-power state. The hub transitions the
targeted port out of the low-power state and notifies the host and device (in-band) that the
packet encountered a port in a low-power state.
Hosts
A USB 3.0 host interacts with USB devices through a host controller. To support the dual-bus
architecture of USB 3.0, a host controller must include both SuperSpeed and USB 2.0 elements,
which can simultaneously manage control, status and information exchanges between the host and
devices over each bus.
The host includes an implementation-specific number of root downstream ports for SuperSpeed and
USB 2.0. Through these ports the host:
• Detects the attachment and removal of USB devices
• Manages control flow between the host and USB devices
• Manages data flow between the host and USB devices
• Collects status and activity statistics
• Provides power to attached USB devices
USB System Software inherits its architectural requirements from USB 2.0, including:
• Device enumeration and configuration
• Scheduling of periodic and asynchronous data transfers
• Device and function power management
• Device and bus management information
3.2.8
Data Flow Models
The data flow models for SuperSpeed are described in Chapter 4. SuperSpeed USB inherits the data
flow models from USB 2.0, including:
• Data and control exchanges between the host and devices are via sets of either unidirectional or
bi-directional pipes.
• Data transfers occur between host software and a particular endpoint on a device. The endpoint
is associated with a particular function on the device. These associations between host software
to endpoints related to a particular function are called pipes. A device may have more than one
active pipe. There are two types of pipes: stream and message. Stream data has no USBdefined structure, while message does. Pipes have associations of data bandwidth, transfer
service type (see below), and endpoint characteristics, like direction and buffer size.
• Most pipes come into existence when the device is configured by system software. However,
one message pipe, the Default Control Pipe, always exists once a device has been powered and
is in the default state, to provide access to the device’s configuration, status, and control
information.
• A pipe supports one of four transfer types as defined in USB 2.0 (bulk, control, interrupt, and
isochronous). The basic architectural elements of these transfer types are unchanged from
USB 2.0.
• The bulk transfer type has an extension for SuperSpeed called Streams. Streams provide inband, protocol-level support for multiplexing multiple independent logical data streams through
a standard bulk pipe.
3-12
4. SuperSpeed Data Flow Model
This chapter presents a high-level description of how data and information move across the
SuperSpeed. Consult the Protocol Layer Chapter for details on the low-level protocol. This
chapter provides device framework overview information that is further expanded in the Device
Framework Chapter. All implementers should read this chapter to understand the key concepts of
SuperSpeed.
4.1 Implementer Viewpoints
SuperSpeed is very similar to USB 2.0 in that it provides communication services between a USB
Host and attached USB Devices. The communication model view preserves the USB 2.0 layered
architecture and basic components of the communication flow (i.e., point-to-point, same transfer
types, etc.). Refer to Chapter 5 in the Universal Serial Bus Specification, Revision 2.0 for more
information about the USB 2.0 communication flow.
This chapter describes the differences (from USB 2.0) of how data and control information is
communicated between a SuperSpeed Host and its attached SuperSpeed Devices. In order to
understand SuperSpeed data flow, the following concepts are useful:
• Communication Flow Models: Section 4.2 describes how communication flows between the
host and devices through the SuperSpeed bus.
• SuperSpeed Protocol Overview: Section 4.3 gives a high level overview of the SuperSpeed
protocol and compares it to the USB 2.0 protocol.
• Generalized Transfer Description: Section 4.4 provides an overview of how data transfers
work in SuperSpeed and subsequent sections define the operating constraints for each transfer
type.
• Device Notifications: Section 4.4.9 provides an overview of Device Notifications, a feature
which allows a device to asynchronously notify its host of events or status on the device.
• Reliability and Efficiency: Sections 4.4.10 and 4.4.11 summarize the information and
mechanisms available in SuperSpeed to ensure reliability and increase efficiency.
4.2 SuperSpeed Communication Flow
SuperSpeed retains the familiar concepts and mechanisms and support for endpoints, pipes, and
transfer types. Refer to the Universal Serial Bus Specification, Revision 2.0 for details. As in
USB 2.0, the ultimate consumer/producer of data is an endpoint.
The endpoint’s characteristics (Max Packet Size, Burst Size, etc.) are reported in the endpoint
descriptor and the SuperSpeed Endpoint Companion Descriptor. As in USB 2.0, the endpoint is
identified using an addressing triple {Device Address, Endpoint Number, Direction}.
All SuperSpeed devices must implement at least the Default Control Pipe (endpoint zero). The
Default Control Pipe is a control pipe as defined in the Universal Serial Bus Specification,
Revision 2.0.
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Universal Serial Bus 3.0 Specification, Revision 1.0
4.2.1
Pipes
A SuperSpeed pipe is an association between an endpoint on a device and software on the host.
Pipes represent the ability to move data between software on the host via a memory buffer and an
endpoint on a device and have the same behavior as defined in the Universal Serial Bus
Specification, Revision 2.0. The main difference is that when a non-isochronous endpoint in
SuperSpeed is busy it returns a Not Ready (NRDY) response and must send an Endpoint Ready
(ERDY) notification when it wants to be serviced again. The host will then reschedule the
transaction at the next available opportunity within the constraints of the transfer type.
4.3 SuperSpeed Protocol Overview
As mentioned in the USB 3.0 Architecture Overview Chapter, the SuperSpeed protocol is
architected to take advantage of the dual-simplex physical layer. All the USB 2.0 transfer types are
supported by the SuperSpeed protocol. The differences between the USB 2.0 protocol and the
SuperSpeed protocol are first discussed followed by a brief description of the packets used in
SuperSpeed.
4.3.1
Differences from USB 2.0
SuperSpeed is backward compatible with USB 2.0 at the framework level. However, there are
some fundamental differences between the USB 2.0 and SuperSpeed protocol:
• USB 2.0 uses a three-part transaction (Token, Data, and Handshake) while SuperSpeed uses the
same three parts differently. For OUTs, the token is incorporated in the data packet; while for
INs, the Token is replaced by a handshake.
• USB 2.0 does not support bursting while SuperSpeed supports continuous bursting.
• USB 2.0 is a half-duplex broadcast bus while SuperSpeed is a dual-simplex unicast bus which
allows concurrent IN and OUT transactions.
• USB 2.0 uses a polling model while SuperSpeed uses asynchronous notifications.
• USB 2.0 does not have a Streaming capability while SuperSpeed supports Streaming for bulk
endpoints.
• USB 2.0 offers no mechanism for isochronous capable devices to enter the low power USB bus
state between service intervals. SuperSpeed allows isochronous capable devices to
autonomously enter low-power link states between service intervals. A SuperSpeed host may
transmit a PING packet to the targeted isochronous device before service interval to allow time
for the path to transition back to the active power state before initiating the isochronous
transfer.
• USB 2.0 offers no mechanism for device to inform the host how much latency the device can
tolerate if the system enters lower system power state. Thus a host may not enter lower system
power states as it might impact a device's performance because it lacks an understanding of a
device's power policy. USB 3.0 provides a mechanism to allow SuperSpeed devices to inform
host of their latency tolerance using Latency Tolerance Messaging. The host may use this
information to establish a system power policy that accounts for the devices’ latency tolerance.
• USB 2.0 transmits SOF/uSOF at fixed 1 ms/125 μs intervals. A device driver may change the
interval with small finite adjustments depending on the implementation of host and system
software. USB 3.0 adds mechanism for devices to send a Bus Interval Adjustment Message that
is used by the host to adjust its 125 μs bus interval up to +/-13.333 μs. In addition, the host
4-2
SuperSpeed Data Flow Model
•
•
4.3.1.1
may send an Isochronous Timestamp Packet (ITP) within a relaxed timing window from a bus
interval boundary.
USB 2.0 power management, including Link Power Management, is always directly initiated
by the host. SuperSpeed supports link-level power management that may be initiated from
either end of the link. Thus, each link can independently enter low-power states whenever idle
and exit whenever communication is needed.
USB 2.0 handles transaction error detection and recovery and flow control only at the end-toend level for each transaction. SuperSpeed splits these functions between the end-to-end and
link levels.
Comparing USB 2.0 and SuperSpeed Transactions
The SuperSpeed dual-simplex physical layer allows information to travel simultaneously in both
directions. The SuperSpeed protocol allows the transmitter to send multiple data packets before
receiving a handshake. For OUT transfers, the information contained in the USB 2.0 Token is
incorporated in the data packet header so a separate Token is not required. For IN transfers, a
handshake is sent to the device to request data. The device may respond by either returning data,
returning a STALL handshake, or by returning a Not Ready (NRDY) handshake to defer the
transfer until the device is ready.
The USB 2.0 broadcasts packets to all enabled downstream ports. Every device is required to
decode the address triple {device address, endpoint, and direction} of each packet to determine if it
needs to respond. SuperSpeed unicasts the packets; downstream packets are sent over a directed
path between the host and the targeted device while upstream packets are sent over the direct path
between the device and the host. SuperSpeed packets contain routing information that the hubs use
to determine which downstream port the packet needs to traverse to reach the device. There is one
exception; the Isochronous Timestamp Packet (ITP) is multicast to all active ports.
USB 2.0 style polling has been replaced with asynchronous notifications. The SuperSpeed
transaction is initiated by the host making a request followed by a response from the device. If the
device can honor the request, it either accepts or sends data. If the endpoint is halted, the device
shall respond with a STALL handshake. If it cannot honor the request due to lack of buffer space
or data, it responds with a Not Ready (NRDY) to tell the host that it is not able to process the
request at this time. When the device can honor the request, it will send an Endpoint Ready
(ERDY) to the host which will then reschedule the transaction.
The move to unicasting and the limited multicasting of packets together with asynchronous
notifications allows links that are not actively passing packets to be put into reduced power states.
Upstream and downstream ports cooperate to place their link into a reduced power state that hubs
will propagate upstream. Allowing link partners to control their independent link power state and a
hub’s propagating the highest link power state seen on any of its downstream ports to its upstream
port, puts the bus into the lowest allowable power state rapidly.
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Universal Serial Bus 3.0 Specification, Revision 1.0
4.3.1.2
Introduction to SuperSpeed Packets
SuperSpeed packets start with a 16-byte header. Some packets consist of a header only. All
headers begin with the Packet Type information used to decide how to handle the packet. The
header is protected by a 16-bit CRC (CRC-16) and ends with a 2-byte link control word.
Depending on the Type, most packets contain routing information (Route String) and a device
address triple {device address, endpoint number, and direction}. The Route String is used to direct
packets sent by the host on a directed path through the topology. Packets sent by the device are
implicitly routed as the hub always forwards a packet seen on any downstream port to its upstream
port. There are four basic types of packets: Link Management Packets, Transaction Packets, Data
Packets, and Isochronous Timestamp Packets:
• A Link Management Packet (LMP) only traverses a pair of directly connected ports and is
primarily used to manage that link.
• A Transaction Packet (TP) traverses all the links in the path directly connecting the host and a
device. It is used to control the flow of data packets, configure devices and hubs, etc. Note that
a Transaction Packet does not have a data payload.
• A Data Packet (DP) traverses all the links in the path directly connecting the host and a device.
Data Packets consist of two parts: a Data Packet Header (DPH) which is similar to a TP and a
Data Packet Payload (DPP) which consists of the data block plus a 32-bit CRC (CRC-32) used
to ensure the data’s integrity.
• An Isochronous Timestamp Packet (ITP) is a multicast packet sent by the host to all active
links.
4.4 Generalized Transfer Description
Each non-isochronous data packet sent to a receiver is acknowledged by a handshake (called an
ACK transaction packet). However, due to the fact that SuperSpeed has independent transmit and
receive paths, the transmitter does not have to wait for an explicit handshake for each data packet
transferred before sending the next packet.
SuperSpeed preserves all of the basic data flow and transfer concepts defined in USB 2.0, including
the transfer types, pipes, and basic data flow model. The differences with USB 2.0 are discussed in
this section, starting at the protocol level, followed by transfer type constraints.
The USB 2.0 specification utilizes a serial transaction model. This essentially means that a host
starts and completes one bus transaction {Token, Data, Handshake} before starting the next
transaction. Split transactions also adhere to this same model since they are comprised of complete
high-speed transactions {Token, Data, Handshake} that are completed under the same model as all
other transactions.
SuperSpeed improves on the USB 2.0 transaction protocol by using the independent transmit and
receive paths. The result is that the SuperSpeed USB transaction protocol is essentially a splittransaction protocol that allows more than one OUT “bus transaction” as well as at most one IN
“bus transaction” to be active on the bus at the same time. The order in which a device responds to
transactions is fixed on a per endpoint basis (for example, if an endpoint received three DPs, the
endpoint must return ACK TPs for each one, in the order that the DPs were received). The order a
device responds to ACKs or DPs that are sent to different endpoints on the device is device
implementation dependent and software can not expect them to occur/complete in any particular
4-4
SuperSpeed Data Flow Model
order. The split-transaction protocol scales well (across multiple transactions to multiple function
endpoints) with signaling bit-rates as it is not subject to propagation delays.
The USB 2.0 protocol completes an entire IN or OUT transaction {Token, Data, Handshake}
before continuing to the next bus transaction for the next scheduled function endpoint. All
transmissions from the host are essentially broadcast on the USB 2.0 bus. In contrast, the
SuperSpeed protocol does not broadcast any packets (except for ITPs) and packets traverse only the
links needed to reach the intended recipient. The host starts all transactions by sending handshakes
or data and devices respond with either data or handshakes. If the device does not have data
available or cannot accept the data, it responds with a packet that states that it is not able to do so.
Subsequently, when the device is ready to either receive or transmit data it sends a notification to
the host that indicates that it is ready to resume transactions. In addition, SuperSpeed provides the
ability to transition links into and out of specific low power states. Lower power link states are
entered either under software control or under autonomous hardware control after being enabled by
software. Mechanisms are provided to automatically transition all links in the path between the
host and a device from a non-active power state to the active power state.
Devices report the maximum packet size for each endpoint in its endpoint descriptor. The size
indicates data payload length only and does not include any of the overhead for link and protocol
level. Bandwidth allocation for SuperSpeed is similar to USB 2.0.
4.4.1
Data Bursting
Data Bursting enhances efficiency by eliminating the wait time for acknowledgements on a per data
packet basis. Each endpoint on a SuperSpeed device indicates the number of packets that it can
send/receive (called the maximum data burst size) before it has to wait for an explicit handshake.
Maximum data burst size is an individual endpoint capability; a host determines an endpoint’s
maximum data burst size from the SuperSpeed Endpoint Companion descriptor associated with this
endpoint (refer to Section 9.6.7).
The host may dynamically change the burst size on a per-transaction basis up to the configured
maximum burst size. Examples of when a host may use different burst sizes include, but are not
limited to, a fairness policy on the host and retries for an interrupt stream. When the endpoint is an
OUT, the host can easily control the burst size (the receiver must always be able to manage a
transaction burst size). When the endpoint is an IN, the host can limit the burst size for the
endpoint on a per-transaction basis via a field in the acknowledgement packet sent to the device.
4.4.2
IN Transfers
The host and device shall adhere to the constraints of the transfer type and endpoint characteristics.
A host initiates a transfer by sending an acknowledgement packet (IN) to the device. This
acknowledgement packet contains the addressing information required to route the packet to the
intended endpoint. The host tells the device the number of data packets it can send and the
sequence number of the first data packet expected from the device. In response the endpoint will
transmit data packet(s) with the appropriate sequence numbers back to the host. The
acknowledgement packet also implicitly acknowledges the previous data packet that was received
successfully.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Note that even though the host is required to send an acknowledgement packet for every data
packet received, the device can send up to the number of data packets requested without waiting for
any acknowledgement packet.
The SuperSpeed IN transaction protocol is illustrated in Figure 4-1. An IN transfer on the
SuperSpeed bus consists of one or more IN transactions consisting of one or more packets and
completes when any one of the following conditions occurs:
• All the data for the transfer is successfully received.
• The endpoint responds with a packet that is less than the endpoint’s maximum packet size.
• The endpoint responds with an error.
IN Session
Transaction(s)
Tx
IN
N Packets
I
Ack
X
Host
Rx
Rx
Device
begin burst
Ack X+1
Tx
DataX
DataX+1
N data
acknowlegements
Ack X+N
N data
packets
DataX+N
May call for continuation
of streaming data
begin next burst
U-002
Figure 4-1. SuperSpeed IN Transaction Protocol
4.4.3
OUT Transfers
The host and device shall adhere to the constraints of the transfer type and endpoint characteristics.
A host initiates a transfer by sending a burst of data packets to the device. Each data packet
contains the addressing information required to route the packet to the intended endpoint. It also
includes the sequence number of the data packet. For a non-isochronous transaction, the device
returns an acknowledgement packet including the sequence number for the next data packet and
implicitly acknowledging the current data packet.
Note that even though the device is required to send an acknowledgement packet for every data
packet received, the host can send up to the maximum burst size number of data packets to the
device without waiting for an acknowledgement.
4-6
SuperSpeed Data Flow Model
The SuperSpeed OUT transaction protocol is illustrated in Figure 4-2. An OUT transfer on the
SuperSpeed bus consists of one or more OUT transactions consisting of one or more packets and
completes when any one of the following conditions occurs:
• All the data for the transfer is successfully transmitted.
• The host sends a packet that is less than the endpoints maximum packet size.
• The endpoint responds with an error.
OUT Session
Transaction(s)
Tx
Begin OUT Burst
Host
DataX
N data
packets
Rx
Rx
Device
Tx
DataX+1
X
X+1 Ack
DataX+N
May continue
streaming data
Ack
N data
acknowlegements
# packets
X+N Ack
U-003
Figure 4-2. SuperSpeed OUT Transaction Protocol
4.4.4
Power Management and Performance
The use of inactivity timers and device-driven link power management provides the ability for very
aggressive power management. When the host sends a packet to a device behind a hub with a port
whose link is in a non-active state, the packet will not be able to traverse the link until it returns to
the active state. In the case of an IN transaction, the host will not be able to start another IN
transaction until the current one completes. The affect of this behavior could have a significant
impact on overall performance.
To balance power management with good performance, the concept of a deferral (to both INs and
OUTs) is used. When a host initiates a transaction that encounters a link in a non-active state, a
deferred response is sent by the hub to tell the host that this particular path is in a reduced power
managed state and that the host should go on to schedule other transactions. In addition, the hub
sends a deferred request to the device to notify it that a transaction was attempted. This mechanism
informs the host of added latency due to power management and allows the host to mitigate
performance impacts that result from the link power management.
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Universal Serial Bus 3.0 Specification, Revision 1.0
4.4.5
Control Transfers
The purpose and characteristics of Control Transfers are identical to those defined in Section 5.5 of
the Universal Serial Bus Specification, Revision 2.0. The Protocol Layer chapter of this
specification describes the details of the packets, bus transactions, and transaction sequences used
to accomplish Control transfers. The Device Framework chapter of this specification defines the
complete set of standard command codes used for devices.
Each device is required to implement the default control pipe as a message pipe. This pipe is
intended for device initialization and management. This pipe is used to access device descriptors
and to make requests of the device to manipulate its behavior (at a device-level). Control transfers
must adhere to the same request definitions described in the Universal Serial Bus Specification,
Revision 2.0.
The SuperSpeed system will make a “best effort” to support delivery of control transfers between
the host and devices. As with USB 2.0, a function and its client software cannot request specific
bandwidth for control transfers.
4.4.5.1
Control Transfer Packet Size
Control endpoints have a fixed maximum control transfer data payload size of 512 bytes and have a
maximum burst size of one. These maximums apply to all data transactions during the data stage of
the control transfer. Refer to Section 8.12.2 for detailed information on the Setup and Status stages
of a control transfer in SuperSpeed.
A SuperSpeed device must report a value of 09H in the bMaxPacketSize field of its Device
Descriptor. The rule for decoding the default maximum packet size for the Default Control Pipe is
given in Section 9.6.1. The Default Control Pipe must support a maximum sequence value of 32
(i.e., sequence values in the range [0-31] are used).
The requirements for data delivery and completion of device-to-host and host-to-device Data stages
are generally not changed between USB 2.0 and SuperSpeed (refer to Section 5.5.3 of the Universal
Serial Bus Specification, Revision 2.0).
4.4.5.2
Control Transfer Bandwidth Requirements
A device has no way to indicate the desired bandwidth for a control pipe. A host balances the bus
access requirements of all control pipes and pending transactions on those pipes to provide a “best
effort” delivery between client software and functions on the device. This policy is the same as the
USB 2.0 policy.
SuperSpeed requires that bus bandwidth be reserved to be available for use by control transfers as
follows:
• The transactions of a control transfer may be scheduled coincident with transactions for other
function endpoints of any defined transfer type.
• Retries of control transfers are not given priority over other best effort transactions.
• If there are control and bulk transfers pending for multiple endpoints, control transfers for
different endpoints are selected for service according to a fair access policy that is host
controller implementation-dependent.
4-8
SuperSpeed Data Flow Model
•
When a control endpoint delivers a flow control event (as defined in Section 8.10.1), the host
will remove the endpoint from the actively scheduled endpoints. The host will resume the
transfer to the endpoint upon receipt of a ready notification from the device.
These requirements allow control transfers between a host and devices to regularly move data
across the SuperSpeed bus with “best effort.” System software’s discretionary behavior defined in
Section 5.5.4 of the Universal Serial Bus Specification, Revision 2.0 applies equally to SuperSpeed
control transfers.
4.4.5.3
Control Transfer Data Sequences
SuperSpeed preserves the message format and general stage sequencing of control transfers defined
in Section 5.5.5 of the Universal Serial Bus Specification, Revision 2.0. The SuperSpeed protocol
defines some changes to the Setup and Status stages of a control transfer. However, all of the
sequencing requirements for normal and error recovery scenarios defined in Section 5.5.5 of the
Universal Serial Bus Specification, Revision 2.0 directly map to the SuperSpeed Protocol.
4.4.6
Bulk Transfers
The purpose and characteristics of Bulk Transfers are similar to those defined in Section 5.8 of the
Universal Serial Bus Specification, Revision 2.0. Section 8.12.1 of this specification describes the
details of the packets, bus transactions and transaction sequences used to accomplish Bulk transfers.
The Bulk transfer type is intended to support devices that want to communicate relatively large
amounts of data at highly variable times where the transfer can use any available SuperSpeed
bandwidth. A SuperSpeed Bulk function endpoint provides the following:
• Access to the SuperSpeed bus on a bandwidth available basis
• Guaranteed delivery of data, but no guarantee of bandwidth or latency
SuperSpeed retains the following characteristics of bulk pipes:
• No data content structure is imposed on the communication flow for bulk pipes.
• A bulk pipe is a stream pipe and, therefore, always has communication flow either into or out
of the host for any pipe instance. If an application requires a bi-directional bulk
communication flow, two bulk pipes must be used (one IN and one OUT).
Standard USB bulk pipes provide the ability to move a stream of data. SuperSpeed adds the
concept of Streams that provide protocol-level support for a multi-stream model.
4.4.6.1
Bulk Transfer Data Packet Size
An endpoint for bulk transfers shall set the maximum data packet payload size in its endpoint
descriptor to 1024 bytes. It also specifies the burst size that the endpoint can accept from or
transmit on the SuperSpeed bus. The allowable burst size for a bulk endpoint shall be in the range
of 1 to 16. All SuperSpeed bulk endpoints shall support sequence values in the range [0-31].
A host is required to support any SuperSpeed bulk endpoint. A host shall support all bulk burst
sizes. The host ensures that no data payload of any data packet in a burst transaction will be sent to
the endpoint that is larger than the maximum packet size. Additionally, it will not send more data
packets than the reported maximum burst size.
A bulk function endpoint must always transmit data payloads with data fields less than or equal to
1024 bytes. If the bulk transfer has more data than that, all data payloads in the burst transaction
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Universal Serial Bus 3.0 Specification, Revision 1.0
are required to be 1024 bytes in length except for the last data payload in the burst, which may
contain the remaining data. A bulk transfer may span multiple bus transactions. A bulk transfer is
complete when the endpoint does one of the following:
• Has transferred exactly the amount of data expected.
• Transfers a data packet with a payload less than 1024 bytes.
• Responds with a STALL handshake.
4.4.6.2
Bulk Transfer Bandwidth Requirements
As with USB 2.0 a bulk function endpoint has no way to indicate a desired bandwidth for a bulk
pipe. Bulk transactions occur on the SuperSpeed bus only on a bandwidth available basis.
SuperSpeed provides a “good effort” delivery of bulk data between client software and device
functions. Moving control transfers over the SuperSpeed bus has priority over moving bulk
transactions. When there are bulk transfers pending for multiple endpoints, the host will provide
transaction opportunities to individual endpoints according to a fair access policy, which is host
implementation dependent.
All bulk transfers pending in a system contend for the same available bus time. An endpoint and its
client software cannot assume a specific rate of service for bulk transfers. Bus time made available
to a software client and its endpoint can be changed as other devices are inserted into and removed
from the system or as bulk transfers are requested for other function endpoints. Client software
cannot assume ordering between bulk and control transfers; i.e., in some situations, bulk transfers
can be delivered ahead of control transfers.
The host can use any burst size between 1 and the reported maximum in transactions with a bulk
endpoint to more effectively utilize the available bandwidth. For example, there may be more bulk
transfers than bandwidth available, so a host can employ a policy of using smaller data bursts per
transactions to provide fair service to all pending bulk data streams.
When a bulk endpoint delivers a flow control event (as defined in Section 8.10.1), the host will
remove it from the actively scheduled endpoints. The host will resume the transfer to the endpoint
upon receipt of a ready notification from the device.
4.4.6.3
Bulk Transfer Data Sequences
Bulk transactions use the standard burst sequence for reliable data delivery defined in
Section 8.10.2. Bulk endpoints are initialized to the initial transmit or receive sequence number
and burst size (refer to Section 8.12.1.2 and Section 8.12.1.3) by an appropriate control transfer
(SetConfiguration, SetInterface, ClearEndpointFeature). Likewise, a host assumes the initial
transmit or receive sequence number and burst size for bulk pipes after it has successfully
completed the appropriate control transfer as mentioned above.
Halt conditions for a SuperSpeed bulk pipe have the identical side effects as defined for a USB 2.0
bulk endpoint. Recovery from halt conditions are also identical to USB 2.0 (refer to Section 5.8.5
of the Universal Serial Bus Specification, Revision 2.0). A bulk pipe halt condition includes a
STALL handshake response to a transaction or exhaustion of the host’s transaction retry policy due
to transmission errors.
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SuperSpeed Data Flow Model
4.4.6.4
Bulk Streams
A standard USB Bulk Pipe represents the ability to move single stream of (FIFO) data between the
host and a device via a host memory buffer and a device endpoint. SuperSpeed streams provide
protocol-level support for a multi-stream model and utilize the “stream” pipe communications
mode (refer to Section 5.3.2 of the Universal Serial Bus Specification, Revision 2.0).
Streams are managed between the host and a device using the Stream Protocol. Each Stream is
assigned a Stream ID (SID).
The Stream Protocol defines a handshake, which allows the device or host to establish the Current
Stream (CStream) ID associated with an endpoint. The host uses the CStream ID to select the
command or operation-specific Endpoint Buffer(s) that will be used for subsequent data transfers
on the pipe (see Figure 4-3). The device uses the CStream ID to select the Function Data buffer(s)
that will be used.
Endpoint
Buffer
Function
Data
Tagged Packets of data
Stream (X)
Stream (X)
Pipe
Stream (G)
Host
Controller
(G)
Device
Controller
Mux
Packet Stream
Packet
m
Endpoint
Packet
Buffers
Stream (A)
Mux
Stream (G)
Stream (A)
CStream ID
CStream ID
U-004
Figure 4-3. USB SuperSpeed IN Stream Example
The example in Figure 4-3 represents an IN Bulk pipe, where a large number of Streams have been
established. Associated with each Stream in host memory is one or more Endpoint Buffers to
receive the Stream data. In the device, there is a corresponding command or operation-specific
Function Data to be transmitted to the host.
When the device has data available for a specific Stream (G in this example), it issues an ERDY
tagged with the CStream ID, and the host will begin issuing IN ACK TP’s to the device that is
tagged with the CStream ID. The device will respond by returning DPs that contain the Function
Data associated with the CStream ID that is also tagged with the CStream ID. When the host
receives the data, it uses the CStream ID to select the set of Endpoint Buffers that will receive the
data.
When the Function Data is exhausted, the device terminates the Stream (refer to Section 8.12.1.4).
The host is also allowed to terminate the Stream if it runs out of Endpoint Buffer space.
Streams may be used, for example, to support out-of-order data transfers required for mass storage
device command queuing.
A standard bulk endpoint has a single set of Endpoint Buffers associated with it. Streams extend
the number of host buffers accessible by an endpoint from 1 to up to 65533. There is a 1:1
mapping between a host buffer and a Stream ID.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Device Class defined methods are used for coordinating the Stream IDs that are used by the host to
select Endpoint Buffers and the device to select Function Data associated with a particular Stream.
Typically this is done via an out-of-band mechanism (e.g., another endpoint) that is used to pass the
list of valid Stream IDs between the host and the device.
The selection of the Current Stream may be initiated by the host or the device and, in either case,
the Stream Protocol provides a method for a selection to be rejected. For example, the host may
reject a Stream selection initiated by the device if it has no Endpoint Buffers available for it. Or the
device may reject a Stream selection initiated by the host if it has no Function Data available for it.
The Device Class defines when a stream may be selected by the host or the device, and the actions
that will be taken when a Stream is rejected (refer to Section 8.12.1.4).
A combination of vendor and Device Class defined algorithms determine how Streams are
scheduled by a device. The Stream protocol provides methods for starting, stopping, and switching
Streams (refer to Section 8.12.1.4).
Mechanisms defined by the Stream protocol allow the device or the host to flow control a Stream.
These mechanisms overlap with the standard bulk flow control mechanism.
The host also may start or stop a Stream. For instance, the host will stop a Stream if it runs out of
buffer space for the Stream. When the host controller informs the device of this condition, the
device may switch to another Stream or wait and continue the same Stream when the host receives
more buffers.
The Stream Protocol also provides a mechanism which allows the host to asynchronously inform
the device when Endpoint Buffers have been added to the pipe. This is useful in cases in which the
host must terminate a stream because it ran out of Endpoint Buffers; however the device still has
more Function Data to transfer. Without this mechanism, the device would have to periodically
retry starting the Stream (impacting power management), or a long latency out-of-band method
would be required.
Since Streams are run over a standard bulk pipe, an error will halt the pipe, stopping all stream
activity. Removal of the halt condition is achieved via software intervention through a separate
control pipe as it is for a standard bulk pipe.
Finally, Streams significantly increase the functionality of a bulk endpoint, while having a minimal
impact on the additional hardware required to support the feature in hosts and devices.
4.4.7
Interrupt Transfers
The purpose and characteristics of interrupt transfers are similar to those defined in USB 2.0 (see
Section 5.7 of the Universal Serial Bus Specification, Revision 2.0). The SuperSpeed interrupt
transfer types are intended to support devices that require a high reliability method to communicate
a small amount of data with a bounded service interval. The Protocol Layer chapter of this
specification describes the details of the packets, bus transactions and transaction sequences used to
accomplish Interrupt transfers. The SuperSpeed Interrupt transfer type nominally provides the
following:
• Guaranteed maximum service interval
• Guaranteed retry of transfer attempts in the next service interval
Interrupt transfers are attempted each service interval for an interrupt endpoint. Bandwidth is
reserved to guarantee a transfer attempt each service interval. Once a transfer is successful, another
4-12
SuperSpeed Data Flow Model
transfer attempt is not made until the next service interval. If the endpoint responds with a not
ready notification or an acknowledgement indicating that it cannot accept any more packets, the
host will not attempt another transfer to that endpoint until it receives a ready notification. The host
must then service the endpoint within twice the service interval after receipt of the notification.
The requested service interval for the endpoint is described in its endpoint descriptor.
SuperSpeed retains the following characteristics of interrupt pipes:
• No data content structure is imposed on communication flow for interrupt pipes
• An interrupt pipe is a stream pipe and, therefore, is always unidirectional
4.4.7.1
Interrupt Transfer Packet Size
An endpoint for interrupt transfers specifies the maximum data packet payload size that it can
accept from or transmit on the SuperSpeed bus. The only allowable maximum data payload size
for interrupt endpoints is 1024 bytes for interrupt endpoints that support a burst size greater than
one and can be any size from 1 to 1024 for an interrupt endpoint with a burst size equal to one. The
maximum allowable burst size for interrupt endpoints is three. All SuperSpeed interrupt endpoints
shall support sequence values in the range [0-31].
SuperSpeed interrupt endpoints are only intended for moving small amounts of data with a bounded
service interval. The SuperSpeed protocol does not require the interrupt transactions to be
maximum size.
A host is required to support SuperSpeed interrupt endpoints. A host shall support all allowed
combinations of interrupt packet sizes and burst sizes. The host ensures that no data payload of any
data packet in a burst transaction shall be sent to the endpoint that is larger than the endpoint’s
maximum packet size. Also, the host shall not send more data packets in a burst transaction than
the endpoint’s maximum burst size.
An interrupt endpoint shall always transmit data payloads with data fields less than or equal to the
endpoint’s maximum packet size. If the interrupt transfer has more information than will fit into
the maximum packet size for the endpoint, all data payloads in the burst transaction are required to
be maximum packet size except for the last data payload in the burst transaction, which may
contain the remaining data. An interrupt transfer may span multiple burst transactions.
An interrupt transfer is complete when the endpoint does one of the following:
• Has transferred exactly the amount of data expected
• Transfers a data packet with a payload less than the maximum packet size
• Responds with a STALL handshake
4.4.7.2
Interrupt Transfer Bandwidth Requirements
Periodic endpoints may be allocated up to 80% of the total available bandwidth on SuperSpeed.
An endpoint for an interrupt pipe specifies its desired service interval bound via its endpoint
descriptor. An interrupt endpoint can specify a desired period 2(bInterval-1) x 125 μs, where bInterval
is in the range 1 up to (and including) 16. The USB System Software will use this information
during configuration to determine a period that can be sustained. The period provided by the
system may be shorter than that desired by the device up to the shortest period defined by the
SuperSpeed (125 μs which is also referred to as a bus interval). Note that errors on the bus can
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Universal Serial Bus 3.0 Specification, Revision 1.0
prevent an interrupt transaction from being successfully delivered over the bus and consequently
exceed the desired period.
A SuperSpeed interrupt endpoint can move up to three maximum sized packets (3 x 1024 bytes) per
service interval. Interrupt transfers are moved over the USB by accessing an interrupt endpoint
every service interval. For interrupt endpoints, the host has no way to determine whether the
endpoint will source/sync data without accessing the endpoint and requesting an interrupt transfer.
If an interrupt IN endpoint has no interrupt data to transmit or an interrupt OUT endpoint has
insufficient buffer to accept data when accessed by the host, it responds with a flow control
response.
An endpoint should only provide interrupt data when it has interrupt data pending to avoid having a
software client erroneously notified of a transfer completion. A zero-length data payload is a valid
transfer and may be useful for some implementations. The host may access an endpoint at any
point during the service interval. The interrupt endpoint should not assume a fixed spacing between
transaction attempts. The interrupt endpoint can assume only that it will receive a transaction
attempt within the service interval bound. Errors can prevent the successful exchange of data
within the service interval bound and a host is not required to retry the transaction in the same
service interval and is only required to retry the transaction in the next service interval.
4.4.7.3
Interrupt Transfer Data Sequences
Interrupt transactions use the standard burst sequence for reliable data delivery protocol defined in
Section 8.10.2. Interrupt endpoints are initialized to the initial transmit or receive sequence number
and burst size (refer to Section 8.12.4.1 and Section 8.12.4.2) by an appropriate control transfer
(SetConfiguration, SetInterface, ClearEndpointFeature). A host sets the initial transmit or receive
sequence number and burst size for interrupt pipes after it has successfully completed the
appropriate control transfer.
Halt conditions for a SuperSpeed interrupt pipe have the identical side effects as defined for a
USB 2.0 interrupt endpoint. Recovery from halt conditions are also identical to the USB 2.0, refer
to Section 5.7.5 in the Universal Serial Bus Specification, Revision 2.0. An interrupt pipe halt
condition includes a STALL handshake response to a transaction or exhaustion of the host’s
transaction retry policy due to transmission errors.
4.4.8
Isochronous Transfers
The purpose of SuperSpeed isochronous transfers is similar to those defined in USB 2.0 (refer to
Section 5.6 of the Universal Serial Bus Specification, Revision 2.0). As in USB 2.0, the
SuperSpeed isochronous transfer type is intended to support streams that want to perform error
tolerant, periodic transfers within a bounded service interval. SuperSpeed does not transmit start of
frames as on USB 2.0, but timing information is transmitted to devices via Isochronous Timestamp
Packets (ITPs). The Protocol Layer chapter of this specification describes the details of the
packets, bus transactions, and transaction sequences used to accomplish isochronous transfers. It
also describes how the timing information is conveyed to devices. The SuperSpeed isochronous
transfer type provides the following:
• Guaranteed bandwidth for transaction attempts on the SuperSpeed bus with bounded latency
• Guaranteed data rate through the pipe as long as data is provided to the pipe
4-14
SuperSpeed Data Flow Model
Isochronous transactions are attempted each service interval for an isochronous endpoint.
Isochronous endpoints that are admitted on the SuperSpeed bus are guaranteed the bandwidth they
require on the bus. The host can request data from the device or send data to the device at any time
during the service interval for a particular endpoint on that device. The requested service interval
for the endpoint is described in its endpoint descriptor. The SuperSpeed isochronous transfer type
is designed to support a source and sink that produce and consume data at the same average rate.
A SuperSpeed isochronous pipe is a stream pipe and is always unidirectional. The endpoint
description identifies whether a given isochronous pipe’s communication flow is into or out of the
host. If a device requires bi-directional isochronous communication flows, two isochronous pipes
must be used, one in each direction.
SuperSpeed power management may interfere with isochronous transfers whenever an isochronous
transfer needs to traverse a non-active link. The resultant delay could result in the data not arriving
within the service interval. To overcome this, SuperSpeed defines a PING and PING_RESPONSE
mechanism (refer to Section 8.5.7). Before initiating an isochronous transfer the host may send a
PING packet to the device. The device responds with a PING_RESPONSE packet that tells the
host that all the links in the path to the device are in the active state.
4.4.8.1
Isochronous Transfer Packet Size
An endpoint for isochronous transfers specifies the maximum data packet payload size that the
endpoint can accept from or transmit on SuperSpeed. The only allowable maximum data payload
size for isochronous endpoints is 1024 bytes for isochronous endpoints that support a burst size
greater than one and can be any size from 0 to 1024 for an isochronous endpoint with a burst size
equal to one. The maximum allowable burst size for isochronous endpoints is 16. However an
isochronous endpoint can request up to three burst transactions in the same service interval.
The SuperSpeed protocol does not require the isochronous data packets to be maximum size. If an
amount of data less than the maximum packet size is being transferred, the data packet shall not be
padded.
A host shall support SuperSpeed isochronous endpoints for all allowed combinations of
isochronous packet sizes and burst sizes. The host shall ensure that no data payload of any data
packet in a burst transaction be sent to the endpoint that is larger than the reported maximum packet
size. Also, the host shall not send more data packets in a burst transaction than the endpoint’s
maximum burst size.
An isochronous endpoint shall always transmit data payloads with data fields less than or equal to
the endpoint’s maximum packet size. If the isochronous transfer has more information than will fit
into the maximum packet size for the endpoint, all data payloads in the burst transaction are
required to be maximum packet size except for the last data payload in the burst transaction, which
may contain the remaining data. An isochronous transfer may span multiple burst transactions.
4.4.8.2
Isochronous Transfer Bandwidth Requirements
Periodic endpoints can be allocated up to 80% of the total available bandwidth on SuperSpeed.
An endpoint for an isochronous pipe specifies its desired service interval bound via its endpoint
descriptor. An isochronous endpoint can specify a desired period 2(bInterval-1) x 125 μs, where
bInterval is in the range 1 to 16. The system software will use this information during
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Universal Serial Bus 3.0 Specification, Revision 1.0
configuration to determine whether the endpoint can be added to the host schedule. Note that errors
on the bus can prevent an isochronous transaction from being successfully delivered over the bus.
A SuperSpeed isochronous endpoint can move up to three burst transactions of up to 16 maximum
sized packets (3 x 16 x 1024 bytes) per service interval. Isochronous transfers are moved over the
USB by accessing an isochronous endpoint every service interval. The host will send data or
request data to or from the endpoint every service interval. Note, if an endpoint has no isochronous
data to transmit when accessed by the host, it shall send a zero length packet in response to the
request for data.
The host may access an endpoint at any point during the appropriate service interval. The
isochronous endpoint should not assume a fixed spacing between transaction attempts. The
isochronous endpoint can assume only that it will receive a transaction attempt within the service
interval bound. Errors may prevent the successful exchange of data within the service interval
bound, however since the packets in an isochronous transaction are not acknowledged, a host has
no way of knowing which packets were not received successfully and hence will not retry packets.
4.4.8.3
Isochronous Transfer Data Sequences
Isochronous endpoints always transmit data packets starting with sequence number zero in each
service interval. Each successive data packet transmitted in the same service interval is sent with
the next higher sequence number. The sequence number shall roll over from thirty one to zero
when transmitting the thirty second packet. Isochronous endpoints do not support retries and
cannot respond with flow control responses.
4.4.9
Device Notifications
Device notifications are a standard method for a device to communicate asynchronous device- and
bus-level event information to the host. This feature does not map to the pipe model defined for the
standard transfer types. Device notifications are always initiated by a device and the flow of data
information is always device to host.
Device notifications are message-oriented data communications that have a specific data format
structure as defined in Section 8.5.6. Device notifications do not have any data payload. Devices
can send a device notification at any time.
4.4.10
Reliability
To ensure reliable operation, several layers of protection are used. This provides reliability for both
flow control and data end to end.
4.4.10.1
Physical Layer
The SuperSpeed physical layer provides bit error rates less than 1 bit in 1012 bits.
4.4.10.2
Link Layer
The SuperSpeed link layer has mechanisms that ensure a bit error rate less than 1 bit in 1020 bits for
header packets. The link layer uses a number of techniques including packet framing ordered sets,
link level flow control and retries to ensure reliable end-to-end delivery for header packets.
4-16
SuperSpeed Data Flow Model
4.4.10.3
Protocol Layer
The SuperSpeed protocol layer depends on a 32-bit CRC appended to the Data Payload and a
timeout coupled with retries to ensure that reliable data is provided to the application.
4.4.11
Efficiency
SuperSpeed efficiency is dependent on a number of factors including 8b/10b symbol encoding,
packet structure and framing, link level flow control, and protocol overhead. At a 5 Gbps signaling
rate with 8b/10b encoding, the raw throughput is 500 MBps. When link flow control, packet
framing, and protocol overhead are considered, it is realistic for 400 MBps or more to be delivered
to an application.
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Universal Serial Bus 3.0 Specification, Revision 1.0
4-18
5
Mechanical
This chapter defines form, fit and function of the USB 3.0 connectors and cable assemblies. It
contains the following:
• Connector mating interfaces
• Cables and cable assemblies
• Electrical requirements
• Mechanical and environmental requirements
• Implementation notes and guidelines
The intention of this chapter is to enable connector, system, and device designers and
manufacturers to build, qualify, and use the USB 3.0 connectors, cables, and cable assemblies.
If any part of this chapter conflicts with the USB 2.0 specification, the USB 3.0 specification
always supersedes the USB 2.0 specification.
5.1
Objective
The mechanical layer specification has been developed with the following objectives:
• Supporting 5 Gbps data rate
• Backward compatible with USB 2.0
• Minimizing connector form factor variations
• Managing EMI
• Supporting On-The-Go (OTG)
• Low cost
5.2
Significant Features
This section identifies the significant features of the USB 3.0 connectors and cable assemblies
specification. The purpose of this section is not to present all the technical details associated with
each major feature, but rather to highlight their existence. Where appropriate, this section
references other parts of the document where further details can be found.
5.2.1
Connectors
The USB 3.0 specification defines the following connectors:
• USB 3.0 Standard-A plug and receptacle
• USB 3.0 Standard-B plug and receptacle
• USB 3.0 Powered-B plug and receptacle
• USB 3.0 Micro-B plug and receptacle
• USB 3.0 Micro-A plug
• USB 3.0 Micro-AB receptacle
Table 5-1 lists the compatible plugs and receptacles.
5-1
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-1. Plugs Accepted By Receptacles
Receptacle
Plugs Accepted
USB 2.0 Standard-A
USB 2.0 Standard-A or USB 3.0 Standard-A
USB 3.0 Standard-A
USB 3.0 Standard-A or USB 2.0 Standard-A
USB 2.0 Standard-B
USB 2.0 Standard-B
USB 3.0 Standard-B
USB 3.0 Standard-B or USB 2.0 Standard-B
USB 3.0 Powered-B
USB 3.0 Powered-B, USB 3.0 Standard-B, or
USB 2.0 Standard-B
USB 2.0 Micro-B
USB 2.0 Micro-B
USB 3.0 Micro-B
USB 3.0 Micro-B or USB 2.0 Micro-B
USB 2.0 Micro-AB
USB 2.0 Micro-B or USB 2.0 Micro-A
USB 3.0 Micro-AB
USB 3.0 Micro-B, USB 3.0 Micro-A, USB 2.0
Micro-B, or USB 2.0 Micro-A
5.2.1.1
USB 3.0 Standard-A Connector
The USB 3.0 Standard-A connector is defined as the host connector, supporting the SuperSpeed
mode. It has the same mating interface as the USB 2.0 Standard-A connector, but with additional
pins for two more differential pairs and a drain. Refer to Section 5.3.1.2 for pin assignments and
descriptions.
A USB 3.0 Standard-A receptacle accepts either a USB 3.0 Standard-A plug or a USB 2.0
Standard-A plug. Similarly, a USB 3.0 Standard-A plug can be mated with either a USB 3.0
Standard-A receptacle or a USB 2.0 Standard-A receptacle.
A unique color coding is recommended for the USB 3.0 Standard-A connector plastic housings to
help users distinguish the USB 3.0 Standard-A connector from the USB 2.0 Standard-A connector
(refer to Section 5.3.1.3 for details).
5.2.1.2
USB 3.0 Standard-B Connector
The USB 3.0 Standard-B connector is defined for relatively large, stationary peripherals, such as
external hard drives and printers. It is defined so that the USB 3.0 Standard-B receptacle accepts
either a USB 3.0 Standard-B plug or a USB 2.0 Standard-B plug. Inserting a USB 3.0 Standard-B
plug into a USB 2.0 Standard-B receptacle is physically disallowed (refer to Section 5.3.2 for
details).
5.2.1.3
USB 3.0 Powered-B Connector
The USB 3.0 Powered-B connector is defined to allow a USB 3.0 device to provide power to a
USB adaptor without the need for an external power supply. It is identical to the USB 3.0
Standard-B connector in form factor, but has two more pins- one for power (DPWR) and one for
ground (DGND). See Section 5.3.3 for details.
5.2.1.4
USB 3.0 Micro-B Connector
The USB 3.0 Micro-B connector is defined for small handheld devices. It is compatible with the
USB 2.0 Micro-B connector; i.e., a USB 2.0 Micro-B plug works in a USB 3.0 Micro-B receptacle.
Section 5.3.4 defines the USB 3.0 Micro connector family.
5-2
Mechanical
5.2.1.5
USB 3.0 Micro-AB and USB 3.0 Micro-A Connectors
The USB 3.0 Micro-AB receptacle is similar to the USB 3.0 Micro-B receptacle, except for
different keying. It accepts a USB 3.0 Micro-A plug, a USB 3.0 Micro-B plug, a USB 2.0 Micro-A
plug, or a USB 2.0 Micro-B plug. The USB 3.0 Micro-AB receptacle is only allowed on OTG
products, which may function as either a host or device. All other uses of the USB 3.0 Micro-AB
receptacle are prohibited.
The USB 3.0 Micro-A plug is similar to the USB 3.0 Micro-B plug, except for different keying and
ID pin connections. The USB 3.0 Micro-A plug, the USB 3.0 Micro-AB receptacle, and the
USB 3.0 Micro-B receptacle and plug all belong to the USB 3.0 Micro connector family since their
interfaces differ only in keying. Similar to the USB 2.0 Micro-A plug, the USB 3.0 Micro-A plug
is defined for OTG applications only.
5.2.2
Compliant Cable Assemblies
The USB 3.0 specification defines the following cable assemblies:
• USB 3.0 Standard-A plug to USB 3.0 Standard-B plug
• USB 3.0 Standard-A plug to USB 3.0 Micro-B plug
• USB 3.0 Standard-A plug to USB 3.0 Standard-A plug
• USB 3.0 Micro-A plug to USB 3.0 Micro-B plug
• USB 3.0 Micro-A plug to USB 3.0 Standard-B plug
• Captive cable with USB 3.0 Standard-A plug
• Permanently attached cable with USB 3.0 Micro-A plug
• Permanently attached cable with USB 3.0 Powered-B plug
A captive cable is a cable assembly that has a Standard-A plug on one end and that is either
permanently attached or has a vendor-specific connector on the other end. A permanently attached
cable is directly wired to the device and it is not detachable from the device. This specification
does not define how the vendor-specific connector or permanent attachment shall be done on the
device side.
For electrical compliance purpose, a USB 3.0 captive cable (permanently attached or with vendorspecific connector on the device end) shall be considered part of the USB 3.0 device.
No other types of cable assemblies are allowed by this specification. Section 5.5 provides detailed
discussion on USB 3.0 cable assemblies.
5.2.3
Raw Cables
Due to EMI and signal integrity requirements, each cable differential pair used for the SuperSpeed
lines in a USB 3.0 cable assembly must be shielded; the Unshielded Twisted Pair (UTP) used for
USB 2.0 is not allowed for SuperSpeed. Section 5.4 defines the cable construction for USB 3.0.
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Universal Serial Bus 3.0 Specification, Revision 1.0
5.3
Connector Mating Interfaces
This section defines the connector mating interfaces, including the connector interface drawings,
pin assignments and descriptions.
5.3.1
USB 3.0 Standard-A Connector
5.3.1.1
Interface Definition
Figure 5-1 to Figure 5-4 show, respectively, the USB 3.0 Standard-A receptacle and plug interface
dimensions, as well as the reference footprints for the USB 3.0 Standard-A receptacle. Note that
only the dimensions that govern the mating interoperability are specified. All the REF dimensions
are provided for reference only, not hard requirements.
Although the USB 3.0 Standard-A connector has basically the same form factor as the USB 2.0
Standard-A connector, it has significant differences inside. Below are the key features and design
areas that need attention:
• Besides the VBUS, D-, D+, and GND pins that are required for USB 2.0, the USB 3.0
Standard-A connector includes five more pins–two differential pairs plus one ground
(GND_DRAIN). The two added differential pairs are for SuperSpeed data transfer, supporting
dual simplex SuperSpeed signaling; the added GND_DRAIN pin is for drain wire termination,
managing signal integrity, and EMI performance.
• The contact areas of the five SuperSpeed pins are located towards the front of the receptacle as
the blades, while the four USB 2.0 pins towards the back of the receptacle as the beams or
springs. Accordingly in the plug, the SuperSpeed contacts, as the beams, seat behind the
USB 2.0 blades. In other words, the USB 3.0 Standard-A connector has a two-tier contact
system.
• The tiered-contact approach within the Standard-A connector form factor inevitably results in
less contact area to work with, as compared to the USB 2.0 Standard-A connector. The
connector interface dimensions take into consideration of contact mating requirements between
the USB 3.0 Standard-A receptacle and USB 3.0 Standard-A plug, the USB 3.0 Standard-A
receptacle and USB 2.0 Standard-A plug, and the USB 2.0 Standard-A receptacle and USB 3.0
Standard-A plug. Connector designers should carefully consider those aspects in design
details.
• The connector interface definition comprehends the need to avoid shorting between the
SuperSpeed and USB 2.0 pins during insertion when plugging a USB 2.0 Standard-A plug into
a USB 3.0 Standard-A receptacle, or a USB 3.0 Standard-A plug into a USB 2.0 Standard-A
receptacle. Connector designers should be conscious of this when detailing out designs.
• There may be some increase in the USB 3.0 Standard-A receptacle connector depth (into a
system board) to support the two-tiered-contacts, as compared to the USB 2.0 Standard-A
receptacle.
• The through-hole footprints in Figure 5-3 and Figure 5-4 are shown as examples. Other
footprints, such as SMT (surface mount) are also allowed.
5-4
Mechanical
•
•
Drawings for stacked USB 3.0 Standard-A receptacles are not shown in this specification. But
they are allowed, as long as they meet all the electrical and mechanical requirements defined in
this specification. In fact, a double-stacked USB 3.0 Standard-A receptacle is expected to be a
common application just like the double-stacked USB 2.0 Standard-A receptacle that has been
widely used in PCs. When designing a stacked USB 3.0 Standard-A receptacle, efforts must be
made to minimize impedance discontinuity of the top connector in the stack because of its long
electrical length. Figure 5-4 shows an example or reference footprint for a double-stacked
Standard-A receptacle connector. Note that pins 1 to 9 correspond to the lower port, while pins
10 to 18 correspond to the upper port. Section 5.8.3 offers further discussion on the stacked
connector.
Attention must be paid to the high speed electrical design of USB 3.0 Standard-A connectors.
Besides minimizing the connector impedance discontinuities, crosstalk among the SuperSpeed
pairs and USB 2.0 D+/D- pair should also be minimized.
5-5
Universal Serial Bus 3.0 Specification, Revision 1.0
continued
5-6
Mechanical
continued
5-7
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-1. USB 3.0 Standard-A Receptacle Interface Dimensions
5-8
Mechanical
continued
5-9
Universal Serial Bus 3.0 Specification, Revision 1.0
continued
5-10
Mechanical
Figure 5-2. USB 3.0 Standard-A Plug Interface Dimensions
5-11
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-3. Reference Footprint for the USB 3.0 Standard-A Receptacle
5-12
Mechanical
Figure 5-4. Reference Footprint for the USB 3.0 Double-Stacked
Standard-A Receptacle
5-13
Universal Serial Bus 3.0 Specification, Revision 1.0
5.3.1.2
Pin Assignments and Description
The usage and assignments of the nine pins in the USB 3.0 Standard-A connector are defined in
Table 5-2.
Table 5-2. USB 3.0 Standard-A Connector Pin Assignments
Pin Number
Signal Name
Description
Mating Sequence
1
VBUS
Power
Second
2
D-
USB 2.0 differential pair
Third
3
D+
4
GND
Ground for power return
Second
5
StdA_SSRX-
SuperSpeed receiver differential
pair
Last
6
StdA_SSRX+
7
GND_DRAIN
Ground for signal return
8
StdA_SSTX-
SuperSpeed transmitter
differential pair
9
StdA_SSTX+
Shell
Shield
Connector metal shell
First
Note: Tx and Rx are defined from the host perspective
The physical location of the pins in the connector is illustrated in Figure 5-1 to Figure 5-4. Note
that pins 1 to 4 are referred to as the USB 2.0 pins, while pins 5 to 9 are referred to as the
SuperSpeed pins.
5.3.1.3
USB 3.0 Standard-A Connector Color Coding
Since both the USB 2.0 Standard-A and USB 3.0 Standard-A receptacles may co-exist on a host,
color coding is recommended for the USB 3.0 Standard-A connector (receptacle and plug) housings
to help users distinguish it from the USB 2.0 Standard-A connector.
Blue (Pantone 300C) is the recommended color for the USB 3.0 Standard-A receptacle and plug
plastic housings. When the recommended color is used, connector manufacturers and system
integrators should make sure that the blue-colored receptacle housing is visible to users. Figure 5-5
illustrates the color coding recommendation for the USB 3.0 Standard-A connector.
5-14
Mechanical
Figure 5-5. Illustration of Color Coding Recommendation for USB 3.0 Standard-A Connector
5.3.2
USB 3.0 Standard-B Connector
5.3.2.1
Interface Definition
Figure 5-6 to Figure 5-8 show, respectively, the USB 3.0 Standard-B receptacle and plug interface
dimensions, as well as the reference footprint.
5-15
Universal Serial Bus 3.0 Specification, Revision 1.0
continued
5-16
Mechanical
Figure 5-6. USB 3.0 Standard-B Receptacle Interface Dimensions
5-17
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-7. USB 3.0 Standard-B Plug Interface Dimensions
5-18
Mechanical
Figure 5-8. Reference Footprint for the USB 3.0 Standard-B Receptacle
The USB 3.0 Standard-B receptacle interfaces have two portions: the USB 2.0 interface and the
SuperSpeed interface. The USB 2.0 interface consists of pins 1 to 4, while the SuperSpeed
interface consists of pins 5 to 9.
When a USB 2.0 Standard-B plug is inserted into the USB 3.0 Standard-B receptacle, only the
USB 2.0 interface is engaged, and the link will not take advantage of the SuperSpeed capability.
However, since the USB 3.0 SuperSpeed portion is visibly not mated when a USB 2.0 Standard-B
plug is inserted in the USB 3.0 Standard-B receptacle, users will get the visual feedback that the
cable plug is not matched with the receptacle. Only when a USB 3.0 Standard-B plug is inserted
into the USB 3.0 Standard-B receptacle, is the interface completely visibly engaged.
5-19
Universal Serial Bus 3.0 Specification, Revision 1.0
5.3.2.2
Pin Assignments and Description
The usage and assignments of the nine pins in the USB 3.0 Standard-B connector are defined in
Table 5-3.
Table 5-3. USB 3.0 Standard-B Connector Pin Assignments
Pin Number
Signal Name
Description
Mating Sequence
1
VBUS
Power
Second
2
D-
USB 2.0 differential pair
Third or beyond
3
D+
4
GND
Ground for power return
Second
5
StdB_SSTX-
SuperSpeed transmitter
differential pair
Third or beyond
6
StdB_SSTX+
7
GND_DRAIN
Ground for signal return
8
StdB_SSRX-
SuperSpeed receiver differential
pair
9
StdB_SSRX+
Shell
Shield
Connector metal shell
First
Note: Tx and Rx are defined from the device perspective
The physical location of the pins in the connector is illustrated in Figure 5-6 to Figure 5-8.
5.3.3
USB 3.0 Powered-B Connector
5.3.3.1
Interface Definition
Figure 5-9 to Figure 5-11 show the USB 3.0 Powered-B receptacle and plug interface dimensions,
as well as the reference footprint.
5-20
Mechanical
continued
5-21
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-9. USB 3.0 Powered-B Receptacle Interface Dimensions
5-22
Mechanical
Figure 5-10. USB 3.0 Powered-B Plug Interface Dimensions
5-23
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-11. Reference Footprint for USB 3.0 Powered-B Receptacle
5-24
Mechanical
5.3.3.2
Pin Assignments and Descriptions
The usage and assignments of the 11 pins in the USB 3.0 Powered-B connector are defined in
Table 5-4.
Table 5-4. USB 3.0 Powered-B Connector Pin Assignments
Pin Number
Signal Name
Description
Mating Sequence
1
VBUS
Power
Second
2
D-
USB 2.0 differential pair
Third or beyond
3
D+
4
GND
Ground for power return
Second
5
StdB_SSTX-
SuperSpeed transmitter
differential pair
Third or beyond
6
StdB_SSTX+
7
GND_DRAIN
Ground for signal return
8
StdB_SSRX-
9
StdB_SSRX+
SuperSpeed receiver differential
pair
10
DPWR
Power provided by device
11
DGND
Ground Return for DPWR
Shell
Shield
Connector metal shell
First
Note: Tx and Rx are defined from the device perspective
The physical location of the pins in the connector is illustrated in Figure 5-9 to Figure 5-11.
5.3.4
USB 3.0 Micro Connector Family
5.3.4.1
Interfaces Definition
The USB 3.0 Micro connector family consists of the USB 3.0 Micro-B receptacle, USB 3.0 MicroAB receptacle, USB 3.0 Micro-B plug and USB 3.0 Micro-A plug. Figure 5-12 and Figure 5-13
show the USB 3.0 Micro family receptacle and plug interface dimensions. Note that only the
dimensions that govern the mating interoperability are specified.
5-25
Universal Serial Bus 3.0 Specification, Revision 1.0
continued
5-26
Mechanical
Figure 5-12. USB 3.0 Micro-B and-AB Receptacles Interface Dimensions
5-27
Universal Serial Bus 3.0 Specification, Revision 1.0
continued
5-28
Mechanical
continued
5-29
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-13. USB 3.0 Micro-B and Micro-A Plug Interface Dimensions
5-30
Mechanical
continued
5-31
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-14. Reference Footprint for the USB 3.0 Micro-B or Micro-AB Receptacle
5-32
Mechanical
The USB 3.0 Micro connector family has the following characteristics:
• The USB 3.0 Micro-B connector may be considered a combination of USB 2.0 Micro-B
interface and the USB 3.0 SuperSpeed contacts. The USB 3.0 Micro-B receptacle accepts a
USB 2.0 Micro-B plug, maintaining backward compatibility.
• The USB 3.0 Micro-B connector maintains the same connector height and contact pitch as the
USB 2.0 Micro-B connector.
• The USB 3.0 Micro-B connector uses the same, proven latch design as the USB 2.0 Micro-B
connector.
• The USB 3.0 Micro-AB receptacle is identical to the USB 3.0 Micro-B receptacle except for a
keying difference in the connector shell outline.
• The USB 3.0 Micro-A plug is similar to the USB 3.0 Micro-B plug with different keying and
ID pin connections. Section 5.3.4.2 discusses the ID pin connections.
• There is no required footprint for the USB 3.0 Micro connector family. Figure 5-14 shows
reference Micro-B and -AB connector footprints.
5.3.4.2
Pin Assignments and Description
Table 5-5 and Table 5-6 show the pin assignments for the USB 3.0 Micro connector family.
Table 5-5. USB 3.0 Micro-B Connector Pin Assignments
Pin Number
Signal Name
Description
Mating Sequence
1
VBUS
Power
Second
2
D-
USB 2.0 differential pair
Last
3
D+
4
ID
OTG identification
5
GND
Ground for power return
Second
6
MicB_SSTXMicB_SSTX+
SuperSpeed transmitter
differential pair
Last
7
8
GND_DRAIN
Ground for SuperSpeed signal
return
Second
9
MicB_SSRX-
Last
10
MicB_SSRX+
SuperSpeed receiver differential
pair
Shell
Shield
Connector metal shell
First
Note: Tx and Rx are defined from the device perspective
5-33
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-6.
Pin Number
USB 3.0 Micro-AB/-A Connector Pin Assignments
Signal Name
Description
Mating Sequence
1
VBUS
Power
Second
2
D-
USB 2.0 differential pair
Last
3
D+
4
ID
OTG identification
5
GND
Ground for power return
Second
6
MicA_SSTX-
SuperSpeed transmitter
differential pair
Last
7
MicA_SSTX+
8
GND_DRAIN
Ground for SuperSpeed signal
return
Second
9
MicA_SSRXMicA_SSRX+
SuperSpeed receiver differential
pair
Last
10
Shell
Shield
Connector metal shell
First
Note: Tx and Rx are defined when an OTG device serves as a host.
The physical location of the pins in the connector is illustrated in Figure 5-12 and Figure 5-14.
5-34
Mechanical
5.4
Cable Construction and Wire Assignments
This section discusses the USB 3.0 cables, including cable construction, wire assignments, and wire
gauges. The performance requirements will be specified in Section 5.6.1.1.
5.4.1
Cable Construction
Figure 5-15 illustrates a USB 3.0 cable cross-section. There are three groups of wires: UTP signal
pair, Shielded Differential Pair (SDP, twisted or twinax signal pairs), and power and ground wires.
UTP Signal Pair
Filler,
optional
SDP Signal Pair
Braid
Power
Jacket
SDP Signal Pair
Ground
U-005
Figure 5-15. Illustration of a USB 3.0 Cable Cross-Section
The UTP is intended to transmit the USB 2.0 signaling while the SDPs are used for SuperSpeed;
the shield is needed for the SuperSpeed differential pairs for signal integrity and EMI performance.
Each SDP is attached with a drain wire, which is eventually connected to the system ground
through the GND_DRAIN pin(s) in the connector.
A metal braid is required to enclose all the wires in the USB 3.0 cable. The braid is to be
terminated to the plug metal shells, as close to 360° as possible, to contain EMI.
5-35
Universal Serial Bus 3.0 Specification, Revision 1.0
5.4.2
Wire Assignments
Table 5-7 defines the wire number, signal assignments, and colors of the wires.
Table 5-7. Cable Wire Assignments
Wire Number
Signal Name
Description
Color
1
2
3
4
5
6
7
8
9
10
Braid
PWR
UTP_DUTP_D+
GND_PWRrt
SDP1SDP1+
SDP1_Drain
SDP2SDP2+
SDP2_Drain
Shield
Power
Unshielded twist pair, negative
Unshielded twist pair, positive
Ground for power return
Shielded differential pair 1, negative
Shielded differential pair 1, positive
Drain wire for SDP1
Shielded differential pair 2, negative
Shielded differential pair 2, positive
Drain wire for SDP2
Cable external braid to be 360°
terminated on to plug metal shell
Red
White
Green
Black
Blue
Yellow
5.4.3
Purple
Orange
Wire Gauges and Cable Diameters
This specification chooses not to specify wire gauges. Table 5-8 lists the typical wire gauges for
reference. A large gauge wire incurs less loss, but at the cost of cable flexibility. One should
choose the smallest possible wire gauges that meet the cable assembly electrical requirements.
To maximize cable flexibility, all wires are required to be stranded and the cable outer diameter
should be minimized as much as possible. A typical USB 3.0 cable outer diameter may range from
3 mm to 6 mm.
Table 5-8. Reference Wire Gauges
5-36
Wire Number
Signal Name
Wire Gauge (AWG)
1
2
3
4
5
6
7
8
9
10
PWR
UTP_DUTP_D+
GND_PWRrt
SDP1SDP1+
SDP1_Drain
SDP2SDP2+
SDP2_Drain
20-28
28-34
28-34
20-28
26-34
26-34
28-34
26-34
26-34
28-34
Mechanical
5.5
Cable Assemblies
5.5.1
USB 3.0 Standard-A to USB 3.0 Standard-B Cable
Assembly
Figure 5-16 shows a USB 3.0 Standard-A to USB 3.0 Standard-B cable assembly.
Figure 5-16. USB 3.0 Standard-A to USB 3.0 Standard-B Cable Assembly
5-37
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-9 defines the wire connections for the USB 3.0 Standard-A to USB 3.0 Standard-B cable
assembly.
Table 5-9. USB 3.0 Standard-A to USB 3.0 Standard-B Cable Assembly Wiring
USB 3.0 Standard-A Plug
Pin Number
Wire
Signal Name
Wire Number
1
VBUS
2
D-
3
4
5
6
USB 3.0 Standard-B Plug
Signal Name
Pin Number
Signal Name
1
PWR
1
VBUS
2
UTP_D-
2
D-
D+
3
UTP_D+
3
D+
GND
4
GND_PWRrt
4
GND
StdA_SSRX-
5
SDP1-
5
StdB_SSTX-
StdA_SSRX+
6
SDP1+
6
StdB_SSTX+
7
GND_DRAIN
7 and 10
SDP1_Drain
SDP2_Drain
7
GND_DRAIN
8
StdA_SSTX-
8
SDP2-
8
StdB_SSRX-
9
StdA_SSTX+
9
SDP2+
9
StdB_SSRX+
Shell
Shield
Braid
Shield
Shell
Shield
5.5.2
USB 3.0 Standard-A to USB 3.0 Standard-A Cable
Assembly
The USB 3.0 Standard-A to USB 3.0 Standard-A cable assembly is defined for operating system
debugging and other host-to-host connection applications. Table 5-10 shows wire connections for
such a cable assembly. Refer to Figure 5-16 for the USB 3.0 Standard-A plug cable overmold
dimensions.
Table 5-10. USB 3.0 Standard-A to USB 3.0 Standard-A Cable Assembly Wiring
USB 3.0 Standard-A Plug #1
5-38
Wire
Pin Number
Signal Name
1
VBUS
Wire Number
2
3
4
GND
4
5
StdA_SSRX-
5
6
StdA_SSRX+
6
7
GND_DRAIN
8
9
Shell
Signal Name
USB 3.0 Standard-A Plug #2
Pin Number
Signal Name
No connect
1
VBUS
D-
No connect
2
D-
D+
No connect
3
D+
GND_PWRrt
4
GND
SDP1-
8
StdA_SSTX-
SDP1+
9
StdA_SSTX+
7 & 10
SDP1_Drain
SDP2_Drain
7
GND_DRAIN
StdA_SSTX-
8
SDP2-
5
StdA_SSRX-
StdA_SSTX+
9
SDP2+
6
StdA_SSRX+
Shield
Braid
Shield
Shell
Shield
Mechanical
5.5.3
USB 3.0 Standard-A to USB 3.0 Micro-B Cable Assembly
Figure 5-17 shows the USB 3.0 Micro-B plug overmold dimensions for a USB 3.0 Standard-A to
USB 3.0 Micro-B cable assembly. The USB 3.0 Standard-A plug overmold dimensions can be
found in Figure 5-16.
Figure 5-17. USB 3.0 Micro-B Plug Cable Overmold Dimensions
5-39
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-11 shows the wire connections for the USB 3.0 Standard-A to USB 3.0 Micro-B cable
assembly. Note that the ID pin in the USB 3.0 Micro-B plug shall not be connected, but left in the
open condition.
Table 5-11. USB 3.0 Standard-A to USB 3.0 Micro-B Cable Assembly Wiring
USB 3.0 Standard-A Plug
USB 3.0 Micro-B Plug
Pin Number
Signal Name
Wire Number
Signal Name
Pin Number
Signal Name
1
VBUS
1
PWR
1
VBUS
2
D-
2
UTP_D-
2
D-
3
D+
3
UTP_D+
3
D+
4
GND
4
GND_PWRrt
5
GND
5
StdA_SSRX-
5
SDP1-
6
MicB_SSTX-
6
StdA_SSRX+
6
SDP1+
7
MicB_SSTX+
7
GND_DRAIN
7 and 10
SDP1_Drain
SDP2_Drain
8
GND_DRAIN
8
StdA_SSTX-
8
SDP2-
9
MicB_SSRX-
9
StdA_SSTX+
9
SDP2+
Shell
5-40
Wire
Shield
Braid
shield
10
MicB_SSRX+
4
ID
Shell
Shield
Mechanical
5.5.4
USB 3.0 Micro-A to USB 3.0 Micro-B Cable Assembly
Figure 5-18 shows the USB 3.0 Micro-A plug cable overmold dimensions in a USB 3.0 Micro-A to
USB 3.0 Micro-B cable assembly. The USB 3.0 Micro-B plug cable overmold dimensions are
shown in Figure 5-17.
Figure 5-18. USB 3.0 Micro-A Cable Overmold Dimensions
5-41
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-12 shows the wire connections for the USB 3.0 Micro-A to USB 3.0 Micro-B cable
assembly. The ID pin on a USB 3.0 Micro-A plug shall be connected to the GND pin. The ID pin
on a USB 3.0 Micro-B plug shall be a no-connect or connected to ground by a resistance of greater
than Rb_PLUG_ID (1 MΩ minimum). An OTG device is required to be able to detect whether a
USB 3.0 Micro-A or USB 3.0 Micro-B plug is inserted by determining if the ID pin resistance to
ground is less than Ra_PLUG_ID (10 Ω maximum) or if the resistance to ground is greater than
Rb_PLUG_ID. Any ID resistance less than Ra_PLUG_ID shall be treated as ID = FALSE and any
resistance greater than Rb_PLUG_ID shall be treated as ID = TRUE.
Table 5-12. USB 3.0 Micro-A to USB 3.0 Micro-B Cable Assembly Wiring
USB 3.0 Micro-A Plug
Wire
USB 3.0 Micro-B Plug
Pin Number
Signal Name
Wire Number
Signal Name
Pin Number
Signal Name
1
VBUS
1
PWR
1
VBUS
2
D-
2
UTP_D-
2
D-
3
D+
3
UTP_D+
3
D+
4
ID (see Note 1)
4
ID (see Note 2)
5
GND
4
No Connect
GND_PWRrt
5
GND
6
MicA_SSTX-
5
SDP1-
9
MicB_SSRX-
7
MicA_SSTX+
6
SDP1+
10
MicB_SSRX+
8
GND_DRAIN
7 and 10
SDP1_Drain
SDP2_Drain
8
GND_DRAIN
9
MicA_SSRX-
8
SDP2-
6
MicB_SSTX-
10
MicA_SSRX+
9
SDP2+
7
MicB_SSTX+
Shell
Shield
Braid
Shield
Shell
Shield
Notes:
1. Connect to the GND.
2. No connect or connect to ground by a resistance greater than 1 MΩ minimum.
5-42
Mechanical
5.5.5
USB 3.0 Micro-A to USB 3.0 Standard-B Cable Assembly
A USB 3.0 Micro-A to USB 3.0 Standard-B cable assembly is also allowed. Figure 5-18 and
Figure 5-16 show, respectively, the UBS 3.0 Micro-A cable overmold and the USB 3.0 Standard-B
cable overmold dimensions.
Table 5-13 shows the wire connections for the USB 3.0 Micro-A to USB 3.0 Standard-B cable
assembly.
Table 5-13. USB 3.0 Micro-A to USB 3.0 Standard-B Cable Assembly Wiring
USB 3.0 Micro-A Plug
Wire
USB 3.0 Standard-B Plug
Pin Number
Signal Name
Wire Number
Signal Name
Pin Number
Signal Name
1
VBUS
1
PWR
1
VBUS
2
D-
2
UTP_D-
2
D-
3
D+
3
UTP_D+
3
D+
4
ID (see Note 1)
5
GND
4
No Connect
GND_PWRrt
4
GND
6
MicA_SSTX-
5
SDP1-
8
StdB_SSRX-
7
MicA_SSTX+
6
SDP1+
9
StdB_SSRX+
8
GND_DRAIN
7 and 10
SDP1_Drain
SDP2_Drain
7
GND_DRAIN
9
MicA_SSRX-
8
SDP2-
5
StdB_SSTX-
10
MicA_SSRX+
9
SDP2+
6
StdB_SSTX+
Shell
Shield
Braid
Shield
Shell
Shield
Notes:
1. Connect to the GND
5-43
Universal Serial Bus 3.0 Specification, Revision 1.0
5.5.6
USB 3.0 Icon Location
The USB 3.0 cable assemblies, compliant with the USB 3.0 Connectors and Cable Assemblies
Compliance Specification, shall display the USB 3.0 Icons illustrated in Figure 5-19.
Figure 5-19. USB 3.0 Icon
The USB 3.0 Icon is embossed, in a recessed area, on the side of the USB 3.0 plug. This provides
easy user recognition and facilitates alignment during the mating process. The USB Icon and
Manufacturer’s logo should not project beyond the overmold surface. The USB 3.0 compliant
cable assembly is required to have the USB 3.0 Icons on the plugs at both ends, while the
manufacturer’s logo is recommended. USB 3.0 receptacles should be orientated to allow the Icon
on the plug to be visible during the mating process. Figure 5-20 shows a typical plug orientation.
5-44
Mechanical
Figure 5-20. Typical Plug Orientation
5.5.7
Cable Assembly Length
This specification does not specify cable assembly lengths. A USB 3.0 cable assembly can be of
any length, as long as it meets all the requirements defined in this specification. The cable
assembly loss budget defined in Section 5.6.1.3.1 and the cable voltage drop budget defined in
Section 11.4.2 will limit the cable assembly length.
5-45
Universal Serial Bus 3.0 Specification, Revision 1.0
5.6
Electrical Requirements
This section covers the electrical requirements for USB 3.0 raw cables, mated connectors, and
mated cable assemblies. USB 3.0 signals, known as SuperSpeed, are governed by this
specification. The USB 2.0 signals are governed by the USB 2.0 specification, unless otherwise
specified. Refer to the USB 3.0 Connectors and Cable Assemblies Compliance Document for
specific D+/D- lines electrical requirements.
Compliance to the USB 3.0 specification is established through normative requirements of mated
connectors and mated cable assemblies. SuperSpeed requirements are specified mainly in terms of
S-parameters, using industry test specification with supporting details when required. DC
requirements, such as contact resistance and current carrying capability, are also specified in this
section.
Any informative specification for cable and connector products is for the purpose of design
guidelines and manufacturing control.
In conjunction with performance requirements, the required test method is referenced for the
parameter stated. A list of the industry standards for DC requirements is found in the Section 5.6.2.
Additional supporting test procedures can be found in the USB 3.0 Connectors and Cable
Assemblies Compliance Document.
The requirements in the section apply to all USB 3.0 connectors and/or cable assemblies unless
specified otherwise.
5.6.1
SuperSpeed Electrical Requirements
The following sections outline the requirements for SuperSpeed signals. The requirements for the
USB 2.0 signals (D+/D- lines) are given in the USB 3.0 Connectors and Cable Assemblies
Compliance Document.
5.6.1.1
Raw Cable
Informative raw cable electrical performance targets are provided here to help cable assembly
manufacturers manage raw cable suppliers. Those targets are not part of the USB 3.0 compliance
items; the ultimate requirements will be the mated cable assembly performance specified in
Section 5.6.1.3.
5.6.1.1.1
Characteristic Impedance
The differential characteristic impedance for the SDP pairs is recommended to be within
90 Ω +/- 7 Ω. It should be measured with a TDR in a differential mode using a 200 ps (10%-90%)
rise time.
5.6.1.1.2
Intra-Pair Skew
The intra-pair skew for the SDP pairs is recommended to be less than 15 ps/m. It should be
measured with a TDT in a differential mode using a 200 ps (10%-90%) rise time with a crossing at
50% of the input voltage.
5-46
Mechanical
5.6.1.1.3
Differential Insertion Loss
Cable loss depends on wire gauges and dielectric materials. Table 5-14 lists the examples of
differential insertion losses for the SDP pairs. Note that the differential loss values are referenced
to a 90 Ω differential impedance.
Table 5-14. SDP Differential Insertion Loss Examples
Frequency
34AWG
30AWG
28AWG
26AWG
0.625 GHz
2.7 dB/m
1.3 dB/m
1.0 dB/m
0.9 dB/m
1.25 GHz
3.3 dB/m
1.9 dB/m
1.5 dB/m
1.3 dB/m
2.50 GHz
4.4 dB/m
3.0 dB/m
2.5 dB/m
1.9 dB/m
5.00 GHz
6.7 dB/m
4.6 dB/m
3.6 dB/m
3.1 dB/m
7.50 GHz
9.0 dB/m
5.9 dB/m
4.7 dB/m
4.2 dB/m
5.6.1.2
Mated Connector
The mated connector impedance requirement is needed to maintain signal integrity. The differential
impedance of a mated connector shall be within 90 Ω +/-15 Ω, as seen from a 50 ps (20%-80%)
risetime of a differential TDR. Figure 5-21 illustrates the impedance limits of a mated connector.
The impedance profile of a mated connector must fall within the limits shown in Figure 5-21. Note
that the impedance profile of the mated connector is defined from the receptacle footprints through
the plug cable termination area. In the case the plug is directly attached to a device PCB, the mated
connector impedance profile includes the path from the receptacle footprints to the plug footprints.
115
110
105 ohms
105
Impedance, ohms
100
95
90
85
80
75
75 ohms
70
65
Time
U-006
Figure 5-21. Impedance Limits of a Mated Connector
5-47
Universal Serial Bus 3.0 Specification, Revision 1.0
5.6.1.3
Mated Cable Assemblies
A mated cable assembly refers to a cable assembly mated with the corresponding receptacles
mounted on a test fixture at the both ends. The requirements are for the entire signal path of the
mated cable assembly, from the host receptacle contact solder pads or through-holes on the host
system board to the device receptacle contact solder pads or through holes on the device system
board, not including PCB traces, as illustrated in Figure 5-22; the measurement is between TP1
(test point 1) and TP2 (test point 2).
TP1
SMA
TP2
Trace
Trace
Cable Assembly
SMA
PCB
PCB
U-007
Figure 5-22. Illustration of Test Points for a Mated Cable Assembly
For proper measurements, the receptacles shall be mounted on a test fixture. The test fixture shall
have uncoupled access traces from SMA or microprobe launches to the reference planes or test
points, preferably with 50 Ω +/-7% Ω single-ended characteristic impedance. The test fixture shall
have appropriate calibration structures to calibrate out the fixturing effect. All non-ground pins that
are adjacent but not connected to measurement ports shall be terminated with 50 Ω loads.
To be consistent with the USB 3.0 channel nominal differential characteristic impedance
requirement of 90 Ω, all measured differential S-parameters shall be normalized with a 90-Ω
reference differential impedance. Most VNA measurement software allows normalization of
measured S-parameters to a different reference impedance. For example, in PLTS, one can set the
port impedance to 45 Ω to normalize the measured 50-Ω single-ended S-parameters to 45 Ω; this
will result in 90-Ω differential S-parameters after the singled-ended-to-differential conversion.
A reference USB 3.0 mated cable assembly test fixture is defined in the USB 3.0 Connectors and
Cable Assemblies Compliance Document, in which the detailed testing procedures are given.
5-48
Mechanical
5.6.1.3.1
Differential Insertion Loss (EIA-360-101)
The differential insertion loss, SDD12, measures the differential signal energy transmitted through
the mated cable assembly. Figure 5-23 shows the differential insertion loss limit, which is
normalized with 90-Ω differential impedance and defined by the following vertices:
(100 MHz, -1.5 dB), (1.25 GHz, -5.0 dB), (2.5 GHz, -7.5 dB), and (7.5 GHz, -25 dB). The
measured differential insertion loss of a mated cable assembly must not exceed the differential
insertion loss limit.
0
X: 1250
Y: -5
X: 2500
Y: -7.5
Differential Insertion Loss, dB
-5
X: 100
Y: -1.5
-10
-15
-20
-25
X: 7500
Y: -25
-30
0
1000
2000
3000
4000
5000
6000
7000
Frequency, MHz
U-009
Figure 5-23. Differential Insertion Loss Requirement
5-49
Universal Serial Bus 3.0 Specification, Revision 1.0
5.6.1.3.2
Differential Near-End Crosstalk Between SuperSpeed Pairs (EIA-360-90)
The differential crosstalk measures the unwanted coupling between differential pairs. Since the Tx
pair is right next to the Rx pair for SuperSpeed, only the differential near-end crosstalk (DDNEXT)
is specified, as shown in Figure 5-24, referencing to a 90-Ω differential impedance. The mated
cable assembly meets the DDNEXT requirement if its DDENXT does not exceed the limit shown
in Figure 5-24; the vertices that defines the DDNEXT limit are: (100 MHz, -27 dB), (2.5 GHz,
-27 dB), (3 GHz,-23 dB) and (7.5GHz, -23 dB).
Differential Near End Crosstalk, dB
-15
-20
X: 7500
Y: -23
X: 3000
Y: -23
X: 100
Y: -27
-25
X: 2500
Y: -27
-30
-35
-40
0
1000
2000
3000
4000
5000
6000
7000
Frequency, MHz
U-010
Figure 5-24. Differential Near-End Crosstalk Requirement Between SuperSpeed Pairs
5-50
Mechanical
5.6.1.3.3
Differential Crosstalk Between D+/D- and SuperSpeed Pairs (EIA-360-90)
The differential near-end and far-end crosstalk between the D+/D- pair and the SuperSpeed pairs
(SSTX+/SSTX- or SSRX+/SSRX-) shall be managed not to exceed the limit shown in Figure 5-25;
the vertices that defines the DDNEXT and DDFEXT limit are: (100 MHz, -21 dB), (2.5 GHz,
-21 dB), (3.0 GHz,-15 dB) and (7.5 GHz, -15 dB). The reference differential impedance shall be
90 Ω.
-5
Differential Crosstalk, dB
-10
X: 7500
Y: -15
X: 3000
Y: -15
-15
X: 100
Y: -21
-20
X: 2500
Y: -21
-25
-30
0
1000
2000
3000
4000
5000
6000
7000
Frequency, MHz
U-011
Figure 5-25. Differential Near-End and Far-End Crosstalk Requirement Between
D+/D- Pair and SuperSpeed Pairs
5-51
Universal Serial Bus 3.0 Specification, Revision 1.0
5.6.1.3.4
Differential-to-Common-Mode Conversion
Since the common mode current is directly responsible for EMI, limiting the differential-tocommon-mode conversion, SCD12, will limit EMI generation within the connector and cable
assembly. Figure 5-26 illustrates the SCD12 requirement; a mated cable assembly passes the
SCD12 requirement if its SCD12 is less than or equal to -20 dB across the frequency range shown
in Figure 5-26.
-10
Differential to Common Mode Conversion, dB
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
0
1
2
3
4
5
6
7
Frequency, GHz
U-012
Figure 5-26. Differential-to-Common-Mode Conversion Requirement
5.6.2
DC Electrical Requirements
5.6.2.1
Low Level Contact Resistance (EIA 364-23B)
The following requirement applies to both the power and signal contacts:
• 30 mΩ (Max) initial for VBUS and GND contacts.
• 50 mΩ (Max) initial for all other contacts.
• Maximum change (delta) of +10 mΩ after environmental stresses.
• Measure at 20 mV (Max) open circuit at 100 mA.
• Refer to Section 5.7.2 for environmental requirements and test sequences.
5.6.2.2
Dielectric Strength (EIA 364-20)
No breakdown shall occur when 100 Volts AC (RMS) is applied between adjacent contacts of
unmated and mated connectors.
5-52
Mechanical
5.6.2.3
Insulation Resistance (EIA 364-21)
A minimum of 100 MΩ insulation resistance is required between adjacent contacts of unmated and
mated connectors.
5.6.2.4
Contact Current Rating (EIA 364-70, Method 2)
A current of 1.8 A shall be applied to VBUS pin and its corresponding GND pin (pin 1 and pin 4 of
the USB 3.0 Standard-A and Standard-B/Powered-B connectors; pin 1 and pin 5 of the USB 3.0
Micro connector family). Additionally, a minimum current of 0.25 A shall be applied to all the
other contacts. When the current is applied to the contacts, the delta temperature shall not exceed
+30 °C at any point on the USB 3.0 connectors under test, when measured at an ambient
temperature of 25 °C.
In the case of the USB 3.0 Powered-B connector, a current of 2.0 A shall be applied to the DPWR
pin and its corresponding DGND pin (pin 10 and pin 11 for USB 3.0 Powered-B connector).
Additionally, a minimum current of 0.25 A shall be applied to all the other contacts. When current
is applied to the contacts, the delta temperature must not exceed +30 °C at any point in the USB 3.0
connectors under test, when measured at an ambient temperature of 25 °C.
5.7
Mechanical and Environmental Requirements
The requirements in the section apply to all USB 3.0 connectors and/or cable assemblies unless
specified otherwise.
5.7.1
Mechanical Requirements
5.7.1.1
Insertion Force (EIA 364-13)
The connector insertion force shall not exceed 35 N at a maximum rate of 12.5 mm (0.492") per
minute.
It is recommended to use a non-silicon based lubricant on the latching mechanism to reduce wear.
If used, the lubricant may not affect any other characteristic of the system.
5.7.1.2
Extraction Force (EIA 364-13)
The connector extraction force shall not be less than 10 N initial and 8 N after the specified
insertion/extraction or durability cycles (at a maximum rate of 12.5 mm (0.492") per minute).
No burs or sharp edges are allowed on top of locking latches (hook surfaces which will rub against
the receptacle shield).
It is recommended to use a non-silicon based lubricant on the latching mechanism to reduce wear.
If used, the lubricant may not affect any other characteristic of the system.
5.7.1.3
Durability or Insertion/Extraction Cycles (EIA 364-09)
The durability ratings listed in Table 5-15 are specified for the USB 3.0 connectors.
5-53
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 5-15. Durability Ratings
Connector
Standard Durability Class
High Durability Class
USB 3.0 Standard-A connector
1500 cycles min
5000 cycles min
USB 3.0 Standard-B connector
1500 cycles min
5000 cycles min
USB 3.0 Powered-B connector
1500 cycles min
5000 cycles min
USB 3.0 Micro connector family
10000 cycles min
The durability test shall be done at a maximum rate of 200 cycles per hour and no physical damage
to any part of the connector and cable assembly shall occur.
5.7.1.4
Cable Flexing (EIA 364-41, Condition I)
No physical damage or discontinuity over 1 ms during flexing shall occur to the cable assembly
with Dimension X = 3.7 times the cable diameter and 100 cycles in each of two planes.
5.7.1.5
Cable Pull-Out (EIA 364-38, Condition A)
No physical damage to the cable assembly shall occur when it is subjected to a 40 N axial load for a
minimum of 1 minute while clamping one end of the cable plug.
5.7.1.6
Peel Strength (USB 3.0 Micro Connector Family Only)
No visible physical damage shall be noticed to a soldered receptacle when it is pulled up from the
PCB in the vertical direction with a minimum force of 150 N.
5.7.1.7
4-Axes Continuity Test (USB 3.0 Micro Connector Family Only)
The USB 3.0 Micro connector family shall be tested for continuity under stress using the test
configurations shown below. Plugs shall be supplied in a cable assembly with a representative
overmold. A USB 3.0 Micro-B or -AB receptacle shall be mounted on a 2-layer printed circuit
board (PCB) between 0.8 and 1.0 mm thickness. The PCB shall be clamped on either side of the
receptacle no further than 5 mm away from the solder tails. The PCB shall initially be placed in a
horizontal plane, and an 8-N tensile force shall be applied to the cable in a downward direction,
perpendicular to the axis of insertion, for a period of at least 10 seconds.
The continuity across each contact shall be measured throughout the application of the tensile force.
The PCB shall then be rotated 90 degrees such that the cable is still inserted horizontally and the
8 N tensile force will be applied again in the downward direction and continuity measured as before.
This test will be repeated for 180-degree and 270-degree rotations. Passing parts shall not exhibit
any discontinuities greater than 1 μs duration in any of the four orientations.
One method for measuring the continuity through the contacts is to short all the wires at the end of
the cable pigtail and apply a voltage through a pull-up to each of VBUS, D+, D-, ID, and the
SuperSpeed pins, with the GND pins connected to ground.
When testing a USB 3.0 Micro-A plug, all the sense resistors shall stay pulled down for the length
of the test. When testing a USB 3.0 Micro-B plug, the ID pin shall stay high and the other pins
shall remain low for the duration of the test. Alternate methods are allowed to verify continuity
through all pins.
5-54
Mechanical
The 4-axes continuity tests shall be done with a USB 3.0 Micro-B/-A plug in a USB 3.0 Micro-B/AB receptacle and with a USB 2.0 Micro-B/-A plug in a USB 3.0 Micro-B/-AB receptacle, as
illustrated in Figure 5-27.
Figure 5-27. 4-Axes Continuity Test
5-55
Universal Serial Bus 3.0 Specification, Revision 1.0
5.7.1.8
Wrenching Strength (Reference, USB 3.0 Micro Connector Family
Only)
The wrenching strength test shall be performed using virgin parts. Perpendicular forces (Fp) are
applied to a plug when inserted at a distance (L) of 15 mm from the edge of the receptacle. Testing
conditions and method shall be agreed to by all parties. These forces shall be applied in all four
directions (left, right, up, down). Compliant connectors shall meet the following force thresholds:
• No plug or receptacle damage shall occur when a force of 0-25 N is applied.
• The plug may be damaged, but only in such a way that the receptacle does not sustain damage
when a force of 25-50 N is applied.
5.7.1.9
Lead Co-Planarity
Co-planarity of all SMT leads shall be within a 0.08 mm range.
5.7.1.10
Solderability
Solder shall cover a minimum of 95% of the surface being immersed, when soldered at a
temperature 255 °C +/-5 °C for an immersion duration of 5 s.
5.7.1.11
Restriction of Hazardous Substances (RoHS) Compliance
It is recommended that components be RoHS compliant. Lead-free plug and receptacle materials
should conform to Directive 2002/95/EC of January 27, 2003 on RoHS or other regulatory
directives.
5.7.2
Environmental Requirements
The connector interface environmental tests shall follow EIA-364-1000.01, Environmental Test
Methodology for Assessing the Performance of Electrical Connectors and Sockets Used in Business
Office Applications.
Since the connector defined has far more than 0.127 mm wipe length, Test Group 6 in EIA-3641000.01 is not required. The temperature life test duration and the mixed flowing gas test duration
values are derived from EIA 364-1000.01 based on the field temperature per the following.
Table 5-16. Environmental Test Conditions
Temperature Life test temperature and duration
105 °C for 120 hours
Temperature Life test temperature and duration for preconditioning
105 °C for 72 hours
Mixed flowing gas test duration
7 days
The pass/fail criterion for the low level contact resistance (LLCR) is as defined in Section 5.6.2.1.
The durability ratings are defined in Section 5.7.1.3.
5-56
Mechanical
5.7.3
Materials
This specification does not specify materials for connectors and cables. Connector and cable
manufactures shall select appropriate materials based on performance requirements. Table 5-17
below is provided for reference only.
Table 5-17. Reference Materials1,2
Component
Materials
Cable
Conductor: copper with tin plating
Comments
SDP Shield: AL foil or AL/mylar foil
Braid: Tin plated copper or aluminum
Jacket: PVC or halogen free substitute material
Cable Overmold
Thermoset
Connector Shell
Copper alloy or stainless steel, depending on durability requirement
Contact
Base material: copper alloy
Under-plating: 2.0 µm Ni
Contact area plating: (Min) 0.05 µm Au + (Min) 0.75 µm Ni-Pd
Solder tail plating: (Min) 0.05 µm Au
Housing
1
2
5.8
Thermoplastics capable of withstanding lead-free soldering
temperature.
The USB 3.0 Standard-A
connector housings are
recommended to be
Pantone 300C (Blue).
Halogen-free materials should be considered for all plastics.
If an application of the part requires a flammability rating less flammable than HB, a suitable
flame retardant compound should be considered for plastics in this part.
Implementation Notes and Design Guides
This section discusses a few implementation notes and design guides to help users design and use
the USB 3.0 connectors and cables.
5.8.1
Mated Connector Dimensions
Figure 5-28, Figure 5-29, and Figure 5-30 show the mated plugs and receptacles for the USB 3.0
Standard-A, USB 3.0 Standard-B, and USB 3.0 Micro connectors, respectively. The distance
between the receptacle front surface and the cable overmold should be observed by system
designers to avoid interference between the system enclosure and the cable plug overmold.
Provisions shall be made in connectors and chassis to ground the connector metal shells to the
metal chassis to contain EMI emission.
5-57
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 5-28. Mated USB 3.0 Standard-A Connector
Figure 5-29. Mated USB 3.0 Standard-B Connector
5-58
Mechanical
Figure 5-30. Mated USB 3.0 Micro-B Connector
5-59
Universal Serial Bus 3.0 Specification, Revision 1.0
5.8.2
EMI Management
Systems that include USB 3.0 connectors and cable assemblies must meet the relevant EMI/EMC
regulations. Because of the complex nature of EMI, it is difficult to specify a component level EMI
test for the cable assemblies. However, connector and cable assembly designers, as well as system
implementers should pay attention to receptacle and cable plug shielding to ensure a low impedance
grounding path. The following are guidelines for EMI management:
• The quality of raw cables should be ensured. The intra-pair skew or the differential to common
mode conversion of the SuperSpeed pairs has a significant impact on cable EMI performance
and should be controlled within the limits of this specification.
• The cable external braid should be terminated to the cable plug metal shell as close to 360˚ as
possible. Without appropriate shielding termination, even a perfect cable with zero intra-pair
skew may not meet EMI requirements.
• If not done properly, the wire termination contributes to the differential-to-common-mode
conversion. The breakout distance for the wire termination should be kept as small as possible
for both EMI and signal integrity. If possible, symmetry should be maintained for the two lines
within a differential pair.
• The mating interface between the receptacle and cable plug should have a sufficient number of
grounding fingers, or springs to provide a continuous return path from the cable plug to system
ground. Friction locks should not compromise ground return connections.
• The receptacle connectors should be designed with a back-shield as part of the receptacle
connector metal shell. The back-shield should be designed with a short return path to the
system ground plane.
• The receptacle connectors should be connected to metal chassis or enclosures through
grounding fingers, screws, or any other way to mitigate EMI.
5.8.3
Stacked Connectors
Stacked USB connectors are commonly used in PC systems. This specification does not explicitly
define the stacked USB 3.0 Standard-A receptacles but they are allowed. The following are a few
points that should be taken into account when designing a stacked USB 3.0 connector:
• A stacked connector introduces additional crosstalk between the top and bottom connectors.
Such crosstalk should be minimized when designing a stacked USB 3.0 connector. The
differential NEXT and FEXT should be managed within ~-32 dB (up to the fundamental
frequency of 2.5 GHz) between differential pairs in the top and bottom connectors.
• Due to the additional electrical length, the top connector will generally not perform as well as
the bottom connector. Connector designers should carefully design the top connector contact
geometries and materials to minimize impedance discontinuity. Regardless of how many
connectors within a stack one may choose to design, the electrical requirements defined in
Section 5.6 must be met.
5-60
Physical Layer
Host
Hub
Device
Device Driver/Application
Pipe Bundle (per Function Interface)
Function
USB System Software
Default Control Pipe
Device
Notifications
Transactions
Transaction
Packets
Notifications
Data
Packets
Port-to-Port
Chip to Chip
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
Localized
Link Power
Management
LFPS
PHYSICAL
8b/10b
encode/
decode
Data
Packets
LINK
Link Cmds
USB Device
Power
Management
(Suspend)
Link Management Packets
Link Control/Mgmt
Pkt
Delims
Transactions
Transaction
Packets
Link Management Packets
USB Function
Power
Management
Device or Host PROTOCOL
End-to-End
6
U-013
Figure 6-1. SuperSpeed Physical Layer
6.1 Physical Layer Overview
The physical layer defines the signaling technology for the SuperSpeed bus. This chapter defines
the electrical requirements of the SuperSpeed physical layer.
This section defines the electrical-layer parameters required for interoperability between
SuperSpeed components. Normative specifications are required. Informative specifications may
assist product designers and testers in understanding the intended behavior of the SuperSpeed bus.
6.2
Physical Layer Functions
The functions of the physical layer are shown in Figure 6-2, Figure 6-3, and Figure 6-4.
6-1
Universal Serial Bus 3.0 Specification, Revision 1.0
D-Code/K-Code
D/K
x8
Scrambler (D only)
x8
Core Clock
8b/10b Encoding
x 10
Parallel to Serial
Bit Clock
x1
Transmitter Differential
Driver
D+ DU-014
Figure 6-2. Transmitter Block Diagram
6-2
Physical Layer
In
D+ D-
Out
Differential Receiver
and Equalization
Bit Rate
Clock Recovery
Circuit
Data Recovery
Circuit (DRC)
Recovered
Bit Clock
x1
RxPolarity
Serial to Parallel
x 10
K28.5 Detection
RxValid
Recovered
Symbol Clock
Elastic Buffer
RxBufErr
RxClkCorCont
x 10
8b/10b Decode
RxDataK
RxCodeErr
RxDisparityErr
x8
Core Clock
Descrambling (D only)
x8
U-015
Figure 6-3. Receiver Block Diagram
6-3
Universal Serial Bus 3.0 Specification, Revision 1.0
Without Cable
Mated
Connector
+
-
Txp
Rxp
Txn
Rxn
AC Capacitor
Host
+
Device
Rxp
Txp
+
- Rxn
Txn
+
-
AC Capacitor
With Cable
Mated
Connector
+
Host
Cable
Mated
Connector
Txp
Rxp
Txn
Rxn
AC Capacitor
+
Device
Rxp
Txp
+
- Rxn
Txn
+
-
AC Capacitor
U-016
Figure 6-4. Channel Models without a Cable (Top) and with a Cable (Bottom)
6.2.1
Measurement Overview
The normative SuperSpeed eye diagram is to be measured through a compliance channel that
represents the sum of a long channel, a short channel, and a 3-meter cable. This requires three
separate tests for compliance. These reference channels are described in the USB SuperSpeed
Compliance Methodology white paper. The eye diagram is measured using the clock recovery
function described in Section 6.5.2.
For the long channel case the eye diagram at the receiver is completely closed. An informative
receiver equalization function is provided in Section 6.8.2 that is optimized to the compliance
channel and is used to open the receiver eye.
This methodology allows a silicon vendor to design the channel and the component as a matched
pair. It is expected that a silicon component will have layout guidelines that must be followed in
order for the component to meet the overall specification and the eye diagram at the end of the
compliance channel.
Note that simultaneous USB 2.0 and SuperSpeed operation is a testing requirement for compliance.
6-4
Physical Layer
6.2.2
Channel Overview
A PHY is a transmitter and receiver that operate together and are located on the same component.
A channel connects two PHYs together with two unidirectional differential pairs of pins for a total
of four wires. The PHYs are required to be AC coupled. The AC coupling capacitors are associated
with the transmitter.
6.3
Symbol Encoding
SuperSpeed uses the 8b/10b transmission code. The definition of this transmission code is identical
to that specified in ANSI X3.230-1994 (also referred to as ANSI INCITS 230-1994), clause 11. As
shown in Figure 6-5, ABCDE maps to abcdei and FGH maps to fghj.
Transmit
Receive
TX<7:0>, Control <Z>
RX<7:0>, Control <Z>
MSB
7
LSB
6
5
4
3
2
1
MSB
0
Z
7
LSB
6
5
4
8 bits + Control
8
7
10b
Encode
10b
j,h,g,f,i,e,d,c,b,a
j,h,g,f,i,e,d,c,b,a
4
3
Z
8b
10 bits
5
0
Decode
10 bits
6
1
H,G,F,E,D,C,B,A,Z
MSB
9
2
8 bits + Control
H,G,F,E,D,C,B,A,Z
8b
3
2
1
LSB
MSB
0
9
LSB
8
7
6
5
4
3
2
1
0
U-017
Figure 6-5. Character to Symbol Mapping
6-5
Universal Serial Bus 3.0 Specification, Revision 1.0
6.3.1
Serialization and Deserialization of Data
The bits of a Symbol are placed starting with bit “a” and ending with bit “j.” This is shown in
Figure 6-6.
Symbol for
Byte 0
Symbol for
Byte 1
Symbol for
Byte 2
Symbol for
Byte 3
Symbol for
Byte 4
ab c de i f gh j ab c de i f gh j ab cde i f gh j ab cde i f gh j abc de i f gh j
time = 0
time =
1x Symbol Time
time =
2x Symbol Time
time =
3x Symbol Time
time =
4x Symbol Time
time =
5x Symbol Time
U-018
Figure 6-6. Bit Transmission Order
6.3.2
Normative 8b/10b Decode Rules
1. A Transmitter is permitted to pick any disparity when first transmitting differential data after
being in an Electrical Idle state. The Transmitter shall then follow proper 8b/10b encoding
rules until the next Electrical Idle state is entered.
2. The initial disparity for a Receiver is the disparity of the first Symbol used to obtain Symbol
lock.
3. Disparity may also be-reinitialized if Symbol lock is lost and regained during the transmission
of differential information due to a burst error event.
4. All following received Symbols after the initial disparity is set shall be in the proper column
corresponding to the current running disparity.
5. Receive disparity errors do not directly cause the link to retrain.
6. If a disparity error or 8b/10 Decode error is detected, the physical layer shall inform the link
layer.
6.3.3
Data Scrambling
The scrambling function is implemented using a free running Linear Feedback Shift Register
(LFSR). On the Transmit side, scrambling is applied to characters prior to the 8b/10b encoding.
On the receive side, descrambling is applied to characters after 8b/10b decoding. The LFSR is reset
whenever a COM symbol is sent or received.
The LFSR is graphically represented in Figure 6-7. Scrambling or unscrambling is performed by
serially XORing the 8-bit (D0-D7) character with the 16-bit (D0-D15) output of the LFSR. An
output of the LFSR, D15, is XORed with D0 of the data to be processed. The LFSR and data
register are then serially advanced and the output processing is repeated for D1 through D7. The
LFSR is advanced after the data is XORed.
The mechanism to notify the physical layer to disable scrambling is implementation specific and
beyond the scope of this specification.
6-6
Physical Layer
The data scrambling rules are as follows:
1. The LFSR implements the polynomial: G(X)=X16+X5+X4+X3+1
2. The LFSR value shall be advanced eight serial shifts for each Symbol except for SKP.
3. All 8b/10b D-codes, except those within the Training Sequence Ordered Sets shall be
scrambled.
4. K codes shall not be scrambled.
5. The initialized value of an LFSR seed (D0-D15) shall be FFFFh. After COM leaves the
Transmitter LFSR, the LFSR on the transmit side shall be initialized. Every time COM enters
the Receive LFSR, the LFSR on the receive side shall be initialized. This also applies to the
BRST sequence during loopback mode (see section 6.8.4.1).
Clock
D0
D1
D2
D3
D4
D5
D6
D14
D15
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
>
>
>
>
>
>
>
>
>
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
D7
D6
D5
D4
D3
D2
D1
D0
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
D SET Q
>
>
>
>
>
>
>
>
Data In
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
CLR Q
Data Out
CLR Q
U-019
Figure 6-7. LFSR with Scrambling Polynomial
IMPLEMENTATION NOTE
Disabling Scrambling
Disabling scrambling is intended to help simplify test and debug equipment. Control of the exact
data patterns is useful in a test and debug environment. Since scrambling is reset at the physical
layer, there is no reasonable way to reliably control the state of the data transitions through
software. The Disable Scrambling bit is provided in the training sequence for this purpose.
The mechanism(s) and/or interface(s) used to notify the physical layer to disable scrambling is
component implementation specific and beyond the scope of this specification.
For more information on scrambling, refer to Appendix B.
6.3.4
8b/10b Decode Errors
An 8b/10b Decode error shall occur when a received Symbol does not match any of the valid
8b/10b Symbols listed in Appendix A. Any received 8b/10b Symbol that does not match any of the
valid 8b/10b Symbols listed in Appendix A shall be forwarded to the link layer by substituting a
K28.4 symbol (refer to Table 6-1). 8b/10b errors may not directly initiate Recovery.
6-7
Universal Serial Bus 3.0 Specification, Revision 1.0
6.3.5
Special Symbols for Framing and Link Management
The 8b/10b encoding scheme provides Special Symbols that are distinct from the Data Symbols
used to represent characters. These Special Symbols are used for various Link Management
mechanisms described later. Table 6-1 lists the Special Symbols used and provides a brief
description for each. Special Symbols must follow the proper 8b/10b disparity rules. The
compliance tests are defined in the USB SuperSpeed Compliance Methodology white paper.
Table 6-1. Special Symbols
6.4
Encoding
Symbol
Name
Description
K28.1
SKP
Skip
Compensates for different bit rates between two
communicating ports. SKPs may be dynamically
inserted or removed from the data stream.
K28.2
SDP
Start Data Packet
Marks the start of a Data Packet Payload
K28.3
EDB
End Bad
Marks the end of a nullified Packet
K28.4
SUB
Decode Error Substitution
Symbol substituted by the 8b/10b decoder when a
Decode error is detected.
K28.5
COM
Comma
Used for symbol alignment
K28.6
-----
-----
Reserved
K27.7
SHP
Start Header Packet
Marks the start of a Data Packet, Transaction Packet
or Link Management Packet
K29.7
END
End
Marks the end of a packet
K30.7
SLC
Start Link Command
Marks the start of a Link Command
K23.7
EPF
End Packet Framing
Marks the end of a packet framing
Link Initialization and Training
This section defines the sequences that are used for configuration and initialization. The sequences
are used by the Initialization State Machine (refer to Chapter 7) for the following functions:
• Configuring and initializing the link
• Bit-lock and symbol lock
• Rx equalization training
• Lane polarity inversion
Training sequences are composed of Ordered Sets used for initializing bit alignment, Symbol
alignment and optimizing the equalization. Training sequence Ordered Sets are never scrambled
but are always 8b/10b encoded.
Bit lock refers to the ability of the Clock/Data Recovery (CDR) circuit to extract the phase and
frequency information from the incoming data stream. Bit lock is accomplished by sending a
sufficiently long sequence of bits (D10.2 symbol containing alternating 0s and 1s) so the CDR
roughly centers the clock within the bit.
Once the CDR is properly recovering data bits, the next step is to locate the start and end of a 10-bit
symbol. For this purpose, the special K-Code called COMMA is selected from the 8b/10b codes.
The bit pattern of the COMMA code is unique, so that it is never found in other data patterns,
6-8
Physical Layer
including any combination of a D-Code appended to any other D-Code or appended to any K-Code.
This applies to any polarity of code. The only exception is for various bit patterns that include a bit
error.
Training sequences (TS1 or TS2) are transmitted consecutively and can only be interrupted by SKP
Ordered Sets occurring between Ordered Sets (between consecutive TS1 sets, consecutive TS2 sets,
or when TS1 is followed by TS2).
6.4.1
Normative Training Sequence Rules
Training sequences are composed of Ordered Sets used for initializing bit alignment, symbol
alignment, and receiver equalization.
The following rules apply to the training sequences:
• Training sequence Ordered Sets shall be 8b/10b encoded.
• Transmission of a TS1 or TS2 Ordered Set shall not be interrupted by SKP Ordered Sets. SKP
Ordered Sets shall be inserted before, or after, completion of any TS1 or TS2 Ordered Set.
• No SKP Ordered Sets are to be transmitted during the entire TSEQ time (65,536 ordered sets).
This means that the PHY must manage elasticity buffer differently than during normal
operation.
Additional rules for the use of TSEQ, TS1, and TS2 Ordered Sets can be found in Chapter 7.
6.4.1.1
Training Control Bits
The training control bits are found in the Link Functionality symbol within the TS1 and TS2
ordered sets. They are described in Table 6-5.
Bit 0 and bit 2 of the link configuration field shall not be set to 1 simultaneously. If a receiver
detects this condition in the received Link configuration field, then all of the training control bits
shall be ignored.
6.4.1.2
Training Sequence Values
The TSEQ training sequence repeats 65,536 times to allow for testing many coefficient settings.
Table 6-2. TSEQ Ordered Set
Symbol Number
Name
Value
0
K28.5
COM (Comma)
1
D31.7
0xFF
2
D23.0
0x17
3
D0.6
0xC0
4
D20.0
0x14
5
D18.5
0xB2
6
D7.7
0xE7
7
D2.0
0x02
8
D2.4
0x82
9
D18.3
0x72
10
D14.3
0x6E
6-9
Universal Serial Bus 3.0 Specification, Revision 1.0
Symbol Number
Name
Value
11
D8.1
0x28
12
D6.5
0xA6
13
D30.5
0xBE
14
D13.3
0x6D
15
D31.5
0xBF
16-31
D10.2
0x4A
Table 6-3. TS1 Ordered Set
Symbol Number
Encoded Values
Description
0-3
K28.5
COM (Comma)
4
D0.0
Reserved for future use
5
See Table 6-5
Link Functionality
6-15
D10.2
TS1 Identifier
Table 6-4. TS2 Ordered Set
Symbol Number
Encoded Values
Description
0-3
K28.5
COM (Comma)
4
D0.0
Reserved
5
See Table 6-5
Link Functionality
6-15
D5.2
TS2 Identifier
Table 6-5. Link Configuration Field
Bit
TS1 Symbol 5
Description
Bit 0
0 = Normal Training
Reset is set by the Host only in order to reset the device.
1 = Reset
Bit 1
Set to 0
Reserved for future use.
Bit 2
0 = Loopback de-asserted
1 = Loopback asserted
When set, the receiving component enters digital
loopback.
0 = Disable Scrambling de-asserted
When set, the receiving component disables scrambling.
Bit 3
1 = Disable Scrambling asserted
Bit 4:7
6-10
Set to 0
Reserved for future use.
Physical Layer
6.4.2
Lane Polarity Inversion
During the TSEQ training sequence, the Receiver must use the D10.2 Symbol within the TSEQ
Ordered Set to determine lane polarity inversion (Rxp and Rxn are swapped). If polarity inversion
has occurred, the D10.2 symbols within the TSEQ ordered set will be received as D21.5 instead of
D10.2 and the receiver must invert the polarity of the received bits. This must be done before the
TSEQ symbols 1-15 are used since these symbols are not all symmetric under inversion in the
8b/10b domain. If the receiver does not use the TSEQ training sequence, then the polarity
inversion may be checked against the D10.2 symbol in the TS1 ordered set.
6.4.3
Elasticity Buffer and SKP Ordered Set
The SuperSpeed architecture supports a separate reference clock source on each side of the
SuperSpeed link. The accuracy of each reference clock is required to be within +-300 ppm. This
gives a maximum frequency difference between the two devices of the link of +- 600 ppm. In
addition, SSC creates a frequency delta that has a maximum difference of 5000 ppm. The total
magnitude of the frequency delta can range from -5300 to 300 ppm. This frequency delta is
managed by an elasticity buffer that consumes or inserts SKP ordered sets.
SKP Ordered Sets shall be used to compensate for frequency differences between the two ends of
the link. The transmitter sends SKP ordered sets at an average of every 354 symbols. However,
SKP ordered sets shall not be inserted within any packet. The transmitter is allowed to buffer the
SKP ordered sets up to a maximum of four SKP ordered sets. The receiver must implement an
elasticity buffer capable of buffering (or starving) eight symbols of data.
SKP Rules (Host/Device/Hub):
• The SKP Ordered Set shall consist of a SKP K-Symbol followed by a SKP K-Symbol. A SKP
Ordered Set represents two Symbols that can be used for clock compensation. Error detection
and recovery from a corrupted SKP Symbol is described in Section 6.4.2.13.
• A device must keep a running count of the number of transmitted symbols since the last SKP
Ordered set. The value of this count will be referred to as Y. The value of Y is reset whenever
the transmitter enters Polling.Active.
• Unless otherwise specified, a transmitter shall insert the integer result of Y/354 calculation
Ordered sets immediately after each transmitted TS1, TS2 Ordered Set, LMP, TP Data Packet
Payload, or Logical idle. During training only, a transmitter is allowed the option of waiting to
insert 2 SKP ordered sets when the integer result of Y/354 reaches 2. A transmitter shall not
transmit SKP Ordered Sets at any other time.
Note: The non-integer remainder of the Y/354 SKP calculation shall not be discarded and shall
be used in the calculation to schedule the next SKP Ordered Set.
• SKP Commands do not count as interruptions when monitoring for Ordered Sets (i.e.,
consecutive TS1, TS2 Ordered Sets in Polling and Recovery).
Table 6-6. SKP Ordered Set Structure
Symbol Number
Encoded Values
Description
0
K28.1
SKP
1
K28.1
SKP
6-11
Universal Serial Bus 3.0 Specification, Revision 1.0
6.4.4
Compliance Pattern
Entry to the Polling.Compliance substate is described in Chapter 7. This initiates the transmission
of the pseudo-random data pattern generated by the scrambled D10.0 compliance sequence. SKPs
are not sent during the compliance pattern. The compliance pattern shall be transmitted
continuously or until a ping LFPS (refer to Section 6.9) is detected at the receiver. Upon detection
of a ping LFPS, the compliance pattern shall advance to the next compliance pattern. Upon
detection of a reset, LFPS the compliance pattern shall be terminated. The compliance pattern
sequences are described in Table 6-7.
Table 6-7. Compliance Pattern Sequences
Compliance Pattern
Value
Description
CP0
D0.0 scrambled
A pseudo-random data pattern that is exactly the same as
logical idle (refer to Chapter 7) but does not include SKP
sequences
CP1
D10.2
Nyquist frequency
CP2
D24.3
Nyquist/2
CP3
K28.5
COM pattern
CP4
LFPS
The low frequency periodic signaling pattern
CP5
K28.7
With de-emphasis
CP6
K28.7
Without de-emphasis
CP7
50-250 1’s and 0’s
With de-emphasis. Repeating 50-250 1’s and then 50-250 0’s.
CP8
50-250 1’s and 0’s
With without de-emphasis. Repeating 50-250 1’s and then
50-250 0’s.
Note: Unless otherwise noted, scrambling is disabled for compliance patterns.
6-12
Physical Layer
6.5
Clock and Jitter
6.5.1
Informative Jitter Budgeting
The jitter for USB 3.0 is budgeted among the components that comprise the end to end connections:
the transmitter, channel (including packaging, connectors, and cables), and the receiver. The jitter
budget is derived at the silicon pads. The Dj distribution is the dual Dirac method. Table 6-8 lists
Tx, Rx, and channel jitter budgets.
Table 6-8. Informative Jitter Budgeting at the Silicon Pads
Jitter Contribution (ps)
6
Tx
Rj1,2
Dj3
Tj4 at 10-12
2.42
41
75
2.13
45
75
Rx
2.42
57
91
Total:
4.03
143
200
Media
5
Notes:
1.
Rj is the sigma value assuming a Gaussian distribution.
2.
Rj Total is computed as the Root Sum Square of the individual Rj components.
3.
Dj budget is using the Dual Dirac method.
4.
Tj at a 10
5.
The media budget includes the cancellation of ISI from the appropriate Rx equalization function.
6.
Tx is measured after application of the JTF.
-12
BER is calculated as 14.068 * Rj + Dj.
Note: Captive cables must meet the mated connector requirements specified in Section 5.6.1.2.
But a captive cable is not considered a stand-alone component. For electrical budgeting purposes, a
captive cable is considered to be part of a device, and must meet the device jitter requirements
listed in Table 6-8. 6-13
Universal Serial Bus 3.0 Specification, Revision 1.0
6.5.2
Normative Clock Recovery Function
The Tx Phase jitter measurement is performed using a standard clock recovery, shown in
Figure 6-8. For information on the golden PLL measurement refer to the latest version of INCITS
TR-35-2004, INCITS Technical Report for Information Technology – Fibre Channel –
Methodologies for Jitter and Signal Quality Specification (FC-MJSQ).
The clock recovery function is given by Equations 1-3. A schematic of the general clock recovery
function is shown in Figure 6-8. As shown, the clock recovery circuit has a low pass response.
After the recovered clock is compared (subtracted) to the data, the overall clock recovery becomes
a high pass function. This is shown in Figure 6-9.
Recovered
Data
Serial Data
>
Recovered
Clock
Clock Recovery
Circuit
Magnitude, dB
Receiver
Clock Recovery Circuitry
has Low-Pass Function HL
Frequency, f
U-020
Figure 6-8. Jitter Filtering – “Golden PLL” and Jitter Transfer Functions
6-14
Physical Layer
Jitter Transfer (frequency response)
101
100
-3 dB Line
f_3dB_HPF = 4.9 MHz;
f_3dB_PLL = 10 MHz;
10-1
10-2
PLL/CDR:
Jitter Tracking
Recovered Clock
does track Jitter
10-3
Jitter Non-tracking
Jitter Filtering
Recovered Clock
does not Track Jitter
JTF/HPF
10-4
10-1
100
101
102
103
Jitter Frequency, MHz
|PLL(s)|: recovered clock
|HPF(s)|=|1-PLL(s)|: data-clock
U-021
Figure 6-9. “Golden PLL” and Jitter Transfer Functions
The equations for these functions are:
2 sζω n + ωn
2
2
s + 2 sζ ω n + ω n
2
(1)
H CDR ( s ) =
and
(2)
JTF ( s ) =
s2
s 2 + 2 ζ ωn s + ω n
2
where ωn is the natural frequency and ξ is the damping factor. The relationship to the 3 dB
frequency is
(3)
⎛
⎜
⎝
[
] ⎞⎟
1
2
2
ω3dB = ωn ⎜1 + 2 ζ 2 + (1 + 2 ζ 2 ) + 1 ⎟
1
2
⎠
As shown in Figure 5-7, the corner frequency ω3dB = 2 π 10 7 and ζ = 0.707. This transfer
function has a maximum peaking of 2 dB.
6-15
Universal Serial Bus 3.0 Specification, Revision 1.0
6.5.3
Normative Spread Spectrum Clocking (SSC)
All ports are required to have Spread Spectrum Clocking (SSC) modulation. Providing the same
SSC clock to two different components is allowed but not required, the SSC can be generated
asynchronously. The SSC profile is not specified and is vendor specific. The SSC modulation
requirement is listed in Table 6-9. The SSC modulation may not violate the phase slew rate
described in Section 6.5.4.
Table 6-9. SSC Parameters
Symbol
Description
Limits
Min
Units
Note
Max
tSSC-MOD-RATE
Modulation Rate
30
33
kHz
tSSC-FREQ-DEVIATION
SSC deviation
+0/-4000
+0/-5000
ppm
1, 2
Note:
1. The data rate is modulated from 0 ppm to -5000 ppm of the nominal data rate frequency and scales with data rate.
2. This is measured below 2 MHz only.
An example of the period modulation from triangular SSC is shown in Figure 6-10.
UI = UI + (5000 ppm)
UI = UI
16.66~ µs
UI = 201 ps
33.33~ µs
UI = 200 ps
U-022
Figure 6-10. Period Modulation from Triangular SSC
6.5.4
Normative Slew Rate Limit
The CDR is a slew rate limited phase tracking device. The combination of SSC and all other jitter
sources within the bandwidth of the CDR must not exceed the maximum allowed slew rate.
This measurement is performed by filtering the phase jitter with the CDR transfer function and
taking the first difference of the phase jitter to obtain the filtered period jitter. The peak of the
period jitter must not exceed TCDR_SLEW_MAX listed in Table 6-10.
Additional details on the slew rate measurement are available in USB 3.0 Jitter Budgeting.
6-16
Physical Layer
6.6
Signaling
6.6.1
Eye Diagrams
The eye diagrams are a graphical representation of the voltage and time limits of the signal. This
eye mask applies to jitter after the application of the appropriate jitter transfer function and
reference receiver equalization. In all cases, the eye is to be measured for 106 consecutive UI. The
budget for the link is derived assuming a total 10-12 bit error rate and is extrapolated to a
measurement of 106 UI assuming the random jitter is Gaussian.
Figure 6-11 shows the eye mask used for all eye diagram measurements. Referring to the figure,
the time is measured from the crossing points of Txp/Txn. The time is called the eye width, and the
voltage is the eye height. The eye height is to be measured at the maximum opening (at the center
of the eye width ± 0.05 UI).
The eye diagrams are to be centered using the jitter transfer function (JTF). The recovered clock is
obtained from the data and processed by the JTF. The center of the recovered clock is used to
position the center of the data in the eye diagram.
The eye diagrams are to be measured into 50-Ω single-ended loads.
Minimum Eye Width
300
250
Differential Voltage, mV
200
150
100
50
Minimum Eye Height
0
-50
-100
-150
-200
-250
-300
0
20
40
60
80
100
120
140
160
180
200
Time, ps
U-023
Figure 6-11. Generic Eye Mask
6-17
Universal Serial Bus 3.0 Specification, Revision 1.0
6.6.2
Voltage Level Definitions
Referring to Figure 6-12, the differential voltage, VDIFF, is the voltage on Txp (Rxp at the receiver)
with respect to Txn (Rxn at the receiver). VDIFF is the same voltage as the swing on the single
signal of one conductor. The differential voltage is
(4)
VDIFF = Txp - Txn
The total differential voltage swing is the peak to peak differential voltage, VDIFF-PP. This is twice
the differential voltage. The peak to peak differential voltage is
(5)
VDIFF-PP=2 * VDIFF
The Common Mode Voltage (VCM) is the average voltage present on the same differential pair with
respect to ground. This is measured, with respect to ground, as
(6)
VCM = (Txp + Txn) / 2
DC is defined as all frequency components below FDC = 30 kHz. AC is defined as all frequency
components at or above FDC = 30 kHz. These definitions pertain to all voltage and current
specifications.
An example waveform is shown in Figure 6-12. In this waveform, the peak-to-peak differential
voltage, VDIFF-PP is 800 mV. The differential voltage, VDIFF, is 400 mVPP. Note that while the
center crossing point for both Txp and Txn is shown at 300 mV, the corresponding crossover point
for the differential voltage is at 0.0 V. The center crossing point at 300 mV is also the common
mode voltage, VCM. Note these waveforms include de-emphasis. The actual amount of
de-emphasis can vary depending on the transmitter setting according to the allowed ranges in
Table 6-10.
0.6
0.4
0.2
0.0
Voltage
at Txp
-0.2
-0.4
Voltage
at Txn
Differential
Voltage Txp - Txn
-0.6
7.0
7.5
8.0
8.5
Time, ns
U-024
Figure 6-12. Single-ended and Differential Voltage Levels
6-18
Physical Layer
6.6.3
Tx and Rx Input Parasitics
Tx and Rx input parasitics are specified by the lumped circuit shown in Figure 6-13.
D+ or DChannel
C_parasitic
R_term
U-025
Figure 6-13. Device Termination Schematic
In this circuit, the input buffer is simplified to a termination resistance in parallel with a parasitic
capacitor. This simplified circuit is the load impedance.
6-19
Universal Serial Bus 3.0 Specification, Revision 1.0
6.7
Transmitter Specifications
6.7.1
Transmitter Electrical Parameters
Peak (p) and peak-peak (p-p) are defined in Section 6.6.2.
Table 6-10. Transmitter Normative Electrical Parameters
Symbol
Parameter
5.0 GT/s
Units
Comments
UI
Unit Interval
199.94 (min)
ps
The specified UI is equivalent to a tolerance of
±300 ppm for each device. Period does not account
for SSC induced variations.
200.06 (max)
VTX-DIFF-PP
Differential p-p
0.8 (min)
Tx voltage swing 1.2 (max)
V
Nominal is 1 V p-p
VTX-DIFF-PP-LOW
Low-Power
0.4 (min)
Differential p-p
1.2 (max)
Tx voltage swing
V
Refer to Section 6.7.2. There is no de-emphasis
requirement in this mode. De-emphasis is
implementation specific for this mode.
VTX-DE-RATIO
Tx de-emphasis
dB
Nominal is 3.5 dB
3.0 (min)
4.0 (max)
RTX-DIFF-DC
Ω
DC differential
impedance
72 (min)
VTX-RCV-DETECT
The amount of
voltage change
allowed during
Receiver
Detection
0.6 (max)
V
Detect voltage transition should be an increase in
voltage on the pin looking at the detect signal to avoid
a high impedance requirement when an “off” receiver’s
input goes below ground.
CAC-COUPLING
AC Coupling
Capacitor
75 (min)
nF
All Transmitters shall be AC coupled. The AC
coupling is required either within the media or within
the transmitting component itself.
Maximum slew
rate
10
ms/s
See the jitter white paper for details on this
measurement. This is a df/ft specification; refer to
Section 6.5.4 for details.
tCDR_SLEW_MAX
120 (max)
200 (max)
The values in Table 6-11 are informative and not normative. They are included in this document to
provide some guidance beyond the normative requirements in Table 6-10 for transmitter design and
development. A transmitter can be fully compliant with the normative requirements of the
specification and not meet all the values in this table (many of which are immeasurable in a
finished product). Similarly, a transmitter that meets all the values in this table is not guaranteed to
be in full compliance with the normative part of this specification.
6-20
Physical Layer
Table 6-11. Transmitter Informative Electrical Parameters at Silicon Pads
Symbol
Parameter
5.0 GT/s
Units Comments
tMIN-PULSE-Dj
Deterministic min
pulse
0.96
UI
Tx pulse width variation that is deterministic
tMIN-PULSE-Tj
Tx min pulse
0.90
UI
Min Tx pulse at 10
tTX-EYE
Transmitter Eye
0.625 (min)
UI
Includes all jitter sources
tTX-DJ-DD
Tx deterministic
jitter
0.205 (max)
UI
Deterministic jitter only assuming the Dual Dirac
distribution
CTX-PARASITIC
Tx input
capacitance for
return loss
1.25 (max)
pf
Parasitic capacitance to ground
RTX-DC
Transmitter DC
common mode
impedance
18 (min)
Ω
DC impedance limits to guarantee Receiver
detect behavior. Measured with respect to AC
ground over a voltage of 0-500 mV.
ITX-SHORT
Transmitter shortcircuit current limit
60 (max)
mA
The total current Transmitter can supply when
shorted to ground.
VTX-DC-CM
Transmitter DC
common-mode
voltage
0 (min)
V
The instantaneous allowed DC common-mode
voltages at the connector side of the AC
coupling capacitors.
Tx AC common
mode voltage
active
100 mV
mVp-p Maximum mismatch from Txp + Txn for both
time and amplitude.
Absolute DC
Common Mode
Voltage between
U1 and U0
200 (max)
mV
VTX-CM-ACPP_ACTIVE
VTX-CM-DC-ACTIVEIDLE-DELTA
30 (max)
2.2 (max)
VTX-IDLE-DIFF-AC-pp
Electrical Idle
0 (min)
Differential Peak – 10 (max)
Peak Output
Voltage
mV
VTX-IDLE-DIFF-DC
DC Electrical Idle
Differential Output
Voltage
mV
6.7.2
0 (min)
10 (max)
-12
including Dj and Rj
Voltage must be low pass filtered to remove any
AC component.
This limits the common mode error when
resuming U1 to U0.
Low Power Transmitter
In addition to the full swing transmitter specification, an optional low power swing transmitter is
also specified for SuperSpeed applications. A low power swing transmitter is typically used in
systems that are sensitive to power and noise interference, and have a relative short channel. The
requirement as to whether a transmitter needs to support full swing, low power swing, or both
swings, is dependent on its usage model. All SuperSpeed transmitters must support full swing,
while support for low power swing is optional. The method by which the output swing is selected
is not defined in the specification, and is implementation specific.
6-21
Universal Serial Bus 3.0 Specification, Revision 1.0
While two different transmitters are specified, only a single receiver specification is defined. This
implies that receiver margins (as specified in Table 6-13) must be met if a low power transmitter is
used.
6.7.3
Transmitter Eye
The eye mask is measured using the compliance data patterns (CP0 for DJ and CP1 for RJ) as
described in Section 6.4.4. Eye height is measured for 106 consecutive UI. Jitter is extrapolated
from 106 UI to 10-12 BER,
Table 6-12. Normative Transmitter Eye Mask at Test Point TP1
Signal Characteristic
Minimal
Eye Height
100
Nominal
Maximum
Units
Note
1200
mV
2, 4
Dj
0.43
UI
1,2,3
Rj
0.23
UI
1,2,3, 5
Tj
0.66
UI
1,2,3
Notes:
6
1. Measured over 10 consecutive UI and extrapolated to 10
-12
BER.
2. Measured after receiver equalization function.
3. Measured at end of reference channel and cables at TP1 in Figure 6-14.
4. The eye height is to be measured at the maximum opening (at the center of the eye
width ± 0.05 UI).
5. The Rj specification is calculated as 14.069 times the RMS random jitter for 10
-12
BER.
The compliance testing setup is shown in Figure 6-14. All measurements are made at the test point
(TP1), and the Tx specifications are applied after processing the measured data with the compliance
reference equalizer transfer function described in the next section.
Measurement
Tool
SMP
Reference
Test Channel
Reference
Cable
DUT
TP1
U-026
Figure 6-14. Tx Normative Setup with Reference Channel
6.7.4
Tx Compliance Reference Receiver Equalize Function
The normative transmitter eye is captured at the end of the reference channel. At this point the eye
may be closed. To open the eye so it can be measured a reference Rx equalizer, is applied to the
signal. Details of the reference equalizer are contained in Section 6.8.2.
6-22
Physical Layer
6.7.5
Informative Transmitter De-emphasis
The channel budgets and eye diagrams were derived using a VTX-DE-RATIO of transmit de-emphasis
for both the Host and the Device reference channels. An example differential peak-to-peak
de-emphasis waveform is shown in Figure 6-15.
0.4
0.3
0.2
Volts
0.1
0
-0.1
-0.2
-0.3
-0.4
3.66
3.68
3.7
3.72
3.74
3.76
Time, s
3.78
x 10-8
U-028
Figure 6-15. De-Emphasis Waveform
6.7.6
Entry into Electrical Idle, U1
Electrical Idle is a steady state condition where the Transmitter Txp and Txn voltages are held
constant at the same value and the Receiver Termination is within the range specified by ZRX-DC.
Electrical Idle is used in the power saving state of U1.
The low impedance common mode and differential Receiver terminations values (see Table 6-13)
must be met in Electrical Idle. The Transmitter can be in either a low or high impedance mode
during Electrical Idle.
6-23
Universal Serial Bus 3.0 Specification, Revision 1.0
6.8
Receiver Specifications
6.8.1
Receiver Equalization Training
The receiver equalization training sequence, detailed in Section 6.3.1, can be used to train the
receiver equalizer. The TSEQ training sequence is designed to provide a spectrally rich data
pattern that is useful for training typical receiver equalization architectures. In addition, a high
edge density pattern is interleaved with the data to help the CDR maintain bit lock. The TSEQ
training sequence repeats 65536 times to allow for testing many coefficient settings. No SKPs are
inserted during the TSEQ training sequence. The frequency spectrum of the TSEQ sequence is
shown in Figure 6-16.
Receiver equalization training is implementation specific.
-80
-90
Power, dBm/Hz
-100
-110
-120
-130
-140
0
0.5
1
1.5
2
2.5
3
3.5
4
4.5
5
Frequency, GHz
U-029
Figure 6-16. Frequency Spectrum of TSEQ
6.8.2
Informative Receiver CTLE Function
USB 3.0 allows the use of receiver equalization to meet system timing and voltage margins. For
long cables and channels the eye at the Rx is closed, and there is no meaningful eye without first
applying an equalization function. The Rx equalizer may be required to adapt to different channel
losses using the Rx EQ training period. The exact Rx equalizer and training method is
implementation specific.
6-24
Physical Layer
The equation for the continuous time linear equalizer (CTLE) used to develop the specification is
the compliance Rx EQ transfer function described below.
(10)
H (s ) =
Adcω p1ω p 2
ωz
⋅
s + ωz
(s + ω p1 )(s + ω p 2 )
Adc = 0.667
ω z = 2 π (650 x106 )
ω p1 = 2 π (1.95 x109 )
(11)
ω p 2 = 2 π (5 x109 )
Figure 6-17 is a plot of the Compliance EQ transfer function.
5
0
Magnitude, dB
-5
-10
-15
-20
-25
108
Adc = 0.667
fz = 650 MHz
fp1 = 1.95 GHz
fp2 = 5 GHz
109
1010
1011
Frequency, Hz
U-027
Figure 6-17. Tx Compliance Rx EQ Transfer Function
6-25
Universal Serial Bus 3.0 Specification, Revision 1.0
6.8.3
Receiver Electrical Parameters
Normative specifications are to be measured at the connector. Peak (p) and peak- peak (p-p) are
defined in Section 6.6.2.
Table 6-13. Receiver Normative Electrical Parameters
Symbol
Parameter
5.0 GT/s
Units
Comments
UI
Unit Interval
199.94 (min)
200.06 (max)
ps
UI does not account for SSC
caused variations.
RRX-DC
Receiver DC
common mode
impedance
18 (min)
Ω
DC impedance limits are needed
to guarantee Receiver detect.
Measured with respect to ground
over a voltage of 500 mV
maximum.
DC differential
impedance
72 (min)
ZRX-HIGH-IMP-DC-POS
DC Input CM Input
Impedance for V>0
during Reset or
power down
25 k (min)
Ω
Rx DC CM impedance with the Rx
terminations not powered,
measured over the range 0 –
500 mV with respect to ground.
VRX-LFPS-DET-DIFFp-p
LFPS Detect
Threshold
100 (min)
mV
Below the minimum is noise.
RRX-DIFF-DC
1
30 (max)
Ω
120 (max)
300 (max)
Must wake up above the
maximum.
Note
1.
Only DC Input CM Input Impedance for V >0 is specified. DC Input CM Input Impedance for V <0 is
not guaranteed and could be as low as 0 Ω.
The values in Table 6-14 are informative and not normative. They are included in this document to
provide some guidance beyond the normative requirements in Table 6-13 for receiver design and
development. A receiver can be fully compliant with the normative requirements of the
specification and not meet all the values in this table (many of which are not measurable in a
finished product). Similarly, a receiver that meets all the values in this table is not guaranteed to be
in full compliance with the normative part of this specification.
Table 6-14. Receiver Informative Electrical Parameters
6-26
Symbol
Parameter
5.0 GT/s
Units
Comments
VRX-DIFF-PP-POST-EQ
Differential Rx peakto-peak voltage
30 (min)
mV
Measured after the Rx EQ function
(Section 6.8.2)
tRX-TJ
Max Rx inherent
timing error
0.45 (max)
UI
Measured after the Rx EQ function
(Section 6.8.2)
tRX-DJ-DD
Max Rx inherent
deterministic timing
error
0.285 (max)
UI
Maximum Rx inherent
deterministic timing error
CRX-PARASITIC
Rx input
capacitance for
return loss
1.1 (max)
pf
Physical Layer
Symbol
Parameter
5.0 GT/s
Units
Comments
VRX-CM-AC-P
Rx AC common
mode voltage
150 (max)
mV
Peak
Measured at Rx pins into a pair of
50 Ω terminations into ground.
Includes Tx and channel
conversion, AC range up to
5 GHz
VRX- CM-DC-ACTIVE-
Rx AC common
mode voltage during
the U1 to U0
transition
200 (max)
mV
Peak
Measured at Rx pins into a pair of
50 Ω terminations into ground.
Includes Tx and channel
conversion, AC range up to
5 GHz
IDLE-DELTA_P
6.8.4
Receiver Loopback
The entry and exit process for receiver loopback is described in Chapter 7.
Receiver loopback must be retimed. Direct connection from the Rx amplifier to the transmitter is
not allowed for loopback mode. The receiver must continue to process SKPs as appropriate. SKP
symbols must be consumed or inserted as required for proper clock tolerance compensation. Over
runs or under runs of the clock tolerance buffers will reset the buffers to the neutral position.
During loopback the receiver must process the Bit Error Rate Test (BERT) commands.
Loopback must occur in the 10-bit domain. No error correction is allowed. All symbols must be
transmitted as received with the exception of SKP and BERT commands.
6.8.4.1
Loopback BERT
During loopback the receiver processes the BERT ordered sets BRST, BDAT, and BERC. These
ordered sets are described in Table 6-15 through Table 6-18. BRST and BDAT are looped back as
received. BERC ordered sets are not looped back but are replaced with BCNT ordered sets. Any
time a BRST is received, the error count register EC is set to 0 and the scrambling LFSR is set to
0FFFFh. Any number of consecutive BRST ordered sets may be received.
BRST followed by BDAT starts the bit error rate test. The BDAT sequence is the output of the
scrambler and is equivalent to the logical idle sequence. It consists of scrambled 0 as described in
Appendix B. As listed in Appendix B, the first 16 characters of the sequence are reprinted here:
FF
17
C0
14
B2
E7
02
82
72
6E
28
A6
BE
6D
BF
8D
The receiver must compare the received data to the BDAT sequence. Errors increment the error
count register (EC) by 1. EC may not roll over but must be held at FFh. The LFSR is advanced
once for every character except SKPs. The LFSR rolls over after 216-1 symbols. SKPs must be
inserted or deleted as necessary for clock tolerance compensation.
The BERC command does not increment the error count register. The LFSR is advanced. The
BERC ordered set is replaced by the BCNT ordered set. The BCNT ordered set includes the nonscrambled 8b/10b encoded error count (EC) register based on the running disparity. Following the
return of the BCNT ordered set, the loopback slave shall continue to repeat symbols as received.
BERC may be sent multiple times. The EC register is not cleared by BERC ordered sets.
6-27
Universal Serial Bus 3.0 Specification, Revision 1.0
BERT continues until the loopback mode is terminated as described in Chapter 7.
Table 6-15. BRST
Symbol Number
Encoded Values
Description
0
K28.5
COM
1
K28.7
BRST
Symbol Number
Encoded Values
Description
D0.0 <0:n>
Logical Idle (refer to
Appendix B)
Scrambled 0
Table 6-16. BDAT
16
Rolls over after 2 -1
symbols
Table 6-17. BERC
Symbol Number
Encoded Values
Description
0
K28.3
BERC
1
K28.3
BERC
2
K28.3
BERC
3
K28.3
BERC
Symbol Number
Encoded Values
Description
0
K28.3
BERC
Table 6-18. BCNT
6-28
0
K28.3
BERC
EC<0:7>
DCODE
Error count (not scrambled)
EC<0:7>
DCODE
Error count (not scrambled)
Physical Layer
6.8.5
Normative Receiver Tolerance Compliance Test
The receiver tolerance test is tested in the compliance reference channel. A pattern generator will
send a compliance test pattern with added jitter through the compliance reference channels to the
receiver. The receiver will loop back the data and any difference in the pattern sent from the
pattern generator and returned will be an error. When running the compliance tests, the receiver
should be put into loopback mode.
Additional details on the receiver compliance test are contained in the reference document, USB
SuperSpeed Compliance Methodology.
Pattern Generator/
Pattern Checker
SMP
Reference
Test Channel
Reference
Cable
DUT
TP1
U-030
Pj Amplitude, UI
Figure 6-18. Rx Tolerance Setup
20 dB/dec
Rj
fend
f1
Frequency, f
U-031
Figure 6-19. Jitter Tolerance Curve
6-29
Universal Serial Bus 3.0 Specification, Revision 1.0
The jitter components used to test the receiver shall meet the requirements of Table 6-19.
Table 6-19. Input Jitter Requirements for Rx Tolerance Testing
Symbol
Parameter
Value
Units
Notes
f1
Tolerance corner
4.9
MHz
JRj
Random Jitter
0.0121
UI rms
1
0.17
UI p-p
1,4
JRj_p-p
Random Jitter peak- peak at 10
-12
JPj_500kHZ
Sinusoidal Jitter
2
UI p-p
1,2,3
JPj_1Mhz
Sinusoidal Jitter
1
UI p-p
1,2,3
JPj_2MHz
Sinusoidal Jitter
0.5
UI p-p
1,2,3
JPj_f1
Sinusoidal Jitter
0.2
UI p-p
1,2,3
JPj_50MHz
Sinusoidal Jitter
0.2
UI p-p
1,2,3
V_full_swing
Transition bit differential voltage swing
0.75
V p-p
1
V_EQ_level
Non transition bit voltage (equalization)
-3
dB
1
Notes:
1.
All parameters measured at TP1. The test point is shown in Figure 6-18.
2.
Due to time limitations at compliance testing, only a subset of frequencies can be tested. However, the Rx is required
to tolerate Pj at all frequencies between the compliance test points.
3.
During the Rx tolerance test, SSC is generated by test equipment and present at all times. Each JPj source is then
added and tested to the specification limit one at a time.
4.
Random jitter is also present during the Rx tolerance test, though it is not shown in Figure 6-19.
6.9
Low Frequency Periodic Signaling (LFPS)
Low frequency periodic signaling (LFPS) is used for side band communication between the two
ports across a link that is in a low power link state. It is also used when a link is under training, or
when a downstream port issues Warm Reset to reset the link.
6.9.1
LFPS Signal Definition
Table 6-20 defines the LFPS electrical specification at the transmitter. An example differential
LFPS waveform is shown in Figure 6-20. tPeriod is the period of an LFPS cycle. An LFPS burst is
the transmission of continuous LFPS signal over a period of time defined by tBurst. An LFPS
sequence is defined by the transmission of a single LFPS burst of duration tBurst over a period of
time defined by tRepeat. The link is in electrical idle between the two contiguous LFPS bursts.
An LFPS message is encoded based on the variation of tBurst. tRepeat is defined as a time interval
when the next LFPS message is transmitted. The LFPS messages include Polling.LFPS and
Ping.LFPS, as defined in Table 6-21. There are also LFPS signaling defined for U1/U2 and
Loopback exit, U3 wakeup, and Warm Reset.
The detailed use of LFPS signaling is specified in the following sections and Chapter 7.
6-30
Physical Layer
tPeriod
Electrical Idle
tBurst
tRepeat
U-032
Figure 6-20. LFPS Signaling
Table 6-20. Normative LFPS Electrical Specification
Symbol
Minimum
tPeriod
20
Typical
Maximum
Units
100
ns
VCM-AC-LFPS
VTX-CM-AC-PP-ACTIVE
mV
VCM-LFPS-Active
10
mV
Comments
See Table 6-11
VTX-DIFF-PP-LFPS
800
1200
mV
Peak-peak differential
amplitude
VTX-DIFF-PP-LFPS-LP
400
600
mV
Low power peak-peak
differential amplitude
4
ns
Measured at compliance
TP1, as shown in
Figure 6-14.
60
%
Measured at compliance
TP1, as shown in
Figure 6-14.
tRiseFall2080
Duty cycle
40
6-31
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 6-21. LFPS Transmitter Timing1
tBurst
Min
Typ
Polling.LFPS
0.6 μs
1.0 μs
Ping.LFPS
40 ns
tReset
3
80 ms
4,5
U1 Exit
U2 / Loopback Exit
U3 Wakeup
100 ms
4,5
Minimum
Number of LFPS
2
Cycles
Min
6 μs
10 μs
14 μs
2
160 ms
200 ms
240 ms
1.4 μs
200 ns
300 ns
4,5
tRepeat
Max
Typ
Max
120 ms
900 ns/2 ms
80 μs
7
2 ms
80 μs
7
10 ms
6
Notes:
1.
2.
3.
4.
5.
6.
7.
If the transmission of an LFPS signal does not meet the specification, the receiver behavior is undefined.
Only Ping.LFPS has a requirement for minimum number of LFPS cycles.
The declaration of Ping.LFPS depends on only the Ping.LFPS burst.
Warm Reset, U1/U2/Loopback Exit, and U3 Wakeup are all single burst LFPS signals. tRepeat is not applicable.
The minimum duration of an LFPS burst must be transmitted as specified. The LFPS handshake process and timing
are defined in Section 6.9.2.
If both ports are in U1, tBurst Max is 900 ns; if one port is in U1 and the port is in U2, tBurst Max is 2 ms.
A Port in U2 or U3 is not required to keep its transmitter DC common mode voltage. When a port begins U2 exit or U3
wakeup, it may start sending LFPS signal while establishing its transmitter DC common mode voltage. To make sure
its link partner receives a proper LFPS signal, a minimum of 80 μs tBurst must be transmitted. The same consideration
also applies to a port receiving LFPS U2 exit or U3 wakeup signal.
IMPLEMENTATION NOTE
Detect and Differentiate Between Ping.LFPS and U1 LFPS Exit Signaling for a Downstream
Port in U1 or U2
When a downstream port is in U1, it may receive either a Ping.LFPS as a message from its link
partner to inform its presence, or an U1 LFPS exit signal to signal that its link partner is attempting
exit from U1. This will also occur when a downstream port is in U2, since there are situations
where a downstream port enters U2 from U1 when its U2 inactivity timer times out, and its link
partner is still in U1.
Upon detecting the break of electrical idle due to receiving an LFPS signal, a downstream port may
start a timer to measure the duration of the LFPS signal. If an electrical idle condition does not
occur when the timer expires at 300 ns, a downstream port can declare the received LFPS signal is
U1 exit and then respond to U1 exit by sending U1 LFPS exit handshake signal. If an electrical idle
condition is detected before the timer reaches 300 ns, a downstream port can declare that the
received LFPS signal is Ping.LFPS.
6-32
Physical Layer
6.9.2
Example LFPS Handshake for U1/U2 Exit, Loopback Exit,
and U3 Wakeup
The LFPS signal used for U1/U2 exit, Loopback exit, and U3 wakeup is defined the same as
continuous LFPS signals with the exception of timeout values defined in Table 6-22. The
handshake process for U1/U2 exit and U3 wakeup is illustrated in Figure 6-21. The timing
requirements are different for U1 exit, U2 exit, Loopback exit, and U3 wakeup. They are listed in
Table 6-22.
Link Partner 1
Link Partner 2
t 10
t 11
t 12
t 13
Time
U-033
Figure 6-21. U1 Exit, U2 Exit, and U3 Wakeup LFPS Handshake Timing Diagram
Note: the timing diagram in Figure 6-21 is for illustration of the LFPS handshake process only.
The handshake process is as follows:
• Link partner 1 initiates exit by transmitting LFPS at time t10 (see Figure 6-21). LFPS
transmission shall continue until the handshake is declared either successful or failed.
• Link partner 2 detects valid LFPS on its receiver and responds by transmitting LFPS at time
t11. LFPS transmission shall continue until the handshake is declared either successful or
failed.
• A successful handshake is declared for link partner 1 if the following conditions are met within
“tNoLFPSResponseTimeout” after t10 (see Figure 6-21 and Table 6-22):
1. Valid LFPS is received from link partner 2.
2. For U1 exit, U2 exit, U3 Wakeup and not Loopback exit, link partner 1 is ready to transmit
the training sequences and the maximum time gap after an LFPS transmitter stops
transmission and before a SuperSpeed transmitter starts transmission is 20 ns.
Note: There is no Near End Cross Talk (NEXT) specification for SuperSpeed transmitters and
receivers. Therefore, when a port enters Recovery and starts transmitting TS1 Ordered Sets and
its link partner is in electrical idle after successful LFPS handshake, a port may potentially train
its receiver using its own TS1 Ordered Sets due to NEXT. The intention of adding the second
exit condition is to prevent a port from electrical idle before transitioning to Recovery.
6-33
Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
•
A successful handshake is declared for link partner 2 if the following conditions are met within
tNoLFPSResponseTimeout after t11:
1. Link partner 2 has transmitted the minimum LFPS defined as (t13 – t11) in Table 6-22.
2. For U1 exit, U2 exit, U3 Wakeup, and not Loopback exit, link partner 2 is ready to transmit
the training sequences and the maximum time gap after an LFPS transmitter stops
transmission and before a SuperSpeed transmitter starts transmission is 20 ns.
A U1 exit, U2 exit, Loopback exit, and U3 wakeup handshake failure shall be declared if the
conditions for a successful handshake are not met.
Link partner 1 shall declare a failed handshake if its successful handshake conditions were not
met.
Link partner 2 shall declare a failed handshake if its successful handshake conditions were not
met.
Note: Except for Ping.LFPS, when an upstream port in Ux or Loopback.Active receives an
LFPS signal, it shall proceed with U1/U2 exit, or U3 wakeup, or Loopback exit handshake even
if the LFPS is later determined to be a Warm Reset. If the LFPS is a Warm Reset, an upstream
port, if in Ux, will enter Recovery and then times out to SS.Inactive, or if in Loopback Active,
will enter Rx.Detect and then transitions to Polling.LFPS. When Warm Reset is detected, an
upstream port will enter Rx.Detect.
Table 6-22. LFPS Handshake Timing for U1/U2 Exit, Loopback Exit, and U3 Wakeup
U1 Exit
Min
U2/Loopback Exit
Max
Min
U3 Wakeup
Max
Min
0.9 μs
0.3 μs
2 ms
t12 – t11
0
0.9 μs
0
2 ms
0
t13 – t11
0.6 μs
0.8 μs
80 μs
2 ms
80 μs
10 ms
80 μs
2 ms
80 μs
10 ms
t13 – t10
2 ms
t12 – t10
tNoLFPSResponseTimeout
0.3 μs
Max
0.3 μs
t11 – t10
0.9 μs/2 ms
1
2 ms
10 ms
20 ms
10 ms
10 ms
Note:
1.
If both link partners are in U1, tNoLFPSResponseTimeout shall be 0.9 µs. If one link partner is in U1 and the other is in
U2, tNoLFPSResponseTimeout shall be 2 ms.
6.9.3 Warm Reset
A Warm Reset is a reset generated only by a downstream port to an upstream port. A downstream
port may issue a Warm Reset at any Link states except SS.Disabled. An upstream port is required
to detect a Warm Reset at any link states except SS.Disabled.
A Warm Reset shares the same continuous LFPS signal as a low power Link state exit handshake
signal. In order for an upstream port to be able to differentiate between the two signals, the tBurst
of a Warm Reset is extended, as is defined in Table 6-20.
The Warm Reset assertion is asynchronous between a downstream port and an upstream port since
it has to take a certain period of time for an upstream port to declare that a Warm Reset is detected.
However, the de-assertion of the Warm Reset between a downstream port and an upstream port
must be made synchronous. Figure 6-22 shows a timing diagram of Warm Reset generation and
detection when a port is U3. Once a Warm Reset is issued by a downstream port, it will take at
6-34
Physical Layer
least tResetDelay for an upstream port to declare the detection of Warm Reset. Once a Warm Reset
is detected, an upstream port must continue to assert the Warm Reset until it no longer receives any
LFPS signals from a downstream port.
• An upstream port shall declare the detection of Warm Reset within tResetDelay. The minimum
tResetDelay shall be 18 ms; the maximum tResetDelay shall be 50 ms.
warm_reset
de-asserted
tReset
Downstream Port
(warm_reset generation)
warm_reset
asserted
warm_reset
de-asserted
warm_reset
asserted
warm_reset
asserted
Upstream Port
(warm_reset detection)
tResetdelay
U-034
Figure 6-22. Example of Warm Reset Out of U3
6.10
6.10.1
Transmitter and Receiver DC Specifications
Informative ESD Protection
All signal and power pins must withstand 2000 V of ESD using the human body model and 500 V
using the charged device model without damage (Class 2 per JEDEC JESE22-A114-A). This ESD
protection mechanism also helps protect the powered down Receiver from potential common mode
transients during certain possible reset or surprise insertion situations.
6.10.2
Informative Short Circuit Requirements
All Transmitters and Receivers must support surprise hot insertion/removal without damage to the
component. The Transmitter and Receiver must be capable of withstanding sustained short circuit
to ground of Txp (Rxp) and Txn (Rxn).
6.10.3
Normative High Impedance Reflections
During an asynchronous reset event, one device may be reset while the other device is transmitting.
The device under reset is required to disconnect the receiver termination. During this time, the
device under reset may be receiving active data. Since the data is not terminated, the differential
voltage into the receiver will be doubled. For a short channel, the receiver may experience a total
of 2* VDIFF.
The receiver must tolerate this doubling of the negative voltage that can occur if the Rx termination
is disconnected. A part must tolerate a 20 ms event that doubles the voltage on the receiver input
when the termination is disconnected 10,000 times over the life time of the part.
6-35
Universal Serial Bus 3.0 Specification, Revision 1.0
6.11
6.11.1
Receiver Detection
Rx Detect Overview
The Receiver Detection circuit is implemented as part of a Transmitter and must correctly detect
whether a load impedance equivalent to a DC impedance RRX-DC (Table 6-13) is present. The Rx
detection operates on the principle of the RC time constant of the circuit. This time constant
changes based on the presence of the receiver termination. This is conceptually illustrated in
Figure 6-23. In this figure, R_Detect is the implementation specific charging resistor. C_AC is the
AC capacitor that is in the circuit only if R_Term is also present, otherwise, only C_Parasitic is
present.
V_Detect
V_Detect
R_Detect
C_AC
C_Parasitic
R_Detect
C_AC
C_Parasitic
R_Term
U-035
Figure 6-23. Rx Detect Schematic
The left side of Figure 6-23 shows the Receiver Detection circuit with no termination present. The
right side of the figure is the same circuit with termination.
Detect voltage transition must be common mode. Detect voltage transition must conform to
VTX_RCV_DETECT as described in Table 6-10.
The receiver detect sequence must be in the positive common mode direction only. Negative
receiver detection is not allowed.
6-36
Physical Layer
6.11.2
Rx Detect Sequence
The recommended behavior of the Receiver Detection sequence is:
1. A Transmitter must start at a stable voltage prior to the detect common mode shift.
2. A Transmitter changes the common mode voltage on Txp and Txn consistent with detection of
Receiver high impedance which is bounded by parameter ZRX -HIGH-IMP-DC-POS listed in
Table 6-13.
3. A Receiver is detected based on the rate that the lines change to the new voltage.
• The Receiver is not present if the voltage at the Transmitter charges at a rate dictated only
by the Transmitter impedance and the capacitance of the interconnect and series capacitor.
•
The Receiver is present if the voltage at the Transmitter charges at a rate dictated by the
Transmitter impedance, the series capacitor, the interconnect capacitance, and the Receiver
termination.
Any time Electrical Idle is exited the detect sequence does not have to execute or may be aborted.
During the Device connect, the Device receiver has to guarantee it is always in high impedance
state while its power plane is stabilizing. This is required to avoid the Host falsely detecting the
Device and starting the training sequence before the Device is ready. Similarly a disabled port has
to keep its receiver termination in high impedance which is bounded by parameters ZRX -HIGH-IMP-DCPOS until directed by higher layer to exit from the Disabled state. In contrast, a port which is at
U1/U2/U3 Electrical Idle must have its Receiver Termination turned on and meet the RRX-DC
specification.
6.11.3
Upper Limit on Channel Capacitance
The interconnect total capacitance to ground seen by the Receiver Detection circuit must not exceed
3 nF to ground, including capacitance added by attached test instrumentation. This limit is needed
to guarantee proper operation during Receiver detect. Note that this capacitance is separate and
distinct from the AC coupling capacitance value.
6-37
Universal Serial Bus 3.0 Specification, Revision 1.0
6-38
7
Link Layer
The link layer has the responsibility of maintaining the link connectivity so that successful data
transfers between the two link partners are ensured. A robust link flow control is defined based on
packets and link commands. Packets are prepared in the link layer to carry data and different
information between the host and a device. Link commands are defined for communications
between the two link partners. Packet frame ordered sets and link command ordered sets are also
constructed such that they are tolerant to one symbol error. In addition, error detections are also
incorporated into a packet and a link command to verify packet and link command integrity.
The link layer also facilitates link training, link testing/debugging, and link power management.
This is accomplished by the introduction of Link Training Status State Machine (LTSSM).
Host
Hub
Device
Device Driver/Application
Pipe Bundle (per Function Interface)
Function
USB System Software
Default Control Pipe
Device
Notifications
Transactions
Transaction
Packets
Notifications
Data
Packets
Port-to-Port
Chip to Chip
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Localized
Link Power
Management
PHYSICAL
8b/10b
encode/
decode
Data
Packets
LINK
Link Cmds
USB Device
Power
Management
(Suspend)
Link Management Packets
Link Control/Mgmt
Pkt
Delims
Transactions
Transaction
Packets
Link Management Packets
USB Function
Power
Management
Device or Host PROTOCOL
End-to-End
The focus of this chapter is to address the following in detail:
• Packet Framing
• Link command definition and usage
• Link initialization and flow control
• Link power management
• Link error rules/recovery
• Resets
• LTSSM specifications
U-036
Figure 7-1. Link Layer
7-1
Universal Serial Bus 3.0 Specification, Revision 1.0
7.1
Byte Ordering
Multiple byte fields in a packet or a link command are moved over to the bus in little-endian order,
i.e., the least significant byte (LSB) first, and the most significant byte (MSB) last. Figure 7-2
shows an example of byte ordering.
Each byte of a packet or link command will be encoded in the physical layer using 8b/10b
encoding. Refer to Section 6.3 regarding 8b/10b encoding and bit ordering.
one byte
byte
Transmitted first
WORD
byte 1
byte 0
Transmitted last
Transmitted first
DWORD
byte 3
byte 2
byte 1
byte 0
Transmitted last
Transmitted first
byte 3
byte 2
byte 1
byte 0
byte 4
N bytes
byte (N-1)
byte (N-2)
byte (N-3)
byte (N-4)
Transmitted last
U-078
Figure 7-2. SuperSpeed Byte Ordering
7-2
Link Layer
7.2
Link Management and Flow Control
This section contains information regarding link data integrity, flow control, and link power
management.
• The packet and packet framing section defines packet types, packet structures, and CRC
requirements for each packet.
• The link command section defines special link command structures that control various
functionalities at the link level.
• The logical idle defines a special symbol used in U0.
• The flow control defines a set of handshake rules for packet transactions.
7.2.1
Packets and Packet Framing
SuperSpeed uses packets to transfer information. Detailed packet formats for Link Management
Packets (LMP), Transaction Packets (TP), Isochronous Timestamp Packets (ITP), and Data Packets
(DP) are defined in Section 8.2.
7.2.1.1
Header Packet Structure
All header packets are 20 symbols long, as is formatted in Figure 7-3. This includes LMPs, TPs,
ITPs, and DPHs. A header packet consists of three parts, a header packet framing, a packet header,
and a Link Control Word.
7.2.1.1.1
Header Packet Framing
Header packet framing, HPSTART ordered set, is a four-symbol header packet starting frame
ordered set based on K-symbols. It is defined as three consecutive symbols of SHP followed by a
K-symbol of EPF. A header packet shall always begin with HPSTART ordered set. The
construction of the header packet framing is to achieve one symbol error tolerance.
20 Bytes of Framing, Header, and Link Control
MSB
LSB (transmitted first)
1 1
2
C
Link
R
Control C
Word
12 Bytes
1
E
P
F
1
S
H
P
1
S
H
P
1
S
H
P
U-037
Figure 7-3. Header Packet with HPSTART, Packet Header, and Link Control Word
7-3
Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.1.1.2
Packet Header
A packet header consists of 14 bytes as formatted in Figure 7-4. It includes 12 bytes of header
information and a 2-byte CRC-16. CRC-16 is used to protect the data integrity of the 12-byte
header information.
14 Bytes
MSB
LSB (transmitted first)
2
C
R
C
12 Bytes
Used for:
1) Link Management Packet
2) Transaction Packet
3) Data Packet Header
4) Isochronous Timestamp Packets
U-038
Figure 7-4. Packet Header
The implementation of CRC-16 on the packet header is defined below:
• The polynomial for CRC-16 shall be 100Bh.
•
•
•
•
•
Note: The CRC-16 polynomial is not the same as the one used for USB 2.0.
The initial value of CRC-16 shall be FFFFh.
CRC-16 shall be calculated for all 12 bytes of the header information, not inclusive of any
packet framing symbols.
CRC-16 calculation shall begin at byte 0, bit 0 and continue to bit 7 of each of the 12 bytes.
The remainder of CRC-16 shall be complemented.
The residual of CRC-16 shall be F6AAh.
Note: The inversion of the CRC-16 remainder adds an offset of FFFFh that will create a constant
CRC-16 residual of F6AAh at the receiver side.
Figure 7-5 is an illustration of CRC-16 remainder generation. The output bit ordering is listed in
Table 7-1.
7-4
byte 0
76 5 4 3 2 10
byte 1
byte 2
byte 11
Link Layer
bit
order
Byte order
0
1
Input
B
0
>
>
>
>
>
>
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
7
6
5
4
3
2
1
0
15
14
13
12
11
10
9
8
>
>
>
>
>
>
>
>
>
>
>
= Flip flop
U-039
Figure 7-5. CRC-16 Remainder Generation
Table 7-1. CRC-16 Mapping
CRC-16 Result Bit
Position in CRC-16 Field
0
15
1
14
2
13
3
12
4
11
5
10
6
9
7
8
8
7
9
6
10
5
11
4
12
3
13
2
14
1
15
0
7-5
Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.1.1.3
Link Control Word
The 2-byte Link Control Word is formatted as shown in Figure 7-6. It is used for both link level
and end-to-end flow control.
The Link Control Word shall contain a 3-bit Header Sequence Number, 3-bit Reserved, a 3-bit Hub
Depth Index, a Delayed bit (DL), a Deferred bit (DF), and a 5-bit CRC-5.
Link Control Word
MSB
byte 1
5
CRC
1
D
E
F
E
R
R
E
D
byte 0
1
D
E
L
A
Y
E
D
3
Hub
Depth #
3
R
E
S
E
R
V
E
D
LSB (transmitted first)
3
Header
Sequence #
U-040
Figure 7-6. Link Control Word
CRC-5 protects the data integrity of the Link Control Word. The implementation of CRC-5 is
defined below:
• The CRC-5 polynomial shall be 00101b.
• The Initial value for the CRC-5 shall be 11111b.
• CRC-5 is calculated for the remaining 11 bits of the Link Control Word.
• CRC-5 calculation shall begin at bit 0 and proceed to bit 10.
• The remainder of CRC-5 shall be complemented, with the MSb mapped to bit 11, the next MSb
mapped to bit 12, and so on, until the LSb mapped to bit 15 of the Link Control Word.
• The residual of CRC-5 shall be 01100b.
Note: The inversion of the CRC-5 remainder adds an offset of 11111b that will create a
constant CRC-5 residual of 01100b at the receiver side.
Figure 7-7 is an illustration of CRC-5 remainder generation.
7-6
Link Layer
10 9 8 7 6 5 4 3 2 1 0
bit order
Input
>
>
>
>
>
11
12
13
14
15
>
= Flip flop
U-041
Figure 7-7. CRC-5 Remainder Generation
7.2.1.2
Data Packet Payload Structure
Data packets are a special type of packet consisting of a Data Packet Header (DPH) and a Data
Packet Payload (DPP). The DPH is defined in Section 7.2.1.1. The DPP, on the other hand,
consists of a data packet payload framing, and a variable length of data followed by 4 bytes of
CRC-32. Figure 7-8 describes the format of a DPP.
7.2.1.2.1
Data Packet Payload Framing
DPP framing consists of eight K-symbols, a four-symbol DPP starting frame ordered set and a foursymbol DPP ending frame ordered set. As indicated by Figure 7-8, a DPPSTART ordered set,
which is a DPP starting frame ordered set, consists of three consecutive K-symbols of SDP
followed by a single K-symbol of EPF. A DPP ending frame ordered set has two different types.
The first type, DPPEND ordered set, is a DPP ending frame ordered set which consists of three
consecutive K-symbol of END followed by a single K-symbol of EPF. The second type,
DPPABORT ordered set, is a DPP aborting frame ordered set which consists of three consecutive
K-symbol of EDB (end of nullified packet) followed by a single K-symbol of EPF. The DPPEND
ordered set is used to indicate a normal ending of a complete DPP. The DPPABORT ordered set is
used to indicate an abnormal ending of a DPP.
Data Packet Payload plus 4 Bytes of
CRC-32 and 8 Bytes of Framing
LSB (transmitted first)
MSB
1
E
P
F
1
E
N
D
1
E
N
D
1
E
N
D
4 CRC
0 to 1024 Data Bytes
1
E
P
F
1
S
D
P
1
S
D
P
1
S
D
P
U-042
Figure 7-8. Data Packet Payload with CRC-32 and Framing
7-7
Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.1.2.2
Data Packet Payload
The DPP section consists of 0 to 1024 data bytes followed by 4 bytes CRC-32. Any premature
termination of a DPP shall contain a DPPABORT ordered set. A DPP shall immediately follow its
corresponding DPH with no spacing in between.
CRC-32 protects the data integrity of the data payload. CRC-32 is as follows:
• The CRC-32 polynomial shall be 04C1 1DB7h.
• The CRC-32 Initial value shall be FFFF FFFFh.
• CRC-32 shall be calculated for all bytes of the DPP, not inclusive of any packet framing
symbols.
• CRC-32 calculation shall begin at byte 0, bit 0 and continue to bit 7 of each of the bytes of the
DPP.
• The remainder of CRC-32 shall be complemented.
• The residual of CRC-32 shall be C704DD7Bh.
Note: The inversion of the CRC-32 remainder adds an offset of FFFF FFFFh that will create a
constant CRC-32 residual of C704DD7Bh at the receiver side.
data byte 2
data byte 1
data byte 0
76 5 4 3 2 10
Figure 7-9 is an illustration of CRC-32 remainder generation. The output bit ordering is listed in
Table 7-2.
bit
order
Byte order
4
0
>
>
>
>
>
>
>
1
C
>
>
>
>
>
>
>
>
D
1
>
>
>
>
>
31 30 29 28
27 26 25 24
23 22 21 20
19 18 17 16 15 14 13 12
7
3
15 14 13 12
11 10 9
>
6
5
4
2
1
0
8 23 22 21 20
>
>
>
11 10 9
Input
7
B
>
8
19 18 17 16
>
7
>
6
>
5
>
4
31 30 29 28
>
3
>
2
>
1
>
0
27 26 25 24
= Flip flop
U-043
Figure 7-9. CRC-32 Remainder Generation
7-8
Link Layer
Table 7-2. CRC-32 Mapping
CRC-32 Result Bit
Position in CRC-32 Field
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
31
30
29
28
27
26
25
24
23
22
21
20
19
18
17
16
15
14
13
12
11
10
9
8
7
6
5
4
3
2
1
0
7-9
Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.1.2.3
Spacing Between Data Packet Header and Data Packet Payload
There shall be no spacing between a DPH and its corresponding DPP. This is illustrated in
Figure 7-10.
Data Packet: Inclusive of a Data Packet Header, Data Packet Payload
Data Packet Payload plus 4 Bytes of
CRC-32 and 8 Bytes of Framing
20 Bytes of Framing, Header, and Link Control
MSB
LSB (transmitted first)
1
E
P
F
1
E
N
D
1
E
N
D
1
E
N
D
4 CRC
0 to 1024 Data Bytes
1
E
P
F
1
S
D
P
1
S
D
P
1 1 1
S
D
P
2
C
12 Bytes
R
C
Link Control Word
1
E
P
F
1
S
H
P
1
S
H
P
1
S
H
P
U-044
Figure 7-10. Data Packet with Data Packet Header Followed by
Data Packet Payload
Additional details on how header packets are transmitted and received at the link level are
described in Section 7.2.4.
7.2.2
Link Commands
Link commands are used for link level data integrity, flow control and link power management.
Link commands are a fixed length of eight symbols and contain repeated symbols to increase the
error tolerance. Refer to Section 7.3 for more details. Link command names have the L-preface to
differentiate their link level usage and to avoid confusion with packets.
7.2.2.1
Link Command Structure
Link command shall be eight symbols long and constructed with the following format shown in
Figure 7-11. The first four symbols, LCSTART, are the link command starting frame ordered set
consisting of three consecutive SLCs followed by EPF. The second four symbols consist of a twosymbol link command word and its replica. Both link command words are scrambled. Table 7-3
summarizes the link command structure.
Table 7-3. Link Command Ordered Set Structure
Symbol Number
7-10
Description
0
SLC (Start Link Command)
1
SLC (Start Link Command)
2
SLC (Start Link Command)
3
EPF
4~5
Link Command Word
6~7
Link Command Word
Link Layer
8-Symbol Link Command
MSB
LSB (transmitted first)
SLC
SLC
SLC
EPF
Link Command Word
Link Command Word
U-045
Figure 7-11. Link Command Structure
7.2.2.2
Link Command Word Definition
Link command word is 16 bits long with the 11-bit link command information protected by a 5-bit
CRC-5 (see Figure 7-12). The 11-bit link command information is defined in Table 7-4. The
calculation of CRC-5 is the same as Link Control Word illustrated in Figure 7-6.
Link Command Word
byte 1
MSB
15
11 10
CRC-5
byte 0
LSB (transmitted first)
2 1 0
Link Command Information
U-046
Figure 7-12. Link Command Word Structure
7-11
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 7-4. Link Command Bit Definitions
Type
Class
b10~9
Link Command
b8~7
b6~4
Sub-Type
b3~0
b3: Reserved
b2~0: HP Sequence Number
000: LGOOD_0
001: LGOOD_1
010: LGOOD_2
00: LGOOD_n
011: LGOOD_3
100: LGOOD_4
00
LGOOD_n
101: LGOOD_5
LRTY
110: LGOOD_6
LBAD
111: LGOOD_7
LCRD_x
b3~2: Reserved
b1~0: Rx Header Buffer Credit
00: LCRD_A
01: LCRD_x
Reserved
(000)
01: LCRD_B
10: LCRD_C
11: LCRD_D
10: LRTY
11: LBAD
Reserved (0000)
0001: LGO_U1
LGO_Ux
01
00: LGO_Ux
LAU
0011: LGO_U3
Others: Reserved
LXU
LPMA
0010: LGO_U2
01: LAU
10: LXU
Reserved (0000)
11: LPMA
10
LUP
11: Reserved
Reserved
00: LUP
Others: Reserved
Reserved (0000)
Reserved (0000)
Reserved (0000)
Link commands are defined for four usage cases. First, link commands are used to ensure the
successful transfer of a packet. Second, link commands are used for link flow control. Third, link
commands are used for link power management. And finally, a special link command is defined
for an upstream port to signal its presence in U0.
Successful header packet transactions between the two link partners require proper header packet
acknowledgement. Rx Header Buffer Credit exchange facilitates link flow control. Header packet
acknowledgement and Rx Header Buffer Credit exchange are realized using different link
commands. LGOOD_n (n = 0 to 7) and LBAD are used to acknowledge whether a header packet
has been received properly or not. LRTY is used to signal that a header packet is re-sent.
LCRD_A, LCRD_B, LCRD_C, and LCRD_D are used to signal the availability of Rx Header
7-12
Link Layer
Buffers in terms of Credit. In the following sections, LCRD_x is used with x denoting either A, B,
C, or D. See Table 7-5 for details.
LGOOD_n uses an explicit numerical index called Header Sequence Number to represent the
sequencing of a header packet. The Header Sequence Number starts from 0 and is incremented by
one based on modulo-8 addition with each header packet. The index corresponds to the received
Header Sequence Number and is used for flow control and detection of lost or corrupted header
packets.
LCRD_x uses an explicit alphabetical index. The index A, B, C, D, A, B, C… is advanced by one
with each header packet being processed and an Rx Header Buffer Credit is available. The index is
used to ensure Rx Header Buffer Credits are received in order such that missing of an LCRD_x can
be detected.
LBAD and LRTY do not use indexes.
LGO_U1, LGO_U2, LGO_U3, LAU, LXU, and LPMA are link commands used for link power
management.
LUP is a special link command used by an upstream port to indicate its port presence in U0. The
usage of LUP is described in Table 7-5.
Additional requirements and examples on the use of link commands are found in Section 7.2.4.
Table 7-5. Link Command Definitions
Link
Command
Definition – See Sections 7.2.4.1, 7.2.4.2, and 7.5.6 for detailed use and requirements.
n (0, 1, 2, ....7 ): Header Sequence Number.
Sent by a port receiving a header packet when all of the following conditions are true:
LGOOD_n
• The header packet has a valid structure and can be recognized by the receiver.
• CRC-5 and CRC-16 are valid.
• Header Sequence Number in the received header packet matches the expected Rx Header Sequence
Number.
• An Rx Header Buffer in the receiver is available for storing the received header packet.
Mismatch between a Header Sequence Number in the received header packet and the expected Rx
Header Sequence Number will result in a port transitioning to Recovery.
Received by a port sending a header packet. This is an acknowledgement from a link partner that a
header packet with the Header Sequence Number of “n” is received properly. Receipt of LGOOD_n
mismatching the expected ACK Tx Header Sequence Number will result in a port transitioning to Recovery.
Also sent by a port upon entry to U0 as the Header Sequence Number Advertisement to initialize the ACK
Tx Header Sequence Number of the two ports.
Refer to Section 7.2.4.1 for details.
Bad header packet.
LBAD
Sent by a port receiving the header packet in response to an invalid header packet. Packet that was
received has corrupted CRC-5 and/or CRC-16.
Receipt of LBAD will cause a port to resend all header packets after the last header packet that has been
acknowledged with LGOOD_n.
Refer to Section 7.2.4.1 for details.
7-13
Universal Serial Bus 3.0 Specification, Revision 1.0
Link
Command
Definition – See Sections 7.2.4.1, 7.2.4.2, and 7.5.6 for detailed use and requirements.
x (A, B, C, D): Rx Header Buffer Credit Index.
Signifies that a single Rx Header Buffer Credit has been made available.
LCRD_x
Sent by a port after receiving a header packet that meets the following criteria:
• LGOOD_n is sent.
• The header packet has been processed, and an Rx Header Buffer Credit is available.
LCRD_x is sent in the alphabetical order of A, B, C, D, and back to A without skipping. Missing LCRD_x
will cause the link to transition to Recovery.
Refer to Section 7.2.4.1 for details.
LRTY
Sent by a port before resending the first header packet in response to receipt of LBAD.
LGO_U1
Sent by a port requesting entry to U1.
LGO_U2
Sent by a port requesting entry to U2.
LGO_U3
Sent by a downstream port requesting entry to U3. An upstream port shall accept the request.
LAU
Sent by a port accepting the request to enter U1, U2, or U3.
LXU
Sent by a port rejecting the request to enter U1 or U2.
LPMA
Sent by a port upon receiving LAU. Used in conjunction with LGO_Ux and LAU handshake to guarantee
both ports are in the same state.
LUP
Device present in U0. Sent by an upstream port every 10 µs when there are no packets or other link
commands to be transmitted. Refer to Section 7.5.6.1 for details.
7.2.2.3
Link Command Placement
The link command placement shall meet the following rules:
• Link commands shall not be placed inside header packet structures (i.e., within LMPs, TPs,
ITPs, or DPHs).
• Link commands shall not be placed within the DPP of a DP structure.
• Link commands shall not be placed between the DPH and the DPP.
• Link commands may be placed before and after a header packet with the exception that they
shall not be placed in between a DPH and its DPP.
• Multiple link commands are allowed to be transmitted back to back.
• Link commands shall not be sent until all scheduled SKP ordered sets have been transmitted.
Note: Additional rules regarding scheduling of link commands are found in Section 10.7.5 to
Section 10.7.12.
7.2.3
Logical Idle
Logical Idle is defined to be a period of one or more symbol periods when no information (packets
or link commands) is being transferred on the link. A special D-Symbol (00h), defined as Idle
Symbol (IS), shall be transmitted by a port at any time in U0 meeting the logical idle definition.
The IS shall be scrambled according to rules described in Section 6.4.3.
Table 7-6. Logical Idle Definition
7-14
Symbol
Data Byte Name
Data Byte Value
Definition
IS
D0.0
00h
Represents Idle state on the bus.
Link Layer
7.2.4
Link Command Usage for Flow Control, Error Recovery,
and Power Management
Link commands are used for link level header packet flow control, to identify lost/corrupted header
packets and to initiate/acknowledge link level power management transitions. The construction and
descriptions for each link command are found in Section 7.2.2.
7.2.4.1
Header Packet Flow Control and Error Recovery
Header packet flow control is used for all header packets. It requires each side of the link to follow
specific header buffer and transmission ordering constraints to guarantee a successful packet
transfer and link interoperability. This section describes, in detail, the rules of packet flow control.
7.2.4.1.1
Initialization
The link initialization refers to initialization of a port once a link transitions to U0 from Polling,
Recovery, or Hot Reset. The initialization includes the Header Sequence Number Advertisement
and the Rx Header Buffer Credit Advertisement between the two ports before a header packet can
be transmitted.
• The following requirements shall be applied to a port:
1. A port shall maintain two Tx Header Sequence Numbers. One is the Tx Header Sequence
Number that is defined as the Header Sequence Number that will be assigned to a header
packet when it is first transmitted (not a re-transmission). The other is the ACK Tx Header
Sequence Number that is defined as the expected Header Sequence Number to be
acknowledged with LGOOD_n that is sent by a port receiving the header packet.
2. A port shall have an Rx Header Sequence Number. It is defined as the expected Header
Sequence Number when a header packet is received.
3. A port shall maintain two Rx Header Buffer Credit Counts. One is the Local Rx Header
Buffer Credit Count that is defined as the number of the available Rx Header Buffer
Credits of its receiver. The other is the Remote Rx Header Buffer Credit Count that is
defined as the number of the available Rx Header Buffer Credits from its link partner.
4. A port shall have enough Tx Header Buffers in its transmitter to hold up to four
unacknowledged header packets.
5. A port shall not transmit any header packet if its Remote Rx Header Buffer Credit Count
is 0.
6. A port shall have enough Rx Header Buffers in its receiver to receive up to four header
packets.
7. Upon entry to U0, the following shall be performed in the sequence presented:
a. A port shall start the PENDING_HP_TIMER and CREDIT_HP_TIMER in expectation
of the Header Sequence Number and the Rx Header Buffer Credit Advertisement.
b. A port shall initiate the Header Sequence Number Advertisement.
c. A port shall initiate the Rx Header Buffer Credit Advertisement.
7-15
Universal Serial Bus 3.0 Specification, Revision 1.0
•
The Header Sequence Number Advertisement refers to ACK Tx Header Sequence Number
initialization by exchanging Header Sequence Numbers between the two ports. This Header
Sequence Number is the Header Sequence Number of the last header packet a port has received
properly. The main purpose of the Header Sequence Number Advertisement is to maintain the
link flow before and after Recovery such that a port upon re-entry to U0 is aware what the last
header packet is that was sent successfully prior to Recovery, and decides what header packets
in its Tx Header Buffers that can be flushed or need to be retransmitted. The following rules
shall be applied during the Header Sequence Number Advertisement:
1. A port shall set its initial Rx Header Sequence Number defined in the following:
a. If a port enters U0 from Polling or Hot Reset, the Rx Header Sequence Number is 0.
b. If a port enters U0 from Recovery, the Rx Header Sequence Number is the header
Sequence Number of the next expected header packet.
2. A port shall set its initial Tx Header Sequence Number defined in the following:
a. If a port enters U0 from Polling or Hot Reset, its Tx Header Sequence Number is 0.
b. If a port enters U0 from Recovery, its Tx Header Sequence Number is the same as the
Tx Header Sequence Number before Recovery.
Note: A header packet that is re-transmitted shall maintain its originally assigned Header
Sequence Number.
3. A port shall initiate the Header Sequence Number Advertisement by transmitting
LGOOD_n with “n” equal to the Rx Header Sequence Number minus one.
Note: The decrement is based on modulo-8 operation.
4. A port shall set its initial ACK Tx Header Sequence Number to the Sequence Number
received during the Rx Header Sequence Number Advertisement plus one.
Note: The increment is based on modulo-8 operation.
5. A port shall not send any header packets until the Header Sequence Number Advertisement
has been received and a Remote Rx Header Buffer Credit is available.
6. A port shall not request for a low power link state entry before receiving and sending the
Header Sequence Number Advertisement.
Note: The rules of Low Power Link State Initiation (refer to Section 7.2.4.2) still apply.
7. A port shall flush the header packets in its Tx Header Buffers upon receiving the Header
Sequence Number Advertisement. A port shall do one of the following:
a. If a port enters U0 from Polling or Hot Reset, it shall flush all the header packets in its
Tx Header Buffers.
b. If a port enters U0 from Recovery, it shall flush all the header packets in its Tx Header
Buffers that have been sent before Recovery except for those with the Header Sequence
Number greater than (modulo 8) the Header Sequence Number received in
Header Sequence Number Advertisement.
Note: If for example, the Header Sequence Number Advertisement of LGOOD_1 is
received, a port shall flush the header packets in its Tx Header Buffers with Header
Sequence Numbers of 1, 0, 7, 6.
7-16
Link Layer
•
•
•
The Rx Header Buffer Credit Advertisement refers to Remote Rx Header Buffer Credit Count
initialization by exchanging the number of available Local Rx Header Buffer Credits between
the two ports. The main purpose of this advertisement is for a port to align its Remote Rx
Header Buffer Credit Count with its link partner upon entry to U0. The following rules shall be
applied during the Rx Header Buffer Credit Advertisement:
1. A port shall initiate the Rx Header Buffer Credit Advertisement upon completion of the
Header Sequence Number Advertisement.
2. A port shall initialize the following before sending the Rx Header Buffer Credit:
a. A port shall initialize its Tx Header Buffer Credit index to A.
b. A port shall initialize its Rx Header Buffer Credit index to A.
c. A port shall initialize its Remote Rx Header Buffer Credit Count to 0.
d. A port shall continue to process those header packets in its Rx Header Buffers that have
been either acknowledged with LGOOD_n prior to entry to Recovery, or validated
during Recovery, and then update the Local Rx Header Buffer Credit Count.
e. A port shall set its Local Rx Header Buffer Credit Count defined in the following:
1. If a port enters U0 from Polling or Hot Reset, its Local Rx Header Buffer Credit
Count is 4.
2. If a port enters U0 from Recovery, its Local Rx Header Buffer Credit Count is the
number of Rx Header Buffers available for incoming header packets.
3. A port shall perform the Rx Header Buffer Credit Advertisement by transmitting LCRD_x
to notify its link partner. A port shall transmit one of the following based on its Local Rx
Header Buffer Credit Count:
a. LCRD_A if the Local Rx Header Buffer Credit Count is one.
b. LCRD_A and LCRD_B if the Local Rx Header Buffer Credit Count is two.
c. LCRD_A, LCRD_B, and LCRD_C if the Local Rx Header Buffer Credit Count is
three.
d. LCRD_A, LCRD_B, LCRD_C and LCRD_D if the Local Rx Header Buffer Credit
Count is four.
4. A port receiving LCRD_x from its link partner shall increment its Remote Rx Header
Buffer Credit Count by one each time an LCRD_x is received up to four.
5. A port shall not transmit any header packet if its Remote Rx Header Buffer Credit Count
is zero.
6. A port shall not request for a low power link state entry before receiving and sending
LCRD_x during the Rx Header Buffer Credit Advertisement.
Note: The rules of Low Power Link State Initiation (refer to Section 7.2.4.2) still apply.
The following rules shall be applied additionally when a port enters U0 from Recovery:
1. A port sending LBAD before Recovery shall not expect to receive LRTY before a retried
header packet from its link partner upon entry to U0.
2. A port receiving LBAD before Recovery shall not send LRTY before a retried header
packet to its link partner upon entry to U0.
Note: There exists a situation where an LBAD was sent by a port before Recovery and it
may or may not be received properly by its link partner. Under this situation, the rules of
LBAD/LRTY do not apply. Refer to Sections 7.2.4.1.4 and 7.2.4.1.9 for details.
3. An upstream port may send LUP during link initialization.
Upon entry to Recovery and the next state is Hot Reset or Loopback, a port may optionally
continue its processing of all the packets received properly.
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Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.4.1.2
General Rules of LGOOD_n and LCRD_x Usage
• The Rx Header Buffer Credit shall be transmitted in the alphabetical order of LCRD_A,
LCRD_B, LCRD_C, LCRD_D, and back to LCRD_A. LCRD_x received out of alphabetical
order is considered as missing of a link command, and transition to Recovery shall be initiated.
• Header packets shall be sent with the Header Sequence Number in the numerical order from 0
to 7, and back to 0. LGOOD_n received out of the numerical order is considered as missing of
a link command, and the transition to Recovery shall be initiated.
• Header packet transmission may be delayed. When this occurs, the DL bit shall be set in the
Link Control Word by a hub and optionally by a peripheral device or host. Some, but not
necessarily all, of the conditions that will cause this delay follow:
1. When a header packet is resent.
2. When the link is in Recovery.
3. When the Remote Rx Header Buffer Credit Count is zero.
4. When the Tx Header Buffer is not empty.
Note: Delay matters primarily for ITPs.
7.2.4.1.3
Transmitting Header Packets
• Before sending a header packet, a port shall add the Tx Header Sequence Number
corresponding to the Header Sequence Number field in the Link Control Word.
• Transmission of a header packet shall consume a Tx Header Buffer. Accordingly, the Tx
Header Sequence Number shall be incremented by one after the transmission or roll over to
zero if the maximum Header sequence number is reached.
• Transmission of a retried header packet shall not consume an additional Tx Header Buffer and
the Tx Header Sequence Number shall remain unchanged.
• Upon receiving LBAD, a port shall send LRTY followed by resending all the header packets
that have not been acknowledged with LGOOD_n except for Recovery. Refer to
Section 7.2.4.1.1 for additional rules applicable when a port enters U0 from Recovery.
• Prior to resending a header packet, a port shall set the Delay bit within the Link Control word
and re-calculate CRC-5.
•
•
•
Note: CRC-16 within header packet remains unchanged.
The Remote Rx Header Buffer Credit Count shall be incremented by one if a valid LCRD_x is
received.
The Remote Rx Header Buffer Credit Count shall be decremented by one if a header packet is
sent for the first time after entering U0, including when it is resent following Recovery.
The Remote Rx Header Buffer Credit Count shall not be changed when a header packet is
retried following LRTY.
7.2.4.1.4
Receiving Header Packets
• Upon receiving a header packet, the following verifications shall be performed:
1. CRC-5
2. CRC-16
3. Matching between the Header Sequence Number in the received header packet and the Rx
Header Sequence Number
4. The availability of an Rx Header Buffer to store a header packet
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Link Layer
•
•
•
•
•
•
7.2.4.1.5
A header packet is defined as “received properly” when it has passed all four criteria described
above.
When a header packet has been received properly, a port shall issue a single LGOOD_n with
“n” corresponding to the Rx Header Sequence Number and increment the Rx Header Sequence
Number by one (or roll over to 0 if the maximum Header Sequence Number is reached).
A port shall consume one Rx Header Buffer until it has been processed.
When a header packet is not “received properly”, one of the following shall occur:
1. If the header packet has one or more CRC-5 or CRC-16 errors, a port shall issue a single
LBAD. A port shall ignore all the header packets received subsequently until an LRTY has
been received, or the link has entered Recovery. Refer to Section 7.2.4.1.1 for additional
rules applicable when a port enters U0 from Recovery.
2. If the Header Sequence Number in the received header packet does not match the Rx
Header Sequence Number, or a port does not have an Rx Header Buffer available to store a
header packet, a port shall transition to Recovery.
After transmitting LBAD, a port shall continue to issue LCRD_x if an Rx Header Buffer Credit
is made available.
A port shall transition directly to Recovery if it fails to receive a header packet three
consecutive times. A port shall not issue the third LBAD upon the third error.
Rx Header Buffer Credit
Each port is required to have four Rx Header Buffer Credits in its receiver. This is referred to the
Local Rx Header Buffer Credit. The number of the Local Rx Header Buffer Credits represents the
number of header packets a port can accept and is managed by the Local Rx Header Buffer Credit
Count.
• A port shall consume one Local Rx Header Buffer Credit if a header packet is “received
properly”. The Local Rx Header Buffer Credit Count shall be decremented by one.
• Upon completion of a header packet processing, a port shall restore a Local Rx Header Buffer
Credit by:
1. Sending a single LCRD_x
2. Advancing the Credit index alphabetically (or roll over to A if the Header Buffer Credit
index of D is reached) and
3. Incrementing the Local Rx Header Buffer Credit Count by one.
Note: The LCRD_x index is used to ensure Rx Header Buffer Credits are sent in an
alphabetical order such that missing of an LCRD_x can be detected.
7.2.4.1.6
Receiving Data Packet Payload
The processing of DPP shall adhere to the following rules:
• A DPP shall be accepted if the following two conditions are met:
1. A DPH is received properly.
2. A DPPStart ordered set is received properly immediately after its DPH.
• The DPP processing shall be completed when a valid DPPEND ordered set is detected.
• The DPP processing shall be aborted when one of the following conditions is met:
1. A valid DPPABORT ordered set is detected.
2. A K-symbol that does not belong to a valid DPPEND or DPPABORT ordered set is
detected before a valid DPPEND or DPPABORT ordered set. A port shall then ignore the
corresponding DPPEND or DPPABORT ordered set associated with the DPP.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
3. A DPP of length exceeding “sDataSymbolsBabble” (see Table 10-15) has been reached and
no valid DPPEND or DPPABORT ordered set is detected.
A DPP shall be dropped if its DPH is corrupted.
A DPP shall be dropped when it does not immediately follow its DPH.
7.2.4.1.7
Receiving LGOOD_n
• A port shall maintain every header packet transmitted within its Tx Header Buffer until it
receives an LGOOD_n. Upon receiving LGOOD_n, a port shall do one of the following:
1. If LGOOD_n is the Header Sequence Number Advertisement and a port is entering U0
from Recovery, a port shall flush all the header packets retained in its Tx Header Buffers
that have their Header Sequence Numbers equal to or less than the received Header
Sequence Number, and initialize its ACK Tx Header Sequence Number to be the received
Header Sequence Number plus one.
Note: The comparison and increment are based on modulo-8 operation.
2. If a port receives an LGOOD_n and this LGOOD_n is not Header Sequence Number
Advertisement, it shall flush the header packet in its Tx Header Buffer with its Header
Sequence Number matching the received Header Sequence Number and increment the
ACK Tx Header Sequence Number by one based on modulo-8 operation.
3. If a port receives an LGOOD_n and this LGOOD_n is not Header Sequence Number
Advertisement, it shall transition to Recovery if the received Header Sequence Number
does not match the ACK Tx Header Sequence Number. The ACK Tx Header Sequence
Number shall be unchanged.
Note: A port that has received an out of order LGOOD_n implies a lost or corrupted link
command and shall initiate transition to Recovery.
7.2.4.1.8
Receiving LCRD_x
• A port shall adjust its Remote Rx Header Buffer Credit Count based on the received LCRD_x:
1. A port shall increment its Remote Rx Header Buffer Credit Count by one upon receipt of
LCRD_x.
2. A port shall transition to Recovery if it receives an out of order LCRD_x.
Note: A port that has received an out of order credit implies a lost or corrupted link command
and shall transition to Recovery.
7.2.4.1.9
Receiving LBAD
• Upon receipt of LBAD, a port shall send a single LRTY before retransmitting all the header
packets in the Tx Header Buffers that have not been acknowledged with LGOOD_n. A port
shall set the DL bit in the Link Control Word on all resent header packets and recalculate
CRC-5.
•
Note: Resending an ITP invalidates the isochronous timestamp value. CRC-16 is unchanged
in a retried header packet.
Upon receipt of LBAD, a port shall send a single LRTY if there is no unacknowledged header
packet in the Tx Header Buffers.
Note: This is an error condition where LBAD is created due to a link error.
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Link Layer
7.2.4.1.10
Transmitter Timers
A PENDING_HP_TIMER is specified to cover the period of time from when a header packet is
sent to a link partner, to when the header packet is acknowledged by a link partner. The purpose of
this time limit is to allow a port to detect if the header packet acknowledgement sent by its link
partner is lost or corrupted. The timeout value for the PENDING_HP_TIMER is listed in
Table 7-7. The operation of the PENDING_HP_TIMER shall be based on the following rules:
• A port shall have a PENDING_HP_TIMER that is active only in U0 and if one of the following
conditions is met:
1. A port has a header packet transmitted but not acknowledged by its link partner, except
during the period between receipt of LBAD and retransmission of the oldest header packet
in the Tx Header Buffer.
2. A port is expecting the Header Sequence Number Advertisement from its link partner.
• The PENDING_HP_TIMER shall be started if one of the following conditions is met:
1. When a port enters U0 in expectation of the Header Sequence Number Advertisement.
2. When a header packet is transmitted and there are no prior header packets transmitted but
unacknowledged in the Tx Header Buffers.
3. When the oldest header packet is retransmitted in response to LBAD.
• The PENDING_HP_TIMER shall be reset and restarted when a header packet is acknowledged
with LGOOD_n and there are still header packets transmitted but unacknowledged in the Tx
Header Buffers.
• The PENDING_HP_TIMER shall be reset and stopped if one of the following conditions is
met:
1. When a Header Sequence Number Advertisement is received.
2. When a header packet acknowledgement of LGOOD_n is received and all the transmitted
header packets in the Tx Header Buffers are acknowledged.
3. When a header packet acknowledgement of LBAD is received.
• A port shall transition to Recovery if the following two conditions are met:
1. PENDING_HP_TIMER times out.
2. The transmission of an outgoing header packet is completed or the transmission of an
outgoing DPP is either completed with DPPEND or terminated with DPPABORT.
Note: This is to allow a graceful transition to Recovery without a header packet being
truncated.
A CREDIT_HP_TIMER is also specified to cover the period of time from when a header packet
has been transmitted and its Remote Rx Header Buffer Credit count is less than four, to when a
Remote Rx Header Buffer Credit is received and its Remote Rx Header Buffer Credit count is back
to four. The purpose of this timer is to make sure that a Remote Rx Header Buffer Credit is
received within a reasonable time limit. This will allow a port sending the header packet to reclaim
a Remote Rx Header Buffer Credit within a time limit in order to continue the process of packet
transmission. This will also allow a port receiving the header packet enough time to process the
header packet. The timeout value for the CREDIT_HP_TIMER is listed in Table 7-7. The
operation of the CREDIT_HP_TIMER shall be based on the following rules:
• A port shall have a CREDIT_HP_TIMER that is active only in U0 and if one of the following
conditions is met:
1. A port has its Remote Rx Header Buffer Credit Count less than four.
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Universal Serial Bus 3.0 Specification, Revision 1.0
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•
•
•
2. A port is expecting the Header Sequence Number Advertisement and the Rx Header Buffer
Credit Advertisement from its link partner.
The CREDIT_HP_TIMER shall be started when a header packet or a retried header packet is
sent, or when a port enters U0.
The CREDIT_HP_TIMER shall be reset when a valid LCRD_x is received.
The CREDIT_HP_TIMER shall be restarted if a valid LCRD_x is received and the Remote Rx
Header Buffer Credit Count is less than four.
A port shall transition to Recovery if the following two conditions are met:
1. CREDIT_HP_TIMER times out.
2. The transmission of an outgoing header packet is completed or the transmission of an
outgoing DPP is either completed with DPPEND or terminated with DPPABORT.
Note: This is to allow a graceful transition to Recovery without a header packet being
truncated.
Table 7-7. Transmitter Timers Summary
Timers
Timeout Value (μs)
PENDING_HP_TIMER
3
CREDIT_HP_TIMER
5000
7.2.4.2
Link Power Management and Flow
Requests to transition to low power link states are done at the link level during U0. Link
commands LGO_U1, LGO_U2, and LGO_U3 are sent by a port as a request to enter a low power
link state. LAU or LXU is sent by the other port as the response. LPMA is sent by a port in
response only to LAU. Details on exit/wake from a low power link state are described in
Sections 7.5.7, 7.5.8, and 7.5.9.
7.2.4.2.1
Power Management Link Timers
A port shall have three timers for link power management. First, a PM_LC_TIMER is used for a
port initiating an entry request to a low power link state. It is designed to ensure a prompt entry to a
low power link state. Second, a PM_ENTRY_TIMER is used for a port accepting the entry request
to a low power link state. It is designed to ensure that both ports across the link are in the same low
power link state regardless if the LAU or LPMA is lost or corrupted. Finally, a Ux_EXIT_TIMER
is used for a port to initiate the exit from U1 or U2. It is specified to ensure that the duration of U1
or U2 exit is bounded and the latency of a header packet transmission is not compromised. The
timeout values of the three timers are specified in Table 7-8.
A port shall operate the PM_LC_TIMER based on the following rules:
• A port requesting a low power link state entry shall start the PM_LC_TIMER after the last
symbol of the LGO_Ux link command is sent.
• A port requesting a low power link state entry shall disable and reset the PM_LC_TIMER upon
receipt of the LAU or LXU.
A port shall operate the PM_ENTRY_TIMER based on the following rules:
• A port accepting the request to enter a low power link state shall start the PM_ENTRY_TIMER
after the last symbol of the LAU is sent.
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Link Layer
•
A port accepting the request to enter a low power link state shall disable and reset the
PM_ENTRY_TIMER upon receipt of an LPMA, a TS1 ordered set, an LFPS meeting U1 or U2
exit, or U3 wakeup signaling specified in Section 6.9.2.
A port shall operate the Ux_EXIT_TIMER based on the following rules.
• A port initiating U1 or U2 exit shall start the Ux_EXIT_TIMER when it starts to send LFPS
Exit handshake signal.
• A port initiating U1 or U2 exit shall disable and reset the Ux_EXIT_TIMER upon entry to U0.
Table 7-8. Link Flow Control Timers Summary
Timers
Timeout Value (μs)
PM_LC_TIMER
3
PM_ENTRY_TIMER
6
Ux_EXIT_TIMER
6000
7.2.4.2.2
Low Power Link State Initiation
• A port shall not send a LGO_U1, LGO_U2 or LGO_U3 unless it meets all of the following:
1. It has transmitted LGOOD_n and LCRD_x for all the header packets received.
2. It has received LGOOD_n and LCRD_x for all the header packets transmitted.
Note: This implies all credits must be received and returned before a port can initiate a
transition to a low power link state.
3. It has no pending packets for transmission.
4. It has completed the Header Sequence Number Advertisement and the Rx Header Buffer
Credit Advertisement upon entry to U0.
•
Note: This implies that a port has sent the Header Sequence Number Advertisement and the Rx
Header Buffer Credit Advertisement to its link partner, and also received the Header Sequence
Number Advertisement and the Rx Header Buffer Credit Advertisement from its link partner.
5. It is directed by a higher layer to initiate entry. Examples of when a higher layer may
direct the link layer to initiate entry are: (a) the U1 or U2 inactivity timer expires (refer to
PORT_U1_TIMEOUT, PORT_U2_TIMEOUT in Chapter 10); (b) reception of a
SetPortFeature(PORT_LINK_STATE) request; and (c) device implementation specific
mechanisms.
6. It has met higher layer conditions for initiating entry. Examples are: (a)
U1_enable/U2_enable is set or U1_TIMEOUT/U2_TIMEOUT is not equal zero; (b) device
has received an ACK TP for each and every previously transmitted packet; (c) device is not
waiting for a TP following a PING; and (d) device is not waiting for a timestamp following
a timestamp request (for these and any other examples, refer to Chapter 8).
A port shall do one of the following in response to receiving an LGO_U1 or LGO_U2:
1. A port shall send an LAU if the Force Link PM Accept field is asserted due to having
received a Set Link Functionality LMP.
2. A port shall send an LAU if all of the following conditions are met:
a. It has transmitted an LGOOD_n, LCRD_x sequence for all packets received.
b. It has received an LGOOD_n, LCRD_x sequence for all packets transmitted.
c. It has no pending packets for transmission.
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Universal Serial Bus 3.0 Specification, Revision 1.0
d. It is not directed by a higher layer to reject entry. Examples of when a higher layer
may direct the link layer to reject entry are: (1) U1 or U2 is not enabled (e.g.,
PORT_U1_TIMEOUT or PORT_U2_TIMEOUT set to zero); (2) When a device has
not received an ACK TP for a previously transmitted packet (refer to Chapter 8); and
(3) When a device receives a ping TP (refer to the ping packet definition in Chapter 8
for more information).
3. A port shall send an LXU if any of the above conditions are not met.
7.2.4.2.3
U1/U2 Entry Flow
Either a downstream port or an upstream port may initiate U1/U2 entry or exit. Entry to a low
power U1 or U2 link state is accomplished by using the link commands defined in Table 7-5.
• A port shall send a single LGO_U1 or LGO_U2 to request a transition to a low power link
state.
• Upon issuing LGO_Ux, a port shall start its PM_LC_TIMER.
• A port shall either accept LGO_Ux with a single LAU or shall reject LGO_U1 or LGO_U2
with a single LXU and remain in U0.
• Upon sending LGO_U1 or LGO_U2, a port shall not send any packets until it has received
LXU or re-entered U0.
• Upon sending LGO_U1 or LGO_U2, a port shall continue receiving and processing packets
and link commands.
• Upon receiving LXU, a port shall remain in U0.
• A port shall initiate transition to Recovery if a single LAU or LXU is not received upon
PM_LC_TIMER timeout.
• Upon issuing LAU, a port shall start PM_ENTRY_TIMER.
• Upon receiving LAU, a port shall send a single LPMA and then enter the requested low power
link state.
• Upon issuing LAU or LPMA, a port shall not send any packets or link commands.
• A port that sends LAU shall enter the corresponding low power link state upon receipt of
LPMA before PM_ENTRY_TIMER timeout.
• A port that sends LAU shall enter the requested low power link state upon
PM_ENTRY_TIMER timeout and if all of the following conditions are met:
1. LPMA is not received.
2. No TS1 ordered set is received.
•
Note: This implies LPMA is corrupted and the port issuing LGO_Ux has entered Ux.
A port that has sent LAU shall enter Recovery before PM_ENTRY_TIMER timeout if a TS1
ordered set is received.
•
Note: This implies LAU was corrupted and the port issuing LGO_Ux has entered Recovery.
A port that has sent LAU shall not respond with Ux LFPS exit handshake defined in
Section 6.9.2 before PM_ENTRY_TIMER timeout and if LFPS Ux_Exit signal is received.
Note: This implies LPMA was corrupted and the port issuing LGO_Ux has initiated Ux exit.
Under this situation, the port sending LAU shall complete the low power link state entry
process and then respond to Ux exit.
There also exists a situation where a port transitions from U1 to U2 directly.
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Link Layer
•
7.2.4.2.4
A port in U1 shall enter U2 directly if the following two conditions are met:
1. The port’s U2 inactivity timer is enabled.
2. The U2 inactivity timer times out and no U1 LFPS exit signal is received.
U3 Entry Flow
Only a downstream port can initiate U3 entry. An upstream port shall not reject U3 entry.
• Upon directed, a downstream port shall initiate U3 entry process by sending LGO_U3.
• Upon issuing LGO_U3, a downstream port shall start PM_LC_TIMER.
• An upstream port shall send LAU in response to LGO_U3 request by a downstream port.
• An upstream port shall not send any packets or link commands subsequent to sending an LAU.
• Upon issuing LGO_U3, a downstream port shall ignore any packets sent by an upstream port.
•
•
•
•
•
•
7.2.4.2.5
Note: This is a corner condition that an upstream port is sending a header packet before
receiving LGO_U3.
Upon Receiving LGO_U3, an upstream port shall respond with an LAU. The processing of all
the unacknowledged packets shall be aborted.
Upon issuing LAU, an upstream port shall start PM_ENTRY_TIMER.
A downstream port shall send a single LPMA and then transition to U3 when LAU is received.
A downstream port shall transition to Recovery and reinitiate U3 entry after re-entry to U0 if all
of the following three conditions are met:
1. The PM_LC_TIMER times out.
2. LAU is not received.
3. The number of consecutive U3 entry attempts is less than three.
An upstream port shall transition U3 when one of the following two conditions is met:
1. LPMA is received
2. The PM_ENTRY_TIMER times out and LPMA is not received
A downstream port shall transition to SS.Inactive when it fails U3 entry on three consecutive
attempts.
Concurrent Low Power Link Management Flow
Concurrent low power link management flow applies to situations where a downstream port and an
upstream port both issue a request to enter a low power link state.
• If a downstream port has sent an LGO_U1, LGO_U2, or LGO_U3 and also received an
LGO_U1 or LGO_U2, it shall send an LXU.
• If an upstream port has sent an LGO_U1 or LGO_U2 and also received an LGO_U1, LGO_U2,
it shall wait until receipt of an LXU and then send either an LAU or LXU.
• If an upstream port has sent an LGO_U1 or LGO_U2 and also received an LGO_U3 from a
downstream port, it shall wait until the reception of an LXU and then send an LAU.
• If a downstream port is directed by a higher layer to initiate a transition to U3, and a transition
to U1 or U2 has been initiated but not yet completed, the port shall first complete the in-process
transition to U1 or U2, then return to U0 and request entry to U3.
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Universal Serial Bus 3.0 Specification, Revision 1.0
7.2.4.2.6
Concurrent Low Power Link Management and Recovery Flow
Concurrent low power link management and Recovery flow applies to situations where a port
issues a low power link state entry and another port issues Recovery. The port that issues the low
power link state entry shall meet the following rules:
• Upon issuing LGO_Ux, the port shall transition to Recovery if a TS1 ordered set is received.
• The port shall reinitiate low power link state entry process described in Section 7.2.4.2.3 and
7.2.4.2.4 upon re-entry to U0 from Recovery if the conditions to enter a low power link state
are still valid.
7.2.4.2.7
Low Power Link State Exit Flow
Exit from a low power link state refers to exit from U1/U2, or wakeup from U3. It is accomplished
by the LFPS Exit signaling defined in Section 6.9.2. A successful LFPS handshake process will
lead both a downstream port and an upstream port to Recovery.
A Ux_EXIT_TIMER defined in Section 7.2.4.2.1 is only applied when a port is attempting an exit
from U1 or U2. It shall not be applied when a port is initiating a U3 wakeup.
The exit from U1/U2 shall meet the following flow. The U3 wakeup follows the same flow with
the exception that Ux_EXIT_TIMER is disabled during U3 wakeup.
• If a port is initiating U1/U2 Exit, it shall start sending U1/U2 LFPS Exit handshake signal
defined in Section 6.9.2 and start the Ux_EXIT_TIMER.
• If a port is initiating U3 wakeup, it shall start sending U3 LFPS wakeup handshake signal
defined in Section 6.9.2.
• A port upon receiving U1/U2 Exit or U3 wakeup LFPS handshake signal shall start U1/U2 exit
or U3 wakeup by responding with U1/U2 Exit or U3 wakeup LFPS signal defined in
Section 6.9.2.
• Upon a successful LFPS handshake before tNoLFPSResponseTimeout defined in Table 6-14, a
port shall transition to Recovery.
• A port initiating U1 or U2 Exit shall transition to SS.Inactive if one of the following two
conditions is met:
1. Upon tNoLFPSResponseTimeout and the condition of a successful LFPS handshake is not
met.
2. Upon Ux_EXIT_TIMER timeout, the link has not transitioned to U0.
• A port initiating U3 wakeup shall remain in U3 when the condition of a successful LFPS
handshake is not met upon tNoLFPSResponseTimeout and it may initiate U3 wakeup again
after a minimum of 100-ms delay.
• A root port not able to respond to U3 LFPS wakeup within tNoLFPSResponseTimeout shall
initiate U3 LFPS wakeup when it is ready to return to U0.
7.3
Link Error Rules/Recovery
7.3.1
Overview of SuperSpeed Bit Errors
The SuperSpeed timing budget is based on a link’s statistical random bit error probability less than
10-12. Packet framings and link command framing are tolerant to one symbol error. Details on bit
error detection under link flow control are described in Section 7.2.4.
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Link Layer
7.3.2
Link Error Types, Detection, and Recovery
Data transfers between the two link partners are carried out using the form of a packet. A set of
link commands is defined to ensure the successful packet flow across the link. Other link
commands are also defined to manage the link connectivity. When symbol errors occur on the link,
the integrity of a packet or a link command can be compromised. Therefore, not only a packet or a
link command needs to be constructed to increase the error tolerance, but the link data integrity
handling also needs to be specified such that any errors that will invalidate or corrupt a packet or a
link command can be detected and a link error can be recovered.
There are various types of errors at the link layer. This includes an error on a packet or a link
command, or an error during the link training process, or an error when a link is in transition from
one state to another. The detection and recovery from those link errors are described with details in
this section.
7.3.3
Header Packet Errors
Several types of header packet errors are detected. They are:
1. Missing of a header packet
2. Invalid header packet due to CRC errors
3. Mismatch of a Rx Header Sequence Number
Regardless, the Link Error Count is incremented for only one class of errors in the link layer, and
those are errors which will cause the link to transition to Recovery. For errors that will not cause
the link to enter Recovery, the Link Error Count shall remain unchanged.
7.3.3.1
Packet Framing Error
A packet framing ordered set is constructed such that any single K-symbol corruption within the
ordered set will not prevent its packet framing recognition.
Header packet framing and DPP framing are all constructed using four K-symbol ordered sets. A
header packet contains only one packet framing ordered set at the beginning of the packet defined
in Section 7.2.1. A DPP begins with start packet framing ordered set and ends with end packet
framing ordered set as defined in Section 7.2.2.
• A valid HPSTART ordered set shall be declared if the following two conditions are met:
1. At least three of the four K-symbols in the four consecutive symbol periods are valid
packet Framing K-symbols.
2. The four symbols are in the order defined in Table 7-9.
Note: If an HPSTART ordered set has two or more K-symbols corrupted, a header packet will not
be detectable and, therefore, result in missing of a header packet.
• Missing of a header packet shall result in a port transitioning to Recovery depending on which
one of the following conditions becomes true first:
1. A port transmitting the header packet upon its PENDING_HP_TIMER timeout.
2. A port receiving the header packet upon detection of a Rx Header Sequence Number error.
• The Link Error Count shall be incremented by one each time a transition to Recovery occurs.
7-27
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 7-9. Valid Packet Framing K-Symbol Order (K is One of SHP, SDP, END or EDB)
7.3.3.2
Symbol 0
Symbol 1
Symbol 2
Symbol 3
Comment
K
K
K
EPF
All K-symbols are valid
Corrupt
K
K
EPF
First K corrupted
K
Corrupt
K
EPF
Second K corrupted
K
K
Corrupt
EPF
Third K corrupted
K
K
K
Corrupt
EPF corrupted
Header Packet Error
Each header packet contains a CRC-5 and a CRC-16 to ensure that the data integrity of a header
packet can be verified. A CRC-5 is used to detect bit errors in the Link Control Word. A CRC-16
is used to detect bit errors in the packet header. A header packet error can be detected using CRC-5
or CRC-16 checks.
• A header packet error shall be declared if the following conditions are true:
1. A valid HPSTART ordered set is detected.
2. Either CRC-5 or CRC-16 check fails as defined in Section 7.2.1 or any K-symbol
occurrence in the packet header or Link Control Word that prevents CRC-5 or CRC-16
checks from being completed.
• A port receiving the header packet shall send an LBAD as defined in Section 7.2.4.1 if it
detects a header packet error. The Link Error Count shall remain unchanged.
• If a port fails to receive a header packet for three consecutive times, it shall transition to
Recovery. The Link Error Count shall be incremented by one. Refer to Section 7.2.4.1.4 for
details.
7.3.3.3
Rx Header Sequence Number Error
Each port contains an Rx Header Sequence Number that is defined in Section 7.2.4.1 and initialized
upon entry to U0. Upon receiving a header packet, a port is required to compare the Header
Sequence Number embedded in the header packet with the Rx Header Sequence Number stored in
its receiver. This ensures that header packets are transmitted and received in an orderly manner. A
missing or corrupted header packet can be detected.
• An Rx Header Sequence Number error shall occur if the following conditions are met:
1. A header packet is received and no header packet error is detected.
2. The Header Sequence Number in the received header packet does not match the Rx Header
Sequence Number.
• A port detecting an Rx Header Packet Sequence Number error shall transition to Recovery.
• The Link Error Count shall be incremented by one each time a transition to Recovery occurs.
7.3.4
Link Command Errors
A link command consists of four K-symbol link command frame ordered set, LCSTART, followed
by a two-symbol link command word, and its repeat. A link command is constructed such that any
single K-symbol corruption within the link command frame ordered set will not invalidate the
recognition of a link command, and any single-bit error in the two scrambled link command words
will not corrupt the correct parsing of a link command.
7-28
Link Layer
•
A detection of a link command shall be declared if the following two conditions are met:
1. At least three of the four K-symbols in four consecutive symbol periods are valid link
command K-symbols.
2. The four symbols are in the order described in Table 7-10.
A valid link command is declared upon detection of a link command and one of the following
two conditions is met:
1. Both link command words are the same. They both contain valid link command
information as defined in Table 7-4. They both pass the CRC-5 check.
2. The two link command words are not the same, with one link command word containing
valid link command information as defined in Table 7-4, passing the CRC-5 check, and the
other link command word either failing the CRC-5 check, or not containing valid link
command information as defined in Table 7-4.
An invalid link command is declared upon detection of a link command and the conditions to
meet a valid link command are not met.
An invalid link command shall be ignored.
A port detecting missing of LGOOD_n or LCRD_x shall transition to Recovery.
Note: Missing LGOOD_n is declared when two consecutive LGOOD_n received are not in
numerical order. Missing LGOOD_n, or LBAD, or LRTY can also be inferred upon
PENDING_HP_TIMER timeout. Missing LCRD_x is declared when two consecutive
LCRD_x received are not in alphabetical order, or upon CREDIT_HP_TIMER times out and
LCRD_x is not received.
A port detecting missing of LGO_Ux, or LAU, or LXU shall transition to Recovery.
•
•
•
•
•
Note: Detection of missing LGO_Ux, or LAU, or LXU is declared upon PM_LC_TIMER
timeout and LAU or LXU is not received.
A downstream port detecting missing of LUP shall transition to Recovery (refer to
Section 7.5.6 for LUP detection).
•
Note: Missing of LPMA will not transition the link to Recovery. It will only cause an Ux entry
delay for the port accepting LGO_Ux (refer to Section 7.2.4.2 for details).
The Link Error Count shall be incremented by one each time a transition to Recovery occurs
due to an error.
•
Table 7-10. Valid Link Command K-Symbol Order
Symbol 0
SLC
Symbol 1
Symbol 2
Symbol 3
Comment
SLC
SLC
EPF
All K-symbols are valid
Corrupt
SLC
SLC
EPF
First SLC corrupted
SLC
Corrupt
SLC
EPF
Second SLC corrupted
SLC
SLC
Corrupt
EPF
Third SLC corrupted
SLC
SLC
SLC
Corrupt
EPF corrupted
7-29
Universal Serial Bus 3.0 Specification, Revision 1.0
7.3.5
ACK Tx Header Sequence Number Error
Each port has an ACK Tx Header Sequence Number that is defined in Section 7.2.4.1. The ACK
Tx Header Sequence Number is initialized during the Header Sequence Number Advertisement.
After a header packet is transmitted, a port is expecting to receive an LGOOD_n from its link
partner as an explicit acknowledgement that the header packet is received properly. Upon receiving
LGOOD_n, the Header Sequence Number contained in LGOOD_n will be compared with the ACK
Tx Header Sequence Number. The outcome of the comparison will determine if an ACK Tx
Header Sequence Number error has occurred.
• An ACK Tx Header Sequence Number error shall be declared if the following conditions are
met:
1. A valid LGOOD_n is received.
2. The Header Sequence Number in the received LGOOD_n does not match the ACK Tx
Header Sequence Number.
3. The LGOOD_n is not for Header Sequence Number Advertisement.
• A port detecting an ACK Tx Header Sequence Number error shall transition to Recovery.
• The Link Error Count shall be incremented by one each time a transition to Recovery occurs.
7.3.6
Header Sequence Number Advertisement Error
Each port is required to first perform a Header Sequence Number Advertisement upon entry to U0.
The details of a Header Sequence Number Advertisement are described in Section 7.2.4. A Header
Sequence Number Advertisement is the first step of the link initialization to ensure that the link
flow is maintained un-interrupted before and after Recovery. Any errors occurred during the
Header Sequence Number Advertisement must be detected and proper error recovery must be
initiated.
• A Header Sequence Number Advertisement error shall occur if one of the following conditions
is true:
1. Upon PENDING_HP_TIMER timeout and the Header Sequence Number Advertisement
not received
2. A header packet received before sending Header Sequence Number Advertisement
3. LCRD_x or LGO_Ux received before receiving Header Sequence Number Advertisement
• A port detecting any Header Sequence Number Advertisement error shall transition to
Recovery.
• The Link Error Count shall be incremented by one each time a transition to Recovery occurs.
7.3.7
Rx Header Buffer Credit Advertisement Error
Each port is required to perform the Rx Header Buffer Credit Advertisement after Header Sequence
Number Advertisement upon entry to U0. The details of Rx Header Buffer Credit Advertisement
are described in Section 7.2.4.
• An Rx Header Buffer Credit Advertisement error shall occur if one of the following conditions
is true:
1. Upon CREDIT_HP_TIMER timeout and no LCRD_x received.
2. A header packet received before sending LCRD_x.
3. LGO_Ux received before receiving LCRD_x.
7-30
Link Layer
•
•
7.3.8
A port detecting an Rx Header Buffer Credit Advertisement Error shall transition to Recovery.
The Link Error Count shall be incremented by one each time a transition to Recovery occurs.
Training Sequence Error
Symbol corruptions during the TS1 and TS2 ordered sets in Polling.Active, Polling.Configuration,
Recovery.Active, and Recovery.Configuration substates are expected until the requirements are met
to transition to the next state. A timeout from any one of these substates is considered Training
Sequence error.
• A timeout from either Polling.Active, Polling.Configuration, Recovery.Active, or
Recovery.Configuration substate shall result in a Training Sequence error.
• Upon detecting a Training Sequence error, one of the following link state transitions shall be
followed:
1. A downstream port shall transition to Rx.Detect if a Training Sequence error occurs during
Polling.
2. An upstream port of a hub shall transition to Rx.Detect if a Training Sequence error occurs
during Polling.
3. An upstream port of a peripheral device shall transition to SS.Disabled if a Training
Sequence error occurs during Polling.
4. A downstream port shall transition to SS.Inactive if a Training Sequence error occurs
during Recovery and the transition to Recovery is not an attempt for Hot Reset.
5. A downstream port shall transition to Rx.Detect if a Training Sequence error occurs during
Recovery.Active and Recovery.Configuration and the transition to Recovery is an attempt
for Hot Reset.
6. An upstream port shall transition to SS.Inactive if a Training Sequence error occurs during
Recovery.
• The Link Error Count shall remain unchanged.
7.3.9
8b/10b Errors
There are two types of errors when a receiver decodes 8b/10b symbols. One is a disparity error that
is declared when the running disparity of the received 8b/10b symbols is not +2, or 0, or -2. The
other is a decode error when an unrecognized 8b/10b symbol is received.
Upon receiving notification of an 8b/10b error:
• A port may optionally do the following:
1. If the link is receiving a header packet, it shall send LBAD.
2. If the link is receiving a link command, it shall ignore the link command.
3. If the link is receiving a DPP, it shall drop the DPP.
• The Link Error Count shall remain unchanged.
7.3.10
Summary of Error Types and Recovery
Table 7-11 summarizes the link error types, error count, and different error paths to restore the link.
• The link error shall be counted each time a link transitions to Recovery due to an error.
• The link error shall be counted by a downstream port.
• The Link Error Count shall be reset upon PowerOn Reset, Warm Reset, Hot Reset, or whenever
a port enters Polling.Idle.
7-31
Universal Serial Bus 3.0 Specification, Revision 1.0
Situations also exist where an unexpected link command or header packet is received. These
include but are not limited to the following:
1. Receiving an unexpected link command such as LBAD, LRTY, LAU, LXU, or LPMA before
receiving the Header Sequence Number Advertisement and the Remote Rx Header Buffer
Credit Advertisement.
2. Receiving the Header Sequence Number Advertisement after entry to U0 from Recovery with
its ACK Tx Header Sequence Number not corresponding to any header packets in the Tx
Header Buffers.
3. Receiving LRTY without sending LBAD.
4. Receiving LGOOD_n that is neither a Header Sequence Number Advertisement, nor for header
packet acknowledgement.
5. Receiving LAU, or LXU without sending LGO_Ux.
6. Receiving LPMA without sending LAU.
7. Receiving an expected header packet during link initialization.
These error situations are largely not due to link errors. A port’s behavior under these situations is
undefined and implementation specific. It is recommended that a port ignore those unexpected link
commands or header packets.
Table 7-11. Error Types and Recovery
Error Type
Description/Example
Error Recovery
Path
Update Link
Error Count?
Missing Header
Packet Framing
Only a valid packet framing ordered set will be declared
in the receiver side.
Delayed transition to
Recovery
Yes
Header Packet
Error
Any header packet CRC is bad.
Header packet retry
process
No
Rx Header
Sequence
Number Error
The Header Sequence Number in the received header
packet does not match the Rx Header Sequence
Number.
Recovery
Yes
ACK Tx Header
Sequence
Number Error
The Header Sequence Number in the received
LGOOD_n (not Header Sequence Number
Advertisement) does not match ACK Tx Header
Sequence Number.
Recovery
Yes
Header Sequence
Number
Advertisement
Error
1.
Recovery
Yes
Recovery
Yes
Timeout from
Recovery to
SS.Inactive requires
software
intervention.
No
Ignored
No
Rx Header Buffer
Credit
Advertisement
Error
Training
Sequence Error
Invalid link
command
7-32
LGOOD_n not received upon PENDING_HP_TIMER
timeout.
2.
A header packet received before sending LGOOD_n.
3.
LCRD_x or LGO_Ux received before receiving
LGOOD_n.
1.
LCRD_x not received upon CREDIT_HP_TIMER
timeout.
2.
A header packet received before sending LCRD_x.
3.
LGO_Ux received before receiving LCRD_x.
1.
Timeout from Polling to Rx.Detect or SS.Disabled
without reaching U0.
2.
Timeout from Recovery to SS.Inactive without
reaching U0.
Valid link command framing but invalid link command
word.
Link Layer
Error Type
Description/Example
Error Recovery
Path
Update Link
Error Count?
Missing link
command
No valid link command framing is detected.
Delayed transition to
Recovery if missing
LGOOD_n or
LCRD_x
Yes
8b/10b Error
Detected in the PHY layer
N.A.
No
7.4
PowerOn Reset and Inband Reset
There are two categories of reset associated with a link. The first, PowerOn Reset, restores storage
elements, registers, or memories to predetermined states when power is applied. Upon PowerOn
Reset, the LTSSM (described in Section 7.5) shall enter Rx.Detect. The second, Inband Reset, uses
SuperSpeed or LFPS signaling to propagate the reset across the link. There are two mechanisms to
complete an Inband Reset, Hot Reset and Warm Reset. Upon completion of either a PowerOn
Reset or an Inband Reset, the link shall transition to U0 as described in Section 7.4.2.
7.4.1
PowerOn Reset
PowerOn Reset restores a storage element, register, or memory to a predetermined state when
power is applied (refer to Section 9.1.1.2 for clarification of when power is applied for self powered
devices). A port must be responsible for its own internal Reset signaling and timing.
The following shall occur when PowerOn Reset is asserted or while VBUS is off:
1. Receiver termination shall meet the ZRX-HIGH-IMP-DC-POS specification defined in Table 6-13.
2. Transmitters shall hold a constant DC common mode voltage (VTX-DC-CM) defined in
Table 6-11.
The following shall occur when PowerOn Reset is completed and VBUS is valid:
1. The LTSSM of a port shall be initialized to Rx.Detect.
2. The LTSSM and the PHY level variables (such as Rx equalization settings) shall be reset to
their default values.
3. The receiver termination of a port shall meet the RRX-DC specification defined in Table 6-13.
Note: Rx termination shall always be maintained throughout operation except for SS.Disabled
7.4.2
Inband Reset
An Inband Reset shall be generated by a downstream port only when it is directed.
There are two mechanisms to generate an Inband Reset. The first mechanism; Hot Reset, is defined
by sending TS2 ordered sets with the Reset bit asserted. A Hot Reset shall cause the LTSSM to
transition to the Hot Reset state. Upon completion of Hot Reset, the following shall occur:
• A downstream port shall reset its Link Error Count.
• The port configuration information of an upstream port shall remain unchanged. Refer to
Sections 8.4.5 and 8.4.6 for details.
• The PHY level variables (such as Rx equalization settings) shall remain unchanged.
• The LTSSM of a port shall transition to U0.
7-33
Universal Serial Bus 3.0 Specification, Revision 1.0
The second mechanism of an Inband Reset is Warm Reset. The signaling of a Warm Reset is
defined as an LFPS signaling meeting the tReset requirements (see Table 6-20). A Warm Reset
will cause the LTSSM to transition to Rx.Detect, retrain the link including the receiver equalizer,
reset an upstream port, and then transition to U0. An upstream port shall enable its LFPS receiver
and Warm Reset detector in all link states except SS.Disabled. A completion of a Warm Reset
shall result in the following.
• A downstream port shall reset its Link Error Count.
• Port configuration information of an upstream port shall be reset to default values. Refer to
Sections 8.4.5 and 8.4.6 for details.
• The PHY level variables (such as Rx equalization settings) shall be reinitialized or retrained.
• The LTSSM of a port shall transition to U0.
A downstream port may be directed to reset the link in two ways, “PORT_RESET”, or
“BH_PORT_RESET” as described in Section 10.3.1.6. When a “PORT_RESET” is directed, a
downstream port shall issue either a Hot Reset, or a Warm Reset, depending on its LTSSM state.
When a “BH_PORT_RESET” is directed, a downstream port shall issue a Warm Reset in any of its
LTSSM states except SS.Disabled.
If a “PORT_RESET” is directed, a downstream port shall issue either a Hot Reset or a Warm Reset
based on the following conditions:
• If the downstream port is U3, or Loopback, or Compliance Mode, or SS.Inactive, it shall use
Warm Reset.
• If the downstream port is in U0, it shall use Hot Reset.
• If the downstream port is in U1 or U2, it shall exit U1 or U2 using the LFPS exit handshake,
transition to Recovery and then transition to Hot Reset.
• If a downstream port is in a transitory state of Polling or Recovery, it shall use Hot Reset.
• If a Hot Reset fails due to a LFPS handshake timeout, a downstream port shall transition to
SS.Inactive until software intervention or upon detection of removal of an upstream port.
• If a Hot Reset fails due to a TS1/TS2 handshake timeout, a downstream port shall transition to
Rx.Detect and attempt a Warm Reset.
• If the downstream port is in SS.Disabled, an Inband Reset is prohibited.
If a “BH_PORT_RESET” is directed, Warm Reset shall be issued, and the following shall occur:
• A downstream port shall initiate a Warm Reset in all the link states except SS.Disabled and
transition to Rx.Detect.
• An upstream port shall enable its LFPS receiver and Warm Reset detector in all the link states
except SS.Disabled.
• An upstream port receiving Warm Reset shall transition to Rx.Detect. Refer to Section 6.9.3 for
Warm Reset Detection.
7-34
Link Layer
7.5
Link Training and Status State Machine (LTSSM)
Link Training and Status State Machine (LTSSM) is a state machine defined for link connectivity
and the link power management. LTSSM consists of 12 different link states that can be
characterized based on their functionalities. First, there are four operational link states, U0, U1,
U2, and U3. U0 is a state where a SuperSpeed link is enabled. Packet transfers are in progress or
the link is idle. U1 is low power link state where no packet transfer is carried out and the
SuperSpeed link connectivity can be disabled to allow opportunities for saving the link power. U2
is also a low power link state. Compared with U1, U2 allows for further power saving
opportunities with a penalty of increased exit latency. U3 is a link suspend state where aggressive
power saving opportunities are possible.
Second, there are four link states, Rx.Detect, Polling, Recovery, and Hot Reset, that are introduced
for link initialization and training. Rx.Detect represents the initial power-on link state where a port
is attempting to determine if its SuperSpeed link partner is present. Upon detecting the presence of
a SuperSpeed link partner, the link training process will be started. Polling is a link state that is
defined for the two link partners to have their SuperSpeed transmitters and receivers trained,
synchronized, and ready for packet transfer. Recovery is a link state defined for retraining the link
when the two link partners exit from a low power link state, or when a link partner has detected that
the link is not operating in U0 properly and the link needs to be retrained, or when a link partner
decides to change the mode of link operation. Hot Reset is a state defined to allow a downstream
port to reset its upstream port.
Third, two other link states, Loopback and Compliance Mode, are introduced for bit error test and
transmitter compliance test. Finally, two more link states are defined. SS.Inactive is a link error
state where a link is in a non-operable state and software intervention is needed. SS.Disabled is a
link state where SuperSpeed connectivity is disabled and the link may operate under USB 2.0
mode.
Configuration information and requests to initiate LTSSM state transitions are mainly controlled by
software. All LTSSM references to “directed” refers to upper layer mechanisms.
There are also various timers defined and implemented for LTSSM in order to ensure the successful
operation of LTSSM. The timeout values are summarized in Table 7-12. All timers used in the
link layer have a tolerance of 0~+50% accuracy with exception of the U2 inactivity timer (refer to
Section 10.4.1 for U2 inactivity timer accuracy). All timeout values must be set to the specified
values after PowerOn Reset or Inband Reset. All counters must be also initialized after PowerOn
Reset or Inband Reset.
In the state machine descriptions, lists of state entry and exit conditions are not prioritized.
State machine diagrams are overviews and may not include all the transition conditions.
7-35
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 7-12. LTSSM State Transition Timeouts
Initial State
Timeout to the Next State
Timeout Value
Rx.Detect.Quiet
Rx.Detect.Active
12 ms
Compliance/Rx.Detect/SS.Disabled
360 ms
Rx.Detect/SS.Disabled
12 ms
Rx.Detect/SS.Disabled
12 ms
Rx.Detect/SS.Disabled
2 ms
U0
Rx.Detect
1 ms
U1
SS.Inactive
2 ms
U2
U2 Inactivity field set in LMP
(refer to Section 8.4 for details)
U1
Rx.Detect
300 ms
U2
SS.Inactive
2 ms
U3
U3
10 ms
Hot Reset.Active
SS.Inactive
12 ms
Hot Reset.Exit
SS.Inactive
2 ms
Loopback.Exit
SS.Inactive
2 ms
Recovery.Idle
SS.Inactive
2 ms
Recovery.Active
SS.Inactive
12 ms
Recovery.Configuration
SS.Inactive
6 ms
Polling.LFPS
1
Polling.Active
1
Polling.Configuration
Polling.Idle
U1
1
1
2
Notes:
1: Upon Polling timeout, a port shall transition to different states. Refer to Section 7.5.4.3 for details.
2: The accuracy of U2 inactivity timer is specified in Section 10.4.1.
All state machines diagrams have descriptions for transition conditions. These descriptions are
informative only. The exact implementation of the state transitions shall follow the description in
each section.
7-36
Link Layer
Directed From
Any Other States
SS.Inactive
Directed, PowerOn Reset,
USB2 Bus Reset
Warm Reset,
Far-end RRX-DC
Absent
SS.Disabled
Rx Detect
Overlimit
(US Port ONLY)
Warm Reset,
Power On Reset
Rx.Detect
Rx Termination
Detected
LFPS
Timeout
LFPS
Timeout
LFPS
Timeout
First LFPS
Timeout
Timeout
Timeout,
Directed
Warm Reset,
Removal
(DS Port ONLY)
Link Nonrecoverable
Compliance
Mode
Timeout
LFPS
Handshake
Directed
Polling
U3
Directed
Loopback
Timeout
Timeout
Training
LGO_U3
LGO_U2
U2
Idle Symbol
Handshake
Hot Reset
Timeout
U0
Directed
LGO_U1
Timeout
Training
Error, Directed
Directed
U1
LFPS Handshake
LFPS Handshake
Recovery
LFPS Handshake
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-047
Figure 7-13. State Diagram of the Link Training and Status State Machine
7-37
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.1
SS.Disabled
SS.Disabled is a state with a port’s low-impedance receiver termination removed. It is a state where
a port’s SuperSpeed connectivity is disabled. Refer to Section 10.16 for details regarding the
behavior of a peripheral device. Refer to Sections 10.3 to 10.6 for behaviors regarding a hub’s
upstream port and downstream port.
SS.Disabled is also a logical power-off state for a self-powered upstream port.
A downstream port shall transition to this state from any other state when directed.
An upstream port shall transition to this state when VBUS is not valid.
SS.Disabled does not contain any substates.
7.5.1.1
•
•
•
7.5.1.2
•
•
7.5.2
SS.Disabled Requirements
VBUS may be present during SS.Disabled.
The port’s receiver termination shall present high impedance to ground of ZRX-HIGH-IMP-DC-POS
defined in Table 6-13.
The port shall be disabled from transmitting and receiving LFPS and SuperSpeed signals.
Exit from SS.Disabled
A downstream port shall transition to Rx.Detect when directed.
An upstream port shall transition to Rx.Detect only when VBUS transitions to valid or a
USB 2.0 bus reset is detected.
SS.Inactive
SS.Inactive is a state where a link has failed SuperSpeed operation. A downstream port can only
exit from this state when directed, or upon detection of an absence of a far-end receiver termination
(RRX-DC) specified in Table 6-13, or upon a Warm Reset. An upstream port can only exit to
Rx.Detect upon a Warm Reset, or upon detecting an absence of a far-end receiver termination
(RRX-DC) specified in Table 6-13.
During SS.Inactive, a port periodically performs a far-end receiver termination detection. If a
disconnection is detected, a port will return to Rx.Detect. If a disconnect is not detected, the link
will stay in SS.Inactive until software intervention.
7.5.2.1
SS.Inactive Substate Machines
SS.Inactive contains the following substate machines shown in Figure 7-14:
• SS.Inactive.Disconnect.Detect
• SS.Inactive.Quiet
7.5.2.2
•
•
•
7-38
SS.Inactive Requirements
VBUS shall be present.
The receiver termination shall meet the requirement (RRX-DC) specified in Table 6-13.
The transmitter common mode is not required to be within specification during this state.
Link Layer
7.5.2.3
SS.Inactive.Quiet
SS.Inactive.Quiet is a substate defined in which a port has disabled its far-end receiver termination
detection so that extra power can be saved while waiting for software intervention.
7.5.2.3.1
SS.Inactive.Quiet Requirements
• The function of the far-end receiver termination detection shall be disabled.
• A 12-ms timer shall be started upon entry to the substate.
7.5.2.3.2
Exit from SS.Inactive.Quiet
• The port shall transition to SS.Inactive.Disconnect.Detect upon the 12-ms timer timeout.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when Warm Reset is issued.
• An upstream port shall transition to Rx.Detect upon detection of Warm Reset.
7.5.2.4
SS.Inactive.Disconnect.Detect
SS.Inactive.Disconnect.Detect is a substate in which a port will perform the far-end receiver
termination detection in order to determine if its link partner is disconnected during SS.Inactive, or
if the transition to SS.Inactive is due to a disconnect from its link partner.
7.5.2.4.1
SS.Inactive.Disconnect.Detect Requirements
The transmitter shall perform the far-end receiver termination detection described in Section 6.11.
7.5.2.4.2
Exit from SS.Inactive.Disconnect.Detect
• The port shall transition to Rx.Detect when a far-end low-impedance receiver termination
(RRX-DC) meeting specification defined in Table 6-13 is not detected.
• The port shall transition to SS.Inactive.Quiet when a far-end low-impedance receiver
termination (RRX-DC) meeting specification defined in Table 6-13 is detected.
7-39
Universal Serial Bus 3.0 Specification, Revision 1.0
SS.Inactive
Entry
Far-end
RRX-DC
Present
SS.Inactive.Disconnect.Detect
SS.Inactive.Quiet
Timeout
Far-end
RRX-DC
Absent
Warm Reset
Directed
(DS Port ONLY)
Exit to
Rx.Detect
Exit to
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-048
Figure 7-14. SS.Inactive Substate Machine
7.5.3
Rx.Detect
Rx.Detect is the power on state of the LTSSM for both a downstream port and an upstream port. It
is also the state for a downstream port upon issuing a Warm Reset, and the state for an upstream
port upon detecting a Warm Reset from any other link state except SS.Disabled. The purpose of
Rx.Detect is to detect the impedance of far-end receiver termination to ground. Rx.Detect.Reset is
a default reset state used by the two ports to synchronize the operation after a Warm Reset; this
substate exits immediately if Warm Reset is not present. Rx.Detect.Active is a substate for far-end
receiver termination detection. Rx.Detect.Quiet is a power saving substate in which the function of
a far-end receiver termination detection is disabled. A port will perform the far-end receiver
termination detection periodically during Rx.Detect.
7.5.3.1
Rx.Detect Substate Machines
Rx.Detect contains a substate machine shown in Figure 7-15 with the following substates:
• Rx.Detect.Reset
• Rx.Detect.Active
• Rx.Detect.Quiet
7.5.3.2
•
•
7-40
Rx.Detect Requirements
The transmitter common mode is not required to be within specification during this state.
The low-impedance receiver termination (RRX-DC) defined in Table 6-13 shall be maintained.
Link Layer
7.5.3.3
Rx.Detect.Reset
Rx.Detect.Reset is a substate designed for the two ports to synchronize their operations on Warm
Reset. In this substate, a downstream port shall generate Warm Reset when directed. If an
upstream port enters Rx.Detect upon detection of Warm Reset, it shall remain in this substate until
the completion of Warm Reset.
For a port entering Rx.Detect not due to a Warm Reset, it shall exit immediately.
7.5.3.3.1
Rx.Detect.Reset Requirements
If a port enters Rx.Detect upon a Warm Reset, the following requirements shall be applied. Refer
to Section 6.9.3 for details.
• A downstream port shall transmit Warm Reset for the duration of tReset as defined in
Table 6-21.
Note: This includes the case when Hot Reset attempt fails in Recovery. Refer to Section 7.4.2
for details.
• An upstream port shall remain in this state until it detects the completion of Warm Reset.
7.5.3.3.2
Exit from Rx.Detect.Reset
• The port shall transition directly to Rx.Detect.Active if the entry to Rx.Detect is not due to a
Warm Reset.
•
•
•
7.5.3.4
Note: Warm Reset is not present during power-on.
A downstream port shall transition to Rx.Detect.Active after it transmits Warm Reset for the
duration of tReset as defined in Table 6-21.
A downstream port shall transition to SS.Disabled when directed.
An upstream port shall transition to Rx.Detect.Active when it receives no more LFPS Warm
Reset signaling from the downstream port as defined in Section 6.9.3.
Rx.Detect.Active
Rx.Detect.Active is a substate to detect the presence of a SuperSpeed link partner. A port will
perform a far-end receiver termination detection as defined in Section 6.11.
7.5.3.5
•
•
Rx.Detect.Active Requirements
The transmitter shall initiate a far-end receiver termination detection described in Section 6.11.
The number of far-end receiver termination detection events shall be counted by an upstream
port. The detection of far-end receiver termination is defined in Section 6.11.
Note: This count value is used by a peripheral device to determine when it needs to transition
to SS.Disabled. It is also used by a hub to control its downstream port state machine. Refer to
Section 10.3.1.1 for details.
7.5.3.6
•
•
•
Exit from Rx.Detect.Active
The port shall transition to Polling upon detection of a far-end low-impedance receiver
termination (RRX-DC) defined in Table 6-13.
A downstream port shall transition to Rx.Detect.Quiet when a far-end low-impedance receiver
termination (RRX-DC) defined in Table 6-13 is not detected.
A downstream port shall transition to SS.Disabled when directed.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
7.5.3.7
An upstream port of a hub shall transition to Rx.Detect.Quiet when a far-end low-impedance
receiver termination (RRX-DC) defined in Table 6-13 is not detected.
An upstream port of a peripheral device shall transition to Rx.Detect.Quiet when the following
two conditions are met:
1. A far-end low-impedance receiver termination (RRX-DC) defined in Table 6-13 is not
detected.
2. The number of far-end receiver termination detection events is less than eight.
An upstream port of a peripheral device shall transition to SS.Disabled when the following two
conditions are met:
1. A far-end low-impedance receiver termination (RRX-DC) defined in Table 6-13 is not
detected.
2. The number of far-end receiver termination detection events has reached eight.
Note: This limit on the number of the far-end receiver termination detections is to allow a
SuperSpeed peripheral device on a legacy platform to transition to USB 2.0 after 80 ms.
Rx.Detect.Quiet
Rx.Detect.Quiet is a substate where a port has disabled its far-end receiver termination detection.
7.5.3.7.1
Rx.Detect.Quiet Requirements
• The far-end receiver termination detection shall be disabled.
• A 12-ms timer shall be started upon entry to the substate.
7.5.3.7.2
Exit from Rx.Detect.Quiet
• The port shall transition to Rx.Detect.Active upon the 12-ms timer timeout.
• A downstream port shall transition to SS.Disabled when directed.
Rx.Detect
Entry
Directed
(DS Port ONLY)
Exit to
SS.Disabled
Rx.Detect.Reset
Warm Reset
De-asserted
Exit to
Polling
Rx Detect Events Over Limit
(Peripheral Device ONLY)
Directed (DS Port ONLY)
Directed
(DS Port ONLY)
Far-end
RRX-DC
Not Detected
Far-end
RRX-DC
Detected
Rx.Detect.Active
Rx.Detect.Quiet
Timeout
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-049
Figure 7-15. Rx.Detect Substate Machine
7-42
Link Layer
7.5.4
Polling
Polling is a state for link training. During Polling, a Polling.LFPS handshake shall take place
between the two ports before the SuperSpeed training is started. Bit lock, symbol lock, and Rx
equalization trainings are achieved using TSEQ, TS1, and TS2 training ordered sets.
7.5.4.1
Polling Substate Machines
Polling contains a substate machine shown in Figure 7-16 with the following substates:
• Polling.LFPS
• Polling.RxEQ
• Polling.Active
• Polling.Configuration
• Polling.Idle
7.5.4.2
Polling Requirements
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
7.5.4.3
Polling.LFPS
Polling.LFPS is a substate designed to establish the PHY’s DC operating point, and to synchronize
the operations between the two link partners after exiting from Rx.Detect.
7.5.4.3.1
Polling.LFPS Requirements
• Upon entry, a LFPS receiver shall be enabled to receive the Polling.LFPS signals defined in
Section 6.9.1.
• Upon entry, a port shall establish its LFPS operating condition within 80 µs.
• A 360-ms timer shall be started upon entry to the substate.
• The operating condition of a SuperSpeed PHY shall be established when a port is ready to exit
to Polling.RxEQ.
• A SuperSpeed receiver may optionally be enabled to receive TSEQ ordered sets for receiver
equalizer training.
Note: The port first entering Polling.RxEQ will start transmitting TSEQ ordered sets while the
other port is still in Polling.LFPS. Enabling a SuperSpeed receiver in Polling.LFPS will allow
a port to start the receiver equalizer training while completing the requirement for Polling.LFPS
exit handshake.
7.5.4.3.2
Exit from Polling.LFPS
• The port shall transition to Polling.RxEQ when the following three conditions are met:
1. At least 16 consecutive Polling.LFPS bursts meeting the Polling.LFPS specification
defined in Section 6.9 are sent.
2. Two consecutive Polling.LFPS bursts are received.
3. Four consecutive Polling.LFPS bursts are sent after receiving one Polling.LFPS burst.
• The port shall transition to Compliance Mode upon the 360-ms timer timeout and the following
two conditions are met:
1. The port has never successfully completed Polling.LFPS after PowerOn Reset.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
•
•
•
7.5.4.4
2. The condition to transition to Polling.RxEQ is not met.
Note: If the very first attempt in Polling.LFPS handshake fails after PowerOn Reset, it implies
that a passive test load may be present and compliance test should be initiated. If the very first
attempt in Polling.LFPS handshake succeeds after PowerOn Reset, it implies the presence of
the SuperSpeed ports on each side of the link and no compliance test is intended. Therefore,
any subsequent handshake timeout in Polling.LFPS when the link is retrained is only an
indication of link training failure, not a signal to enter Compliance Mode.
A downstream port shall transition to Rx.Detect upon the 360-ms timer timeout after having
trained once since PowerOn Reset and the conditions to transition to Polling.RxEQ are not met.
An upstream port of a hub shall transition to Rx.Detect upon the 360-ms timeout after having
trained once since PowerOn Reset and the conditions to transition to Polling.RxEQ are not met.
A peripheral device shall transition to SS.Disabled upon the 360-ms timeout after having
trained once since PowerOn Reset and the conditions to transition to Polling.RxEQ are not met.
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
Polling.RxEQ
Polling.RxEQ is a substate for receiver equalization training. A port is required to complete its
receiver equalization training.
7.5.4.4.1
Polling.RxEQ Requirements
• The detection and correction of the lane polarity inversion shall be enabled, as is described in
Section 6.4.2.
• The port shall transmit the TSEQ ordered sets defined in Table 6-2.
• The port shall complete receiver equalizer training upon exit from this substate.
Note: A situation may exist where the port entering Polling.RxEQ earlier is transmitting TSEQ
ordered sets while its link partner is still sending Polling.LFPS to satisfy the exit conditions from
Polling.LFPS to Polling.RxEQ. In this situation, if its link partner is in electrical idle, near-end
cross talk may cause the port to train its Rx equalizer using its own TSEQ ordered sets. To avoid a
receiver from training itself, a port may either ignore the beginning part (about 30 µs) of the TSEQ
ordered sets, or continue the equalizer training until it completes the transmission of TSEQ ordered
sets.
7.5.4.4.2
Exit from Polling.RxEQ
• The port shall transition to Polling.Active after 65,536 consecutive TSEQ ordered sets defined
in Table 6-2 are transmitted.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
7.5.4.5
Polling.Active
Polling.Active is a substate that continues the link’s SuperSpeed training.
7-44
Link Layer
7.5.4.5.1
Polling.Active Requirements
• A 12-ms timer shall be started upon entry to this substate.
• The port shall transmit TS1 ordered sets.
• The receiver is in training using TS1 or TS2 ordered sets.
Note: Depending on the link condition and different receiver implementations, one port’s receiver
may train faster than the other. When this occurs, the port whose receiver trains first will enter
Polling.Configuration and start transmitting TS2 ordered sets while the port whose receiver is not
yet trained is still in Polling.Active using TS2 ordered sets to train its receiver.
7.5.4.5.2
Exit from Polling.Active
• The port shall transition to Polling.Configuration upon receiving eight consecutive and
identical TS1 or TS2 ordered sets.
• A downstream port shall transition to Rx.Detect upon the 12-ms timer timeout and the
conditions to transition to Polling.Configuration are not met.
• An upstream port of a hub shall transition to Rx.Detect upon the 12-ms timer timeout and the
conditions to transition to Polling.Configuration are not met.
• An upstream port of a peripheral device shall transition to SS.Disabled upon the 12-ms timer
timeout and the conditions to transition to Polling.Configuration are not met.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
7.5.4.6
Polling.Configuration
Polling.Configuration is a substate where the two link partners complete the SuperSpeed training.
7.5.4.6.1
Polling.Configuration Requirements
• The port shall transmit identical TS2 ordered sets upon entry to this substate and set the link
configuration field in the TS2 ordered set based on the following.
1. When directed, a downstream port shall set Reset bit in the TS2 ordered set.
Note: An upstream port can only set the Reset bit in the TS2 Ordered set when in Hot
Reset. Active. Refer to Section 7.5.12.3 for details.
2. When directed, the port shall set Loopback bit in the TS2 ordered set.
3. When directed, the port shall set the Disabling Scrambling bit in the TS2 ordered set.
• A 12-ms timer shall be started upon entry to this substate.
7.5.4.6.2
Exit from Polling.Configuration
• The port shall transition to Polling.Idle when the following two conditions are met:
1. Eight consecutive and identical TS2 ordered sets are received.
2. Sixteen TS2 ordered sets are sent after receiving the first of the eight consecutive and
identical TS2 ordered sets.
• A downstream port shall transition to Rx.Detect upon the 12-ms timer timeout and the
conditions to transition to Polling.Idle are not met.
• An upstream port of a hub shall transition to Rx.Detect upon the 12-ms timer timeout and the
conditions to transition to Polling.Idle are not met.
• An upstream port of a peripheral device shall transition to SS.Disabled upon the 12-ms timer
timeout and the conditions to transition to Polling.Idle are not met.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
7.5.4.7
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
Polling.Idle
Polling.Idle is a substate where the port decodes the TS2 ordered set received in
Polling.Configuration and determines the next state.
7.5.4.7.1
Polling.Idle Requirements
• The port shall decode the TS2 ordered set received during Polling.Configuration and proceeds
to the next state.
• A downstream port shall reset its Link Error Count.
• An upstream port shall reset its port configuration information to default values. Refer to
Sections 8.4.5 and 8.4.6 for details.
• The port shall enable the scrambling by default if the Disabling Scrambling bit is not asserted
in the TS2 ordered set received in Polling.configuration.
• The port shall disable the scrambling if directed, or if the Disabling Scrambling bit is asserted
in the TS2 ordered set received in Polling.configuration.
• The port shall transmit Idle Symbols if the next state is U0.
• A 2-ms timer shall be started upon entry to this state.
• The port shall be able to receive the Header Sequence Number Advertisement from its link
partner.
Note: The exit time difference between the two ports will result in one port entering U0 first
and starting the Header Sequence Number Advertisement while the other port is still in
Polling.Idle.
7.5.4.7.2
Exit from Polling.Idle
• The port shall transition to Loopback when directed as a loopback master and the port is
capable of being a loopback master.
• The port shall transition to Loopback as a loopback slave if the Loopback bit is asserted in the
TS2 ordered set received in Polling.Configuration.
• A downstream port shall transition to Hot Reset when directed.
• An upstream port shall transition to Hot Reset when the Reset bit is asserted in the TS2 ordered
set received in Polling.Configuration.
• The port shall transition to U0 when the following two conditions are met:
1. Eight consecutive Idle Symbols are received.
2. Sixteen Idle Symbols are sent after receiving one Idle Symbol.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect upon the 2-ms timer timeout and the conditions
to transition to U0 are not met.
• An upstream port of a hub shall transition to Rx.Detect upon the 2-ms timer timeout and the
conditions to transition to U0 are not met.
• An upstream port of a peripheral device shall transition to SS.Disabled upon the 2-ms timer
timeout and the conditions to transition to U0 are not met.
7-46
Link Layer
•
•
A downstream port shall transition to Rx.Detect when Warm Reset is directed.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
Polling
First LFPS
Timeout
Polling.LFPS
LFPS
Handshake
Subsequent LFPS Timeouts,
(DS Port ONLY or Hub US PORT)
Exit to
Compliance Mode
Subsequent LFPS Timeouts,
(Peripheral Device ONLY)
Directed (DS Port ONLY)
Polling.RxEQ
TSEQ Ordered
Sets Transmitted
Directed
(DS Port ONLY)
Polling.Active
Warm Reset
Timeout (DS Port ONLY
or Hub US Port)
Exit to
Rx.Detect
8 Consecutive TS1
or TS2 Received
Timeout (DS Port ONLY
or Hub US Port)
Polling.Configuration
TS2
Handshake
Timeout (DS Port ONLY
or Hub US Port)
Exit to
Hot Reset
Timeout (Peripheral Device ONLY)
Directed (DS Port ONLY)
Directed
Timeout (Peripheral Device
ONLY) Directed
(DS Port ONLY)
Exit to
SS.Disabled
Timeout (Peripheral Device ONLY)
Directed (DS Port ONLY)
Polling.Idle
Directed
Exit to
Loopback
Idle Symbol
Handshake
Exit to U0
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-050
Figure 7-16. Polling Substate Machine
7.5.5
Compliance Mode
Compliance Mode is used to test the transmitter for compliance to voltage and timing
specifications. Several different test patterns are transmitted as defined in Table 6-7. Compliance
Mode does not contain any substate machines.
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Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.5.1
•
•
•
•
•
7.5.5.2
•
•
•
7.5.6
Compliance Mode Requirements
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
The LFPS receiver is used to control the test pattern sequencing.
Upon entry to Compliance Mode, the port shall wait until its SuperSpeed Tx DC common
mode voltage meets the VTX-DC-CM specification defined in Table 6-11 before it starts to send the
first compliance test pattern defined in Table 6-7.
The port shall transmit the next compliance test pattern continuously upon detection of a
Ping.LFPS as defined in Section 6.9.1.
The port shall transmit the first compliance test pattern continuously upon detection of a
Ping.LFPS and the test pattern has reached the final test pattern.
Exit from Compliance Mode
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect upon detection of Warm Reset.
A downstream port shall transition to SS.Disabled when directed.
U0
U0 is the normal operational state where packets can be transmitted and received. U0 does not
contain any substate machines.
7.5.6.1
•
•
•
•
•
•
7.5.6.2
•
•
•
•
•
•
•
7-48
U0 Requirements
The port shall meet the transmitter specifications defined in Table 6-10.
The port shall maintain the low-impedance receiver termination (RRX-DC) defined in Table 6-13.
The LFPS receiver shall be enabled.
A downstream port shall enable a 1-ms timer to measure the time interval between two
consecutive link commands. This timer will be reset and restarted every time a link command
is received.
An upstream port shall enable a 10-µs timer. This timer shall be reset when the first symbol of
any link command or packet is sent and restarted after the last symbol of any link command or
packet is sent. This timer shall be active when the link is in logical idle.
An upstream port shall transmit a single LUP when the 10-µs timer expires.
Exit from U0
The port shall transition to U1 upon successful completion of LGO_U1 entry sequence. Refer
to Section 7.2.4.2 for details.
The port shall transition to U2 upon successful completion of LGO_U2 entry sequence. Refer
to Section 7.2.4.2 for details.
The port shall transition to U3 upon successful completion of LGO_U3 entry sequence. Refer
to Section 7.2.4.2 for details.
A downstream port shall transition to SS.Inactive when it fails U3 entry on three consecutive
attempts.
The port shall transition to Recovery upon any errors stated in Section 7.3 that will cause a link
to transition to Recovery.
The port shall transition to Recovery upon detection of a TS1 ordered set.
The port shall transition to Recovery when directed.
Link Layer
•
•
•
•
•
•
•
•
The port shall transition to SS.Inactive when PENDING_HP_TIMER times out for the fourth
consecutive time.
Note: This implies the link has transitioned to Recovery for three consecutive times and each
time the transition to Recovery is due to PENDING_HP_TIMER timeout.
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to SS.Inactive when directed.
An upstream port shall transition to SS.Disabled when directed.
Note: After entry to U0, both ports are required to exchange port capabilities information using
LMP within tPortConfiguration time as defined in Section 8.4.5. If the port has not received
LMP within tPortConfiguration time, a downstream port shall be directed to transition to
SS.Inactive and an upstream port shall be directed to transition to SS.Disabled.
A downstream port shall transition to Recovery upon not receiving any link commands
within 1 ms.
Note: Not receiving any link commands including LUP within 1 ms implies either a link is
under serious error condition, or an upstream port has been removed. To accommodate for
both situations, a downstream port will transition to Recovery and attempt to retrain the link. If
the retraining fails, it will then transition to SS.Inactive. During SS.Inactive, a downstream port
will attempt a far-end receiver termination detection. If it determines that a far-end lowimpedance receiver termination (RRX-DC) defined in Table 6-13 is not present, it will enter
Rx.Detect. Otherwise, it will wait for software intervention.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
An upstream port shall transition to SS.Disabled upon detection of VBUS off.
Note: this condition only applies to a self-powered upstream port. SS.Disabled is a logical
power-off state for a self-powered upstream port.
7.5.7
U1
U1 is a low power state where no packets are to be transmitted and both ports agree to enter a link
state where a SuperSpeed PHY can be placed into a low power state.
U1 does not contain any substates. Transitions to other states are shown in Figure 7-17.
7.5.7.1
•
•
•
•
•
•
•
•
U1 Requirements
The SuperSpeed transmitter DC common mode voltage shall be within specification (VTX-CM-DCACTIVE-IDLE-DELTA) defined in Table 6-10.
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
The port shall enable its U1 exit detect functionality as defined in Section 6.9.2.
The port shall enable its LFPS transmitter when it initiates the exit from U1.
The port shall enable its U2 inactivity timer upon entry to this state if the U2 inactivity timer
has a non-zero timeout value.
A downstream port shall enable its Ping.LFPS detection.
A downstream port shall enable a 300-ms timer. This timer will be reset and restarted when a
Ping.LFPS is received.
An upstream port shall transmit Ping.LFPS as defined in Table 6-20.
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Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.7.2
•
•
•
•
•
•
•
•
Exit from U1
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to Rx.Detect when the 300-ms timer expires.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
A self-powered upstream port shall transition to SS.Disabled upon not detecting valid Vbus as
defined in Section 11.4.5.
The port shall transition to U2 upon the timeout of the U2 inactivity timer defined in
Sections 10.4.2.4 and 10.6.2.4.
The port shall transition to Recovery upon successful completion of a LFPS handshake meeting
the U1 LFPS exit handshake signaling in Section 6.9.2.
The port shall transition to SS.Inactive upon the 2-ms LFPS handshake timer timeout and a
successful LFPS handshake meeting the U1 LFPS exit handshake signaling in Section 6.9.2 is
not achieved.
Entry
U2
U2 Inactivity
Timer Timeout
LFPS Handshake
Timeout
SS.Inactive
U1
Warm Reset, Removal
(DS Port ONLY)
Rx.Detect
LFPS
Handshake
Successful
Recovery
VBUS Removal
(US Port ONLY),
Directed (DS Port ONLY)
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-051
Figure 7-17. U1
7.5.8
U2
U2 is a link state where more power saving opportunities are allowed compare to U1, but with an
increased exit latency.
U2 does not contain any substates. The transitions to other states are shown in Figure 7-18.
7.5.8.1
•
•
•
•
7-50
U2 Requirements
The SuperSpeed transmitter DC common mode voltage does not need to be within specification
(VTX-CM-DC-ACTIVE-IDLE-DELTA ) defined in Table 6-10.
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
When a downstream port is in U2, its upstream port may be in U1 or U2. If the upstream port
is in U1, it will send Ping.LFPS periodically. A downstream port shall differentiate between
Ping.LFPS and U1 LFPS exit handshake signaling.
The port shall enable its U2 exit detect functionality as defined in Section 6.9.2.
Link Layer
•
•
7.5.8.2
•
•
•
•
•
•
•
The port shall enable its LFPS transmitter when it initiates the exit from U2.
A downstream port shall perform a far-end receiver termination detection every 100 ms.
Exit from U2
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to Rx.Detect upon detection of a far-end high-impedance
receiver termination (ZRX-HIGH-IMP-DC-POS) defined in Table 6-13.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
A self-powered upstream port shall transition to SS.Disabled upon not detecting valid Vbus as
defined in Section 11.4.5.
The port shall transition to Recovery upon successful completion of a LFPS handshake meeting
the U2 LFPS exit signaling defined in Section 6.9.2.
The port shall transition to SS.Inactive upon the 2-ms LFPS handshake timer timeout and a
successful LFPS handshake meeting the U2 LFPS exit handshake signaling in Section 6.9.2 is
not achieved.
Entry
U2
LFPS Handshake
Timeout
SS.Inactive
Warm Reset, Removal
(DS Port ONLY)
Rx.Detect
LFPS
Handshake
Successful
Recovery
VBUS Removal
(US Port ONLY),
Directed (DS Port ONLY)
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-052
Figure 7-18. U2
7.5.9
U3
U3 is a link state where a device is put into a suspend state. Significant link and device powers are
saved.
U3 does not contain any substates. Transitions to other states are shown in Figure 7-19.
7.5.9.1
•
•
•
•
U3 Requirements
The SuperSpeed transmitter DC common mode voltage does not need to be within specification
(VTX-CM-DC-ACTIVE-IDLE-DELTA ) defined in Table 6-10.
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
LFPS Ping detection shall be disabled.
The port shall enable its U3 wakeup detect functionality as defined in Section 6.9.2.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
7.5.9.2
•
•
•
•
•
•
•
The port shall enable its LFPS transmitter when it initiates the exit from U3.
A downstream port shall perform a far-end receiver termination detection every 100 ms.
The port not able to respond to U3 LFPS wakeup within tNoLFPSResponseTimeout may
initiate U3 LFPS wakeup when it is ready to return to U0.
Exit from U3
A downstream port shall transition to SS.Disabled when directed.
A downstream port shall transition to Rx.Detect upon detection of a far-end high-impedance
receiver termination (ZRX-HIGH-IMP-DC-POS) defined in Table 6-13.
A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
An upstream port shall transition to Rx.Detect when Warm Reset is detected.
A self-powered upstream port shall transition to SS.Disabled upon not detecting valid VBUS as
defined in Section 11.4.5.
The port shall transition to Recovery upon successful completion of a LFPS handshake meeting
the U3 wakeup signaling defined in Section 6.9.2.
The port shall remain in U3 when the 10-ms LFPS handshake timer times out and a successful
LFPS handshake meeting the U3 wakeup handshake signaling in Section 6.9.2 is not achieved.
The port may initiate U3 wakeup again after a minimum of 100-ms delay.
Entry
LFPS Handshake
Timeout
U3
Warm Reset, Removal
(DS Port ONLY)
LFPS
Handshake
Successful
Recovery
VBUS Removal
(US Port ONLY),
Directed (DS Port ONLY)
Rx.Detect
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-053
Figure 7-19. U3
7.5.10
Recovery
The Recovery link state is entered to retrain the link, or to perform Hot Reset, or to switch to
Loopback mode. In order to retrain the link and also minimize the recovery latency, the two link
partners do not train the receiver equalizers. Instead, the last trained equalizer configurations are
maintained. Only TS1 and TS2 ordered sets are transmitted to synchronize the link and to
exchange the link configuration information defined in Table 6-5.
7-52
Link Layer
7.5.10.1
Recovery Substate Machines
Recovery contains a substate machine shown in Figure 7-20 with the following substates:
• Recovery.Active
• Recovery.Configuration
• Recovery.Idle
7.5.10.2
•
•
•
7.5.10.3
Recovery Requirements
The port shall meet the transmitter specifications as defined in Table 6-10.
The port shall maintain the low-impedance receiver termination (RRX-DC) as defined in
Table 6-13.
All header packets in the Tx Header Buffers and the Rx Header Buffers shall be handled based
on the requirements specified in Section 7.2.4.
Recovery.Active
Recovery.Active is a substate to train the SuperSpeed link by transmitting the TS1 ordered sets.
7.5.10.3.1
Recovery.Active Requirements
• A 12-ms timer shall be started upon entry to this substate.
• The port shall transmit the TS1 ordered sets upon entry to this substate.
• The port shall train its receiver with TS1 or TS2 ordered sets.
Note: Depending on the link condition and different receiver implementations, one port’s receiver
may train faster than the other. When this occurs, the port whose receiver trains first will enter
Recovery.Configuration and start transmitting TS2 ordered sets while the port whose receiver is not
yet trained is still in Recovery.Active using the TS2 ordered sets to train its receiver.
7.5.10.3.2
Exit from Recovery.Active
• The port shall transition to Recovery.Configuration after eight consecutive and identical TS1 or
TS2 Ordered sets are received.
• The port shall transition to SS.Inactive when the following conditions are met:
1. Either the Ux_EXIT_TIMER or the 12-ms timer times out.
2. For a downstream port, the transition to Recovery is not to attempt a Hot Reset.
• A downstream port shall transition to Rx.Detect when the following conditions are met:
1. Either the Ux_EXIT_TIMER or the 12-ms timer times out.
2. The transition to Recovery is to attempt a Hot Reset.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
7.5.10.4
Recovery.Configuration
Recovery.Configuration is a substate designed to allow the two link partners to achieve the
SuperSpeed handshake by exchanging the TS2 ordered sets.
7-53
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.10.4.1
Recovery.Configuration Requirements
• The port shall transmit identical TS2 ordered sets upon entry to this substate and set the link
configuration field in the TS2 ordered set based on the following:
1. When directed, a downstream port shall set Reset bit in the TS2 ordered set.
Note: An upstream port can only set the Reset bit in the TS2 Ordered set when in Hot
Reset. Active. Refer to Section 7.5.12.3 for details.
2. When directed, the port shall set Loopback bit in the TS2 ordered set.
3. When directed, the port shall set the Disabling Scrambling bit in the TS2 ordered set.
• A 6-ms timer shall be started upon entry to this substate.
7.5.10.4.2
Exit from Recovery.Configuration
• The port shall transition to Recovery.Idle after the following two conditions are met:
1. Eight consecutive and identical TS2 ordered sets are received.
2. Sixteen TS2 ordered sets are sent after receiving the first of the eight consecutive and
identical TS2 ordered sets.
• The port shall transition to SS.Inactive when the following conditions are met:
1. Either the Ux_EXIT_TIMER or the 6-ms timer times out.
2. The conditions to transition to Recovery.Idle are not met.
3. For a downstream port, the transition to Recovery is not to attempt a Hot Reset.
• A downstream port shall transition to Rx.Detect when the following conditions are met:
1. Either the Ux_EXIT_TIMER or the 6-ms timer times out.
2. The transition to Recovery is to attempt a Hot Reset.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
7.5.10.5
Recovery.Idle
Recovery.Idle is a substate where a port decodes the link configuration field defined in the TS2
ordered set received during Recovery.Configuration and determines the next state.
7.5.10.5.1
Recovery.Idle Requirements
• A 2-ms timer shall be started upon entry to this substate.
• The port shall transmit Idle Symbols if the next state is U0.
• The port shall decode the link configuration field defined in the TS2 ordered sets received
during Recovery.Configuration and proceed to the next state.
• The port shall enable the scrambling by default if the Disabling Scrambling bit is not asserted
in the TS2 ordered set received in Recovery.configuration.
• The port shall disable the scrambling if directed, or if the Disabling Scrambling bit is asserted
in the TS2 ordered set received in Recovery.configuration.
• The port shall be able to receive the Header Sequence Number Advertisement from its link
partner.
Note: The exit time difference between the two ports will result in one port entering U0 first
and starting the Header Sequence Number Advertisement while the other port is still in
Recovery.Idle.
7-54
Link Layer
7.5.10.5.2
Exit from Recovery.Idle
• The port shall transition to Loopback when directed as a loopback master and the port is
capable of being a loopback master.
• The port shall transition to Loopback as a loopback slave if the Loopback bit is asserted in TS2
ordered sets.
• The port shall transition to U0 when the following two conditions are met:
1. Eight consecutive Idle Symbols are received.
2. Sixteen Idle Symbols are sent after receiving one Idle Symbol.
• The port shall transition to SS.Inactive when one of the following timers times out and the
conditions to transition to U0 are not met:
1. Ux_EXIT_TIMER
2. The 2-ms timer
• A downstream port shall transition to Hot Reset when directed.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
• An upstream port shall transition to Hot Reset if the Reset bit is asserted in TS2 ordered sets.
Recovery
Entry
Recovery.Active
8 Consecutive
TS1 or TS2
Received
Timeout
Exit to
SS.Inactive
Timeout
Recovery.Configuration
Timeout
Successful TS2
Handshake
Warm
Reset
Directed
(DS Port ONLY)
Warm
Reset
Exit to
SS.Disabled
Directed
(DS Port ONLY)
Recovery.Idle
Warm
Reset
Exit to
Rx.Detect
Directed
(DS Port ONLY)
Idle Symbol
Handshake
Directed
Exit to
Loopback
Directed
Exit to U0
Exit to
Hot Reset
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-054
Figure 7-20. Recovery Substate Machine
7-55
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.11
Loopback
Loopback is intended for test and fault isolation. Loopback includes a bit error rate test (BERT)
state machine, described in Chapter 6.
A loopback master is the port requesting loopback. A loopback slave is the port that retransmits the
symbols received from the loopback master.
During Loopback.Active, the loopback slave must support the BERT protocol described in
Chapter 6. The loopback slave must respond to the command for BERT error counter reset and
BERT report error count. The loopback slave must check the incoming data for the loopback data
pattern.
7.5.11.1
Loopback Substate Machines
Loopback contains a substate machine shown in Figure 7-21 with the following substates:
• Loopback.Active
• Loopback.Exit
7.5.11.2
•
•
•
7.5.11.3
Loopback Requirements
There shall be one loopback master and one loopback slave. The loopback master is the port
that has the Loopback bit asserted in TS2 ordered sets.
The port shall maintain its transmitter specifications defined in Table 6-10.
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
Loopback.Active
Loopback.Active is a substate where the loopback test is active. The loopback master is sending
data/commands to its loopback slave. The loopback slave is either looping back the data or
detecting/executing the commands it received from the loopback master.
7.5.11.3.1
Loopback.Active Requirements
• The loopback master shall send valid 8b/10b data with SKPs as necessary.
• The loopback slave shall retransmit the received 10-bit symbols.
• The loopback slave shall not modify the received 10-bit symbols, other than lane polarity
inversion if necessary, and SKP ordered set, which may be added or dropped as required.
•
•
Note: This implies that the loopback slave should disable or bypass its own 8b/10b
encoder/decoder and scrambler/descrambler.
The loopback slave must process the BERT commands as defined in Section 6.8.4.
The LFPS receiver shall be enabled.
7.5.11.3.2
Exit from Loopback.Active
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
• When directed, the loopback master shall transition to Loopback.Exit.
• The loopback slave shall transition to Loopback.Exit upon detection of Loopback LFPS exit
handshake signal meeting Loopback LFPS exit signaling defined in Section 6.9.2.
7-56
Link Layer
7.5.11.4
Loopback.Exit
Loopback.Exit is a substate where a loopback master has completed the loopback test and starts the
exit from Loopback.
7.5.11.4.1
Loopback.Exit Requirements
• A 2-ms timer shall be started upon entry to the substate.
• The LFPS transmitter and the LFPS receiver shall be enabled.
• The port shall transmit and receive Loopback LFPS exit handshake signal defined in
Section 6.9.2.
7.5.11.4.2
Exit from Loopback.Exit
• The port shall transition to Rx.Detect upon a successful Loopback LFPS exit handshake
defined in Section 6.9.2.
• The port shall transition to SS.Inactive upon the 2-ms timer timeout and the condition to
transition to Rx.Detect is not met.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
Loopback
Entry
Loopback.Active
Directed,
LFPS
Directed
(DS Port ONLY)
Warm
Reset
Loopback.Exit
Successful
LFPS Handshake,
Warm Reset
Exit to
Rx.Detect
Timeout
Directed
(DS Port ONLY)
Exit to
SS.Inactive
Exit to
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-055
Figure 7-21. Loopback Substate Machine
7-57
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.12
Hot Reset
Only a downstream port can be directed to initiate a Hot Reset.
When the downstream port initiates reset, it shall transmit TS2 ordered sets with the Reset bit
asserted. The upstream port shall respond by sending the TS2 ordered sets with Reset bit asserted.
Upon completion of Hot Reset processing, the upstream port shall signal the downstream port by
sending the TS2 ordered sets with the Reset bit de-asserted. The downstream port shall respond
with the Reset bit de-asserted in the TS2 ordered sets. Once both ports receive the TS2 ordered sets
with the Reset bit de-asserted, they shall exit from Hot Reset.Active and transition to Hot
Reset.Exit. Once a successful idle symbol handshake is achieved, the port shall return to U0.
7.5.12.1
Hot Reset Substate Machines
Hot Reset contains a substate machine shown in Figure 7-22 with the following substates:
• Hot Reset Active
• Hot Reset.Exit
7.5.12.2
•
•
•
•
•
7.5.12.3
Hot Reset Requirements
A downstream port shall reset its Link Error Count as defined in Section 7.4.2.
A downstream port shall reset its PM timers and the associated U1 and U2 timeout values to
zero.
The port Configuration information shall remain unchanged (refer to Section 8.4.6 for details).
The port shall maintain its transmitter specifications defined in Table 6-10.
The port shall maintain its low-impedance receiver termination (RRX-DC) defined in Table 6-13.
Hot Reset.Active
Hot Reset.Active is a substate where a port will perform the reset as defined in Section 7.4.12.2.
7.5.12.3.1
Hot Reset.Active Requirements
• Upon entry to this substate, the port shall first transmit at least 16 TS2 ordered sets
continuously with the Reset bit asserted.
•
•
•
•
•
7-58
Note: Depending on the time delay between the two ports entering Hot Reset, when the
downstream port is transmitting the first 16 TS2 ordered sets with the Reset bit asserted, it may
still receive part of the TS2 ordered sets from the upstream port exiting from
Polling.Configuration or Recovery.Configuration. The downstream port shall ignore those TS2
ordered sets.
A 12-ms timer shall be started upon entry to this substate.
A downstream port shall continue to transmit TS2 ordered sets with the Reset bit asserted until
the upstream port transitions from sending TS2 ordered sets with the Reset bit asserted to
sending the TS2 ordered sets with the Reset bit de-asserted.
An upstream port shall transmit TS2 ordered sets with the Reset bit asserted while performing
the Hot Reset.
An upstream port shall transmit TS2 ordered sets with the Reset bit de-asserted after
completing the Hot Reset.
The port shall perform Hot Reset described in Hot Reset requirement of this section.
Link Layer
7.5.12.3.2
Exit from Hot Reset.Active
• The port shall transition to Hot Reset.Exit when the following three conditions are met.
1. At least 16 TS2 ordered sets with the Reset bit asserted are transmitted.
2. Two consecutive TS2 ordered sets are received with the Reset bit de-asserted.
3. Four consecutive TS2 ordered sets with the Reset bit de-asserted are sent after receiving
one TS2 ordered set with the Reset bit de-asserted.
• The port shall transition to SS.Inactive upon the 12-ms timer timeout and the conditions to
transition to Hot Reset.Exit are not met.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
7.5.12.4
Hot Reset.Exit
Hot Reset.Exit is a substate where the port has completed Hot Reset and is ready to exit from Hot
Reset.
7.5.12.4.1
Hot Reset.Exit Requirements
• The port shall transmit idle symbols.
• A 2-ms timer shall be started upon entry to this substate.
• The port shall be able to receive the Header Sequence Number Advertisement from its link
partner.
Note: The exit time difference between the two ports will result in one port entering U0 first and
starting the Header Sequence Number Advertisement while the other port is still in Hot Reset.Idle.
7-59
Universal Serial Bus 3.0 Specification, Revision 1.0
7.5.12.4.2
Exit from Hot Reset.Exit
• The port shall transition to U0 when the following two conditions are met:
1. Eight consecutive Idle Symbols are received.
2. Sixteen Idle Symbols are sent after receiving one Idle Symbol.
• The port shall transition to SS.Inactive upon the 2-ms timer timeout and the conditions to
transition to U0 are not met.
• A downstream port shall transition to SS.Disabled when directed.
• A downstream port shall transition to Rx.Detect when directed to issue Warm Reset.
• An upstream port shall transition to Rx.Detect when Warm Reset is detected.
Hot Reset
Entry
Exit to
Rx.Detect
Warm Reset
Warm Reset
Hot Reset.Active
TS2 Handshake
Directed
(DS Port ONLY)
Hot Reset.Exit
Timeout
Timeout
Exit to
SS.Inactive
Idle Symbol
Handshake
Directed
(DS Port ONLY)
Exit to U0
Exit to
SS.Disabled
Note: Transition conditions are illustrative only. Not all of the transition conditions are listed.
U-056
Figure 7-22. Hot Reset Substate Machine
7-60
8
Protocol Layer
The protocol layer manages the end to end flow of data between a device and its host. This layer is
built on the assumption that the link layer guarantees delivery of certain types of packets and this
layer adds on end to end reliability for the rest of the packets depending on the transfer type.
Host
Hub
Device
Device Driver/Application
Pipe Bundle (per Function Interface)
Function
USB System Software
Default Control Pipe
Device
Notifications
Transactions
Transaction
Packets
Notifications
Data
Packets
Port-to-Port
Chip to Chip
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Link Control/Mgmt
Pkt
Delims
Link Cmds
8b/10b
encode/
decode
Scramble/
descramble
Spread
Clock CDR
Elasticity
Buffer/Skips
LFPS
Localized
Link Power
Management
PHYSICAL
8b/10b
encode/
decode
Data
Packets
LINK
Link Cmds
USB Device
Power
Management
(Suspend)
Link Management Packets
Link Control/Mgmt
Pkt
Delims
Transactions
Transaction
Packets
Link Management Packets
USB Function
Power
Management
Device or Host PROTOCOL
End-to-End
The chapter describes the following in detail:
• Types of packets
• Format of the packets
• Expected responses to packets sent by the host and a device
• The four SuperSpeed transaction types
• Support for Streams for the bulk transfer type
• Timing parameters for the various responses and packets the host or a device may receive or
transmit
U-135
Figure 8-1. Protocol Layer Highlighted
8-1
Universal Serial Bus 3.0 Specification, Revision 1.0
8.1
SuperSpeed Transactions
SuperSpeed transactions are initiated by the host when it either requests or sends data to an
endpoint on a device and are completed when the endpoint sends the data or acknowledges receipt
of the data. A transfer on the SuperSpeed bus is a request for data made by a device application to
the host which then breaks it up into one or more burst transactions. A SuperSpeed host may
initiate one or more OUT bus transactions to one or more endpoints while it waits for the
completion of the current bus transaction. However a SuperSpeed host shall not initiate another IN
bus transaction to any endpoint until the host either:
•
•
Receives a DP or NRDY or STALL TP or the transaction times out for the current ACK TP
sent to a non-isochronous endpoint or
Receives all the DPs that were requested or it receives a short packet or it receives a DP with
last packet flag field set or the transaction times out for the current ACK TP sent to an
isochronous endpoint.
For non-isochronous transfers, an endpoint may respond to valid transactions by:
• Returning an NRDY Transaction Packet
• Accepting it by returning an ACK Transaction Packet in the case of an OUT transaction
• Returning one or more data packets in the case of an IN transaction
• Returning a STALL Transaction Packet if there is an internal endpoint error
An NRDY Transaction Packet (TP) response indicates that an endpoint is not ready to sink or
source data. Consequently, there shall be no further activity between the host and the endpoint on
the device until the endpoint notifies the host that it is ready. This allows the links between the
device and the host to be placed in a reduced power state until an endpoint is ready to receive or
send data. When ready, the endpoint asynchronously sends a notification (ERDY TP) to the host to
tell it that it is now ready to move data and the host responds by rescheduling the request. Note that
isochronous transfers do not use ERDY or NRDY TPs as they are serviced by the host at periodic
intervals. Additionally, data packets sent to or received from an isochronous endpoint are not
acknowledged, i.e., no ACK TPs are sent to acknowledge the receipt of data packets.
Endpoints only respond to requests made by the host. The host is responsible for scheduling
transactions on the bus and maintaining the priority and fairness of the data movement on the bus; it
does this by the timing and ordering of IN and OUT requests. Transactions are not broadcast;
packets traverse a direct path between the host and device. Any unused links may be placed into
reduced power states making the bus amenable to aggressive power management.
8.2
Packet Types
SuperSpeed USB uses four basic packet types each with one or more subtypes. The four packet
types are:
• Link Management Packets (LMP) only travel between a pair of links (e.g., a pair of directly
connected ports) and is primarily used to manage that link.
• Transaction Packets (TP) traverse all the links directly connecting the host to a device. They
are used to control the flow of data packets, configure devices, and hubs, etc. Transaction
Packets have no data payload.
8-2
Protocol Layer
•
•
Data Packets (DP) traverse all the links directly connecting the host to a device. Data Packets
have two parts: a Data Packet Header (DPH) and a Data Packet Payload (DPP).
Isochronous Timestamp Packets (ITP) are multicast on all the active links from the host to
one or more devices.
All packets consist of a 14-byte header, followed by a 2-byte Link Control Word at the end of the
packet (16 bytes total). All headers have two common fields (Revision and Type) that are used by
the receiving entity (e.g., host, hub, or device) to determine how to process the packet. All headers
include a 2-byte CRC (CRC-16). Packet headers have an uncorrectable or undetectable error rate
less than one error in 1020 bits.
All devices (including hubs) and the host consume the LMPs they receive. Hubs have the
additional responsibility to forward DPs, ITPs, and TPs to the downstream port nearer a device or
to the upstream port nearer the host. Note that ITPs are only sent by the host and received by
devices. All packets except LMPs are forwarded by hubs unless the packet is routed to the hub
itself. Additional rules for forwarding ITPs are described in Section 8.7. Note that the Link
Control Word in a TP, ITP, or DPH may be changed by a hub before it is forwarded. The fields in
the Link Control Word are described in Section 8.3.1.2.
If the value of the Type field is Transaction Packet or Data Packet Header, the Route String and
Device Address fields follow the Type field. The Route String field is used by hubs to route
packets which appear on their upstream port to the appropriate downstream port. Packets flowing
from a device to the host are always routed from a downstream port on a hub to its upstream port.
The Device Address field is provided to the host so that it can identify the source of a packet. All
other fields are discussed further in this chapter.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
Reserved
Reserved PP
8 7 6 5 4 3 2 1 0
Route String
Seq Num
Reserved
Link Control Word
NumP
HE Rsvd
Type
Ept Num
D rty Rsvd SubType
DWORD 0
DWORD 1
Stream ID/Reserved
DWORD 2
CRC-16
DWORD 3
U-091
Figure 8-2. Example Transaction Packet
Data Packets include additional information in the header that describes the data block. The Data
Block is always followed by a 4-byte CRC-32 used to determine the correctness of the data. The
Data Block and the CRC-32 together are referred to as the Data Packet Payload.
8-3
Universal Serial Bus 3.0 Specification, Revision 1.0
8.3
Packet Formats
This section defines the SuperSpeed packets. It defines the fields that make up the various packet
type and subtypes.
Packet byte and bit definitions in this section are described in an un-encoded data format. The
effects of symbols added to the serial stream (i.e., to frame packets or control or modify the link),
bit encoding, bit scrambling, and link level framing have been removed for the sake of clarity.
Refer to Chapters 6 and 7 for detailed information. In cases where bus performance, efficiency, or
timing are discussed, the effects of these lower level operations will be discussed to provide
additional context.
8.3.1
Fields Common to all Headers
All SuperSpeed headers start with the Type field that is used to determine how to interpret the
packet. At a high level this tells the recipient of the packet what to do with it: either to use it to
manage the link or to move and control the flow of data between a device and the host.
8.3.1.1
Reserved Values and Reserved Field Handling
Reserved fields and Reserved values shall not be used in a vendor-specific manner.
A transmitter shall set all Reserved fields to zero and a receiver shall ignore any Reserved field.
A transmitter shall not set a defined field to a reserved value and a receiver shall ignore any packet
that has any of its defined fields set to a reserved value. Note that the receiver shall acknowledge
the packet and return credit for the same as per the requirement specified in Section 7.2.4.1.
8.3.1.2
Type Field
The Type field is a 5-bit field that identifies the format of the packet. The type is used to determine
how the packet is to be used or forwarded by intervening links.
Table 8-1. Type Field Description
Width
Offset
(bits)
(DW:bit)
5
0:0
Description
Type. These 5 bits identify the packet’s Type.
Value
Description
00000b
Link Management Packet.
00100b
Transaction Packet
01000b
Data Packet Header
01100b
Isochronous Timestamp Packet
All other values are Reserved.
8.3.1.3
CRC-16
All header packets have a 16-bit CRC field. This field is the CRC calculated over the preceding
12 bytes in the header packet. Refer to Section 7.2.1.1.2 for the polynomial used to calculate this
value.
8-4
Protocol Layer
8.3.1.4
Link Control Word
The usage of the Link Control Word is defined in Section 7.2.1.1.3.
15 14 13 12 11 10
CRC-5
9
8
7
6
DF DL Hub Depth
5
4
3
2
1
0
Header
Seq #
R
Bit
Offset
U-092
Figure 8-3. Link Control Word Detail
Table 8-2. Link Control Word Format
Width
Offset
(bits)
(DW:bit)
Description
3
3:16
Header Sequence Number. The valid values in this field are 0 through 7.
3
3:19
Reserved (R).
3
3:22
Hub Depth. This field is only valid when the Deferred bit is set and identifies to the host the
hierarchical on the USB that the hub is located at in the deferred TP or DPH returned to the host.
This informs the host that the port on which the packet was supposed to be forwarded on is
currently in a low power state (either U1 or U2).
The only valid values in this field are 0 through 4.
1
3:25
Delayed (DL). This bit shall be set if a Header Packet is resent or the transmission of a Header
Packet is delayed. Chapter 7 and Chapter 10 provide more details on when this bit shall be set.
This bit shall not be reset by any subsequent hub that this packet traverses.
1
3:26
Deferred (DF). This bit may only be set by a hub. This bit shall be set when the downstream port
on which the packet needs to be sent is in a power managed state.
This bit shall not be reset by any subsequent hub that this packet traverses.
5
8.4
3:27
CRC-5. This field is the CRC used to verify the correctness of the preceding 11 bits in this word.
Refer to Section 7.2.1.1.3 for the polynomial used to calculate this value.
Link Management Packet (LMP)
Packets that have the Type field set to Link Management Packet are referred to as LMPs. These
packets are used to manage a single link. They carry no addressing information and as such are not
routable. They may be generated as the result of hub port commands. For example, a hub port
command is used to set the U2 inactivity timeout. In addition, they are used to exchange port
capability information and testing purposes.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
SubType Specific
Link Control Word
8 7 6 5 4 3 2 1 0
SubType
Type
DWORD 0
SubType Specific
DWORD 1
SubType Specific
DWORD 2
CRC-16
DWORD 3
U-093
Figure 8-4. Link Management Packet Structure
8-5
Universal Serial Bus 3.0 Specification, Revision 1.0
8.4.1
Subtype Field
The value in the LMP Subtype field further identifies the content of the LMP.
Table 8-3. Link Management Packet Subtype Field
Width
Offset
(bits)
(DW:bit)
4
0:5
16
8.4.2
3:0
Description
Subtype. These 4 bits identify the Link Packet Subtype.
Value
Type of LMP
0000b
Reserved
0001b
Set Link Function
0010b
U2 Inactivity Timeout
0011b
Vendor Device Test
0100b
Port Capability
0101b
Port Configuration
0110b
Port Configuration Response
0111b-1111b
Reserved
CRC-16. This field is the CRC calculated over the preceding 12 bytes. Refer to Section 7.2.1.1.2
for the polynomial used to calculate this value.
Set Link Function
The Set Link Function LMP shall be used to configure functionality that can be changed without
leaving the active (U0) state.
Upon receipt of a LMP with the Force_LinkPM_Accept bit asserted, the port shall accept all
LGO_U1 and LGO_U2 Link Commands until the port receives a LMP with the
Force_LinkPM_Accept bit de-asserted.
Note: Improper use of the Force_LinkPM_Accept functionality can impact the performance of the
link significantly. This capability shall only be used for compliance and testing purposes. Software
must ensure that there are no pending packets at the link level before issuing a SetPortFeature
command that generates an LGO_U1 or LGO_U2 link command.
This LMP is sent by a hub to a device connected on a specific port when it receives a
SetPortFeature (FORCE_LINKPM_ACCEPT) command. Refer to Section 10.4.2.2 and
Section 10.4.2.9 for more details.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
Set Link Function
Link Control Word
8 7 6 5 4 3 2 1 0
SubType
Type
DWORD 0
Reserved
DWORD 1
Reserved
DWORD 2
CRC-16
DWORD 3
U-094
Figure 8-5. Set Link Function LMP
8-6
Protocol Layer
Table 8-4. Set Link Function
Width
Offset
(bits)
(DW:bit)
4
0:5
Subtype. This field shall be set to Set Link Function for a Set Link Function LMP.
7
0:9
Set Link Function. These 7 bits identify the Set Link Function.
Description
Bits
Description
0
Reserved.
1
Force_LinkPM_Accept
6:2
8.4.3
Value
Meaning
0
De-assert
1
Assert
Reserved.
U2 Inactivity Timeout
The U2 Inactivity Timeout LMP shall be used to define the timeout from U1 to U2, or the timeout
from U0 to U2 if the U1 Inactivity Timeout is disabled. Refer to Section 10.4.2.1 for details on this
LMP.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
U2 Inactivity Timeout
8 7 6 5 4 3 2 1 0
SubType
Type
DWORD 0
Reserved
DWORD 1
Reserved
DWORD 2
Link Control Word
CRC-16
DWORD 3
U-095
Figure 8-6. U2 Inactivity Timeout LMP
Table 8-5. U2 Inactivity Timer Functionality
Width
Offset
(bits)
(DW:bit)
4
0:5
Subtype. This field shall be set to U2 Inactivity Timeout for a U2 Inactivity Timeout LMP.
8
0:9
U2 Inactivity Timeout. These 8 bits represent the U2 Inactivity Timeout value. The value placed
in this field is the same value that is sent to the hub in a Set Port Feature (PORT_U2_TIMEOUT)
command. Refer to Section 10.14.2.9 for details on the encoding of this field.
Description
8-7
Universal Serial Bus 3.0 Specification, Revision 1.0
8.4.4
Vendor Device Test
Use of this LMP is intended for vendor-specific device testing and shall not be used during normal
operation of the link.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
8 7 6 5 4 3 2 1 0
Vendor Device Test
SubType
Type
DWORD 0
Vendor Defined Data
DWORD 1
Vendor Defined Data
DWORD 2
Link Control Word
CRC-16
DWORD 3
U-096
Figure 8-7. Vendor Device Test LMP
Table 8-6. Vendor-specific Device Test Function
8.4.5
Width
Offset
(bits)
(DW:bit)
4
0:5
Subtype. This field shall be set to Vendor Device Test.
8
0:9
Vendor-specific device test. The function of these 8 bits is vendor specific.
64
1:0
Vendor-defined data. This value is vendor-defined.
Description
Port Capabilities
The Port Capability LMP describes each port's link capabilities and is sent by both link partners
after the successful completion of training and link initialization. All ports shall send this LMP
within tPortConfiguration time after completion of link initialization (refer to Section 7.3.4.1.1).
If a link partner does not receive this LMP within tPortConfiguration time then:
• If the link partner has downstream capability, it shall signal an error as described in
Section 10.14.2.6.
• If the link partner only supports upstream capability, then the upstream port shall transition to
SS.Disabled and it shall try to connect at the other speeds this device supports.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
Reserved
Link Speed
Tiebreaker
R
D
8 7 6 5 4 3 2 1 0
SubType
Reserved
Num HP Buffers
Reserved
Link Control Word
Type
DWORD 0
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-097
Figure 8-8. Port Capability LMP
8-8
Protocol Layer
Table 8-7. Port Capability LMP Format
Width
Offset
(bits)
(DW:bit)
4
0:5
SubType. This field shall be set to Port Capability.
7
0:9
Link speed. This field is a bitmask that describes the link speeds supported by this device.
Description
Bits
Description
0
This bit shall be set to 1 to indicate this device supports signaling at
5 Gbps
6:1
Reserved.
16
0:16
Reserved (R).
8
1:0
Num HP Buffers. This field specifies the number of header packet buffers (in each direction
Transmit or Receive) this device supports. All devices that are compliant to this revision of the
specification shall return a value of 4 in this field. All other values are reserved.
8
1:8
Reserved (R).
2
1:16
Direction (D). This field is used to identify the upstream or downstream capabilities of the port. All
ports shall have at least one of these bits set.
Bits
Description
0
If this bit is set to 1, then this port can be configured to be a
downstream port.
1
If this bit is set to 1, then this port can be configured to be an
upstream port.
2
1:18
Reserved (R).
4
1:20
Tiebreaker. This field is only valid when both bits 0 and 1 of the Direction field are set. This field
is used to determine the port type when two devices with both upstream and downstream
capability are connected to each other. See Table 8-8 for details.
40
1:24
Reserved.
This field shall be set to zero in all other cases.
After exchanging Port Capability LMPs, the link partners shall determine which of the link partners
shall be configured as the downstream facing port as specified in Table 8-8.
Table 8-8. Port Type Selection Matrix
Port 2
Upstream Only
Downstream Only
Both
Upstream Only
Not Defined
Port 2 is the downstream
port.
Port 2 is the downstream
port.
Downstream Only
Port 1 is the
downstream port.
Not Defined
Port 1 is the downstream
port.
Both
Port 1 is the
downstream port.
Port 2 is the downstream
port.
The port with the higher
value in the Tiebreaker
field shall become the
1
downstream port .
Port 1
Note:
1
If the TieBreaker field contents are equal, then the two link partners shall exchange Port Capability LMPs again with
new and different value in the TieBreaker field. The sequence of TieBreaker field values generated by a port shall
be sufficiently random.
8-9
Universal Serial Bus 3.0 Specification, Revision 1.0
8.4.6
Port Configuration
Only the fields that are different from the Port Capability LMP are described in this section.
All SuperSpeed ports that support downstream port capability shall be capable of sending this
LMP.
If the port that was to be configured in the upstream facing mode does not receive this LMP within
tPortConfiguration time after link initialization, then the upstream port shall transition to
SS.Disabled and it shall try and connect at the other speeds this device supports.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
Link Speed
Link Control Word
8 7 6 5 4 3 2 1 0
SubType
Type
DWORD 0
Reserved
DWORD 1
Reserved
DWORD 2
CRC-16
DWORD 3
U-098
Figure 8-9. Port Configuration LMP
Table 8-9. Port Configuration LMP Format (Differences with Port Capability LMP)
Width
Offset
(bits)
(DW:bit)
4
0:5
SubType. This field shall be set to Port Configuration.
7
0:9
Link speed. This field describes the link speed at which the upstream port shall operate. Only
one of the bits in this field shall be set in the Port Configuration LMP sent by the link partner
configured in the downstream mode.
80
0:16b
Description
Bits
Description
0
If this bit is set to 1, then this device shall operate at 5 Gbps.
6:1
Reserved.
Reserved.
A port configured in the downstream mode shall send the Port Configuration LMP to the upstream
port. The port sending this LMP shall select only one bit for the Link Speed field.
If a downstream capable port cannot work with its link partner, then the downstream capable port
shall signal an error as described in Section 10.14.2.6.
8-10
Protocol Layer
8.4.7
Port Configuration Response
This LMP is sent by the upstream port in response to a Port Configuration. It is used to indicate
acceptance or rejection of the Port Configuration LMP. Only the fields that are different from the
Port Capability LMP are described in this section.
All SuperSpeed ports that support upstream port capability shall be capable of sending this LMP.
If the downstream port does not receive this LMP within tPortConfiguration time, it shall signal an
error as described in Section 10.14.2.6.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Reserved
Link Control Word
Response Code
8 7 6 5 4 3 2 1 0
SubType
Type
DWORD 0
Reserved
DWORD 1
Reserved
DWORD 2
CRC-16
DWORD 3
U-099
Figure 8-10. Port Configuration Response LMP
Table 8-10. Port Configuration Response LMP Format (Differences with Port Capability LMP)
Width
Offset
(bits)
(DW:bit)
4
0:5
SubType. This field shall be set to Port Configuration Response.
7
0:9
Response Code. This field indicates the settings that were accepted in the Port Configuration
LMP that was sent to a device.
80
0:16
Description
Bits
Description
0
If this bit is set to 1, then this device accepted the Link Speed setting.
6:1
Reserved.
Reserved.
If the Response Code indicates that the Link Speed was rejected by the upstream port, the
downstream port shall signal an error as described in Section 10.14.2.6.
8-11
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5
Transaction Packet (TP)
Transaction Packets (TPs) traverse the direct path between the host and a device. TPs are used to
control data flow and manage the end-to-end connection. The value in the Type field shall be set to
Transaction Packet. The Route String field is used by hubs to route a packet that appears on its
upstream port to the correct downstream port. The route string is set to zero for a TP sent by a
device. When the host sends a TP, the Device Address field contains the address of the intended
recipient. When a device sends a TP to the host then it sets the Device Address field to its own
address. This field is used by the host to identify the source of the TP. The SubType field in a TP
is used by the recipient to determine the format and usage of the TP.
Table 8-11. Transaction Packet Subtype Field
Width
Offset
(bits)
(DW:bit)
4
1:0
8.5.1
Description
Subtype. The subtype field is used to identify a specific type of TP.
Value
Type of TP
0000b
Reserved
0001b
ACK
0010b
NRDY
0011b
ERDY
0100b
STATUS
0101b
STALL
0110b
DEV_NOTIFICATION
0111b
PING
1000b
PING_RESPONSE
1001b – 1111b
Reserved
Acknowledgement (ACK) Transaction Packet
This TP is used for two purposes:
• For IN endpoints, this TP is sent by the host to request data from a device as well as to
acknowledge the previously received data packet.
• For OUT endpoints, this TP is sent by a device to acknowledge receipt of the previous data
packet sent by the host, as well as to inform the host of the number of data packet buffers it has
available after receipt of this packet.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
Reserved
Reserved PP
8 7 6 5 4 3 2 1 0
Route String/Reserved
Seq Num
Reserved
Link Control Word
NumP
HE Rsvd
Type
Ept Num
D rty Rsvd SubType
DWORD 0
DWORD 1
Stream ID/Reserved
DWORD 2
CRC-16
DWORD 3
U-100
Figure 8-11. ACK Transaction Packet
8-12
Protocol Layer
Table 8-12. ACK TP Format
Description
Width
Offset
(bits)
(DW:bit)
20
0:5
Route String/Reserved. This field is only used by hubs. In conjunction with the hub depth, it is
used to route a packet to the correct downstream port. Refer to Section 8.9 for details. When
sent by a device, this field is Reserved.
7
0:25
Device Address. This field specifies the device, via its address, that is the recipient or the source
of the TP. Refer to Section 8.8.
4
1:0
SubType. This field shall be set to ACK for an ACK TP.
2
1:4
Reserved (Rsvd).
1
1:6
Retry Data Packet (rty). This field is used to signal that the host or a device did not receive a data
packet or received a corrupted data packet and requests the transmitter to resend one or more
data packets starting at the specified sequence number.
1
1:7
Direction (D). This field defines the direction of an endpoint within the device that is the source or
recipient of this TP. Refer to Section 8.8.
Value
Direction of Data Flow
0b
Host to Device
1b
Device to Host
4
1:8
Endpoint Number (Ept Num). This field determines an endpoint within the device that is the
source or recipient of this TP. Refer to Section 8.8.
3
1:12
Reserved (Rsvd).
1
1:15
Host Error (HE). This field is only valid when the ACK TP is sent from the host to a device. This
bit shall be set if the host was unable to accept a valid data packet due to internal host issues.
When the host sets this field, it must also set the Retry Data Packet field for a non-isochronous
transfer.
5
1:16
Number of Packets (NumP). This field is used to indicate the number of Data Packet buffers that
the receiver can accept. The value in this field shall be less than or equal to the maximum burst
size supported by the endpoint as determined by the value in the Burst Size field in the Endpoint
Companion Descriptor (refer to Section 9.6.7).
5
1:21
Sequence Number (Seq Num). This field is used to identify the sequence number of the next
expected data packet.
6
1:26
Reserved.
16
2:0
Stream ID/Reserved. If this ACK TP is targeted at a Bulk endpoint, this field contains a Stream ID
value between 1 and 65535. The Stream ID value of 0 is reserved for Stream pipes. The usage
of this field is class dependent. This field shall be set to zero if the Bulk endpoint does not support
Streams.
11
2:16
Reserved.
1
2:27
Packets Pending (PP). This field can only be set by the Host. If the field is set the host has
another packet available for the endpoint identified by the Endpoint Number and Direction field.
If no endpoints on this device have packets pending, then the device can use this information to
aggressively power manage its upstream link, e.g., set the link to a lower power U1 or U2 state.
4
2:28
Reserved.
8-13
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5.2
Not Ready (NRDY) Transaction Packet
This TP can only be sent by a device for a non-isochronous endpoint. An OUT endpoint sends this
TP to the host if it has no packet buffer space available to accept the DP sent by the host. An IN
endpoint sends this TP to the host if it cannot return a DP in response to an ACK TP sent by the
host.
Only the fields that are different from an ACK TP are described in this section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
Type
Ept Num
D
Rsvd
SubType
DWORD 0
DWORD 1
Reserved
Stream ID/Reserved
DWORD 2
Link Control Word
CRC-16
DWORD 3
U-101
Figure 8-12. NRDY Transaction Packet
Table 8-13. NRDY TP Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
4
1:0
8.5.3
Description
SubType. This field shall be set to NRDY.
3
1:4
Reserved (Rsvd).
20
1:12
Reserved.
5
2:27
Reserved.
Endpoint Ready (ERDY) Transaction Packet
This TP can only be sent by a device for a non-isochronous endpoint. It is used to inform the host
that an endpoint is ready to send or receive data packets. Only the fields that are different from an
ACK TP are described in this section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
NumP
Reserved
Ept Num
D
Rsvd
Type
DWORD 0
SubType
DWORD 1
Reserved
Stream ID/Reserved
DWORD 2
Link Control Word
CRC-16
DWORD 3
U-102
Figure 8-13. ERDY Transaction Packet
8-14
Protocol Layer
Table 8-14. ERDY TP Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
4
1:0
SubType. This field shall be set to ERDY.
3
1:4
Reserved (Rsvd).
4
1:12
Reserved.
5
1:16
Number of Packets (NumP).
Description
For an OUT endpoint, refer to Table 8-12 for the description of this field.
For an IN endpoint this field is set by the endpoint to the number of packets it can transmit when
the host resumes transactions to it. This field shall not have a value greater than the maximum
burst size supported by the endpoint as indicated by the value in the Burst Size field in the
Endpoint Companion Descriptor. Note that the value reported in this field may be treated by the
host as informative only.
11
1:21
Reserved.
5
2:27
Reserved.
8.5.4
STATUS Transaction Packet
This TP can only be sent by the host. It is used to inform a control endpoint that the host has
initiated the Status stage of a control transfer. This TP shall only be sent to a control endpoint.
Only the fields that are different from an ACK TP are described in this section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Route String
Reserved
Ept Num
D
Rsvd
Reserved
Link Control Word
Type
DWORD 0
SubType
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-103
Figure 8-14. STATUS Transaction Packet
Table 8-15. STATUS TP Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
4
1:0
Description
SubType. This field shall be set to STATUS.
3
0:4
Reserved (Rsvd).
52
1:12
Reserved.
8-15
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5.5
STALL Transaction Packet
This TP can only be sent by an endpoint on the device. It is used to inform the host that the
endpoint is halted or that a control transfer is invalid. Only the fields that are different from an
ACK TP are described in this section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
Ept Num
D
Rsvd
Type
DWORD 0
SubType
DWORD 1
Reserved
Link Control Word
DWORD 2
CRC-16
DWORD 3
U-104
Figure 8-15. STALL Transaction Packet
Table 8-16. STALL TP Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
4
1:0
SubType. This field shall be set to STALL.
3
1:4
Reserved (Rsvd).
52
1:12
Reserved.
8.5.6
Description
Device Notification (DEV_NOTIFICATION) Transaction
Packet
This TP can only be sent by a device. It is used by devices to inform the host of an asynchronous
change in a device or interface state, e.g., to identify the function within a device that caused the
device to perform a remote wake operation. This TP is not sent from a particular endpoint but from
the device in general. Only the fields that are different from an ACK TP are described in this
section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Notification Type Specific
Notification
Type
Type
DWORD 0
SubType
DWORD 1
Notification Type Specific
Link Control Word
DWORD 2
CRC-16
DWORD 3
U-105
Figure 8-16. Device Notification Transaction Packet
8-16
Protocol Layer
Table 8-17. Device Notification TP Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
4
1:0
SubType. This field shall be set to DEV_NOTIFICATION.
4
1:4
Notification Type. The field identifies the type of the device notification.
8.5.6.1
Description
Value
Type of Notification Packet
0000b
Reserved
0001b
FUNCTION_WAKE
0010b
LATENCY_TOLERANCE_MESSAGE
0011b
BUS_INTERVAL_ADJUSTMENT_MESSAGE
0100b – 1111b
Reserved
Function Wake Device Notification
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
Type
Notification
Type
Interface
SubType
Reserved
Link Control Word
DWORD 0
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-106
Figure 8-17. Function Wake Device Notification
Table 8-18. Function Wake Device Notification
Width
Offset
(bits)
(DW:bit)
Description
4
1:0
SubType. This field shall be set to DEV_NOTIFICATION.
4
1:4
Notification Type. FUNCTION_WAKE
8
1:8
Interface. This field identifies the first interface in the function that caused the
device to perform a remote wake operation.
48
1:16
Reserved.
8-17
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5.6.2
Latency Tolerance Message (LTM) Device Notification
Latency Tolerance Message Device Notification is an optional normative feature enabling more
power efficient platform operation.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
Notification
Type
BELT
Type
DWORD 0
SubType
DWORD 1
Reserved
Link Control Word
DWORD 2
CRC-16
DWORD 3
U-107
Figure 8-18. Latency Tolerance Message Device Notification
Table 8-19. Latency Tolerance Message Device Notification
Width
Offset
(bits)
(DW:bit)
4
1:0
Description
SubType. This field shall be set to DEV_NOTIFICATION.
4
1:4
Notification Type. LATENCY_TOLERANCE_MESSAGE.
12
1:8
BELT. This field describes the Best Effort Latency Tolerance value, representing the time in
nanoseconds that a device can wait for service before experiencing unintended operational side
effects.
Bits
44
8-18
1:20
Description
9:0
LatencyValue (ns)
11:10
LatencyScale
Reserved.
Value
Description
00b
Reserved
01b
LatencyValue is to be multiplied by 1024
10b
LatencyValue is to be multiplied by 32,768
11b
LatencyValue is to be multiplied by 1,048,576
Protocol Layer
8.5.6.3
Bus Interval Adjustment Message Device Notification
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Bus Interval Adjustment
Type
Notification
Type
Reserved
SubType
Reserved
Link Control Word
DWORD 0
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-108
Figure 8-19. Bus Interval Adjustment Message Device Notification
Table 8-20. Bus Interval Adjustment Message Device Notification
Width
Offset
(bits)
(DW:bit)
4
1:0
SubType. This field shall be set to DEV_NOTIFICATION.
4
1:4
Notification Type. BUS_INTERVAL_ADJUSTMENT_MESSAGE.
8
1:8
Reserved.
16
1:16
Bus Interval Adjustment. This field is a two's complement value ranging from -32768 to +32767
expressed in BusIntervalAdjustmentGranularity units.
8.5.6.4
Description
Function Wake Notification
A function may signal that it wants to exit from device suspend (after transitioning the link to U0)
or function suspend by sending a Function Wake Device Notification to the host if it is enabled for
remote wakeup. Refer to Section 9.2.5 for more details.
8.5.6.5
Latency Tolerance Messaging
Latency Tolerance Messaging is an optional normative USB power management feature that
utilizes reported BELT (Best Effort Latency Tolerance) values to enable more power efficient
platform operation.
The BELT value is the maximum time (factoring in the service needs of all configured endpoints)
for leaving a device without service from the host. Specifically, the BELT value is the time
between the host’s receipt of an ERDY from a device, and the host’s transmission of the response
to the ERDY.
Devices indicate whether they are capable of sending LTM TPs using the LTM Capable field in
the SUPERSPEED_USB Device Capability descriptor in the BOS descriptor (refer to
Section 9.6.2). The LTM Enable (refer to Section 9.4.10) feature selector enables (or disables) an
LTM capable device to send LTM TPs.
8-19
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5.6.5.1
Optional Normative LTM and BELT Requirements
General Device Requirements
• LTM TPs shall be originated only by peripheral devices.
• LTM TPs apply to all endpoint types except for isochronous endpoints.
• Once a BELT value has been sent to the host by a device, all configured endpoints for that
device shall expect to be serviced within the specified BELT time.
• A device shall send an LTM TP with a value of tBELTdefault in the BELT field in response to
any change in state of LTM Enable within tMinLTMStateChange.
• A device shall ensure that its BELT value is determined frequently enough that it is able to
provide reasonable estimate of the device’s service latency tolerance prior to its need to change
BELT value. In addition, the following conditions shall be met:
⎯ The maximum number of LTM TPs is bounded by tBeltRepeat.
⎯ Each LTM TP shall have a different BELT value.
• The system shall default to a BELT of 1 ms for all devices (refer to Table 8-33).
• The minimum value for a BELT is 125 µs (refer to Table 8-33).
Device Requirements Governing Establishment of BELT Value
• The LTM mechanism shall utilize U1SEL and U2SEL to provide devices with system latency
information (see Section 9.4.12 – Set SEL). In this context, the system latency is the time
between when a device transmits an ERDY and when it will receive a transaction packet (type
is direction-specific) from the host when the deepest allowed link state is U1 or U2. These
values are used by the device to properly adjust their BELT value, factoring in their location
within the USB link topology.
⎯ Devices that allow their link to enter U1, but not U2, shall subtract the U1 System Exit
Latency (U1SEL) from its total latency tolerance and send the resultant value as the BELT
field value in an LTM TP.
⎯ Devices that allow their link to enter U1 and U2, shall subtract U2SEL from its total
latency tolerance and send the resulting value as the BELT field value in an LTM TP.
8.5.6.6
Bus Interval Adjustment Message
This device notification may be sent by a device to request an increase or decrease in the length of
the bus interval. This would typically be used by a device trying to synchronize the host’s bus
interval clock with an external clock. Bus interval adjustment requests are relative to the current
bus interval. For example, if a device requests an increase of one
BusIntervalAdjustmentGranularity unit and then later requests an increase of two
BusIntervalAdjustmentGranularity units the overall increase by the host would be three
BusIntervalAdjustmentGranularity units.
The host shall support adjustments through an absolute range of -37268 to 37267
BusIntervalAdjustmentGranularity units. A device shall not request adjustments more than once
every eight bus intervals. A device shall not send another bus interval adjustment request until it
has waited long enough to accurately observe the effect of the previous bus interval adjustment
request on the timestamp value in subsequent ITPs. A device shall not make a single
BusIntervalAdjustment request for more than ±4096 units. A device may make multiple
BusIntervalAdjustment requests over time for a combined total of more than 4096 units. A device
8-20
Protocol Layer
shall not request a bus interval adjustment unless the device received an ITP within the past 125 μs,
the ITP contained a Bus Interval Adjustment Control field with a value equal to zero or the
device’s address and the device is in the Address or Configured state.
Only one device can control the bus interval length at a time. The host controller implements a first
come first serve policy for handling bus interval adjustment requests as described in this section.
When the host controller begins operation it shall transmit ITPs with the Bus Interval Adjustment
Control field set to zero. When the host controller first receives a bus interval adjustment control
request, it shall set the Bus Interval Adjustment Control field in subsequent ITPs to the address
of the device that sent the request. The host shall ignore bus interval adjustment requests from all
other devices once the Bus Interval Adjustment Control field is set to a non-zero address. If the
controlling device is disconnected, the host controller shall reset the Bus Interval Adjustment
Control field to zero. The host controller may provide a way for software to override default bus
interval adjustment control field behavior and select a controlling device. The host controller shall
begin applying bus interval adjustments within two bus intervals from when the bus interval
adjustment request is received.
The smallest bus interval adjustment (one BusIntervalAdjustmentGranularity) requires the host to
make an average adjustment of eight high speed bit times every 4096 bus intervals. The host is
allowed to make this adjustment in a single bus interval such that the clock used to generate ITP
times and bus interval boundaries does not need a period smaller than eight high speed bit times.
The host shall make bus interval adjustments at regular intervals. When the host is required to
make an average of one or more eight high speed bit time adjustments every 4096 bus intervals the
adjustments shall be evenly distributed as defined by the following constraints:
• Intervals that contain one more eight high speed bit time adjustment than other intervals are
referred to as maximum adjustment bus intervals.
• The number of eight high speed bit time adjustments made in any bus interval shall not be more
than one greater than the number of high speed bit time adjustments made in any other bus
interval.
• The distance in bus intervals between consecutive maximum adjustment bus intervals shall not
vary by more than one bus interval.
The even distribution and average adjustment requirements for bus interval adjustments shall apply
from one bus interval after a bus interval adjustment request is received by the host until the bus
interval where a subsequent valid bus interval adjustment request is received by the host.
The following is an example of valid host behavior for a specific bus interval adjustment request.
After power on, the host receives a bus interval adjustment request for a bus interval decrease of
10 BusIntervalAdjustmentGranularity units in bus interval X-1. The host controller uses a clock
with a period of eight high speed bit times to drive a counter that produces timestamps and bus
interval boundaries. The host controller adds an extra eight high speed bit time clock tick to its
counter in each of the following bus intervals: X+409, X+819, X+1228, X+1638, X+2048,
X+2457, X+2867, X+3276, X+3686, X+4096, X+4505,….
8-21
Universal Serial Bus 3.0 Specification, Revision 1.0
8.5.7
PING Transaction Packet
This TP can only be sent by the host. It is used by the host to transition all links in the path to a
device back to U0 prior to initiating an isochronous transfer. Refer to Appendix C for details on the
usage of this TP. Only the fields that are different from an ACK TP are described in this section.
A device shall respond to the PING TP by sending a PING_RESPONSE TP (refer to Section 8.5.8)
to the host within the tPingResponse time (refer to Table 8-33).
A device shall keep its link in U0 until it receives a subsequent packet from the host, or until the
tPingTimeout time (refer to Table 8-33) elapses.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Route String
Reserved
Type
EPT Num D RsvdP
SubType
Reserved
DWORD 0
DWORD 1
DWORD 2
Link Control Word
CRC-16
DWORD 3
U-109
Figure 8-20. PING Transaction Packet
Table 8-21. PING TP Format (differences with ACK TP)
8.5.8
Width
Offset
(bits)
(DW:bit)
4
1:0
Description
SubType. This field shall be set to PING.
3
1:4
Reserved.
52
1:12
Reserved.
PING_RESPONSE Transaction Packet
This TP can only be sent by a device in response to a PING TP sent by the host. A
PING_RESPONSE TP shall be sent for each PING TP received. Refer to Appendix C for details
on the usage of this TP. Only the fields that are different from an ACK TP are described in this
section.
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
8 7 6 5 4 3 2 1 0
Reserved
Reserved
Type
EPT Num D RsvdP
SubType
Reserved
Link Control Word
DWORD 0
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-110
Figure 8-21. PING_RESPONSE Transaction Packet
8-22
Protocol Layer
Table 8-22. PING_RESPONSE TP Format (Differences with ACK TP)
Offset
(bits)
(DW:bit)
4
1:0
SubType. This field shall be set to PING_RESPONSE.
3
1:4
Reserved.
1
1:7
Direction (D). This field shall be set to the value of the Direction field in the PING TP for
which this PING_RESPONSE TP is being sent.
4
1:8
Endpoint Number (Ept Num). This field shall be set to the value of the Ept Num field in
the PING TP for which this PING_RESPONSE TP is being sent.
52
1:12
Reserved.
Description
Data Packet (DP)
This packet can be sent by either the host or a device. The host uses this packet to send data to a
device. Devices use this packet to return data to the host in response to an ACK TP. All data
packets are comprised of a Data Packet Header and a Data Packet Payload. Only the fields that are
different from an ACK TP are described in this section.
Data packets traverse the direct path between the host and a device. Note that it is permissible to
send a data packet with a zero length data block; however, it shall have a CRC-32.
Data Packet
Header (DPH)
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Data Packet
Payload (DPP)
8.6
Width
Device Address
Data Length
Reserved PP
8 7 6 5 4 3 2 1 0
Route String/Reserved
S
Rsvd
Reserved
Link Control Word
Ept Num
D
eob/
lpf
R
Type
DWORD 0
Seq Num
DWORD 1
Stream ID/Reserved
DWORD 2
CRC-16
DWORD 3
Data DWORD 0
DWORD 0
xx-xxH
CRC-32
xx+4xx+8H
Note: The framing symbols around the DPH and DPP are left out of this figure for the sake of readability.
U-111
Figure 8-22. Example Data Packet
8-23
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 8-23. Data Packet Format (Differences with ACK TP)
Width
Offset
(bits)
(DW:bit)
5
1:0
Sequence Number (Seq Num). This field is used to identify the sequence number of the DP.
Note that the sequence number wraps around at 31.
1
1:5
Reserved (R).
1
1:6
End Of Burst (EOB)/Last Packet Flag (LPF). For non-isochronous endpoints, this field is
referred to as EOB and for isochronous endpoints this field is referred to as LPF.
Description
For non-isochronous IN endpoints, this field is used to identify that this is the last packet of a burst.
When a device is ready to continue the transfer, it shall send an ERDY TP to signal the host. Note
that an endpoint shall re-evaluate the EOB value in a retried DP. The EOB field shall be set in the
last packet of a burst if the device returns fewer than the number of packets requested in the
NumP field of the last ACK TP it received and the last packet is not a short packet. The EOB field
may be set when the device sends a short packet.
For non-isochronous OUT and control endpoints, this field shall be set to zero.
For isochronous endpoints this field is used to identify that this is the last packet of the last burst in
the current service interval. LPF can be set by a device and the host. Please refer to
Section 8.12.6 for the usage of this field when the target or source of this DP is an isochronous
endpoint.
4
1:8
Endpoint Number (Ept Num). This field determines an endpoint within the device that is the
source or recipient of this DP.
3
1:12
Reserved (R).
1
1:15
Setup (S). This field is set by the host to indicate that this DP is a Setup data packet. This field
can only be set by the host.
16b
1:16
Data Length. This field is used to indicate the number of bytes in the DPP excluding the data
CRC-32.
xx
4:0
Data Block. This field contains the data in the DPP. The size of this field in bytes is indicated by
the value in the Data Length field.
32
4:0 + xx
CRC-32. The data CRC is calculated over the data block of the DPP. Refer to Section 7.2.1.2.1
for the polynomial used to calculate this value.
Note that this field is not necessarily aligned on a DWORD boundary as the data block length may
not be a multiple of four.
8.7
Isochronous Timestamp Packet (ITP)
The value in the Type field is Isochronous Timestamp Packet for an ITP. ITPs are used to deliver
timestamps from the host to all active devices. ITPs carry no addressing or routing information and
are multicast by hubs to all of their downstream ports with links in the U0 state. A device shall not
respond to an ITP. ITPs are used to provide host timing information to devices for synchronization.
Note that any device or hub may receive an ITP. The host shall transmit an ITP on a root port link
if and only if the link is already in U0. Only the host shall initiate an ITP transmission. The host
shall not bring a root port link to U0 for the purpose of transmitting an ITP. The host shall transmit
an ITP in every bus interval within tTimestampWindow from a bus interval boundary if the root
port link is in U0. The host shall begin transmitting ITPs within tIsochronousTimestampStart from
when the host root port’s link enters U0 from the polling state. An ITP may be transmitted in
between packets in a burst. If a device receives an ITP with the delayed flag (DL) set in the link
control word, the timestamp value may be significantly inaccurate and may be ignored by the
device.
8-24
Protocol Layer
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
8 7 6 5 4 3 2 1 0
Isochronous Timestamp
Type
Bus Interval
Adjustment Control
Reserved
Reserved
Link Control Word
DWORD 0
DWORD 1
DWORD 2
CRC-16
DWORD 3
U-112
Figure 8-23. Isochronous Timestamp Packet
Table 8-24. Isochronous Timestamp Packet Format
Width
Offset
(bits)
(DW:bit)
27
0:5
Description
Isochronous Timestamp (ITS). The isochronous timestamp field is used to identify the current
time value from the perspective of the host transmitting the ITP. The timestamp field is split into
two sub-fields:
Bits
Description
13:0
Bus interval counter. The current 1/8 of a millisecond counter.
The count value rolls over to zero when the value reaches 0x3FFF
and continues to increment.
26:14
Delta. The time delta from the start of the current ITP packet to the
previous bus interval boundary. This value is a number of
tIsochTimestampGranularity units. The value used shall specify the
delta that comes closest to the previous bus interval boundary
without going before the boundary.
Note: If a packet starts exactly on a bus interval boundary, the delta
time is set to 0.
7
1:0
Bus Interval Adjustment Control. This field specifies the address of the device that controls the
bus interval adjustment mechanism. Upon reset, power-up, or if the device is disconnected, the
host shall set this field to zero.
57
1:7
Reserved.
The ITS value in the ITP shall have an accuracy of ±1 tIsochTimestampGranularity units of the
value of the host clock (for ITP generation) measured when the first framing symbol of the ITP is
transmitted by the host.
8.8
Addressing Triple
Data Packets and most Transaction Packets provide access to specific data flow using a composite
of three fields. They are the Device Address, the Endpoint Number, and the Direction fields.
Upon reset and power-up, a device’s address defaults to a value of zero and shall be programmed
by the host during the enumeration process with a value in the range from 1 to 127. Device address
zero is reserved as the default address and may not be assigned to any other use.
Devices may support up to a maximum of 15 IN and 15 OUT endpoints (as indicated by the
Direction field) apart from the required default control endpoint that has an endpoint number set to
zero.
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.9
Route String Field
The Route String is a 20-bit field in downstream directed packet that the hub uses to route the
packet to the designated downstream port. It is composed of a concatenation of the downstream
port numbers (4 bits per hub) for each hub traversed to reach a device. The hub uses a Hub Depth
value multiplied by four as an offset into the Route String to locate the bits it uses to determine the
downstream port number. The Hub Depth value is determined and assigned to every hub during
the enumeration process.
Note that this field is only valid in packets sent by the host and when sent by a device, this field is
Reserved.
A value of zero
indicates that the
target is the upstream
port on the hub
40 39 38 37 36 35 34 33 32 31 30 29 28 27 26 25 24 23 22 21
Bit
[email protected] [email protected] [email protected] [email protected] [email protected] Offset
Targetted downstream port number
Valid Values: Zero through number of ports on hub
U-113
Figure 8-24. Route String Detail
In Figure 8-24 the value in [email protected] field is the downstream port number of the hub connected
directly to one of the root ports on the host to which a second hub is attached and so on.
8.9.1
Route String Port Field
This 4-bit wide field in the Route String represents the port in the hub being addressed.
8.9.2
Route String Port Field Width
The Route String Port field width is fixed at 4 bits, limiting the maximum number of ports a hub
may support to 15.
8.9.3
Port Number
The specific port on a hub to which the packet is directed is identified by the value in the Route
String Port field. When addressing the hub controller then the Port Number field at the hub’s tier
level shall be set to zero in the Route String. The hub’s downstream ports are addressed beginning
with one and count up sequentially.
8.10
Transaction Packet Usages
TPs are used to report the status of data transactions and can return values indicating successful
reception of data packets, command acceptance or rejection, flow control, and halt conditions.
8-26
Protocol Layer
8.10.1
Flow Control Conditions
This section describes the interaction between the host and a device when an endpoint returns a
flow control response. The flow control is at an end-to-end level between the host and the endpoint
on the device. Only bulk, control and interrupt endpoints may send flow control responses.
Isochronous endpoints cannot send flow control responses.
An IN endpoint shall be considered to be in a flow control condition if it returns one of the
following responses to an ACK TP:
• Responding with an NRDY TP
• Sending a DP with the EOB field set to 1 in the DPH
An OUT endpoint shall be considered to be in a flow control condition if it returns one of the
following responses to a DP:
• Responding with an NRDY TP
• Sending an ACK TP with the NumP field set to 0
The Packets Pending field is only valid when set by the host and does not affect whether or not an
endpoint enters the flow control state. Refer to Section 8.11 for further details on host and device
TP responses.
When an endpoint is in a flow control condition, it shall send an ERDY TP to be moved back into
the active state. Further, if the endpoint is an IN endpoint, then it shall wait until it receives an
ACK TP for the last DP it transmitted before it can send an ERDY TP. When an endpoint is not in
a flow control condition, it shall not send an ERDY TP unless the endpoint is a Bulk endpoint that
supports streams. Refer to Section 8.12.1.4.2 and Section 8.12.1.4.3 for further information about
when a Bulk endpoint that supports streams can send an ERDY TP. Note that the host may resume
transactions to any endpoint – even if the endpoint had not returned an ERDY TP after returning a
flow control response.
8.10.2
Burst Transactions
The SuperSpeed USB protocol allows the host to continually send data to a device or receive data
from a device as long as the device can receive the data or transmit the data. The number of
packets an endpoint on a device can send or receive at a time without an intermediate
acknowledgement packet is reported by the device in the endpoint companion descriptor (refer to
Section 9.6.7) for that endpoint. An endpoint that reports more than one packet in its maximum
burst size is considered to be able to support “Burst” Transactions.
While bursting the following rules apply:
•
The maximum number of packets that can be sent in a burst prior to receiving an
acknowledgement is limited to the minimum of the maximum burst size of the endpoint and the
value of the NumP field in the last ACK TP received by the endpoint or the host, minus the
number of packets that the endpoint or the host has already sent after the packet acknowledged
by the last ACK TP.
•
Each individual packet in the burst shall have a data payload of maximum packet size. Only
the last packet in a burst may be of a size smaller than the reported maximum packet size. If
the last one is smaller, then the same rules for short packets apply to a short packet at the end of
a burst (refer to Section 8.10.3).
8-27
Universal Serial Bus 3.0 Specification, Revision 1.0
•
The burst transaction continues as long as the NumP field in the ACK TP is not set to zero and
each packet has a data payload of maximum packet size.
•
The NumP field can be incremented at any time by the host or a device sending the ACK TP as
long as the device or host wants to continue receiving data. The only requirement is that the
NumP field shall not have a value greater than the maximum burst supported by the device.
•
If a device or host sending an ACK TP decrements the NumP field, then it shall do so by no
more than one. For example, if the previous ACK TP had a value of five in the NumP field,
then the next ACK TP to acknowledge the next packet received shall have a value of no less
than four in the NumP field. The only exceptions to this rule are:
⎯ If the device can receive the data but cannot accept any more data, then it shall send an
ACK TP with the NumP field set to zero.
⎯ The host shall send an ACK TP with the NumP field set to zero in response to a device
sending a DP with the EOB field set or that is a short packet (see Section 8.10.3).
However, if the host receives a short packet and the host has another transfer to initiate
with the same endpoint, then the host may instead send an ACK TP with the NumP field set
to a non-zero value.
8.10.3
Short Packets
SuperSpeed retains the semantics of short packet behavior that USB 2.0 supports. When the host or
a device receives a DP with the Data Length field shorter than the maximum packet size for that
endpoint it shall deem that that transfer is complete.
In the case of an IN transfer, a device shall stop sending DPs after sending a short DP. The host
shall respond to the short DP with an ACK TP with the NumP field set to zero. The host shall
schedule transactions to an endpoint on the device when another transfer is initiated for that
endpoint.
In the case of an OUT transaction, the host may stop sending DPs after sending a short DP. The
host shall schedule transactions to an endpoint on the device when another transfer is initiated for
that endpoint. Note that this shall be the start of a new burst to the endpoint.
8-28
Protocol Layer
8.11
TP or DP Responses
Transmitting and receiving devices shall return DPs or TPs as detailed in Table 8-25 through
Table 8-27. Not all TPs are allowed, depending on the transfer type and depending on the direction
of flow of the TP.
8.11.1
Device Response to TP Requesting Data
Table 8-25 shows the possible ways a device shall respond to a TP requesting data for bulk, control,
and interrupt endpoints. A TP is considered to be invalid if it has an incorrect Device Address or
the endpoint number and direction does not refer to an endpoint that is part of the current
configuration or it does not have the expected sequence number.
Table 8-25. Device Responses to TP Requesting Data (Bulk, Control, and Interrupt
Endpoints)
Invalid TP
Received
TP Received with
Deferred Bit Set
Device Tx
Endpoint Halt
Feature Set
Device Ready to
Transmit Data
Action Taken
Yes
Do not care
Do not care
Do not care
The device shall ignore the TP.
No
Yes
Yes
Do not care
The device shall send an
ERDY TP.
No
Yes
No
No
The device shall not respond.
It shall send an ERDY TP
when it is ready to resume.
No
Yes
No
Yes
The device shall send an
ERDY TP indicating that it is
ready to send data.
No
No
Yes
Do not care
Issue STALL TP
No
No
No
No
Issue NRDY TP
No
No
No
Yes
Start transmitting DPs with
sequence numbers requested
by the host
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.11.2
Host Response to Data Received from a Device
Table 8-26 shows the host responses to data received from a device for bulk, control, and interrupt
endpoints. The host is able to return only an ACK TP. A DPH is considered to be invalid if it has
an incorrect Device Address or the endpoint number and direction does not refer to an endpoint that
is part of the current configuration or it does not have the expected sequence number. In
Table 8-26, DPP Error may be due to one or more of the following:
• CRC incorrect
• DPP aborted
• DPP missing
• Data length in the DPH does not match the actual data payload length
Table 8-26. Host Responses to Data Received from a Device (Bulk, Control, and Interrupt
Endpoints)
8-30
DPH has
Invalid Values
Data Packet
Payload Error
Host Can
Accept Data
TP Returned by Host
Yes
Do not care
Do not care
Discard data and do not send any TP.
No
Yes
Do not care
Discard data and send an ACK TP with the Retry bit set
requesting for one or more DPs with the Sequence
Number field set to the sequence number of the DP that
was corrupted.
No
No
No
Discard data; send an ACK TP with the Retry bit set
requesting for one or more DPs with the Sequence
Number field set to the sequence number of the DP that
the host was unable to receive. The ACK TP shall have
the Host Error bit set to one to indicate that the host
was unable to accept the data.
No
No
Yes
Accept data and send an ACK TP requesting for zero or
more DPs with the Sequence Number field set to the
sequence number of the next DP expected. This is also
an implicit acknowledgement that this DP was received
successfully.
Protocol Layer
8.11.3
Device Response to Data Received from the Host
TP responses by a device to data received from the host for bulk, control, and interrupt endpoints
are shown in Table 8-27. A DPH is considered to be invalid if it has an incorrect Device Address
or the endpoint number and direction does not refer to an endpoint that is part of the current
configuration or it does not have the expected sequence number. In Table 8-27, DPP Error may be
due to one or more of the following:
• CRC incorrect
• DPP aborted
• DPP missing
• Data length in the DPH does not match the actual data payload length
Note: Receipt of an ACK TP indicates to the host the DP with the previous sequence number was
successfully received by a device as well as the number of data packet buffers the device has
available to receive any pending DPs the host has. A device shall send an ACK TP for each DP
received.
Table 8-27. Device Responses to OUT Transactions (Bulk, Control, and Interrupt Endpoints)
DPH has
Invalid
Values
DPH has
Deferred Bit
Set
Receiver
Halt
Feature
Set
Data Packet
Payload
Error
Device Can
Accept Data
TP Returned by Device
Yes
No
Do not care
Yes
Do not care
Yes
Do not care
Do not care
Do not care
Do not care
No
Yes
No
Do not care
No
No
Yes
No
Do not care
Yes
No
No
Yes
Do not care
Do not care
No
No
No
No
No
No
Do not care
Yes
No
Yes
No
No
No
No
Yes
Discard DP.
The device shall send an ERDY
TP.
The device shall not respond. It
shall send an ERDY TP when it is
ready to resume.
The device shall send an ERDY
TP.
The device shall send a STALL
TP.
Discard DP, send an NRDY TP.
Discard DP, send an ACK TP with
the sequence number of the DP
expected (thereby indicating that
the DP was not received), the
Retry bit set and the number of
DPs that the device can receive for
this endpoint.
Send an ACK TP indicating the
sequence number of the next DP
expected (thereby indicating that
this DP was received successfully)
and the number of DPs that the
device can receive for this
endpoint.
8-31
Universal Serial Bus 3.0 Specification, Revision 1.0
8.11.4
Device Response to a SETUP DP
A SETUP DP is a special DP that is identified by the Setup field set to one and addressed to any
control endpoint. SETUP is a special type of host-to-device data transaction that permits the host to
initiate a command that the device shall perform. Upon receiving a SETUP DP, a device shall
respond as shown in Table 8-28.
Note that a SETUP DPH shall be considered invalid if it has any one of the following:
• Incorrect Device Address
• Endpoint number and direction does not refer to an endpoint that is part of the current
configuration
• Endpoint number does not refer to a control endpoint
• Non-zero sequence number
• Data length is not set to eight
In Table 8-28, DPP Error may be due to one or more of the following:
• CRC incorrect
• DPP aborted
• DPP missing
• Data length in the Setup DPH does not match the actual data payload length.
Table 8-28. Device Responses to SETUP Transactions (Only for Control Endpoints)
8-32
DPH has
Invalid Values
DPH has
Deferred Bit Set
Data Packet
Payload Error
TP Returned by Device
Yes
N/A
N/A
Discard DP.
No
Yes
N/A
The device shall send an ERDY TP indicating that it is
ready to receive the SETUP DP.
No
No
Yes
Discard SETUP DP, send an ACK TP with the sequence
number set to zero, the rty bit set and the NumP field set
to one.
No
No
No
Send an ACK TP with the sequence number set to one
(thereby indicating that this SETUP DP was received
successfully) and the NumP field set to one.
Protocol Layer
8.12
TP Sequences
The packets that comprise a transaction vary depending on the endpoint type. There are four
endpoint types: bulk, control, interrupt, and isochronous.
8.12.1
Bulk Transactions
Bulk transaction types are characterized by the ability to guarantee error-free delivery of data
between the host and a device by means of error detection and retry. Bulk transactions use a twophase transaction consisting of TPs and DPs. Under certain flow control and halt conditions, the
data phase may be replaced with a TP.
8.12.1.1
State Machine Notation Information
This section shows detailed host and device state machines required to advance the Protocol on an
IN or OUT pipe. The diagrams should not be taken as a required implementation, but to specify the
required behavior.
Figure 8-25 shows the legend for the state machine diagrams. A circle with a three line border
indicates a reference to another (hierarchical) state machine. A circle with a two line border
indicates an initial state. A circle with a single line border is a simple state.
A diamond (joint) is used to join several transitions to a common point. A joint allows a single
input transition with multiple output transitions or multiple input transitions and a single output
transition. All conditions on the transitions of a path involving a joint must be true for the path to
be taken. A path is simply a sequence of transitions involving one or more joints.
A transition is labeled with a block with a line in the middle separating the (upper) condition and
the (lower) actions. A transition without a line is a condition only. The condition is required to be
true to take the transition. The actions are performed if the transition is taken. The syntax for
actions and conditions is VHDL. A circle includes a name in bold and optionally one or more
actions that are performed upon entry to the state.
Transitions using a solid arrow are generated by the host. Transitions using a dashed arrow are
generated by a device. Transitions using a dot-dot-dash arrow are generated by the either a device
or the host.
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Universal Serial Bus 3.0 Specification, Revision 1.0
State
Hierarchy
- Contains other state machines
Initial
State
- Initial state of state machine
State
- State in a state machine
- Entry and exit of state machine
- Joint used to connect transitions
&
Conditions
Actions
- Transition: Take when condition
is true and performs actions
(generated by the host)
Conditions
Actions
- Transition: Take when condition
is true and performs actions
(generated by the device)
Conditions
Actions
- Transition: Take when condition
is true and performs actions
(generated by either the device or the host)
U-114
Figure 8-25. Legend for State Machines
8.12.1.2
Bulk IN Transactions
When the host is ready to receive bulk data, it sends an ACK TP to a device indicating the sequence
number and number of packets it expects from the device. An interrupt endpoint shall respond as
defined in Section 8.11.1.
The host shall send an ACK TP for each valid DP it receives from a device. A device does not
need to wait for the ACK TP to send the next DP to the host if the previous ACK TP indicated that
the host expected the device to send more than one DP (depending on the value of the Number of
Packets field in the TP). The ACK TP implicitly acknowledges the last DP with the previous
sequence number as being successfully received by the host and also indicates to the device the
next DP with the sequence number and number of packets the host expects from the device. If the
host detects an error while receiving any of the DPs, it shall send an ACK TP with the sequence
number value set to the first DP that was received with an error with the Retry bit set, even if
subsequent packets in the burst asked for by the host were received without error. A device is
required to resend all DPs starting from the sequence number set in the ACK TP in which the Retry
bit set.
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Protocol Layer
The host expects the first DP to have a sequence number set to zero when it starts the first transfer
from an endpoint after the endpoint has been initialized (via a Set Configuration, Set Interface, or a
ClearFeature (STALL) command – refer to Chapter 9 for details on these commands). The second
DP sent by the device from that endpoint shall have a sequence number set to one; the third DP has
a sequence number set to two; and so on until sequence number 31. The next DP after sequence
number 31 uses a sequence number of zero. An endpoint on the device keeps incrementing the
sequence number of the packets it transmits unless it receives an ACK TP with the Retry bit set to
one that indicates that it has to retransmit an earlier DP.
If the host asks for multiple DPs from a device and the device does not have that number of DPs
available to send at the time, the device shall send the last DP with the End Of Burst flag in the
DPH set to one. Note that it is not necessary to set the End Of Burst flag if the DP sent to the host
has a payload that is less than the MaxPacketSize for that endpoint.
A transfer is complete when a device sends all the data that is expected by the host or it sends a DP
with a payload that is less than the MaxPacketSize. When the host wants to start a new transfer, it
shall send another ACK TP with the next sequence number and number of DPs expected from a
device. For example, if the DP with the payload less than MaxPacketSize was two, the host shall
initiate the next transfer by sending an ACK TP with the expected sequence number set to three.
8.12.1.3
Bulk OUT Transactions
When the host is ready to transmit bulk data, it sends one or more DPs to a device. If a DPH with
valid values (valid device address, endpoint number, and direction as well as the expected sequence
number) is received by a device, it shall respond as defined in Section 8.11.3.
The host always initializes the first DP sequence number to zero in the first transfer it performs to
an endpoint after the endpoint is initialized (via a Set Configuration, Set Interface, or ClearFeature
(STALL) command – refer to Chapter 9 for details on these commands). The second DP has a
sequence number set to one; the third DP has a sequence number set to two; and so on until 31.
The next DP after sequence number 31 uses a sequence number of zero. The host keeps
incrementing the sequence number of the DPs it transmits unless it receives an ACK TP with the
Retry bit set to one that indicates that it has to retransmit an earlier packet.
A transfer is complete when the host sends all the data it has to a device; however the last DP of the
transfer may or may not have a payload which is equal to the MaxPacketSize of the endpoint.
When the host wants to start a new transfer it shall send another DP, with the next sequence
number, targeted at an endpoint in the device.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Host Tx
Host Rx
IN (ACK TP)
Seq0, 4
Data
Seq0
IN (ACK TP)
Seq1, 4
Data
Seq1
IN (ACK TP)
Data
Seq2, 4
Seq2
IN (ACK TP)
Data
Seq3, 4
Seq3
Data
Seq31
IN (ACK TP)
Seq0, 4
Data
Seq0
IN (ACK TP)
Seq0, 4, rty
DP with Seq1 sent before
device receives the ACK
to retry DP with Seq0
Data
Seq1, eob
Data
Seq0
IN (ACK TP)
Data
Seq1, 4
Seq1, eob
IN (ACK TP)
Seq2, 0
Device has no more data to send.
Sets eob flag in data packet.
Device must send ERDY to
resume traffic to endpoint.
U-115
Figure 8-26. Sample BULK IN Sequence
8-36
Protocol Layer
Host Tx
Host Rx
Data
Seq0
ACK TP
Data
Seq1, 4
Seq1
ACK TP
Seq2, 4
Data
Seq31
ACK TP
Data
Seq0, 4
Seq0
ACK TP
Data
Seq1, 4
Seq1
ACK TP
Data
Seq2
Data
Seq1, 4, rty
DP with Seq2 sent before
host receives the ACK
to retry DP with Seq1
Seq1
Data
ACK TP
Seq2
Seq2, 4
ACK TP
Seq3, 4
U-116
Figure 8-27. Sample BULK OUT Sequence
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.12.1.4
Bulk Streaming Protocol
The Stream Protocol adheres to the semantics of the standard SuperSpeed Bulk protocol, so the
packet exchanges on a SuperSpeed bulk pipe that supports Streams are indistinguishable from a
SuperSpeed bulk pipe that does not. The Stream Protocol is managed strictly through manipulation
of the Stream ID field in the packet header.
Note: As described in this section, the Stream Protocol applies to the state of the “pipe” and is
described as single entity. In reality, the Stream Protocol is being tracked independently by the host
at one end of the pipe and the device at the other. So at any instant in time the two ends may
momentarily be out of phase due to packet propagation delays between the host and the device.
Error
Disabled
Move
Data
Prime
Pipe
Host
Initiated
Stream
Complete
Idle
Accept
Reject
Device
Initiated
Start
Stream
U-117
Figure 8-28. General Stream Protocol State Machine (SPSM)
Figure 8-28 illustrates the basic state transitions of the Stream Protocol State Machine (SPSM).
This section describes the general transitions of the SPSM as they apply to both IN and OUT
endpoints. Detailed operation of the SPSM for IN and OUT endpoints is described in subsequent
sections.
Disabled – This is the initial state of the pipe after it is configured, as well as the state that is
transitioned to if an error is detected in any of the other states. The first time an Endpoint Buffer is
assigned to the pipe, the host shall transition the SPSM to the Prime Pipe state. If the Disabled state
was entered due to an error, then the error condition must be removed by software intervention
before the state may be exited. Note that an error (Stall, timeout, etc.) shall transition any SPSM
state to the Disabled state.
Prime Pipe – This state is always initiated by host, and informs a device that an Endpoint Buffer
set has been added or modified by software.
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Protocol Layer
Idle – This state indicates that there is no Current Stream selected. In this state, the SPSM is
waiting for Prime Pipe or Host Initiated transition to Move Data, or a Device Initiated transition to
Start Stream. The object of the Host and Device Initiated transitions is to start a Stream (setting the
Current Stream, by the Host or a Device, respectively) and begin moving data.
Start Stream – This state is always initiated by a Device when it wants to select a Stream and start
a data transfer. If the device selected Stream is accepted by the host, the Current Stream is set and
the pipe enters the Move Data state. If the device selected Stream is rejected by the host, the pipe
returns to Idle state.
Move Data – In this state, Stream data is transferred. If this state is entered by a Host Initiated
Stream selection, the Current Stream shall be set by the host. If this state is entered from the Start
Stream state, the Current Stream selection will have already been set by a device. The SPSM
transitions back to the Idle state when the Stream transfer is complete, or if the host or a device
decides to terminate the Stream transfer. The transition to Idle invalidates the Current Stream for
the pipe.
8.12.1.4.1
Stream IDs
A 16-bit field Stream ID field is reserved in DP headers and in ACK, NRDY, and ERDY TPs for
passing SIDs between the host and a device. Specific SID values that are reserved by the Stream
Protocol and other SID notations are:
• NoStream – This SID indicates that no Stream ID is associated with the respective bus packet
and the Stream ID field should not be interpreted as referencing a valid Stream. The NoStream
SID value is FFFFh.
• Prime – This SID is used to define transitions into and out of the Prime Pipe state. As with
NoStream, no Stream ID is associated with the respective bus packet and the Stream ID field
should not be interpreted as referencing a valid Stream. The Prime SID value is FFFEh.
• Stream n – Where n is a value between 1 and 65533 (FFFDh). This notation is used to
reference a valid Stream ID. The Stream ID field in the packet header is valid if it uses this
notation. Valid Stream n SID values are between 1 and 65533 (FFFDh), where the numeric
value is identical to n.
• Stream 0 – This value is reserved and not used by a pipe that supports Streams. The Stream 0
SID value is 0000h. Its use is required by a standard bulk pipe.
• CStream – represents the value of the “Current” Stream ID assigned to the pipe. A CStream
value is maintained by both the host and a device. The Stream Protocol ensures that the
CStream values are consistent in the host and the device. Valid values are NoStream or
Stream n.
• LCStream – represents the value of the CStream SID assigned to the pipe before the last state
transition. An LCStream value is maintained by the host. Valid values are Prime, NoStream,
or Stream n. For example, while the pipe in the Move Data state CStream = Stream n, when
the pipe transitions from Move Data to Idle state, LCStream is set to Stream n, and CStream is
set to NoStream, thus LCStream records the “Last CStream” value.
Stream n SID values are assigned by the host and passed to a device (typically through an out-ofband, Device Class defined method). The value of a Stream n SID shall be treated as a “logical
value” by a device, i.e., the device should not infer any meaning from the value or modify it.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Note: The Bulk IN and OUT Stream Protocols below describe simplified state machines that do not
explicitly detail the burst feature of SuperSpeed endpoints which allows DPs to be sent without
receiving an ACK. An implementation shall extend these state machines to manage bursting.
8.12.1.4.2
Bulk IN Stream Protocol
This section defines the SuperSpeed packet exchanges that transition the Stream Protocol from one
state to another on an IN bulk endpoint.
For an IN pipe, Endpoint Buffers in the host receive Function Data from a device.
Device Host Host or Device
Packet Packet
Packet
Disabled
Stall or Error
ACK (Prime, NumP=0, PP=0)
Prime
Pipe
Move
Data
ACK (Stream n, NumP>0)
CStream = Stream n
ACK (Prime,
NumP>0, PP=0)
CStream = NoStream
NRDY (Prime)
ACK (Stream n, NumP>0)
CStream = Stream n
ACK (NoStream, NumP=0, PP=0)
Start
Stream
Idle
ACK (Prime, PP=0)
NRDY (Prime)
Prime
Pipe
ACK
ERDY (Stream n, NumP>0)
U-118
Figure 8-29. Bulk IN Stream Protocol State Machine (ISPSM)
After an endpoint is configured, the pipe is in the Disabled state. The host shall transition the pipe
to the Prime Pipe state by issuing an ACK TP with the Stream ID field set to Prime. This
transition occurs after Endpoint Buffers are assigned to the pipe by system software.
A device shall cause the pipe to exit the Prime Pipe state and transition to the Idle state by
asserting an NRDY TP with its Stream ID field set to Prime.
Note: If an intermediate hub deferred the ACK TP, the host and a device shall act as if the device
sent an NRDY TP. That is, the host shall transition to the Idle state when it receives the Deferred
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Protocol Layer
Response. A device shall transition to the Prime Pipe state when it receives the Deferred ACK TP
and then it shall immediately transition to the Idle state as if it has sent the NRDY TP with its
Stream ID field set to Prime.
In the Idle state, the pipe is waiting for a Stream selection (e.g., a transition to Start Stream or
Move Data) or a notification from the host that an Endpoint Buffer as been added or modified for
the pipe (transition to Prime Pipe). In the Idle state, Stream selection initiated by the host is
identified by an ACK TP with its Stream ID set to Stream n and a NumP value > 0. This packet
shall transition the ISPSM from the Idle state to the Move Data state. If the last ISPSM transition
was from Start Stream or Move Data, the host shall initiate an Idle to Move Data transition due
to two possible conditions: 1) if an Endpoint Buffer posted to the pipe was for LCStream and the
last ISPSM transition was not due to an NRDY(Stream n) Move Data exit, or 2) if an endpoint
buffer is posted for a new stream (i.e., newly posted SID not equal LCStream). In the Idle state,
Stream selection initiated by a device is identified by an ERDY TP with its Stream ID set to Stream
n and a NumP value > 0. This packet shall transition the ISPSM from the Idle state to the Start
Stream state. A device shall initiate this transition when it wishes to start a Stream transfer
regardless of whether it is in a flow control condition or not.
In the Start Stream state, the pipe is waiting for the host to accept or reject the Stream selection
proposed by a device. The host shall indicate the acceptance of a device initiated Stream selection
by asserting an ACK TP with the following field settings, Stream ID = Stream n and NumP > 0.
This packet shall transition the ISPSM from the Start Stream state to the Move Data state. The
host shall indicate the rejection of a device initiated Stream selection by asserting an ACK TP with
the following field settings, Stream ID = NoStream, NumP = 0, and Packet Pending (PP) = 0. This
packet shall transition the ISPSM from the Start Stream state to the Idle state. The host shall
reject a stream selection if there are no Endpoint Buffers available for a device selected SID.
The ISPSM executes independently on the host and device. A race condition occurs if a device
issues an ERDY to the host and enters the Start Stream state, at the same time that the host issues
a ACK(Prime,PP=0) to the device and enters the Prime Pipe state. To recover from this condition,
if a device receives a ACK(Prime,PP=0) while in the Start Stream state, it shall transition to the
Prime Pipe Ack state and issue an NRDY(Prime) to the host, to complete the Prime Pipe to Idle
transition for the host, and the Prime Pipe Ack to Idle transition for the device.
In the Move Data state, CStream is set at both ends of the pipe and the pipe is actively moving data
to the host. The details of the bus transactions executed in the Move Data state and its exit
conditions are defined in the IN Move Data State Machine defined below.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Device Host
Packet Packet
ACK (Stream n, NumP=0, PP=0)
INMvData
Device
Terminate
ACK (Stream n, NumP=0, PP=0)
NRDY (Stream n)
DP (Stream n, EOB=1) or
DP (Stream n,
Data Length < MaxPacketSize
ACK (Stream n, NumP>0, PP=1, Rty)
INMvData
Host
DP (Stream n, EOB=0)
Data Length = MaxPacketSize
INMvData
Device
ACK (Stream n, NumP>0)
ACK (NumP=0, PP=1)
INMvData
Burst
End
ACK (Stream n,
NumP>0)
U-119
Figure 8-30. IN Move Data State Machine (IMDSM)
The IN Move Data State Machine (IMDSM) is entered from the Start Stream or Idle states as
described above. The entry into the IMDSM immediately transitions to the INMvData Device
state. The Stream ID field of all packets generated by the IMDSM shall be Stream n.
Each time the INMvData Device state is entered, a device performs the following actions to
advance the IMDSM:
if ( Device Function Data bytes > Max Packet Size )
The device shall generate a DP with EOB field = 0, which shall cause the pipe to transition
to the INMvData Host state.
else if ( Device Function Data bytes = Max Packet Size )
The device shall generate a DP with EOB field = 1, which shall cause the pipe to transition
to the INMvData Device Terminate state.
else ( Device Function Data bytes < Max Packet Size )
The device shall generate a short DP, which shall cause the pipe to transition to the
INMvData Device Terminate state.
Optionally, a device may generate an NRDY TP with the Stream ID set to Stream n, which
terminates the stream, and shall cause the pipe to exit the IMDSM and transition to Idle state. A
device may use this transition to reject a Host Initiated Move Data.
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Protocol Layer
Note: If an intermediate hub deferred the ACK TP, the host and a device shall act as if the device
sent an NRDY TP. That is, the host shall transition to the Idle state when it receives the Deferred
Response. A device shall exit the IMDSM and transition to the Idle state when it receives the
Deferred ACK TP as if it has sent an NRDY TP with its Stream ID field set to Stream n. If a
device accepts the host initiated Stream ID, it shall send an ERDY with its Stream ID field set to
Stream n. If a device rejects the host initiated Stream ID, it shall stay in the Idle state and wait for
next Stream selection either by the host or a device.
The INMvData Host state is entered because a device has more Function Data to send, so the host
performs the following actions to advance the IMDSM:
if ( Another DP can be scheduled in this burst )
if ( The host has more Endpoint Buffer space available )
Generate an ACK TP with NumP > 0, which shall cause the pipe to transition to the
INMvData Device state.
else the host is out of Endpoint Buffer space.
Generate a Terminating ACK TP with NumP = 0 and PP = 0, which shall cause the
pipe to exit the IMDSM and transition to the Idle state.
else ( the last DP of the burst has just been received )
Terminate the burst.
if ( The host has more Endpoint Buffer space available)
Inform the device that the burst is complete (NumP = 0) and another burst shall be
scheduled by the host (PP = 1) for CStream. Generate an ACK TP with NumP = 0 and
PP = 1, which shall cause the pipe to transition to the INMvData Burst End state.
else the host is out of Endpoint Buffer space.
Generate a Terminating ACK TP with NumP = 0 and PP = 0, which shall cause the
pipe to exit the IMDSM and transition to the Idle state.
In the INMvData Burst End state, the host shall generate an ACK with NumP > 0 and PP = 1 to
initiate the next burst and cause the pipe to transition to the INMvData Device state.
The pseudo code describing the IMDSM assumes that the received DP is valid. If it is invalid, an
ACK TP shall be generated, which shall transition the pipe to the INMvData Device state. The
Sequence Number in the ACK TP shall not advance, however, the retry may decrement the
transmitted NumP value. If NumP = 0 and there are still Endpoint Buffers available in the host, PP
shall be set to 1; otherwise, PP is set to 0.
The INMvData Device Terminate state is entered because a device has no more Function Data to
be sent, so the host shall generate a Terminating ACK TP with NumP = 0 and PP = 0, which shall
cause the pipe to exit the IMDSM and transition to the Idle state. If the host detects an error on the
last DP sent by a device, it shall respond with a Retry ACK TP (Steam n, NumP>0, Rty) and the
IMDSM shall transition to the INMvDataDevice state.
Note: If a DP error is detected in the INMvDataHost state, the host shall generate an ACK TP with
NumP > 0 and Rty = 1, which shall cause the pipe to transition to the INMvDataDevice state and
resend the packet.
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.12.1.4.3
Bulk OUT Stream Protocol
This section defines the SuperSpeed packet exchanges that transition the Stream Protocol from one
state to another on an OUT bulk endpoint.
For an OUT pipe, Endpoint Data in host is transmitted to Function Buffers in a device. Unless
otherwise stated, a DP will contain Endpoint Data.
Device Host Host or Device
Packet Packet
Packet
Disabled
Stall or Error
DP (Prime, PP=0)
DP (Stream n)
CStream = Stream n
Prime
Pipe
DP (Prime, PP=0)
Move
Data
CStream = NoStream
Accept DP (Stream n)
CStream = Stream n
NRDY (Prime)
Start
Stream
End
DP (NoStream, PP=0)
CStream = NoStream
NRDY (NoStream)
Start
Stream
Idle
DP (Prime, PP=0)
NRDY (Prime)
Prime
Pipe
ACK
ERDY (Stream n, NumP>0)
U-120
Figure 8-31. OUT Stream Protocol State Machine (OSPSM)
After an endpoint is configured, the pipe is in the Disabled state. The host shall transition the pipe
to the Prime Pipe state by issuing a DP with the Stream ID field set to Prime. This transition
occurs after Endpoint Buffers are assigned to the pipe by system software.
A device shall cause the pipe to exit the Prime Pipe state and transition to the Idle state by
asserting an NRDY TP with its Stream ID field set to Prime.
Note: If an intermediate hub deferred the DP, the host and a device shall act as if the device sent an
NRDY TP. That is, the host shall transition to the Idle state when it receives the Deferred
Response. A device shall transition to the Prime Pipe state when it receives the Deferred DPH.
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Protocol Layer
Then it shall immediately transition to the Idle state as if it has sent an NRDY TP with its Stream
ID field set to Prime.
In the Idle state, the pipe is waiting for a Stream selection (e.g., a transition to Start Stream or
Move Data) or a notification from the host that Endpoint Data has been added or modified for the
pipe (transition to Prime Pipe). In the Idle state, Stream selection initiated by the host is identified
by a DP with its Stream ID set to Stream n. The value of PP will depend on whether the host has
one (PP = 0) or more (PP = 1) packets to transfer. This packet shall transition the OSPSM from the
Idle state to the Move Data state. If the last OSPSM transition was from Start Stream or Move
Data the host shall initiate an Idle to Move Data transition due to two possible conditions: 1) if an
Endpoint Buffer posted to the pipe was for LCStream and the last OSPSM transition was not due to
an NRDY(Stream n) Move Data exit, or 2) if an endpoint buffer is posted for a new stream. In the
Idle state, Stream selection initiated by a device is identified by an ERDY TP with its Stream ID set
to Stream n and a NumP value > 0. This packet shall transition the OSPSM from the Idle state to
the Start Stream state. A device shall initiate this transition when it wishes to start a Stream
transfer regardless of whether it is in a flow control condition or not.
In the Start Stream state, the pipe is waiting for the host to accept or reject the Stream selection
proposed by a device. The host shall indicate the acceptance of a device initiated Stream selection
by sending a DP with the following field settings; Stream ID = Stream n. The value of PP will
depend on whether the host has one (PP = 0) or more (PP = 1) packets to transfer. This packet shall
transition the OSPSM from the Start Stream state to the Move Data state. The host shall indicate
the rejection of a device initiated Stream selection by asserting a DP with the following field
settings; Length = 0, Stream ID = NoStream and PP = 0. This packet shall transition the OSPSM
from the Start Stream state to the Start Stream End state. The host shall reject a stream selection
if there is no Endpoint Data Buffer available for a device selected SID.
The OSPSM executes independently on the host and device. A race condition occurs if the device
issues an ERDY to the host and enters the Start Stream state, at the same time that the host issues
a DP(Prime,PP=0) to the device and enters the Prime Pipe state. To recover from this condition, if
the device receives a DP(Prime,PP=0) while in the Start Stream state it shall transition to the
Prime Pipe Ack state and issue an NRDY(Prime) to the host, to complete the Prime Pipe to Idle
transition for the host, and the Prime Pipe Ack to Idle transition for the device.
The Start Stream End state is an intermediate state for exiting the Start Stream state when a
selection is rejected. The device shall always force a transition to the Idle state by issuing an
NRDY TP, with Stream ID = NoStream. This transition fulfills the requirement that a device must
respond to a DP from the host.
In the Move Data state CStream is set at both ends of the pipe and the pipe is actively moving data
to a device. The details of the bus transactions executed in the Move Data state and its exit
conditions are defined in the OUT Move Data State Machine defined below.
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Universal Serial Bus 3.0 Specification, Revision 1.0
NRDY (Stream n)
Device Host
Packet Packet
ACK (Stream n, NumP=0)
OUTMvData
Host
Terminate
ACK (Stream n, NumP=0)
ACK (Stream n, NumP>0, Rty)
NRDY (Stream n)
DP (Stream n, PP=0)
PP=0
OUTMvData
Host
ACK (Stream n, NumP>0)
DP (Stream n, PP=1)
OUTMvData
Device
PP=1
U-121
Figure 8-32. OUT Move Data State Machine (OMDSM)
The OUT Move Data State Machine (OMDSM) is entered from the Start Stream or Idle states as
described above. The Stream ID field of all packets generated by the OMDSM shall be Stream n.
Upon entering the OMDSM, the value of the PP field in the received DP is evaluated. PP = 1
transitions the OMDSM to the OUTMvData Device state. PP = 0 transitions the OMDSM to the
OUTMvData Host Terminate state.
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Protocol Layer
Each time the OUTMvData Device state is entered, a device performs the following actions to
advance the OMDSM:
if (Device Function Buffer space >= Host Endpoint Data size 1)
The device shall generate an ACK TP with the NumP field > 0, which shall cause the pipe
to transition to the OUTMvData Host state.
else (Device Function Buffer space < Host Endpoint Data size)
The device shall generate a Terminating ACK TP with the NumP field = 0, which shall
cause the pipe to exit the OMDSM, and transition to the Idle state.
Optionally, the device may generate an NRDY TP with the Stream ID set to Stream n, which
terminates the stream, and shall cause the pipe to exit the OMDSM and transition to the Idle
state. A device may use this transition to reject a Host Initiated Move Data.
Note: If an intermediate hub deferred the DP, the host and a device shall act as if the device sent an
NRDY TP. That is, the host shall transition to the Idle state when it receives the Deferred
Response. A device shall exit the OMDSM and transition to the Idle state when it receives the
Deferred DP as if it has sent an NRDY TP with its Stream ID field set to Stream n. If a device
accepts the host initiated Stream ID, it shall send an ERDY TP with its Stream ID field set to
Stream n. If a device rejects the host initiated Stream ID, it shall stay in the Idle state and wait for
next Stream selection either by the host or a device.
The OUTMvData Host state is entered because a device has more Function Buffer space available
for receiving data, so the host performs the following actions to advance the OMDSM.
if (Host Endpoint Data size > Max Packet Size)
Generate a DP with PP = 1, which shall cause the pipe to transition to the
OUTMvData Device state.
else the Host Endpoint Data size <= Max Packet Size
Generate a DP with PP = 0, which shall cause the pipe to transition to the
OUTMvData Host Terminate state.
The pseudo code describing the OMDSM is independent of whether the received ACK TP indicates
a retry or not. An ACK TP with Retry shall affect the transmitted DP Sequence Number and cause
Endpoint Data to be retransmitted.
The OUTMvData Host Terminate state is entered because the host has no more Endpoint Data to
be sent (PP = 0), so a device shall generate a Terminating ACK TP with NumP = 0, which shall
cause the pipe to exit the OMDSM and transition to the Idle state. If a device detects an error on
the last DP sent by the host, it shall respond with a Retry ACK TP (Steam n, NumP>0, Rty=1) and
the OMDSM shall transition to the OUTMvData Host state.
Note that if a DP error is detected in the OUTMvData Device state, a device shall generate an
ACK TP with NumP > 0 and Rty=1, which shall cause the pipe to transition to the OUTMvData
Host state and resend the packet.
1
The Host Endpoint Data size is communicated to a device through a Device Class define mechanism.
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.12.2
Control Transfers
Control transfers have a minimum of two transaction stages: Setup and Status. A control transfer
may optionally contain a Data stage between the Setup and Status stages. The direction of the Data
stage is indicated by the bmRequestType field which is present in the first byte of the data payload
of the Setup packet. During the Setup stage, a SETUP transaction is used to transmit information to
a control endpoint of the device. SETUP transactions are similar in format to a Bulk OUT
transaction but have the Setup field set to one in the DPH along with the Data Length field set to
eight. In addition, the Setup packet always uses a Data sequence number of zero. A device
receiving a Setup packet shall respond as defined in Section 8.11.4. The Direction field shall be set
to zero in TPs or DPs exchanged between the host and any control endpoint on the device.
Note that an endpoint may return an ACK TP with the NumP field set to zero in response to a
SETUP packet if it wants to flow control the control transfer. A device must send an ERDY to start
the Data or Status stage.
The Data stage, if present, of a control transfer consists of one or more IN or OUT transactions and
follows the same protocol rules as bulk transfers with a burst set to one. The Data stage always
starts with the sequence number set to zero. All the transactions in the Data stage shall be in the
same direction (i.e., all INs or all OUTs). The maximum amount of data to be sent during the data
stage and its direction are specified during the Setup stage. If the amount of data exceeds the data
packet size, the data is sent in multiple data packets that carry the maximum packet size. Any
remaining data is sent as a residual in the last data packet.
Note that all control endpoints only support a burst of one and hence the host can only send or
receive one packet at a time to or from a control endpoint.
The Status stage of a control transfer is the last transaction in the sequence. The status stage
transaction is identified by a TP with the SubType set to STATUS. In response to a STATUS TP
with zero in the Deferred bit, a device shall send an NRDY, STALL, or ACK TP. If a device
sends an NRDY TP, the host shall wait for it to send an ERDY TP for that control endpoint before
sending another STATUS TP to the device. If the Deferred bit is set in the STATUS TP, then the
device shall send an ERDY TP to indicate to the host that is ready to complete the status stage of
the control transfer.
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Protocol Layer
Figure 8-33 and Figure 8-34 show the transaction order, the data sequence number value, and the
data packet types for control read and write sequences.
Control Read
Host Tx
Host Rx
Setup
Seq0
ACK TP
Seq1, 1
Setup Stage
IN (ACK TP)
Seq0, 1
Data
Seq0
Data Stage
IN (ACK TP)
Seq3, 1
Data
Seq3
IN (ACK TP)
Seq4, 0
STATUS TP
ACK TP
Seq1, 0
Status Stage
U-122a
Figure 8-33. Control Read Sequence
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Universal Serial Bus 3.0 Specification, Revision 1.0
Control Write
Host Tx
Host Rx
Setup
Seq0
ACK TP
Seq1, 1
Setup Stage
Data
Seq0
ACK TP
Seq1, 1
Data Stage
Data
Seq5
ACK TP
Seq6, 1
STATUS TP
ACK TP
Seq1, 0
Status Stage
U-122b
Figure 8-34. Control Write Sequence
When a STALL TP is sent by a control endpoint in either the Data or Status stages of a control
transfer, a STALL TP shall be returned on all succeeding accesses to that endpoint until a SETUP
DP is received. An endpoint shall return an ACK TP when it receives a subsequent SETUP DP.
For control endpoints, if an ACK TP is returned for the SETUP transaction, the host expects that
the endpoint has automatically recovered from the condition that caused the STALL and the
endpoint shall operate normally.
8.12.2.1
Reporting Status Results
During the Status stage, a device reports to the host the outcome of the previous Setup and Data
stages of the transfer. Three possible results may be returned:
• The command sequence completed successfully.
• The command sequence failed to complete.
• The device is still busy completing the command.
Status reporting is always in the device-to-host direction. Table 8-29 summarizes the type of
responses required for each. All Control transfers return status in the TP that is returned to the host
in response to a STATUS TP transaction.
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Protocol Layer
Table 8-29. Status Stage Responses
Status Response
TP Sent by Device
Request completes
ACK TP
Request has an error
STALL TP
Device is busy
NRDY TP
The host shall send a STATUS TP to the control pipe to initiate the Status stage. The pipe’s
handshake response to this TP indicates the current status. An NRDY TP indicates that a device is
still processing the command and that the device shall send an ERDY TP when it completes the
command. An ACK TP indicates that a device has completed the command and is ready to accept
a new command. A STALL TP indicates that a device has an error that prevents it from completing
the command.
The NumP field of the ACK TP sent by a control endpoint on the device shall be set to zero.
However this is not considered a flow control condition for a control endpoint.
If during a Data stage a control pipe is sent more data or is requested to return more data than was
indicated in the Setup stage, it shall return a STALL TP. If a control pipe returns a STALL TP
during the Data stage, there shall not be a Status stage for that control transfer.
8.12.2.2
Variable-length Data Stage
A control pipe may have a variable-length data phase in which the host requests more data than is
contained in the specified data structure. When all of the data structure is returned to the host, a
device indicates that the Data stage is ended by returning a DP that has a payload less than the
maximum packet size for that endpoint.
Note that if the amount of data in the data structure that is returned to the host is less than the
amount requested by the host and is an exact multiple of maximum packet size then a control
endpoint shall send a zero length DP to terminate the data stage.
8.12.2.3
STALL TPs Returned by Control Pipes
Control pipes have the unique ability to return a STALL TP due to problems in control transfers. If
a device is unable to complete a command, it returns a STALL TP in the Data and/or Status stages
of the control transfer. Unlike the case of a functional stall, protocol stall does not indicate an error
with the device. The protocol STALL condition lasts until the receipt of the next SETUP DP, and
the device shall return a STALL TP in response to any IN or OUT transaction on the pipe until the
SETUP DP is received. In general, protocol stall indicates that the request or its parameters are not
understood by a device and thus provides a mechanism for extending USB requests.
Devices do not support functional stall on a control pipe.
8.12.3
Bus Interval and Service Interval
For all periodic (interrupt and isochronous) endpoints, the interval at which an endpoint must be
serviced is called a “Service Interval”. In this specification the term “Bus Interval” is used to refer
to a 125 µs period.
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8.12.4
Interrupt Transactions
The interrupt transfer type is used for infrequent data transfers with a bounded service period. It
supports a reliable data transport with guaranteed bounded latency. It offers guaranteed constant
data rate as long as data is available. If an error is detected in the data delivered, the host is not
required to retry the transaction in the same service interval. However, if a device is momentarily
unable to transmit or receive the data (i.e., responds with an NRDY TP), the host shall resume
transactions to an endpoint only after it receives an ERDY TP from that device for that endpoint.
Interrupt transactions are very similar to bulk transactions – but are limited to a burst of three DPs
in each service interval. The host shall continue to perform transactions to an interrupt endpoint at
the agreed upon service interval as long as a device accepts data (in the case of OUT endpoints) or
returns data (in the case of IN endpoints). The host is required to send an ACK TP for every DP
successfully received in the service interval even if it is the last DP in that service interval. The
final ACK TP shall acknowledge the last DP received and shall have the Number of Packets field
set to zero. If an error occurs while performing transactions to an interrupt endpoint in the current
service interval, then the host is not required to retry the transaction in the current service interval
but the host shall retry the transaction in the next service interval at the latest.
8.12.4.1
Interrupt IN Transactions
When the host wants to start an Interrupt IN transaction to an endpoint, it sends an ACK TP to the
endpoint with the expected sequence number and the number of packets it expects to receive from
the endpoint. If an interrupt endpoint is able to send data in response to the ACK TP from the host,
it may send up to the number of packets requested by the host within the same service interval. The
host shall respond to each of the DPs with an ACK TP indicating successful reception of the data or
an ACK TP requesting the DP to be retried in case the DPP was corrupted.
Note that the host expects the first DP to have its sequence number set to zero when it starts the first
transfer from a specific endpoint, after the endpoint has been initialized (via a Set Configuration or
Set Interface or ClearFeature (STALL) command – refer to Chapter 9 for details on these
commands).
An interrupt endpoint shall respond to TPs received from the host as described in Section 8.11.1.
As long as a device returns data in response to the host sending ACK TPs and the transfer is not
complete, the host shall continue to send ACK TPs to the device during every service interval for
that endpoint.
The host shall stop performing transactions to an endpoint on the device when any of the following
happen:
• The endpoint responds with an NRDY or STALL TP.
• All the data for the transfer is successfully received.
• The endpoint sets the EOB flag in the last DP sent to the host.
When an endpoint receives an ACK TP from the host and cannot respond by sending data, it shall
send an NRDY (or STALL in case of an internal endpoint or device error) TP to the host. The host
shall not perform any more transactions to the endpoint in subsequent service intervals.
The host shall resume interrupt transactions to an endpoint that responded with a flow control
response in a previous service interval only after it receives an ERDY TP from the endpoint. This
notifies the host about the endpoint’s readiness to transmit data again. Once the host receives the
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Protocol Layer
ERDY TP, it shall send an IN request (via an ACK TP) to the endpoint no later than twice the
service interval as determined by the value of the bInterval field in the interrupt endpoint
descriptor. An interrupt endpoint responds by returning either the DP (the sequence number of the
packet being one more than the sequence number of the last successful data sent) or, should it be
unable to return data, an NRDY or a STALL TP.
If a device receives a deferred interrupt IN TP, and the device needs to send interrupt IN data, the
device shall respond with an ERDY TP and keep its link in U0 until it receives the subsequent
interrupt transaction from the host, or until tPingTimeout (refer to Table 8-33) time elapses.
As in the case of Bulk transactions, the sequence number is continually incremented with each
packet sent by an interrupt endpoint. When the sequence number reaches 31 it wraps around to
zero.
Interrupt IN
Host Tx
Host Rx
Host has a buffer
to receive data
IN (ACK TP)
Seq0, 1
Data
Seq0
IN (ACK TP)
Seq1, 0
ACKs the above DP.
Does not request another packet.
Next Service Interval
Host has a buffer
to receive data
IN (ACK TP)
Seq1, 1
Data
Seq1
IN (ACK TP)
Seq2, 0
U-123
Figure 8-35. Host Sends Interrupt IN Transaction in Each Service Interval
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Universal Serial Bus 3.0 Specification, Revision 1.0
Interrupt IN
Host Tx
Host Rx
Host has a buffer
to receive data
IN (ACK TP)
Seq2, 1
NRDY TP
Host stops servicing the same endpoint until endpoint sends ERDY
U-124
Figure 8-36. Host Stops Servicing Interrupt IN Transaction Once NRDY is Received
Interrupt IN
Host Tx
Host Rx
Device has data to send
ERDY TP
1
Less than 2 x bInterval
Host has a buffer
to receive data
IN (ACK TP)
Seq2, 1
Data
Seq2
IN (ACK TP)
Seq3, 0
U-125
Figure 8-37. Host Resumes IN Transaction after Device Sent ERDY
Interrupt IN
Host Tx
Host Rx
Host has a buffer
to receive data
IN (ACK TP)
Seq3, 1
Device failed to
provide data
STALL TP
U-126
Figure 8-38. Endpoint Sends STALL TP
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Protocol Layer
Interrupt IN
Host Tx
Host Rx
Host has a buffer
to receive data
IN (ACK TP)
Seq0, 1
Host has detected error
in received packet
Data
Seq0
IN (ACK TP)
Seq0, 1 Retry bit set
Data
Seq0
IN (ACK TP)
Seq1, 0
Next Service Interval
Host has a buffer
to receive data
IN (ACK TP)
Seq1, 1
Data
Seq1
IN (ACK TP)
Seq2, 0
U-127
Figure 8-39. Host Detects Error in Data and Device Resends Data
Note: In Figure 8-39 the host retries the data packet received with an error in the same service
interval. It is not required to do so and may retry the transaction in the next service interval.
8.12.4.2
Interrupt OUT Transactions
When the host wants to start an Interrupt OUT transaction to an endpoint, it sends the first DP with
the expected sequence number. The host may send more packets to the endpoint in the same
service interval if the endpoint supports a burst size greater than one. If an endpoint was able to
receive that data from the host, it sends an ACK TP to acknowledge the successful receipt of data.
Note that the host always initializes the first DP sequence number to zero in the first transfer it
performs to an endpoint after the endpoint is initialized (via a Set Configuration or Set Interface or
ClearFeature (STALL) command – refer to Chapter 9 for details on these commands).
As long as a device returns ACK TPs in response to the host sending data packets and the transfer
is not complete, the host shall continue to send data to the device during every service interval for
that endpoint. A device shall acknowledge the successful reception of the DP or ask the host to
retry the transaction if the data packet was corrupted.
In response to the OUT data sent by the host an interrupt endpoint shall respond as described in
Section 8.11.3.
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Universal Serial Bus 3.0 Specification, Revision 1.0
When an endpoint receives data from the host, and it cannot receive data momentarily, it shall send
an NRDY (or STALL in case of an internal endpoint or device error) TP to the host. The host shall
not perform any more transactions to the endpoint in subsequent service intervals.
A host shall only resume interrupt transactions to an endpoint that responded with a flow control
response after it receives an ERDY TP from that endpoint. This notifies the host about the
endpoint’s readiness to receive data again. Once the host receives an ERDY TP, the host shall
transmit the data packet to the endpoint no later than twice the service interval as determined by the
value of the bInterval field in the interrupt endpoint descriptor for that endpoint.
If a device receives a deferred interrupt OUT DPH, and the device needs to receive interrupt OUT
data, the device shall respond with an ERDY TP and keep its link in U0 until it receives the
subsequent interrupt transaction from the host, or until tPingTimeout (see Table 8-33) elapses.
As in the case of Bulk transactions, the sequence number is continually incremented with each
packet sent by host. When the sequence number reaches 31 it wraps around to zero.
Interrupt OUT
Host Tx
Host Rx
Host has data to send
Data
Seq0
ACK TP
Seq1, 1
Next Service Interval
Host has data to send
Data
Seq1
ACK TP
Seq2, 1
U-128
Figure 8-40. Host Sends Interrupt OUT Transaction in Each Service Interval
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Protocol Layer
Interrupt OUT
Host Tx
Host Rx
Host has data to send
Data
Seq2
NRDY TP
Host stops servicing the same endpoint until endpoint sends ERDY
U-129
Figure 8-41. Host Stops Servicing Interrupt OUT Transaction Once NRDY is Received
Interrupt OUT
Host Tx
Host Rx
Device has buffer
to receive data
ERDY TP
1
Less than 2 x bInterval
Host has data to send
Data
Seq2
ACK TP
Seq3, 1
U-130
Figure 8-42. Host Resumes Sending Interrupt OUT Transaction After Device Sent ERDY
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Universal Serial Bus 3.0 Specification, Revision 1.0
Interrupt OUT
Host Tx
Host Rx
Host has data to send
Data
Data has detected error
in received data
Seq3
ACK TP
Host resends the
same data
Data
Seq3, 1 Retry bit set
Data has received
data successfully
Seq3
ACK TP
Seq4, 1
U-131
Figure 8-43. Device Detects Error in Data and Host Resends Data
Note: In Figure 8-43 the host retries the data packet received with an error in the same service
interval. It is not required to do so and may retry the transaction in the next service interval.
Interrupt OUT
Host Tx
Host Rx
Host has data to send
Data
Seq4
Hardware failure
STALL TP
U-132
Figure 8-44. Endpoint Sends STALL TP
8.12.5
Host Timing Information
USB 3.0 host controllers do not broadcast regular start of frame (SOF) packets to all devices on a
SuperSpeed USB link. Host timing information is only sent by the host via isochronous timestamp
packets (ITP) when the root port link is in U0 around a bus interval boundary. Hubs forward
isochronous timestamp packets to any downstream port with a link in U0. The host shall provide
isochronous timestamps based on a non-spread clock. Devices are responsible for keeping the link
in U0 around bus interval boundaries when isochronous timestamps are required for device
operation. A device should never keep the link in U0 for the sole purpose of receiving timestamps
unless the timestamps are required for device operation.
Note: A device will receive an isochronous timestamp if its link is in U0 around a bus interval
boundary. This means that devices without any isochronous endpoints or need for synchronization
may discard isochronous timestamp packets without negative side effects. If a device implements
an inactivity timer for deciding when to drive the link into a lower power state, the device may
choose to not reset the inactivity timer upon receiving an isochronous timestamps.
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Protocol Layer
The timing information is sent in an isochronous timestamp packet around each bus interval
boundary and communicates the current bus interval and the time from the start of the timestamp
packet to the previous bus interval. Isochronous endpoints request a service interval of 125 * 2n µs,
where n is an integer value from 0 to 15 inclusive.
ITPs communicate timing information such that all isochronous endpoints receive the same bus
interval boundaries. The host shall keep service interval boundaries aligned for all endpoints at all
times unless the host link enters U3. ITPs issued after the host root port link exits U3 may be
aligned with boundaries from before the host root port link entered U3. The host shall begin
transmitting ITPs within tIsochronousTimestampStart from when the host root port’s link enters U0
after the link was in U3. Figure 8-45 shows an example with an active isochronous IN endpoint
and isochronous OUT endpoint connected below the same USB 3.0 host controller. The service
interval for the isochronous IN endpoint is X and the service interval for the isochronous OUT
endpoint is 2X. Note that the host is free to schedule an isochronous IN (via an ACK TP) or
isochronous OUT data anywhere within the appropriate service interval. A device shall not assume
that transactions occur at the same location within each service interval. The host shall schedule
isochronous transactions such that they do not cross service interval boundaries.
X
X
X
X
Time to Bus
Interval Boundary
Time to Bus
Interval Boundary
Time to Bus
Interval Boundary
Time to Bus
Interval Boundary
Bus Interval N
Bus Interval N+1
Bus Interval N+2
Bus Interval N+3
2X
2X
Time to Bus
Interval Boundary
Time to Bus
Interval Boundary
Service Interval N
Service Interval N+1
Isochronous Out Header and Data Payload
Isochronous Timestamp Packet
Isochronous IN Handshake from Host
Isochronous IN Header and Data Payload
U-136
Figure 8-45. Multiple Active Isochronous Endpoints with
Aligned Service Interval Boundaries
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.12.6
Isochronous Transactions
IN isochronous transactions are shown in Figure 8-46 and OUT isochronous transactions are shown
in Figure 8-47. For INs, the host issues an ACK TP followed by a data phase in which the endpoint
transmits data for INs. For OUTs, the host simply transmits data when there is data to be sent in the
current service interval. Isochronous transactions do not support retry capability.
Isochronous IN
Host Tx
Host Rx
When host has a buffer to
receive data for current
isochronous service interval
ACK TP
Seq0, N
Data
Seq0
Data
Seq1
Data
Seq2
Data
SeqN, Ipf
U-137a
Figure 8-46. Isochronous IN Transaction Format
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Protocol Layer
Isochronous OUT
Host Tx
Host Rx
When host has data to send
for current isochronous
service interval
Data
Seq0
Data
Seq1
Data
Seq2
Data
SeqN, Ipf
U-137b
Figure 8-47. Isochronous OUT Transaction Format
SuperSpeed isochronous transactions with a single data packet per service interval always use
sequence number zero. For isochronous transactions that include multiple data packets in a service
interval the sequence number is increased by one for each subsequent data packet. The first data
packet sent in any service interval always uses sequence number zero. The host shall be able to
accept and send up to 48 data packets (DP) per service interval. The first DP in each service
interval shall start with the sequence number set to 0. The second DP shall have a sequence
number set to one; the third DP has a sequence number set to two; and so on until sequence
number 31. The next DP after sequence number 31 uses a sequence number of zero. A
SuperSpeed device with an isochronous endpoint shall be able to send or receive the number of
packets (with sequence numbers 0 – N) as indicated in its endpoint and endpoint companion
descriptors.
If the data is less than endpoint maximum packet size, then it will be sent as the last packet within
the service interval with the lpf field set to 1. If there is no data to send to an isochronous OUT
endpoint during a service interval, the host does not send anything during the interval. If a device
with an isochronous IN endpoint does not have data to send when an isochronous IN ACK TP is
received from the host, it shall send a zero length data packet.
Figure 8-48 and Figure 8-49 show sample isochronous IN and OUT transactions for endpoints that
have requested 2000 bytes of bandwidth per service interval (i.e., no more than two packets can be
sent or received each service interval).
If the host is not able to send isochronous OUT data during the specified interval due to an error
condition, the host discards the data and notifies host software of the error. If the host is not able to
send an isochronous ACK TP during the specified service interval due to an error condition, the
host notifies host software of the error.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Isochronous IN
Host Tx
Host Rx
Host has a buffer
to receive data
ACK TP
Seq0, 2
Data
Seq0
Data
Interval N
Seq1, Ipf
Host has a buffer
to receive data
Device has no
data to send
ACK TP
Seq0, 2
Data - 0 Bytes
Seq0, Ipf
Interval N + 1
Host has a buffer
to receive data
Device has only one
packet to send
ACK TP
Seq0, 2
Data
Seq0, Ipf
Interval N + 2
U-138a
Figure 8-48. Sample Isochronous IN Transaction
8-62
Protocol Layer
Isochronous OUT
Host Tx
Host Rx
Host has data to send
Data
Seq0
Data
Seq1, Ipf
Host has no data to send
Host has only one data
packet to send
Data
Seq0, Ipf
U-138b
Figure 8-49. Sample Isochronous OUT Transaction
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Universal Serial Bus 3.0 Specification, Revision 1.0
Isochronous IN
Host Tx
Host Rx
Host has a buffer
to receive data
ACK TP
Seq0, 4
Data
Seq0
Data
Seq1
Data
Seq2
Data
Seq3
Host has a buffer
to receive data
ACK TP
Seq4, 4
Data
Seq4
Data
Seq5
Data
Seq6
Data
Seq7
Host has a buffer
to receive data
ACK TP
Seq8, 4
Data
Seq8
Data
Seq9
Data
Interval N
Seq10, Ipf
U-139a
Figure 8-50. Isochronous IN Transaction Example
8-64
Protocol Layer
Isochronous OUT
Host Tx
Host Rx
Host has data to send
Data
Seq0
Data
Seq1
Data
Seq2
Data
Seq3
Host has more data to send
Data
Seq4
Data
Seq5
Data
Seq6
Data
Seq7
Host has last data to send
Data
Seq8
Data
Seq9
Data
Seq10, Ipf
U-139b
Figure 8-51. Isochronous OUT Transaction Example
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.12.6.1
Host Flexibility in Performing Isochronous Transactions
The host is allowed some flexibility in performing isochronous service during a service interval.
The host may transfer all the DPs to or from an endpoint as a single isochronous burst transaction
or it may split the transfer into smaller bursts of two, four, or eight DPs followed by a final
isochronous burst with the remaining DPs for that service interval. The host shall not perform
isochronous transactions in any other way. For isochronous endpoints that have a multiplier value
greater than one, these rules apply to the burst transactions associated with each multiplier value
separately. A device shall support all possible host burst transactions allowed by these rules. For
example, if an isochronous OUT endpoint requests a maximum number of packets in a burst of 11
and the host has 11 packets to send to the endpoint during a service interval there are four possible
ways the host could perform the transaction:
• A single burst of 11 packets
• A burst of eight followed by a burst of three
• Two bursts of four followed by a burst of three
• Five bursts of two followed by a burst of one
The host shall not reset the sequence number within the service interval. The host shall set the LPF
flag only on the last packet in the last burst within the service interval.
8.12.6.2
Device Response to Isochronous IN Transactions
Table 8-30 lists the possible responses a device may make in response to an ACK TP. An ACK TP
is considered to be invalid if it has an incorrect Device Address or the endpoint number and
direction does not refer to an endpoint that is part of the current configuration or it does not have
the expected sequence number.
Table 8-30. Device Responses to Isochronous IN Transactions
ACK TP Received
Invalid
Device Can
Transmit Data
Yes
Do not care
No
No
Return zero length data packet with
sequence number 0
No
Yes
Return N data packets with
sequence numbers 0 to N-1. Each
packet except the last shall be
MaxPacketSize bytes. The last
packet shall have the LPF flag set.
8.12.6.3
Action Taken
Return no response
Host Processing of Isochronous IN Transactions
Table 8-31 lists the host processing of data from an IN transaction. The host never returns a
response to isochronous IN data received. In Table 8-31, DP Error may be due to one or more of
the following:
• CRC-32 incorrect
• DPP aborted
• DPP missing
• Data length in the DPH does not match the actual data payload length.
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Protocol Layer
If the host receives a corrupted data packet, it discards the remaining data in the current service
interval and informs host software of the error.
Table 8-31. Host Responses to IN Transactions
Data Packet Error
Host Can
Accept Data
Host Data Processing
Yes
N/A
Discard data
No
No. (This should never
happen for a compliant host
implementation.)
Discard data
No – Data Packet Has
Expected Sequence
Number
Yes
Accept data
No – Data Packet Does Not
Have Expected Sequence
Number.
Yes
Discard data
8.12.6.4
Device Response to an Isochronous OUT Data Packet
Table 8-32 lists the device processing of data from an OUT data packet. A device never returns a
TP in response. In Table 8-32, DP Error may be due to one or more of the following:
• CRC-32 incorrect.
• DPP aborted.
• DPP missing.
• Data length in the DPH does not match the actual data payload length.
Table 8-32. Device Responses to OUT Data Packets
Data Packet
Error
Expected
Sequence
Number
Device Can
Accept Data
Device Data Processing
Yes
Do not care
Do not care
Discard data
No
Yes
Yes
Accept data
No
Yes
No
Data discarded
No
No
No
Data discarded. Device may discard any additional data for
current service interval.
No
No
Yes
Data discarded. Device may discard any additional data for
current service interval.
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Universal Serial Bus 3.0 Specification, Revision 1.0
8.13
Timing Parameters
Table 8-33 lists the minimum and/or maximum times a device shall adhere to when responding to
various types of packets it receives. It also lists the default and minimum times a device may set in
Latency Tolerance messages as well as the minimum time after receipt of certain TPs and when it
can initiate a U1 or U2 entry. In addition, it lists the maximum time between DPs a device must
adhere to while bursting.
Note that all txxxResponse (e.g., tNRDYResponse) times are all timings that a device shall meet
when the device has nothing else to send on its upstream link.
Table 8-33. Timing Parameters
Name
Description
tPortConfiguration
Maximum time after a successful warm reset or a
power on reset that the link partners must
complete the port configuration process. This
includes the time to exchange port capabilities,
send the port configuration and receive
acknowledgement.
Timeout after a device receives a ping from the
host and when it can initiate U1 or U2. This
parameter is measured in terms of the maximum
of all the service intervals for all isochronous
endpoints within the device.
Time between device reception of the last framing
symbol of a ping and the first framing symbol of
the ping_response
Default for best effort latency tolerance
Minimum value of best effort latency tolerance
allowed in a Latency Tolerance Message
Time between device reception of the last framing
symbol for an ACK TP or a DPP and the first
framing symbol of an NRDY response
Time between device reception of the last framing
symbol for an ACK TP and the first framing
symbol of a DP response
Time between device reception of the last framing
symbol for a DPP and the first framing symbol of
an ACK response
Time between host reception of the last framing
symbol for a DPP and the first framing symbol of
an ACK response
Timeout after a device sends an ERDY to the
host and when it can initiate U1 or U2 if not
serviced
Rate at which a device shall send a function wake
notification if the device has not been accessed
(since sending the last function wake notification)
Time between DPs when a device or host is
bursting. If the device cannot meet this maximun
time, then it should set the EOB flag in the last DP
it sends.
tPingTimeout
tPingResponse
tBELTDefault
tBELTmin
tNRDYResponse
tDPResponse
tACKResponse
tHostACKResponse
tERDYTimeout
TNotification
tMaxBurstInterval
8-68
Min
Max
20
2
Units
μs
Service
intervals
250
1
125
ns
ms
μs
250
ns
250
ns
250
ns
3
μs
500
ms
2500
ms
100
ns
Protocol Layer
Name
Description
tTimestampWindow
The host shall transmit an isochronous timestamp
from a bus interval boundary to
tTimestampWindow after the bus interval
boundary if the root port’s link is in U0.
The granularity of isochronous timestamps
tIsochTimestampGranularity
BusIntervalAdjustmentGranularity
tIsochronousTimestampStart
tBELTRepeat
tMinLTMStateChange
1
Min
Max
0
8
μs
8
8
USB 2.0
HighSpeed
bit times
ps
The adjustment unit for device requested changes
to the bus interval
Time by which the host shall start transmitting
isochronous timestamps after a root port link
enters U0 from polling or after the root port link
enters U0 after the link was in U3
Duration within which devices are limited to send
more than two LTM TPs
Time by which a peripheral device must send an
LTM notification after completion of request to
enable or disable LTM_Enable feature selector
4.0690104
250
1
Units
1
μs
ms
10
μs
(tIsochTimestampGranularity/4096)
Note: If the host does not see a response to a Data Transaction (either IN or OUT) within 10 μs, it
shall assume that the transaction has failed and halt the endpoint. No retries shall be performed.
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8-70
9
Device Framework
A device may be divided into three layers:
• The bottom layer is a bus interface that transmits and receives packets.
• The middle layer handles routing data between the bus interface and various endpoints on the
device. As in USB 2.0, the endpoint is the ultimate consumer or provider of data. It may be
thought of as a source or sink for data. The characteristics of an endpoint; e.g., the endpoint’s
transfer type, the maximum payload (MaxPacketSize), and the number of packets (Burst Size)
it can receive or send at a time are described in the endpoint’s descriptor.
• The top layer is the functionality provided by the serial bus device, for instance, a mouse or
video camera interface.
This chapter describes the common attributes and operations of the middle layer of a device. These
attributes and operations are used by the function-specific portions of the device to communicate
through the bus interface and ultimately with the host.
9.1
USB Device States
A device has several possible states. Some of these states are visible to the USB and the host, while
others are internal to the device. This section describes those states.
9.1.1
Visible Device States
This section describes device states that are externally visible (see Figure 9-1). Table 9-1
summarizes the visible device states.
Note: Devices perform a reset operation in response to reset signaling on the upstream facing port.
When reset signaling has completed, the device is reset. The reset signaling depends on the link
state. Refer to Section 7.3 for details.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Port Power
Removed
Attached
Port Power
Present
Far-end Rx Termination NOT Detected
OR
Link Training Unsuccessful
Powered
USB 2.0 Reset
Warm
Reset
USB 2.0 Device
States
Link Training
Successful
Far-end
Rx Termination
Removed
Port Suspend
Default
Suspended,
Default
Port Resumed
Hot
Reset
Address
Assigned
Port Suspend
Address
Port Resumed
Device
Deconfigured
Suspended,
Address
Device
Configured
Port Suspend
Suspended,
Configured
Configured
Port Resumed
U-080
Figure 9-1. Peripheral Device State Diagram
9-2
Device Framework
Port Power
Removed
Attached
Port Power
Present
Far-end Rx
Termination
Not Detected
Far-end Rx
Termination
Far-end
Rx Termination
Detected
Link Training
Not Successful
Far-end Rx
Termination
Removed
Powered
Link Training
Successful
Warm
Reset
Hot Reset
Port Suspend
Default
Suspended,
Default
Port Resumed
Address
Assigned
Port Suspend
Address
Port Resumed
Device
Deconfigured
Suspended,
Address
Device
Configured
Port Suspend
Suspended,
Configured
Configured
Port Resumed
U-079
Figure 9-2. Hub State Diagram (SuperSpeed Portion Only)
Note that a USB 3.0 Hub has two discrete state diagrams, one for the SuperSpeed portion shown in
Figure 9-2 and another for the non-SuperSpeed portion which may be found in Figure 9-1 in the
USB 2.0 Specification.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Table 9-1. Visible SuperSpeed Device States
Attached
Powered
Default
Address
Configured
Suspended1
State
No
--
--
--
--
--
Device is not attached to the
USB. Other attributes are not
significant.
Yes
No
--
--
--
--
Device is attached to the
USB, but is not powered.
Other attributes are not
significant.
Yes
Yes
No
--
--
--
Device is attached to the
USB and powered and its
upstream link has not
successfully completed
training.
Yes
Yes
Yes
No
--
--
Device is attached to the
USB and powered and has
been reset, but has not been
assigned a unique address.
Device responds at the
default address.
Yes
Yes
Yes
Yes
No
--
Device is attached to the
USB, powered, has been
reset, and a unique device
address has been assigned.
Device is not configured.
Yes
Yes
Yes
Yes
Yes
No
Device is attached to the
USB, powered, has been
reset, has a unique address,
is configured, and is not
suspended. The host may
now use the function
provided by the device.
Yes
Yes
Yes
--
--
Yes
Device is, at minimum, in the
Default State (attached to the
USB, is powered and its
upstream link has been
successfully trained) and its
upstream link has been set to
U3 by its upstream link
partner. It may also have a
unique address and be
configured for use. However,
because the device is
suspended, the host may not
use the device’s function.
1
Suspended from the Default, Address, or Configured state.
9-4
Device Framework
9.1.1.1
Attached
A device may be attached or detached from the USB. The state of a device when it is detached
from the USB is not defined by this specification. This specification only addresses required
operations and attributes once the device is attached.
9.1.1.2
Powered
Devices may obtain power from an external source and/or from the USB through the hub to which
they are attached. Externally powered devices are termed self-powered. Although self-powered
devices may already be powered before they are attached to the USB, they are not considered to be
in the Powered state until they are attached to the USB and VBUS is applied to the device.
A device may support both self-powered and bus-powered configurations. Some device
configurations support either power source. Other device configurations may be available only if
the device is self-powered. Devices report their power source capability through the configuration
descriptor. The current power source is reported as part of a device’s status. Devices may change
their power source at any time, e.g., from self- to bus-powered. If a configuration is capable of
supporting both power modes, the power maximum reported for that configuration is the maximum
the device will draw from VBUS in either mode. The device shall observe this maximum, regardless
of its mode. If a configuration supports only one power mode and the power source of the device
changes, the device will lose its current configuration and address and return to the Powered state.
If a device operating in SuperSpeed mode is self-powered and its current configuration requires
more than 150 mA, then if the device switches to being bus-powered, it shall return to the Powered
state. Self-powered hubs that use VBUS to power the Hub Controller are allowed to remain in the
Configured state if local power is lost. Note that the maximum power draw for a SuperSpeed
device operating in non-SuperSpeed mode is governed by the limits set in the USB 2.0
specification.
A hub port shall be powered in order to detect port status changes, including attach and detach.
Bus-powered hubs do not provide any downstream power until they are configured, at which point
they will provide power as allowed by their configuration and power source. A device shall be able
to be addressed within a specified time period from when power is initially applied (refer to
Chapter 7). After an attachment to a port has been detected, the host may reset the port, which will
also reset the device attached to the port.
9.1.1.3
Default
When operating in SuperSpeed mode, after the device has been powered, it shall not respond to any
bus transactions until its link has successfully trained. The device is then addressable at the default
address.
A device that is capable of SuperSpeed operation determines whether it will operate at SuperSpeed
as a part of the connection process (see the Device Connection State Diagram in Chapter 10 for
more details).
A USB 3.0 device shall reset successfully at one of the supported USB 2.0 speeds when in an
USB 2.0 only electrical environment. After the device is successfully reset, the device shall also
respond successfully to device and configuration descriptor requests and return appropriate
information according to the requirements laid out in the USB 2.0 specification. The device may or
may not be able to support its intended functionality when operating in the USB 2.0 mode.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.1.1.4
Address
All devices use the default address when initially powered or after the device has been reset. Each
device is assigned a unique address by the host after reset. A device maintains its assigned address
while suspended.
A device responds to requests on its default pipe whether the device is currently assigned a unique
address or is using the default address.
9.1.1.5
Configured
Before a device’s function may be used, the device shall be configured. From the device’s
perspective, configuration involves correctly processing a SetConfiguration() request with a nonzero configuration value. Configuring a device or changing an alternate setting causes all of the
status and configuration values associated with all the endpoints in the affected interfaces to be set
to their default values. This includes resetting the sequence numbers of any endpoint in the
affected interfaces to zero. On initial entry into the configured state a device shall default into the
fully functional D0 State.
9.1.1.6
Suspended
In order to conserve power, devices automatically enter the Suspended state (one of Suspended
Default, Address, or Configured) when they observe that their upstream link is being driven to the
U3 state (refer to Section 7.1.4.2.4). When suspended, the device maintains any internal status,
including its address and configuration.
Attached devices shall be prepared to suspend at any time from the Default, Address, or Configured
states. A device shall enter the Suspended state when the hub port it is attached to is set to go into
U3. This is referred to as selective suspend.
A device exits suspend mode when it observes wake-up signaling (refer to Section 7.4.9) on its
upstream port. A device may also request the host to exit suspend mode or selective suspend by
driving resume signaling (refer to Section 7.4.9) and sending a Function Wake Notification (refer to
Section 8.5.6) on its upstream link to indicate remote wakeup. The ability of a device to signal
remote wakeup is optional. If a device is capable of remote wakeup, the device shall support the
ability of the host to enable and disable this capability. When the device is reset, remote wakeup
shall be disabled. Refer to Section 9.2.5 for more information.
9.1.2
Bus Enumeration
When a device is attached to or removed from the USB, the host uses a process known as bus
enumeration to identify and manage the device state changes necessary. When a device is attached
to a powered port, the following actions are taken:
1. The hub to which the device is now attached informs the host of the event via a reply on its
status change pipe (refer to Section 10.11.1). At this point, the device has been reset, is in the
Default state and the port to which it is attached is enabled and ready to respond to control
transfer requests on the default control pipe.
2. The host determines the exact nature of the change by querying the hub.
3. Now that the host knows the port to which the new device has been attached, the host then may
reset the device again if it wishes but it is not required to do so.
9-6
Device Framework
4. If the host resets the port, the hub performs the required reset processing for that port (refer to
Section 10.3.1.6). When the reset is completed, the port will be back in the enabled state.
5. The device is now in the Default state and can draw no more than 150 mA from VBUS. All of
its registers and state have been reset and it answers to the default address.
6. The host assigns a unique address to the device, moving the device to the Address state.
7. Before the device receives a unique address, its default control pipe is still accessible via the
default address. The host reads the device descriptor to determine what the actual maximum
data payload size this device’s default pipe can use.
8. The host shall set the isochronous delay to inform the device of the delay from the time a host
transmits a packet to the time it is received by the device.
9. The host shall inform the device of the system exit latency using the Set SEL request.
10. The host reads the configuration information from the device by reading each configuration
from zero to n-1, where n is the number of configurations. This process may take several
milliseconds to complete.
11. Based on the configuration information and how the device will be used, the host assigns a
configuration value to the device. The device is now in the Configured state and all of the
endpoints in this configuration have taken on their described characteristics. The device may
now draw the amount of VBUS power described in its descriptor for the selected configuration.
From the device’s point of view, it is now ready for use.
When the device is detached, the hub again sends a notification to the host. Detaching a device
disables the port to which it had been attached and the port moves into the Disconnected state (refer
to Section 10.3.1.2). Upon receiving the detach notification, the host will update its local
topological information.
9.2
Generic Device Operations
All devices support a common set of operations. This section describes those operations.
9.2.1
Dynamic Attachment and Removal
Devices may be attached or detached at any time. The hub provides the attachment point or
downstream port and is responsible for reporting any change in the state of the port.
The hub resets and enables the hub downstream port where the device is attached upon detection of
an attachment, which also has the effect of resetting the device. A reset device has the following
characteristics:
• Its USB address is set to zero (the default USB address)
• It is not configured
• It is not suspended
When a device is removed from a hub port, the hub disables the port where the device was attached,
the port moves into the DSPORT.Disconnected state (refer to Section 10.3.1.2) and notifies the host
of the removal.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.2.2
Address Assignment
When a device is attached, the host is responsible for assigning a unique address to the device.
Before assigning an address, the host may explicitly reset the device; however, note that the device
implicitly gets reset during the connection process before the host is notified of a device being
attached to the port.
9.2.3
Configuration
A device shall be configured before its function(s) may be used. The host is responsible for
configuring a device. The host typically requests configuration information from the device to
determine its capabilities.
As part of the configuration process, the host sets the device configuration and, where necessary,
selects the appropriate alternate settings for the interfaces.
Within a single configuration, a device may support multiple interfaces. An interface is a related
set of endpoints that present a single feature or function of the device to the host. The protocol used
to communicate with this related set of endpoints and the purpose of each endpoint within the
interface may be specified as part of a device class or vendor-specific definition.
In addition, an interface within a configuration may have alternate settings that redefine the number
or characteristics of the associated endpoints. If this is the case, the device shall support the
GetInterface() request to report the current alternate setting for the specified interface and
SetInterface() request to select the alternate setting for the specified interface.
Within each configuration, each interface descriptor contains fields that identify the interface
number and the alternate setting. Interfaces are numbered from zero to one less than the number of
concurrent interfaces supported by the configuration. Alternate settings range from zero to one less
than the number of alternate settings for a specific interface. The default setting when a device is
initially configured is alternate setting zero.
In support of adaptive device drivers that are capable of managing a related group of devices, the
device and interface descriptors contain Class, SubClass, and Protocol fields. These fields are used
to identify the function(s) provided by a device and the protocols used to communicate with the
function(s) on the device. A class code is assigned to a group of related devices that has been
characterized as a part of a USB Class Specification. A class of devices may be further subdivided
into subclasses and, within a class or subclass, a protocol code may define how the host software
communicates with the device.
Note: The assignment of class, subclass, and protocol codes shall be coordinated but is beyond the
scope of this specification.
9-8
Device Framework
9.2.4
Data Transfer
Data may be transferred between an endpoint within a device and the host in one of four ways.
Refer to Chapter 4 for the definition of the four types of transfers. An endpoint number may be
used for different types of data transfers in different alternate settings. However, once an alternate
setting is selected (including the default setting of an interface), a device endpoint uses only one
data transfer method until a different alternate setting is selected.
9.2.5
Power Management
Power management on devices involves the issues described in the following sections.
9.2.5.1
Power Budgeting
USB bus power is a limited resource. During device enumeration, a host evaluates a device's power
requirements. If the power requirements of a particular configuration exceed the power available to
the device, host software shall not select that configuration.
Devices shall limit the power they consume from VBUS to one unit load or less until configured.
When operating in SuperSpeed mode, 150 mA equals one unit load. Suspended devices, whether
configured or not, shall limit their bus power consumption as to the suspend mode power
requirements in the USB 2.0 specification. Depending on the power capabilities of the port to
which the device is attached, a SuperSpeed device operating in SuperSpeed mode may be able to
draw up to six unit loads from VBUS after configuration. The amount of current draw for
SuperSpeed devices are increased to 150 mA for low-power devices and 900 mA for high-power
devices when operating in SuperSpeed mode.
Device power management is comprised of suspend and function suspend. Suspend refers to a
device-wide state that is entered when its upstream link is placed in U3. Function suspend refers to
a state of an individual function within a device. Suspending a device with more than one function
effectively suspends all the functions within the device.
Note that placing all functions in the device into function suspend does not suspend the device. A
device is suspended only when its upstream link is placed in U3.
9.2.5.2
Changing Device Suspend State
Device suspend is entered and exited intrinsically as part of the suspend entry and exit processes
(refer to Section 10.8). The minimum set of device state information that shall be retained is listed
below:
• Port status change (downstream ports)
• Device address
• Device configuration value
• Function suspend and function remote wake enable state
Some additional device state information may also be retained during suspend.
A device shall send a Function Wake Notification after driving resume signaling (refer to
Section 7.4.9). If the device has not been accessed for longer than tNotification (refer to
Section 8.13) since sending the last Function Wake Notification, the device shall send the Function
Wake Notification again until it has been accessed.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Device classes may require additional information to be retained during suspend, beyond what is
identified in this specification and is beyond the scope of this specification. Devices can optionally
remove power from circuitry that is not needed while in suspend.
9.2.5.3
Function Suspend
The function suspend state is a reduced power state associated with an individual function. The
function may or may not be part of a composite device.
A function may be placed into function suspend independently of other functions within a
composite device. A device may be transitioned into device suspend regardless of the function
suspend state of any function within the device. Function suspend state is retained while in device
suspend and throughout the device suspend entry and exit processes.
9.2.5.4
Changing Function Suspend State
Functions are placed into function suspend using the FUNCTION_SUSPEND feature selector (see
Table 9-6). The FUNCTION_SUSPEND feature selector also controls whether the function may
initiate a function remote wakeup. Whether a function is capable of initiating a Function Remote
Wake is determined by the status returned when the first interface in that function is queried using a
Get Status command (refer to Section 9.4.5).
Remote wakeup (i.e., wakeup from a device suspend state) is enabled when any function within a
device is enabled for function remote wakeup (note the distinction between “function remote wake”
and “remote wake”). The DEVICE_REMOTE_WAKEUP feature selector is ignored and not used
by SuperSpeed devices.
A function may signal that it wants to exit from function suspend by sending a Function Wake
Notification to the host if it is enabled for function remote wakeup. This applies to single function
devices as well as multiple function (i.e., composite) devices. If the link is in a non-U0 state, then
the device must transition the link to U0 prior to sending the remote wake message. If a remote
wake event occurs in multiple functions, each function shall send a Function Wake Notification. If
the function has not been accessed for longer than tNotification (refer to Section 8.13) since
sending the last Function Wake Notification, the function shall send the Function Wake
Notification again until it has been accessed.
When all functions within a device are in function suspend and the PORT_U2_TIMEOUT field
(refer to Section 10.14.2.9) is programmed to 0xFF, the device shall initiate U2 after 10 ms of link
inactivity.
9.2.6
Request Processing
With the exception of SetAddress() requests (refer to Section 9.4.6), a device may begin processing
a request as soon as the device receives the Setup Packet. The device is expected to “complete”
processing of the request before it allows the Status stage to complete successfully. Some requests
initiate operations that take many milliseconds to complete. For such requests, the device class is
required to define a method other than Status stage completion to indicate that the operation has
completed. For example, a reset on a hub port may take multiple milliseconds to complete
depending on the status of the link attached to the port. The SetPortFeature(PORT_RESET) (refer
to Section 10.14.2.9) request “completes” when the reset on the port is initiated. Completion of the
reset operation is signaled when the port’s status change is set to indicate that the port is now
9-10
Device Framework
enabled. This technique prevents the host from having to poll for completion when it is known that
the operation will take a relatively long period of time to complete.
9.2.6.1
Request Processing Timing
All devices are expected to handle requests in a timely manner. USB sets an upper limit of
5 seconds for any command to be processed. This limit is not applicable in all instances. The
limitations are described in the following sections. It should be noted that the limitations are
intended to encompass a wide range of implementations. If all devices in a USB system used the
maximum allotted time for request processing, the user experience would suffer. For this reason,
implementations should strive to complete requests in times that are as short as possible.
9.2.6.2
Reset/Resume Recovery Time
After a port is successfully reset or resumed, the USB system software is allowed to access the
device attached to the port immediately and it is expected to respond to data transfers.
9.2.6.3
Set Address Processing
After the reset or resume, when a device receives a SetAddress() request, the device shall be able to
complete processing of the request and be able to successfully complete the Status stage of the
request within 50 ms. In the case of the SetAddress() request, the Status stage successfully
completes when the device sends an ACK Transaction Packet in response to Status stage STATUS
Transaction Packet.
After successful completion of the Status stage, the device shall be able to accept Setup packets
addressed to the new address. Also, after successful completion of the Status stage, the device shall
not respond to transactions sent to the old address (unless, of course, the old address and the new
address are the same).
9.2.6.4
Standard Device Requests
For standard device requests that require no Data stage, a device shall be able to complete the
request and be able to successfully complete the Status stage of the request within 50 ms of receipt
of the request. This limitation applies to requests targeted to the device, interface, or endpoint.
For standard device requests that require a data stage transfer to the host, the device shall be able to
return the first data packet to the host within 500 ms of receipt of the request. For subsequent data
packets, if any, the device shall be able to return them within 500 ms of successful completion of
the transmission of the previous packet. The device shall then be able to successfully complete the
status stage within 50 ms after returning the last data packet.
For standard device requests that require a data stage transfer to the device, the 5-second limit
applies. This means that the device shall be capable of accepting all data packets from the host and
successfully completing the Status stage if the host provides the data at the maximum rate at which
the device can accept it. Delays between packets introduced by the host add to the time allowed for
the device to complete the request.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.2.6.5
Class-specific Requests
Unless specifically exempted in the class document, all class-specific requests shall meet the timing
limitations for standard device requests. If a class document provides an exemption, the exemption
may only be specified on a request-by-request basis.
A class document may require that a device respond more quickly than is specified in this section.
Faster response may be required for standard and class-specific requests.
9.2.6.6
Speed Dependent Descriptors
A device capable of operation at SuperSpeed shall be capable of operating at one of the USB 2.0
defined speeds. The device always knows its operational speed as part of connection processing
(refer to Section 10.5 for more details on the connection process). A device operates at a single
speed after completing the reset sequence. In particular, there is no speed switch during normal
operation. However, a SuperSpeed capable device may have configurations that are speed
dependent. That is, it may have some configurations that are only possible when operating at
SuperSpeed or some that are only possible when operating at high speed. SuperSpeed capable
devices shall support reporting the speeds they can operate at. Note that a USB 3.0 hub is the only
device that is allowed to operate at both USB 2.0 and SuperSpeed simultaneously.
A SuperSpeed capable device responds with descriptor information that is valid for the current
operating speed. For example, when a device is asked for configuration descriptors, it only returns
those for the current operating speed (e.g., high speed). When operating in SuperSpeed mode, the
device shall report the other speeds it can operate via its BOS descriptor (refer to Section 9.6.2).
Note that when operating at USB 2.0 speeds, the device shall report the other USB 2.0 speeds it
supports using the standard mechanism defined in the USB 2.0 specification in addition to reporting
the other speeds supported by the device in its BOS descriptor. Devices with a value of at least
0210H in the bcdUSB field of their device descriptor shall support GetDescriptor (BOS Descriptor)
requests.
Note: These descriptors are not retrieved unless the host explicitly issues the corresponding
GetDescriptor requests.
9.2.7
Request Error
When a request not defined for the device is inappropriate for the current setting of the device or
has values that are not compatible with the request is received, a Request Error exists. The device
deals with the Request Error by returning a STALL Transaction Packet in response to the next Data
stage transaction or in the Status stage of the message. It is preferred that the STALL Transaction
Packet be returned at the next Data stage transaction to avoid unnecessary bus activity.
9-12
Device Framework
9.3
USB Device Requests
All devices respond to requests from the host on the device’s Default Control Pipe. These requests
are made using control transfers. The request and the request’s parameters are sent to the device in
the Setup packet. The host is responsible for establishing the values passed in the fields listed in
Table 9-2. Every Setup packet has 8 bytes.
Table 9-2. Format of Setup Data
Offset
Field
Size
Value
Description
0
bmRequestType
1
Bitmap
Characteristics of request:
D7:
Data transfer direction
0 = Host-to-device
1 = Device-to-host
D6...5:
Type
0 = Standard
1 = Class
2 = Vendor
3 = Reserved
D4...0:
Recipient
0 = Device
1 = Interface
2 = Endpoint
3 = Other
4...31 = Reserved
1
bRequest
1
Value
Specific request (refer to Table 9-3)
2
wValue
2
Value
Word-sized field that varies according to
request
4
wIndex
2
Index or
Offset
Word-sized field that varies according to
request; typically used to pass an index or
offset
6
wLength
2
Count
Number of bytes to transfer if there is a Data
stage
9.3.1
bmRequestType
This bitmapped field identifies the characteristics of the specific request. In particular, this field
identifies the direction of data transfer in the second phase of the control transfer. The state of the
Direction bit is ignored if the wLength field is zero, signifying there is no Data stage.
USB 3.0 defines a series of standard requests that all devices shall support. These are listed in
Table 9-3. In addition, a device class may define additional requests. A device vendor may also
define requests supported by the device.
Requests may be directed to the device, an interface on the device, or a specific endpoint on a
device. This field also specifies the intended recipient of the request. When an interface is
specified, the wIndex field identifies the interface. When an endpoint is specified, the wIndex field
identifies the endpoint.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.3.2
bRequest
This field specifies the particular request. The Type bits in the bmRequestType field modify the
meaning of this field. This specification defines values for the bRequest field only when the bits
are reset to zero, indicating a standard request (refer to Table 9-3).
9.3.3
wValue
The contents of this field vary according to the request. It is used to pass a parameter to the device,
specific to the request.
9.3.4
wIndex
The contents of this field vary according to the request. It is used to pass a parameter to the device,
specific to the request.
The wIndex field is often used in requests to specify an endpoint or an interface. Figure 9-3 shows
the format of wIndex when it is used to specify an endpoint.
D7
Direction
D15
D6
D5
D4
D3
Reserved (Reset to Zero)
D14
D13
D12
D2
D1
D0
Endpoint Number
D11
D10
D7
D8
Reserved (Reset to Zero)
U-081
Figure 9-3. wIndex Format when Specifying an Endpoint
The Direction bit is set to zero to indicate the OUT endpoint with the specified Endpoint Number
and to one to indicate the IN endpoint. In the case of a control pipe, the request should have the
Direction bit set to zero but the device may accept either value of the Direction bit.
Figure 9-4 shows the format of wIndex when it is used to specify an interface.
D7
D6
D5
D4
D3
D2
D1
D0
D10
D7
D8
Interface Number
D15
D14
D13
D12
D11
Reserved (Reset to Zero)
U-082
Figure 9-4. wIndex Format when Specifying an Interface
9-14
Device Framework
9.3.5
wLength
This field specifies the length of the data transferred during the second phase of the control transfer.
The direction of data transfer (host-to-device or device-to-host) is indicated by the Direction bit of
the bmRequestType field. If this field is zero, there is no data transfer phase.
On an input request, a device shall never return more data than is indicated by the wLength value; it
may return less. On an output request, wLength will always indicate the exact amount of data to be
sent by the host. Device behavior is undefined if the host should send more or less data than is
specified in wLength.
9.4
Standard Device Requests
This section describes the standard device requests defined for all devices. Table 9-3 outlines the
standard device requests, while Table 9-4 and Table 9-5 give the standard request codes and
descriptor types, respectively.
Devices shall respond to standard device requests, even if the device has not yet been assigned an
address or has not been configured.
Table 9-3. Standard Device Requests
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
00000001B
00000010B
CLEAR_FEATURE
Feature Selector
Zero
Interface
Endpoint
Zero
None
10000000B
GET_CONFIGURATION
Zero
Zero
One
Configurat
ion Value
10000000B
GET_DESCRIPTOR
Descriptor Type
and Descriptor
Index
Zero or Language ID
Descriptor
Length
Descriptor
10000001B
GET_INTERFACE
Zero
Interface
One
Alternate
Interface
10000000B
10000001B
10000010B
GET_STATUS
Zero
Zero Interface Endpoint
Two
Device,
Interface,
or
Endpoint
Status
00000000B
SET_ADDRESS
Device Address
Zero
Zero
None
00000000B
SET_CONFIGURATION
Configuration
Value
Zero
Zero
None
00000000B
SET_DESCRIPTOR
Descriptor Type
and Descriptor
Index
Zero or Language ID
Descriptor
Length
Descriptor
00000000B
00000001B
00000010B
SET_FEATURE
Feature Selector
Zero
Interface
Endpoint
Zero
None
00000001B
SET_INTERFACE
Alternate Setting
Interface
Zero
None
Suspend
Options
9-15
Universal Serial Bus 3.0 Specification, Revision 1.0
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_ISOCH_DELAY
Delay in ns
Zero
Zero
None
00000000B
SET_SEL
Zero
Zero
Six
Exit
Latency
Values
10000010B
SYNCH_FRAME
Zero
Endpoint
Two
Frame
Number
Table 9-4. Standard Request Codes
9-16
bRequest
Value
GET_STATUS
0
CLEAR_FEATURE
1
Reserved for future use
2
SET_FEATURE
3
Reserved for future use
4
SET_ADDRESS
5
GET_DESCRIPTOR
6
SET_DESCRIPTOR
7
GET_CONFIGURATION
8
SET_CONFIGURATION
9
GET_INTERFACE
10
SET_INTERFACE
11
SYNCH_FRAME
12
SET_SEL
48
SET_ISOCH_DELAY
49
Device Framework
Table 9-5. Descriptor Types
Descriptor Types
Value
DEVICE
1
CONFIGURATION
2
STRING
3
INTERFACE
4
ENDPOINT
5
Reserved
6
Reserved
INTERFACE_POWER
7
1
8
OTG
9
DEBUG
10
INTERFACE_ASSOCIATION
11
BOS
15
DEVICE CAPABILITY
16
SUPERSPEED_USB_ENDPOINT_COMPANION
48
Feature selectors are used when enabling or setting features, such as function remote wakeup,
specific to a device, interface, or endpoint. The values for the feature selectors are given in
Table 9-6.
Table 9-6. Standard Feature Selectors
Feature Selector
Recipient
Value
ENDPOINT_HALT
Endpoint
0
FUNCTION_SUSPEND
Interface
0
U1_ENABLE
Device
48
U2_ENABLE
Device
49
LTM_ENABLE
Device
50
If an unsupported or invalid request is made to a device, the device responds by returning a STALL
Transaction Packet in the Data or Status stage of the request. If the device detects the error in the
Setup stage, it is preferred that the device returns a STALL Transaction Packet at the earlier of the
Data or Status stage. Receipt of an unsupported or invalid request does not cause the Halt feature
on the control pipe to be set. If, for any reason, the device becomes unable to communicate via its
Default Control Pipe due to an error condition, the device shall be reset to clear the condition and
restart the Default Control Pipe.
1
The INTERFACE_POWER descriptor is defined in the current revision of the USB Interface Power Management
Specification.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.4.1
Clear Feature
This request is used to clear or disable a specific feature.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
00000001B
00000010B
CLEAR_FEATURE
Feature
Selector
Zero
Zero
None
Interface
Endpoint
Feature selector values in wValue shall be appropriate to the recipient. Only device feature selector
values may be used when the recipient is a device, only interface feature selector values may be
used when the recipient is an interface, and only endpoint feature selector values may be used when
the recipient is an endpoint.
Refer to Table 9-6 for a definition of which feature selector values are defined for which recipients.
A ClearFeature() request that references a feature that cannot be cleared, that does not exist, or that
references an interface or an endpoint that does not exist, will cause the device to respond with a
Request Error.
If wLength is non-zero, then the device behavior is not specified.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
This request is valid when the device is in the Address state; references to
interfaces or to endpoints other than the Default Control Pipe shall cause the
device to respond with a Request Error.
Configured state:
This request is valid when the device is in the Configured state.
Note: The device shall process a Clear Feature (U1_Enable or U2_Enable or LTM_Enable) only if
the device is in the configured state.
9-18
Device Framework
9.4.2
Get Configuration
This request returns the current device configuration value.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10000000B
GET_CONFIGURATION
Zero
Zero
One
Configuration
Value
If the returned value is zero, the device is not configured.
If wValue, wIndex, or wLength are not as specified above, then the device behavior is not specified.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
The value zero shall be returned.
Configured state:
The non-zero bConfigurationValue of the current configuration shall be
returned.
9.4.3
Get Descriptor
This request returns the specified descriptor if the descriptor exists.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10000000B
GET_DESCRIPTOR
Descriptor
Type and
Descriptor
Index
Zero or
Language ID
(refer to
Section 9.6.7)
Descriptor
Length
Descriptor
The wValue field specifies the descriptor type in the high byte (refer to Table 9-5) and the
descriptor index in the low byte. The descriptor index is used to select a specific descriptor (only
for configuration and string descriptors) when several descriptors of the same type are implemented
in a device. For example, a device can implement several configuration descriptors. For other
standard descriptors that can be retrieved via a GetDescriptor() request, a descriptor index of zero
shall be used. The range of values used for a descriptor index is from 0 to one less than the number
of descriptors of that type (excluding string descriptors) implemented by the device.
The wIndex field specifies the Language ID for string descriptors or is reset to zero for other
descriptors. The wLength field specifies the number of bytes to return. If the descriptor is longer
than the wLength field, only the initial bytes of the descriptor are returned. If the descriptor is
shorter than the wLength field, the device indicates the end of the control transfer by sending a short
packet when further data is requested.
The standard request to a device supports four types of descriptors: device, configuration, BOS
(Binary device Object Store), and string. As noted in Section 9.2.6.6, a device operating in
SuperSpeed mode reports the other speeds it supports via the BOS descriptor and shall not support
the device_qualifier and other_speed_configuration descriptors. A request for a configuration
descriptor returns the configuration descriptor, all interface descriptors, endpoint descriptors and
endpoint companion descriptors (when operating in SuperSpeed mode) for all of the interfaces in a
single request. The first interface descriptor follows the configuration descriptor. The endpoint
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Universal Serial Bus 3.0 Specification, Revision 1.0
descriptors for the first interface follow the first interface descriptor. In addition, SuperSpeed
devices shall return Endpoint Companion descriptors for each of the endpoints in that interface to
return the endpoint capabilities required for SuperSpeed capable devices, which would not fit inside
the existing endpoint descriptor footprint. If there are additional interfaces, their interface
descriptor, endpoint descriptors, and endpoint companion descriptors (when operating in
SuperSpeed mode) follow the first interface’s endpoint and endpoint companion (when operating in
SuperSpeed mode) descriptors.
This specification also defines a flexible and extensible framework for describing and adding
device-level capabilities to the set of USB standard specifications. The BOS descriptor (refer to
Section 9.6.2) defines a root descriptor that is similar to the configuration descriptor, and is the base
descriptor for accessing a family of related descriptors. A host can read a BOS descriptor and learn
from the wTotalLength field the entire size of the device-level descriptor set, or it can read in the
entire BOS descriptor set of device capabilities. There is no way for a host to read individual
device capability descriptors. The entire set can only be accessed via reading the BOS descriptor
with a GetDescriptor() request and using the length reported in the wTotalLength field.
Class-specific and/or vendor-specific descriptors follow the standard descriptors they extend or
modify.
All devices shall provide a device descriptor and at least one configuration descriptor. If a device
does not support a requested descriptor, it responds with a Request Error.
Default state:
This is a valid request when the device is in the Default state.
Address state:
This is a valid request when the device is in the Address state.
Configured state:
This is a valid request when the device is in the Configured state.
9.4.4
Get Interface
This request returns the selected alternate setting for the specified interface.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10000001B
GET_INTERFACE
Zero
Interface
One
Alternate
Setting
Some devices have configurations with interfaces that have mutually exclusive settings. This
request allows the host to determine the currently selected alternate setting.
If wValue or wLength are not as specified above, then the device behavior is not specified.
If the interface specified does not exist, then the device responds with a Request Error.
9-20
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
A Request Error response is given by the device.
Configured state:
This is a valid request when the device is in the Configured state.
Device Framework
9.4.5
Get Status
This request returns status for the specified recipient.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10000000B
10000001B
10000010B
GET_STATUS
Zero
Zero
Two
Device,
Interface, or
Endpoint
Status
Interface
Endpoint
The Recipient bits of the bmRequestType field specify the desired recipient. The data returned is
the current status of the specified recipient. If the recipient is an endpoint, then the lower byte of
wIndex identifies the endpoint whose status is being queried.
If wValue or wLength are not as specified above or if wIndex is non-zero for a device status request,
then the behavior of the device is not specified.
If an interface or an endpoint is specified that does not exist, then the device responds with a
Request Error.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
If an interface or an endpoint other than the Default Control Pipe is specified,
then the device responds with a Request Error.
Configured state:
If an interface or an endpoint that does not exist is specified, then the device
responds with a Request Error.
A GetStatus() request to a device returns the information shown in Figure 9-5.
D7
D6
D5
Reserved (Reset to Zero)
D15
D14
D13
D4
D3
D2
D1
D0
SelfPowered
D8
LTM Enable
U2 Enable
U1 Enable
Remote
Wakeup
D12
D11
D10
D7
Reserved (Reset to Zero)
U-083
Figure 9-5. Information Returned by a GetStatus() Request to a Device
The Self Powered field indicates whether the device is currently self-powered. If D0 is reset to
zero, the device is bus-powered. If D0 is set to one, the device is self-powered. The Self Powered
field may not be changed by the SetFeature() or ClearFeature() requests.
The Remote Wakeup field is reserved and must be set to zero by SuperSpeed devices. SuperSpeed
devices use the Function Remote Wake enable/disable field to indicate whether they are enabled for
Remote Wake.
The U1 Enable field indicates whether the device is currently enabled to initiate U1 entry. If D2 is
set to zero, the device is disabled from initiating U1 entry, otherwise, it is enabled to initiate U1
entry. The U1 Enable field can be modified by the SetFeature() and ClearFeature() requests using
the U1_ENABLE feature selector. This field is reset to zero when the device is reset.
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Universal Serial Bus 3.0 Specification, Revision 1.0
The U2 Enable field indicates whether the device is currently enabled to initiate U2 entry. If D3 is
set to zero, the device is disabled from initiating U2 entry otherwise it is enabled to initiate U2
entry. The U2 Enable field can be modified by the SetFeature() and ClearFeature() requests using
the U2_ENABLE feature selector. This field is reset to zero when the device is reset.
The LTM Enable field indicates whether the device is currently enabled to send Latency Tolerance
Messages. If D4 is set to zero, the device is disabled from sending Latency Tolerance Messages
otherwise it is enabled to send Latency Tolerance Messages. The LTM Enable field can be
modified by the SetFeature() and ClearFeature() requests using the LTM_ENABLE feature
selector. This field is reset to zero when the device is reset.
A GetStatus() request to the first interface in a function returns the information shown in
Figure 9-6.
D7
D6
D5
D4
D3
D2
Reserved (Reset to Zero)
D15
D14
D13
D12
D11
D10
D1
D0
Function
Remote
Wakeup
Function
Remote
Wake
Capable
D7
D8
Reserved (Reset to Zero)
U-084
Figure 9-6. Information Returned by a GetStatus() Request to an Interface
The Function Remote Wake Capable field indicates whether the function supports remote wake up.
The Function Remote Wakeup field indicates whether the function is currently enabled to request
remote wakeup. The default mode for functions that support function remote wakeup is disabled.
If D1 is reset to zero, the ability of the function to signal remote wakeup is disabled. If D1 is set to
one, the ability of the function to signal remote wakeup is enabled. The Function Remote Wakeup
field can be modified by the SetFeature() requests using the FUNCTION_SUSPEND feature
selector. This Function Remote Wakeup field is reset to zero when the function is reset.
A GetStatus() request to any other interface in a function shall return all zeros.
A GetStatus() request to an endpoint returns the information shown in Figure 9-7.
D7
D6
D5
D4
D15
D14
D13
D3
D2
D1
D10
D7
Reserved (Reset to Zero)
D12
D11
D0
Halt
D8
Reserved (Reset to Zero)
U-085
Figure 9-7. Information Returned by a GetStatus() Request to an Endpoint
The Halt feature is required to be implemented for all interrupt and bulk endpoint types. If the
endpoint is currently halted, then the Halt feature is set to one. Otherwise, the Halt feature is reset
to zero. The Halt feature may optionally be set with the SetFeature(ENDPOINT_HALT ) request.
When set by the SetFeature() request, the endpoint exhibits the same stall behavior as if the field
9-22
Device Framework
had been set by a hardware condition. If the condition causing a halt has been removed, clearing
the Halt feature via a ClearFeature(ENDPOINT_HALT ) request results in the endpoint no longer
returning a STALL Transaction Packet. Regardless of whether an endpoint has the Halt feature set,
a ClearFeature(ENDPOINT_HALT) request always results in the data sequence being reinitialized
to zero, and if Streams are enabled, the Stream State Machine shall be reinitialized to the Disabled
state. The Halt feature is reset to zero after either a SetConfiguration() or SetInterface() request
even if the requested configuration or interface is the same as the current configuration or interface.
SuperSpeed devices do not support functional stall on control endpoints and hence do not require
the Halt feature be implemented for any control endpoints.
9.4.6
Set Address
This request sets the device address for all future device accesses.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_ADDRESS
Device
Address
Zero
Zero
None
The wValue field specifies the device address to use for all subsequent accesses.
The Status stage after the initial Setup packet assumes the same device address as the Setup packet.
The device does not change its device address until after the Status stage of this request is
completed successfully. Note that this is a difference between this request and all other requests.
For all other requests, the operation indicated shall be completed before the Status stage.
If the specified device address is greater than 127, or if wIndex or wLength is non-zero, then the
behavior of the device is not specified.
Default state:
If the address specified is non-zero, then the device shall enter the Address
state; otherwise, the device remains in the Default state (this is not an error
condition).
Address state:
If the address specified is zero, then the device shall enter the Default state;
otherwise, the device remains in the Address state but uses the newlyspecified address.
Configured state:
Device behavior when this request is received while the device is in the
Configured state is not specified.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.4.7
Set Configuration
This request sets the device configuration.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_CONFIGURATION
Configuration Value
Zero
Zero
None
The lower byte of the wValue field specifies the desired configuration. This configuration value
shall be zero or match a configuration value from a configuration descriptor. If the configuration
value is zero, the device is placed in its Address state. The upper byte of the wValue field is
reserved.
If wIndex, wLength, or the upper byte of wValue is non-zero, then the behavior of this request is not
specified.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
If the specified configuration value is zero, then the device remains in the
Address state. If the specified configuration value matches the configuration
value from a configuration descriptor, then that configuration is selected and
the device enters the Configured state. Otherwise, the device responds with a
Request Error.
Configured state:
If the specified configuration value is zero, then the device enters the
Address state. If the specified configuration value matches the configuration
value from a configuration descriptor, then that configuration is selected and
the device remains in the Configured state. Otherwise, the device responds
with a Request Error.
9.4.8
Set Descriptor
This request is optional and may be used to update existing descriptors or new descriptors may be
added.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_DESCRIPTOR
Descriptor
Type and
Descriptor
Index
Language ID
(refer to
Section 9.6.7)
or zero
Descriptor
Length
Descriptor
The wValue field specifies the descriptor type in the high byte (refer to Table 9-5) and the
descriptor index in the low byte. The descriptor index is used to select a specific descriptor (only
for configuration and string descriptors) when several descriptors of the same type are implemented
in a device. For example, a device can implement several configuration descriptors. For other
standard descriptors that can be set via a SetDescriptor() request, a descriptor index of zero shall be
used. The range of values used for a descriptor index is from 0 to one less than the number of
descriptors of that type (excluding string descriptors) implemented by the device.
9-24
Device Framework
The wIndex field specifies the Language ID for string descriptors or is reset to zero for other
descriptors. The wLength field specifies the number of bytes to transfer from the host to the
device.
The only allowed values for descriptor type are device, configuration, and string descriptor types.
If this request is not supported, the device will respond with a Request Error.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
If supported, this is a valid request when the device is in the Address state.
Configured state:
If supported, this is a valid request when the device is in the Configured
state.
9.4.9
Set Feature
This request is used to set or enable a specific feature.
bmRequestType
bRequest
wValue
wIndex
00000000B
00000001B
00000010B
SET_FEATURE
Feature
Selector
Zero Interface
Endpoint
Suspend
Options
wLength
Data
Zero
None
Feature selector values in wValue shall be appropriate to the recipient. Only device feature selector
values may be used when the recipient is a device; only interface feature selector values may be
used when the recipient is an interface; and only endpoint feature selector values may be used when
the recipient is an endpoint. If the recipient is an endpoint, then the lower byte of wIndex identifies
the endpoint.
Refer to Table 9-6 for a definition of which feature selector values are defined for which recipients.
The FUNCTION_SUSPEND feature is only defined for an interface recipient. The lower byte of
wIndex shall be set to the first interface that is part of that function.
The U1/U2_ENABLE feature is only defined for a device recipient and wIndex shall be set to zero.
Setting the U1/U2_ENABLE feature allows the device to initiate U1/U2 entry respectively. A
device shall support the U1/U2ENABLE feature when in the Configured SuperSpeed state only.
System software must not enable the device to initiate U1 if the time for U1 System Exit Latency
initiated by Host plus one Bus Interval time is greater than the minimum of the service intervals of
any periodic endpoints in the device. In addition, system software must not enable the device to
initiate U2 if the time for U2 System Exit Latency initiated by Host plus one Bus Interval time is
greater than the minimum of the service intervals of any periodic endpoints in the device.
The LTM_ENABLE feature is only defined for a device recipient and wIndex shall be set to zero.
Setting the LTM_ENABLE feature allows the device to send Latency Tolerance Messages. A
device shall support the LTM_ENABLE feature if it is in the Configured SuperSpeed state and
supports the LTM capability.
A SetFeature() request that references a feature that cannot be set or that does not exist causes a
STALL Transaction Packet to be returned in the Status stage of the request.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Table 9-7. Suspend Options
Bit
Description
0
1
2-7
Value
Meaning
0
Normal operation state (default)
1
Low power suspend state
Value
Meaning
0
Function Remote Wake Disabled
(Default)
1
Function Remote Wake Enabled
Reserved
If the feature selector is FUNCTION_SUSPEND, then the most significant byte of wIndex is used to
specify Suspend options. The recipient of a SetFeature (FUNCTION_SUSPEND…) shall be the
first interface in the function; and, hence, the bmRequestType shall be set to one. The valid
encodings for the FUNCTION_SUSPEND suspend options are listed in Table 9-7.
If wLength is non-zero, then the behavior of the device is not specified.
If an endpoint or interface is specified that does not exist, then the device responds with a Request
Error.
9-26
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
If an interface or an endpoint other than the Default Control Pipe is specified
then the device responds with a Request Error. If the device receives a
SetFeature(U1/U2 Enable or LTM Enable or FUNCTION_SUSPEND), then
the device responds with a Request Error.
Configured state:
This is a valid request when the device is in the Configured state.
Device Framework
9.4.10
Set Interface
This request allows the host to select an alternate setting for the specified interface.
bmRequestType
bRequest
WValue
wIndex
wLength
Data
00000001B
SET_INTERFACE
Alternate
Setting
Interface
Zero
None
Some devices have configurations with interfaces that have mutually exclusive settings. This
request allows the host to select the desired alternate setting. If a device only supports a default
setting for the specified interface, then a STALL Transaction Packet may be returned in the Status
stage of the request. This request cannot be used to change the set of configured interfaces (the
SetConfiguration() request shall be used instead).
If the interface or the alternate setting does not exist, then the device responds with a Request Error.
If wLength is non-zero, then the behavior of the device is not specified.
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
The device shall respond with a Request Error.
Configured state:
This is a valid request when the device is in the Configured state.
9.4.11
Set Isochronous Delay
This request informs the device of the delay from the time a host transmits a packet to the time it is
received by the device.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_ISOCH_DELAY
Delay in ns
Zero
Zero
None
The wValue field specifies a delay from 0 to 65535 ns. This delay represents the time from when
the host starts transmitting the first framing symbol of the packet to when the device receives the
first framing symbol of that packet.
If wIndex or wLength is non-zero, then the behavior of this request is not specified.
Default state:
This is a valid request when the device is in the Default state.
Address state:
This is a valid request when the device is in the Address state.
Configured state:
This is a valid request when the device is in the Configured state.
9-27
Universal Serial Bus 3.0 Specification, Revision 1.0
9.4.12
Set SEL
This request sets both the U1 and U2 System Exit Latency and the U1 or U2 exit latency for all the
links between a device and a root port on the host.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00000000B
SET_SEL
Zero
Zero
Six
Exit
Latency
Values
The latency values are sent to the device in the data stage of the control transfer in the following
format:
Offset
Name
Meaning
0
U1SEL
Time in μs for U1 System Exit Latency
1
U1PEL
Time in μs for U1 Device to Host Exit Latency
2
U2SEL
Time in μs for U2 System Exit Latency
4
U2PEL
Time in μs for U2 Device to Host Exit Latency
Figure C-2 in Appendix C illustrates the total latency a device may experience. The components of
latency include the following:
•
t1: the time to transition all links in the path to the host to U0 when the transition is initiated by
the device
•
t2: the time for the ERDY to traverse the interconnect hierarchy from the device to the host
•
t3: the time for the host to consume the ERDY and transmit a response to that request
•
t4: the time for the response to traverse the interconnect hierarchy from the host to the device
The U1SEL and U2SEL values represent the total round trip path latency when transitioning the
links between the device and host from U1 or U2 respectively to U0 under worst case
circumstances when the transition is initiated by the device. This is the sum of times t1 through t4.
The U1PEL and U2PEL values represent the device to host latency to transition the entire path of
links between the device and host from U1 or U2 respectively to U0 under worst case
circumstances when the transition is initiated by the device. This time includes only t1.
For more information, refer to Section C.1.5.1.
If wIndex or wValue is not set to zero or wLength is not six, then the behavior of the device is not
specified.
9-28
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
This is a valid request when the device is in the Address state.
Configured state:
This is a valid request when the device is in the Configured state.
Device Framework
9.4.13
Synch Frame
This request is used to set and then report an endpoint’s synchronization frame.
bmRequestType
bRequest
WValue
wIndex
wLength
Data
10000010B
synch_frame
Zero
Endpoint
Two
Frame
Number
When an endpoint supports isochronous transfers, the endpoint may also require per-frame transfers
to vary in size according to a specific pattern. The host and the endpoint must agree on which
frame the repeating pattern begins. The number of the frame in which the pattern began is returned
to the host.
If a SuperSpeed device supports the Synch Frame request, it shall internally synchronize itself to
the zeroth microframe and have a time notion of classic frame. Only the frame number is used to
synchronize and reported by the device endpoint (i.e., no microframe number). The endpoint must
synchronize to the zeroth microframe.
This value is only used for isochronous data transfers using implicit pattern synchronization. If
wValue is non-zero or wLength is not two, then the behavior of the device is not specified.
If the specified endpoint does not support this request, then the device will respond with a Request
Error.
9.5
Default state:
Device behavior when this request is received while the device is in the
Default state is not specified.
Address state:
The device shall respond with a Request Error.
Configured state:
This is a valid request when the device is in the Configured state.
Descriptors
Devices report their attributes using descriptors. A descriptor is a data structure with a defined
format. Each descriptor begins with a byte-wide field that contains the total number of bytes in the
descriptor followed by a byte-wide field that identifies the descriptor type.
Using descriptors allows concise storage of the attributes of individual configurations because each
configuration may reuse descriptors or portions of descriptors from other configurations that have
the same characteristics. In this manner, the descriptors resemble individual data records in a
relational database.
Where appropriate, descriptors contain references to string descriptors that provide displayable
information describing a descriptor in human-readable form. The inclusion of string descriptors is
optional. However, the reference fields within descriptors are mandatory. If a device does not
support string descriptors, string reference fields shall be reset to zero to indicate no string
descriptor is available.
If a descriptor returns with a value in its length field that is less than defined by this specification,
the descriptor is invalid and should be rejected by the host. If the descriptor returns with a value in
its length field that is greater than defined by this specification, the extra bytes are ignored by the
host, but the next descriptor is located using the length returned rather than the length expected.
9-29
Universal Serial Bus 3.0 Specification, Revision 1.0
A device may return class- or vendor-specific descriptors in two ways:
1. If the class or vendor specific descriptors use the same format as standard descriptors (e.g., start
with a length byte and followed by a type byte), they shall be returned interleaved with standard
descriptors in the configuration information returned by a GetDescriptor(Configuration)
request. In this case, the class or vendor-specific descriptors shall follow a related standard
descriptor they modify or extend.
2. If the class or vendor specific descriptors are independent of configuration information or use a
non-standard format, a GetDescriptor() request specifying the class or vendor specific
descriptor type and index may be used to retrieve the descriptor from the device. A class or
vendor specification will define the appropriate way to retrieve these descriptors.
9.6
Standard USB Descriptor Definitions
The standard descriptors defined in this specification may only be modified or extended by revision
of this specification.
9.6.1
Device
A device descriptor describes general information about a device. It includes information that
applies globally to the device and all of the device’s configurations. A device has only one device
descriptor.
The device descriptor of a SuperSpeed capable device has a version number of 3.0 (0300H).
The bcdUSB field contains a BCD version number. The value of the bcdUSB field is 0xJJMN for
version JJ.M.N (JJ – major version number, M – minor version number, N – sub-minor version
number), e.g., version 2.1.3 is represented with value 0x0213 and version 3.0 is represented with a
value of 0x0300.
The bNumConfigurations field indicates the number of configurations at the current operating
speed. Configurations for the other operating speed are not included in the count. If there are
specific configurations of the device for specific speeds, the bNumConfigurations field only reflects
the number of configurations for a single speed, not the total number of configurations for both
speeds.
If the device is operating at SuperSpeed, the bMaxPacketSize0 field shall be set to 09H (see
Table 9-8) indicating a 512-byte maximum packet. SuperSpeed operation does not allow other
maximum packet sizes for the default control pipe (endpoint 0) control endpoint.
All devices have a default control pipe. The maximum packet size of a device’s default control
pipe is described in the device descriptor. Endpoints specific to a configuration and its interface(s)
are described in the configuration descriptor. A configuration and its interface(s) do not include an
endpoint descriptor for the default control pipe. Other than the maximum packet size, the
characteristics of the default control pipe are defined by this specification and are the same for all
SuperSpeed devices.
The bNumConfigurations field identifies the number of configurations the device supports.
Table 9-8 shows the standard device descriptor.
9-30
Device Framework
Table 9-8. Standard Device Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
DEVICE Descriptor Type
2
bcdUSB
2
BCD
USB Specification Release Number in Binary-Coded
Decimal (i.e., 2.10 is 210H). This field identifies the release
of the USB Specification with which the device and its
descriptors are compliant.
4
bDeviceClass
1
Class
Class code (assigned by the USB-IF).
If this field is reset to zero, each interface within a
configuration specifies its own class information and the
various interfaces operate independently.
If this field is set to a value between 1 and FEH, the device
supports different class specifications on different interfaces
and the interfaces may not operate independently. This
value identifies the class definition used for the aggregate
interfaces.
If this field is set to FFH, the device class is vendor-specific.
5
bDeviceSubClass
1
SubClass
Subclass code (assigned by the USB-IF).
These codes are qualified by the value of the bDeviceClass
field.
If the bDeviceClass field is reset to zero, this field shall also
be reset to zero.
If the bDeviceClass field is not set to FFH, all values are
reserved for assignment by the USB-IF.
6
bDeviceProtocol
1
Protocol
Protocol code (assigned by the USB-IF). These codes are
qualified by the value of the bDeviceClass and the
bDeviceSubClass fields. If a device supports class-specific
protocols on a device basis as opposed to an interface
basis, this code identifies the protocols that the device uses
as defined by the specification of the device class.
If this field is reset to zero, the device does not use classspecific protocols on a device basis. However, it may use
class-specific protocols on an interface basis.
If this field is set to FFH, the device uses a vendor-specific
protocol on a device basis.
7
bMaxPacketSize0
1
Number
Maximum packet size for endpoint zero. The
bMaxPacketSize0 value is used as the exponent for a
bMaxPacketSize0
2
value; e.g., a bMaxPacketSize0 of 4 means a
4
Max Packet size of 16 (2 → 16).
09H is the only valid value in this field when operating in
SuperSpeed mode.
8
idVendor
2
ID
Vendor ID (assigned by the USB-IF)
10
idProduct
2
ID
Product ID (assigned by the manufacturer)
12
bcdDevice
2
BCD
Device release number in binary-coded decimal
14
iManufacturer
1
Index
Index of string descriptor describing manufacturer
15
iProduct
1
Index
Index of string descriptor describing product
16
iSerialNumber
1
Index
Index of string descriptor describing the device’s serial
number
17
bNumConfigurations
1
Number
Number of possible configurations
9-31
Universal Serial Bus 3.0 Specification, Revision 1.0
9.6.2
Binary Device Object Store (BOS)
This section defines a flexible and extensible framework for describing and adding device-level
capabilities to the set of USB standard specifications. As mentioned above, there exists a device
descriptor, but all device-level capability extensions are defined using the following framework.
The BOS descriptor defines a root descriptor that is similar to the configuration descriptor, and is
the base descriptor for accessing a family of related descriptors. A host can read a BOS descriptor
and learn from the wTotalLength field the entire size of the device-level descriptor set, or it can
read in the entire BOS descriptor set of device capabilities. The host accesses this descriptor using
the GetDescriptor() request. The descriptor type in the GetDescriptor() request is set to BOS (see
Table 9-9). There is no way for a host to read individual device capability descriptors. The entire
set can only be accessed via reading the BOS descriptor with a GetDescriptor() request and using
the length reported in the wTotalLength field.
Table 9-9. BOS Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of descriptor
1
bDescriptorType
1
Constant
BOS Descriptor type
2
wTotalLength
2
Number
Length of this descriptor and all of its sub descriptors
4
bNumDeviceCaps
1
Number
The number of separate device capability descriptors in
the BOS
Individual technology-specific or generic device-level capabilities are reported via Device
Capability descriptors. The format of the Device Capability descriptor is defined in Table 9-10.
The Device Capability descriptor has a generic header, with a sub-type field (bDevCapabilityType)
which defines the layout of the remainder of the descriptor. The codes for bDevCapabilityType are
defined in Table 9-11.
Table 9-10. Format of a Device Capability Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor.
1
bDescriptorType
1
Constant
Descriptor type: DEVICE CAPABILITY Type.
2
bDevCapabilityType
1
Number
Valid values are listed in Table 9-11.
3
Capability-Dependent
Var
Variable
Capability-specific format.
Device Capability descriptors are always returned as part of the BOS information returned by a
GetDescriptor(BOS) request. A Device Capability cannot be directly accessed with a
GetDescriptor() or SetDescriptor() request.
9-32
Device Framework
Table 9-11. Device Capability Type Codes
Capability Code
Value
Description
Wireless_USB
01H
Defines the set of Wireless USB-specific device level capabilities
USB 2.0
EXTENSION
02H
USB 2.0 Extension Descriptor
SUPERSPEED_USB
03H
Defines the set of SuperSpeed USB specific device level capabilities
CONTAINER_ID
04H
Reserved
00H, 05-FFH
Defines the instance unique ID used to identify the instance across all operating
modes
Reserved for future use
The following section defines the USB_30 device capability and the USB 2.0 Extension Descriptor
a SuperSpeed device shall return.
9.6.2.1
USB 2.0 Extension
A SuperSpeed device shall include the USB 2.0 Extension descriptor and shall support LPM when
operating in USB 2.0 High-Speed mode.
Table 9-12. USB 2.0 Extension Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of descriptor
1
bDescriptorType
1
Constant
DEVICE CAPABILITY Descriptor type
2
bDevCapabilityType
1
Constant
Capability type: USB 2.0 EXTENSION
3
bmAttributes
4
Bitmap
Bitmap encoding of supported device level features. A
value of one in a bit location indicates a feature is
supported; a value of zero indicates it is not supported.
Encodings are:
Bit
Encoding
0
Reserved. Shall be set to zero.
1
LPM. A value of one in this bit location
indicates that this device supports the
Link Power Management protocol.
SuperSpeed devices shall set this bit to
one.
31:2
Reserved. Shall be set to zero.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.6.2.2
SuperSpeed USB Device Capability
This section defines the required device-level capabilities descriptor which shall be implemented by
all SuperSpeed devices. This capability descriptor cannot be directly accessed with a
GetDescriptor() or SetDescriptor() request.
Table 9-13. SuperSpeed Device Capabilities Descriptor
Offset
Field
Size
Value
0
bLength
1
Number
Size of descriptor
1
bDescriptorType
1
Constant
DEVICE CAPABILITY Descriptor type
2
bDevCapabilityType
1
Constant
Capability type: SUPERSPEED_USB
3
bmAttributes
1
Bitmap
Bitmap encoding of supported device level features. A
value of one in a bit location indicates a feature is
supported; a value of zero indicates it is not supported.
Encodings are:
4
6
wSpeedsSupported
bFunctionalitySupport
2
1
Bitmap
Number
Description
Bit
Encoding
0
Reserved. Shall be set to zero.
1
LTM Capable. A value of one in this bit
location indicates that this device has is
capable of generating Latency
Tolerance Messages.
7:2
Reserved. Shall be set to zero.
Bitmap encoding of the speed supported by this device
when operating in SuperSpeed mode.
Bit
Encoding
0
If this bit is set, then the device
supports operation at low-Speed USB.
1
If this bit is set, then the device
supports operation at full-Speed USB.
2
If this bit is set, then the device
supports operation at high-Speed USB.
3
If this bit is set, then the device
supports operation at 5 Gbps.
15:4
Reserved. Shall be set to zero.
The lowest speed at which all the functionality supported by
the device is available to the user. For example if the
device supports all its functionality when connected at full
speed and above then it sets this value to 1.
Refer to the wSpeedsSupported field for valid values that
can be placed in this field.
9-34
Device Framework
Offset
Field
Size
Value
Description
7
bU1DevExitLat
1
Number
U1 Device Exit Latency. Worst case latency to transition
from U1 to U0, assuming the latency is limited only by the
device and not the device’s link partner.
This field applies only to the exit latency associated with an
individual port, and does not apply to the total latency
through a hub (e.g., from downstream port to upstream
port).
The following are permissible values:
Value
Meaning
00H
Zero.
01H
Less than 1 µs
02H
Less than 2 µs
03H
Less than 3 µs
04H
Less than 4 µs
…
…
0AH
Less than 10 µs
0BH –
FFH
Reserved
For a hub, this is the value for both its upstream and
downstream ports.
8
wU2DevExitLat
2
Number
U2 Device Exit Latency. Worst case latency to transition
from U2 to U0, assuming the latency is limited only by the
device and not the device’s link partner. Applies to all ports
on a device.
The following are permissible values:
Value
Meaning
0000H
Zero
0001H
Less than 1 µs
0002H
Less than 2 µs
0003H
Less than 3 µs
0004H
Less than 4 µs
…
…
07FFH
Less than 2047 µs
0800H –
FFFFH
Reserved
For a hub, this is the value for both its upstream and
downstream ports.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.6.2.3
Container ID
This section defines the device-level Container ID descriptor which shall be implemented by all
USB 3.0 hubs, and is optional for other devices. If this descriptor is provided when operating in
one mode, it shall be provided when operating in any mode. This descriptor may be used by a host
in order to identify a unique device instance across all operating modes. If a device can also
connect to a host through other technologies, the same Container ID value contained in this
descriptor should also be provided over those other technologies in a technology specific manner.
This capability descriptor cannot be directly accessed with a GetDescriptor() or SetDescriptor()
request.
Table 9-14. Container ID Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of descriptor
1
bDescriptorType
1
Constant
DEVICE CAPABILITY Descriptor type
2
bDevCapabilityType
1
Constant
Capability type: CONTAINER_ID
3
bReserved
1
Number
This field is reserved and shall be set to zero.
4
ContainerID
16
UUID
This is a 128-bit number that is unique to a device instance
that is used to uniquely identify the device instance across
all modes of operation. This same value may be provided
over other technologies as well to allow the host to identify
the device independent of means of connectivity.
Refer to IETF RFC 4122 for details on generation of a
UUID.
9.6.3
Configuration
The configuration descriptor describes information about a specific device configuration. The
descriptor contains a bConfigurationValue field with a value that, when used as a parameter to the
SetConfiguration() request, causes the device to assume the described configuration.
The descriptor describes the number of interfaces provided by the configuration. Each interface
may operate independently. For example, a Video Class device might be configured with two
interfaces, each providing 64-MBps bi-directional channels that have separate data sources or sinks
on the host. Another configuration might present the Video Class device as a single interface,
bonding the two channels into one 128-MBps bi-directional channel.
When the host requests the configuration descriptor, all related interface, endpoint, and endpoint
companion descriptors are returned (refer to Section 9.4.3).
A device has one or more configuration descriptors. Each configuration has one or more interfaces
and each interface has zero or more endpoints. An endpoint is not shared among interfaces within a
single configuration unless the endpoint is used by alternate settings of the same interface.
Endpoints may be shared among interfaces that are part of different configurations without this
restriction.
Once configured, devices may support limited adjustments to the configuration. If a particular
interface has alternate settings, an alternate may be selected after configuration. Table 9-15 shows
the standard configuration descriptor.
9-36
Device Framework
Table 9-15. Standard Configuration Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
CONFIGURATION Descriptor Type
2
wTotalLength
2
Number
Total length of data returned for this configuration.
Includes the combined length of all descriptors
(configuration, interface, endpoint, and class- or
vendor-specific) returned for this configuration
4
bNumInterfaces
1
Number
Number of interfaces supported by this configuration
5
bConfigurationValue
1
Number
Value to use as an argument to the
SetConfiguration() request to select this configuration
6
iConfiguration
1
Index
Index of string descriptor describing this configuration
7
bmAttributes
1
Bitmap
Configuration characteristics:
D7:
D6:
D5:
D4...0:
Reserved (set to one)
Self-powered
Remote Wakeup
Reserved (reset to zero)
D7 is reserved and shall be set to one for historical
reasons.
A device configuration that uses power from the bus
and a local source reports a non-zero value in
bMaxPower to indicate the amount of bus power
required and sets D6. The actual power source at
runtime may be determined using the
GetStatus(DEVICE) request (refer to Section 9.4.5).
If a device configuration supports remote wakeup, D5
is set to one.
8
bMaxPower
1
mA
Maximum power consumption of the device from the
bus in this specific configuration when the device is
fully operational. Expressed in 2-mA units when the
device is operating in high-speed mode and in 8-mA
units when operating in SuperSpeed mode.
(i.e., 50 = 100 mA in high-speed mode and 50 =
400 mA in SuperSpeed mode).
Note: A device configuration reports whether the
configuration is bus-powered or self-powered.
Device status reports whether the device is currently
self-powered. If a device is disconnected from its
external power source, it updates device status to
indicate that it is no longer self-powered.
A device may not increase its power draw from the
bus, when it loses its external power source, beyond
the amount reported by its configuration.
If a device can continue to operate when
disconnected from its external power source, it
continues to do so. If the device cannot continue to
operate, it shall return to the Powered state.
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Universal Serial Bus 3.0 Specification, Revision 1.0
9.6.4
Interface Association
The Interface Association Descriptor is used to describe that two or more interfaces are associated
to the same function. An “association” includes two or more interfaces and all of their alternate
setting interfaces. A device must use an Interface Association descriptor for each device function
that requires more than one interface. An Interface Association descriptor is always returned as
part of the configuration information returned by a GetDescriptor(Configuration) request. An
interface association descriptor cannot be directly accessed with a GetDescriptor() or
SetDescriptor() request. An interface association descriptor must be located before the set of
interface descriptors (including all alternate settings) for the interfaces it associates. All of the
interface numbers in the set of associated interfaces must be contiguous. Table 9-15 shows the
standard interface association descriptor. The interface association descriptor includes function
class, subclass, and protocol fields. The values in these fields can be the same as the interface class,
subclass, and protocol values from any one of the associated interfaces. The preferred
implementation, for existing device classes, is to use the interface class, subclass, and protocol field
values from the first interface in the list of associated interfaces.
Table 9-16. Standard Interface Association Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
INTERFACE ASSOCIATION Descriptor
2
bFirstInterface
1
Number
Interface number of the first interface that is associated with
this function
3
bInterfaceCount
1
Number
Number of contiguous interfaces that are associated with
this function
4
bFunctionClass
1
Class
Class code (assigned by USB-IF).
A value of zero is not allowed in this descriptor.
If this field is FFH, the function class is vendor-specific.
All other values are reserved for assignment by the USB-IF.
5
bFunctionSubClass
1
SubClass
Subclass code (assigned by USB-IF).
If the bFunctionClass field is not set to FFH, all values are
reserved for assignment by the USB-IF.
6
bFunctionProtocol
1
Protocol
Protocol code (assigned by USB-IF). These codes are
qualified by the values of the bFunctionClass and
bFunctionSubClass fields.
7
iFunction
1
Index
Index of string descriptor describing this function
Note: Since this particular feature was not included in earlier versions of the USB specification,
there is an issue with how existing USB operating system implementations will support devices that
use this descriptor. It is strongly recommended that device implementations utilizing the interface
association descriptor use the Multi-interface Function Class codes in the device descriptor. This
allows simple and easy identification of these devices and allows on some operating systems,
installation of an upgrade driver that can parse and enumerate configurations that include the
Interface Association Descriptor. The Multi-interface Function Class code is documented at
http://www.usb.org/developers/docs.
9-38
Device Framework
9.6.5
Interface
The interface descriptor describes a specific interface within a configuration. A configuration
provides one or more interfaces, each with zero or more endpoint descriptors. When a
configuration supports more than one interface, the endpoint descriptors for a particular interface
follow the interface descriptor in the data returned by the GetConfiguration() request. As
mentioned earlier in this chapter, SuperSpeed devices shall return Endpoint Companion descriptors
for each of the endpoints in that interface to return additional information about its endpoint
capabilities. The Endpoint Companion descriptor shall immediately follow the endpoint descriptor
it is associated with in the configuration information. An interface descriptor is always returned as
part of a configuration descriptor. Interface descriptors cannot be directly accessed with a
GetDescriptor() or SetDescriptor() request.
An interface may include alternate settings that allow the endpoints and/or their characteristics to be
varied after the device has been configured. The default setting for an interface is always alternate
setting zero. The SetInterface() request is used to select an alternate setting or to return to the
default setting. The GetInterface() request returns the selected alternate setting.
Alternate settings allow a portion of the device configuration to be varied while other interfaces
remain in operation. If a configuration has alternate settings for one or more of its interfaces, a
separate interface descriptor and its associated endpoint and endpoint companion (when reporting
its SuperSpeed configuration) descriptors are included for each setting.
If a device configuration supported a single interface with two alternate settings, the configuration
descriptor would be followed by an interface descriptor with the bInterfaceNumber and
bAlternateSetting fields set to zero and then the endpoint and endpoint companion (when reporting
its SuperSpeed configuration) descriptors for that setting, followed by another interface descriptor
and its associated endpoint and endpoint companion descriptors. The second interface descriptor’s
bInterfaceNumber field would also be set to zero, but the bAlternateSetting field of the second
interface descriptor would be set to one.
If an interface uses only the Default Control Pipe, no endpoint descriptors follow the interface
descriptor. In this case, the bNumEndpoints field shall be set to zero.
An interface descriptor never includes the Default Control Pipe in the number of endpoints.
Table 9-17 shows the standard interface descriptor.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Table 9-17. Standard Interface Descriptor
Offset
Field
Size
Value
0
Description
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
INTERFACE Descriptor Type
2
bInterfaceNumber
1
Number
Number of this interface. Zero-based value
identifying the index in the array of concurrent
interfaces supported by this configuration.
3
bAlternateSetting
1
Number
Value used to select this alternate setting for the
interface identified in the prior field
4
bNumEndpoints
1
Number
Number of endpoints used by this interface
(excluding the Default Control Pipe). If this value
is zero, this interface only uses the Default
Control Pipe.
5
bInterfaceClass
1
Class
Class code (assigned by the USB-IF).
A value of zero is reserved for future
standardization.
If this field is set to FFH, the interface class is
vendor-specific.
All other values are reserved for assignment by
the USB-IF.
6
bInterfaceSubClass
1
SubClass
Subclass code (assigned by the USB-IF). These
codes are qualified by the value of the
bInterfaceClass field.
If the bInterfaceClass field is reset to zero, this
field shall also be reset to zero.
If the bInterfaceClass field is not set to FFH, all
values are reserved for assignment by the
USB-IF.
7
bInterfaceProtocol
1
Protocol
Protocol code (assigned by the USB). These
codes are qualified by the value of the
bInterfaceClass and the bInterfaceSubClass
fields. If an interface supports class-specific
requests, this code identifies the protocols that
the device uses as defined by the specification of
the device class.
If this field is reset to zero, the device does not
use a class-specific protocol on this interface.
If this field is set to FFH, the device uses a
vendor-specific protocol for this interface.
8
9-40
iInterface
1
Index
Index of string descriptor describing this interface
Device Framework
9.6.6
Endpoint
Each endpoint used for an interface has its own descriptor. This descriptor contains the information
required by the host to determine the bandwidth requirements of each endpoint. An endpoint
descriptor is always returned as part of the configuration information returned by a
GetDescriptor(Configuration) request. An endpoint descriptor cannot be directly accessed with a
GetDescriptor() or SetDescriptor() request. There is never an endpoint descriptor for endpoint zero.
Table 9-18 shows the standard endpoint descriptor.
Table 9-18. Standard Endpoint Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
ENDPOINT Descriptor Type
2
bEndpointAddress
1
Endpoint
The address of the endpoint on the device described by this
descriptor. The address is encoded as follows:
Bit 3...0: The endpoint number
Bit 6...4: Reserved, reset to zero
Bit 7:
Direction, ignored for
control endpoints
0 = OUT endpoint
1 = IN endpoint
9-41
Universal Serial Bus 3.0 Specification, Revision 1.0
Offset
Field
Size
Value
Description
3
bmAttributes
1
Bitmap
This field describes the endpoint’s attributes when it is configured
using the bConfigurationValue.
Bits 1..0: Transfer Type
00 = Control
01 = Isochronous
10 = Bulk
11 = Interrupt
If an interrupt endpoint, bits 5..2 are defined as follows:
Bits 3..2: Reserved
Bits 5..4: Usage Type
00 = Periodic
01 = Notification
10 = Reserved
11 = Reserved
If isochronous, they are defined as follows:
Bits 3..2: Synchronization Type
00 = No Synchronization
01 = Asynchronous
10 = Adaptive
11 = Synchronous
Bits 5..4: Usage Type
00 = Data endpoint
01 = Feedback endpoint
10 = Implicit feedback Data endpoint
11 = Reserved
If not an isochronous or interrupt endpoint, bits 5..2 are reserved and
shall be set to zero.
All other bits are reserved and shall be reset to zero. Reserved bits
shall be ignored by the host.
4
wMaxPacketSize
2
Number
Maximum packet size this endpoint is capable of sending or receiving
when this configuration is selected.
There are only two legal values for this field. For control endpoints this
field shall be set to 512. For bulk endpoint types this field shall be set
to 1024.
For interrupt and isochronous endpoints this field shall be set to 1024 if
this endpoint defines a value in the bMaxBurst field greater than zero.
If the value in the bMaxBurst field is set to zero then this field can
have any value from 0 to 1024 for an isochronous endpoint and 1 to
1024 for an interrupt endpoint.
6
bInterval
1
Number
Interval for servicing the endpoint for data transfers. Expressed in
125-µs units.
For SuperSpeed isochronous and interrupt endpoints, this value shall
be in the range from 1 to 16. The bInterval value is used as the
(bInterval-1)
exponent for a 2
value; e.g., a bInterval of 4 means a period of
(4-1)
3
→ 2 → 8).
8 (2
This field is reserved and shall not be used for SuperSpeed bulk or
control endpoints.
9-42
Device Framework
The bmAttributes field provides information about the endpoint’s Transfer Type (bits 1..0) and
Synchronization Type (bits 3..2). For interrupt endpoints, the Usage Type bits (bits 5..4) indicate
whether the endpoint is used for infrequent notifications that can tolerate varying latencies (bits 5..4
= 01b), or if it regularly transfers data in consecutive service intervals or is dependent on bounded
latencies (bits 5..4 = 00b). For example, a hub’s interrupt endpoint would specify that it is a
notification type, while a mouse would specify a periodic type. For endpoints that sometimes
operate in infrequent notification mode and at other times operate in periodic mode then this field
shall be set to Periodic (bits 5..4 = 00b). These values may be used by software to determine
appropriate power management settings. See Appendix C for details on how this value may impact
power management. In addition, for isochronous endpoints the Usage Type bit (bits 5..4) indicate
whether this is an endpoint used for normal data transfers (bits 5..4 = 00b), whether it is used to
convey explicit feedback information for one or more data endpoints (bits 5..4 = 01b) or whether it
is a data endpoint that also serves as an implicit feedback endpoint for one or more data endpoints
(bits 5..4=10b).
If the endpoint is used as an explicit feedback endpoint (bits 5..4 = 01b), then the Transfer Type
shall be set to isochronous (bits 1..0 = 01b) and the Synchronization Type shall be set to No
Synchronization (bits 3..2 = 00b).
A feedback endpoint (explicit or implicit) needs to be associated with one (or more) isochronous
data endpoints to which it provides feedback service. The association is based on endpoint number
matching. A feedback endpoint always has the opposite direction from the data endpoint(s) it
services. If multiple data endpoints are to be serviced by the same feedback endpoint, the data
endpoints shall have ascending ordered–but not necessarily consecutive–endpoint numbers. The
first data endpoint and the feedback endpoint shall have the same endpoint number (and opposite
direction). This ensures that a data endpoint can uniquely identify its feedback endpoint by
searching for the first feedback endpoint that has an endpoint number equal or less than its own
endpoint number.
Example: Consider the extreme case where there is a need for five groups of OUT asynchronous
isochronous endpoints and at the same time four groups of IN adaptive isochronous endpoints.
Each group needs a separate feedback endpoint and the groups are composed as shown in
Table 9-19.
Table 9-19. Example of Feedback Endpoint Numbers
OUT
Group
Number of
OUT
Endpoints
IN
Group
Number of
IN
Endpoints
1
1
6
1
2
2
7
2
3
2
8
3
4
3
9
4
5
3
The endpoint numbers can be intertwined as illustrated in Figure 9-8.
9-43
Universal Serial Bus 3.0 Specification, Revision 1.0
1
2
3
4
5
OUT
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
1
2
3
IN
4
Data Endpoint
Feedback Endpoint
U-086
Figure 9-8. Example of Feedback Endpoint Relationships
For high-speed bulk and control OUT endpoints, the bInterval field is only used for compliance
purposes; the host controller is not required to change its behavior based on the value in this field.
9-44
Device Framework
9.6.7
SuperSpeed Endpoint Companion
Each SuperSpeed endpoint described in an interface is followed by a SuperSpeed Endpoint
Companion descriptor. This descriptor contains additional endpoint characteristics that are only
defined for SuperSpeed endpoints. This descriptor is always returned as part of the configuration
information returned by a GetDescriptor(Configuration) request and cannot be directly accessed
with a GetDescriptor() or SetDescriptor() request. The Default Control Pipe does not have an
Endpoint Companion descriptor. The Endpoint Companion descriptor shall immediately follow the
endpoint descriptor it is associated with in the configuration information.
Table 9-20. SuperSpeed Endpoint Companion Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
SUPERSPEED_USB_ENDPOINT_COMPANION Descriptor
Type
2
bMaxBurst
1
Number
The maximum number of packets the endpoint can send or
receive as part of a burst. Valid values are from 0 to 15. A
value of 0 indicates that the endpoint can only burst one
packet at a time and a value of 15 indicates that the endpoint
can burst up to 16 packets at a time.
For endpoints of type control this shall be set to 0.
9-45
Universal Serial Bus 3.0 Specification, Revision 1.0
Offset
Field
Size
Value
Description
3
bmAttributes
1
Bitmap
If this is a Bulk Endpoint:
Bits
Description
4:0
MaxStreams. The maximum number of
streams this endpoint supports. Valid values
are from 0 to 16, where a value of 0 indicates
that the endpoint does not define streams. For
the values 1 to 16, the number of streams
MaxStream
supported equals 2
.
7:5
Reserved. These bits are reserved and shall
be set to zero.
If this is a Control or Interrupt Endpoint:
Bits
Description
7:0
Reserved. These bits are reserved and shall
be set to zero.
If this is an isochronous endpoint:
Bits
Description
1:0
Mult. A zero based value that determines the
maximum number of packets within a service
interval that this endpoint supports.
Maximum number of packets = bMaxBurst x
(Mult + 1)
The maximum value that can be set in this field
is 2.
7:2
4
wBytesPerInterval
2
Number
Reserved. These bits are reserved and shall
be set to zero.
The total number of bytes this endpoint will transfer every
service interval. This field is only valid for periodic endpoints.
For isochronous endpoints, this value is used to reserve the
bus time in the schedule, required for the frame data
payloads per 125 μs. The pipe may, on an ongoing basis,
actually use less bandwidth than that reserved. The device
reports, if necessary, the actual bandwidth used via its
normal, non-USB defined mechanisms.
9-46
Device Framework
9.6.8
String
String descriptors are optional. As noted previously, if a device does not support string descriptors,
all references to string descriptors within device, configuration, and interface descriptors shall be
reset to zero.
String descriptors use UNICODE UTF16LE encodings as defined by The Unicode Standard,
Worldwide Character Encoding, Version 5.0, The Unicode Consortium, Addison-Wesley
Publishing Company, Reading, Massachusetts (http://www.unicode.org). The strings in a device
may support multiple languages. When requesting a string descriptor, the requester specifies the
desired language using a 16-bit language ID (LANGID) defined by the USB-IF. The list of
currently defined USB LANGIDs can be found at http://www.usb.org/developers/docs.html. String
index zero for all languages returns a string descriptor that contains an array of 2-byte LANGID
codes supported by the device. Table 9-21 shows the LANGID code array. A device may omit all
string descriptors. Devices that omit all string descriptors shall not return an array of LANGID
codes.
The array of LANGID codes is not NULL-terminated. The size of the array (in bytes) is computed
by subtracting two from the value of the first byte of the descriptor.
Table 9-21. String Descriptor Zero, Specifying Languages Supported by the Device
Offset
Field
Size
Value
Description
0
bLength
1
N+2
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
STRING Descriptor Type
2
wLANGID[0]
2
Number
LANGID code zero
...
...
...
...
...
N
wLANGID[x]
2
Number
LANGID code x
The UNICODE string descriptor (shown in Table 9-22) is not NULL-terminated. The string length
is computed by subtracting two from the value of the first byte of the descriptor.
Table 9-22. UNICODE String Descriptor
Offset
Field
Size
Value
Description
0
bLength
1
Number
Size of this descriptor in bytes
1
bDescriptorType
1
Constant
STRING Descriptor Type
2
bString
N
Number
UNICODE encoded string
9-47
Universal Serial Bus 3.0 Specification, Revision 1.0
9.7
Device Class Definitions
All devices shall support the requests and descriptor definitions described in this chapter. Most
devices provide additional requests and, possibly, descriptors for device-specific extensions. In
addition, devices may provide extended services that are common to a group of devices. In order to
define a class of devices, the following information shall be provided to completely define the
appearance and behavior of the device class.
9.7.1
Descriptors
If the class requires any specific definition of the standard descriptors, the class definition shall
include those requirements as part of the class definition. In addition, if the class defines a standard
extended set of descriptors, they shall also be fully defined in the class definition. Any extended
descriptor definitions shall follow the approach used for standard descriptors; for example, all
descriptors shall begin with a length field.
9.7.2
Interface(s)
When a class of devices is standardized, the interfaces used by the devices shall be included in the
device class definition. Devices may further extend a class definition with proprietary features as
long as they meet the base definition of the class.
9.7.3
Requests
All of the requests specific to the class shall be defined.
9-48
10
Hub, Host Downstream Port, and Device
Upstream Port Specification
This chapter describes the architectural requirements for a USB 3.0 hub. The chapter also describes
differences between functional requirements for a host downstream port and a hub downstream port
as well as differences between a device upstream port and a hub upstream port. The chapter
contains descriptions of two of the three principal sub-blocks: the SuperSpeed hub
repeater/forwarder and the SuperSpeed hub controller. The USB 2.0 hub sub-block is described in
the Universal Serial Bus Specification, Revision 2.0. This chapter also describes the hub's
operation for error recovery, reset, suspend/resume, hub request behavior, and hub descriptors.
The hub specification chapter along with the Universal Serial Bus Specification, Revision 2.0
supply the information needed for an implementer to design a hub that conforms to the USB 3.0
specification.
10.1
Hub Feature Summary
Hubs provide the electrical interface between USB devices and the host. Hubs are directly
responsible for supporting many of the attributes that make USB user friendly and hide its
complexity from the user. Listed below are the major aspects of USB functionality that hubs
support:
• Connectivity behavior
• Power management
• Device connect/disconnect detection
• Bus fault detection and recovery
• SuperSpeed and USB 2.0 (high-speed, full-speed, and low-speed) device support
A USB 3.0 hub incorporates a USB 2.0 hub and a SuperSpeed hub consisting of two principal
components: the SuperSpeed Hub Repeater/Forwarder and the SuperSpeed Hub Controller. The
USB 2.0 hub is described in the USB 2.0 specification. All subsequent references in this
specification are to components of the SuperSpeed hub unless otherwise noted. The Hub
Repeater/Forwarder is responsible for connectivity setup and tear-down. It also supports exception
handling, such as bus fault detection and recovery and connect/disconnect detect. The Hub
Controller provides the mechanism for host-to-hub communication. Hub-specific status and control
commands permit the host to configure a hub and to monitor and control its individual downstream
facing ports.
10-1
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 10-2 shows a high level block diagram of a four port USB 3.0 hub and the locations of its
upstream and downstream facing ports. A USB 3.0 hub is the logical combination of two hubs: a
USB 2.0 hub and a SuperSpeed hub. Each hub operates independently on a separate data bus.
Typically, the only signal shared logic between them is to control VBUS. If either the USB 2.0 hub
or SuperSpeed hub controllers requires, a downstream port is powered. A USB 3.0 hub connects
on both interfaces upstream whenever possible. All exposed downstream ports on a USB 3.0 hub
shall support both SuperSpeed and USB 2.0 connections. Host controller ports may have different
requirements.
US Port
SuperSpeed
Hub
DS Port 1
VBUS
Control
Logic
DS Port 2
DS Port 3
USB 2.0
Hub
DS Port 4
U-140
Figure 10-1. Hub Architecture
Figure 10-2 shows the SuperSpeed portion of a USB 3.0 hub consisting of a Hub
Repeater/Forwarder section and a Hub Controller section.
The USB 2.0 portion of a USB 3.0 hub shall meet all requirements of the USB 2.0 specification
unless specific exceptions are noted.
The Hub Repeater/Forwarder is responsible for managing connectivity between upstream and
downstream facing ports which are operating at SuperSpeed. The Hub Controller provides status
and control and permits host access to the SuperSpeed Hub.
10-2
Hub, Host Downstream Port, and Device Upstream Port Specification
Upstream
Facing Port
Upstream Facing Port
State Machines
Hub
Repeater/
Forwarder
Hub
Controller
Downstream Facing Port
State Machine(s)
Port 1
Port 2
Port N
Downstream Facing Ports
U-141
Figure 10-2. SuperSpeed Portion of the Hub Architecture
When the hub upstream facing port is attached to an electrical environment that is only operating at
high-speed or full-speed, SuperSpeed connectivity is not available to devices attached to
downstream facing ports.
Unlike USB 3.0 peripheral devices, a USB 3.0 hub is required to connect upstream on both the
USB 3.0 and USB 2.0 buses. SuperSpeed connections may be enabled or disabled under the
control of system software for a USB 3.0 hub’s downstream ports. If the hub upstream SuperSpeed
connection is not supported by the port to which the USB 3.0 hub is connected, the hub disables
SuperSpeed support on all of its downstream ports. If a USB 3.0 hub upstream port is not
connected on either USB 2.0 or SuperSpeed, the hub does not provide power to the downstream
ports unless it supports the USB Implementers Forum, Inc.’s Battery Charging Specification. Refer
to Section 10.3.1.1 for a detailed discussion on when a hub is allowed to remove VBUS from a
downstream facing port. The USB 3.0 specification allows self-powered and bus-powered hubs.
The following sections present the typical flow for connection management in various types of
systems for the simple topology shown in Figure 10-3 when the host system is first powered on.
Note: These connection examples outline cases where the system operates as expected. The
handling of error cases are specified later in this chapter.
10-3
Universal Serial Bus 3.0 Specification, Revision 1.0
Non-SuperSpeed
Super
Speed
HighSpeed
FullSpeed
LowSpeed
SuperSpeed
USB 3.0 Host
Non-SuperSpeed
(USB 2.0)
Composite Cable
SuperSpeed
Hub
SuperSpeed
Function
USB 2.0
Hub
NonSuperSpeed
Function
USB 3.0 Hub
USB 3.0 Peripheral Device
U-142
Figure 10-3. Simple USB 3.0 Topology
10.1.1
SuperSpeed Capable Host with SuperSpeed Capable
Software
When the host is powered off, the hub does not provide power to its downstream ports unless the
hub supports charging applications (refer to Section 10.3.1.1).
When the host is powered on with SuperSpeed support enabled on its downstream ports by default
the following is the typical sequence of events:
• Hub detects VBUS and SuperSpeed support and powers its downstream ports with SuperSpeed
enabled.
• Hub connects both as a SuperSpeed and as a high-speed device.
• Device detects VBUS and SuperSpeed support and connects as a SuperSpeed device.
• Host system begins hub enumeration at high-speed and SuperSpeed.
• Host system begins device enumeration at SuperSpeed.
10.1.2
USB 2.0 Host
When the host is powered off, the hub does not provide power to its downstream ports unless the
hub supports charging applications (refer to Section 10.3.1.1).
When the host is powered on and there is no SuperSpeed hardware support, the following is the
typical sequence of events:
• Hub detects VBUS and connects as a high-speed device.
• Host system begins hub enumeration at high-speed.
10-4
Hub, Host Downstream Port, and Device Upstream Port Specification
•
•
•
10.1.3
Hubs power downstream ports when directed by software (USB 2.0) with SuperSpeed support
disabled.
Device connects at high-speed.
Host system begins device enumeration at high-speed.
Hub Connectivity
Hubs exhibit different connectivity behavior depending on whether they are propagating data
packet header/data packet payload packet traffic, other packet traffic, resume signaling, or are in an
Idle state.
10.1.3.1
Packet Signaling Connectivity
The Hub Repeater/Forwarder contains one port that shall always connect in the upstream direction
(referred to as the upstream facing port) and one or more downstream facing ports. Upstream
connectivity is defined as being towards the host, and downstream connectivity is defined as being
towards a device. A SuperSpeed hub controller contains buffering for header and data packets. A
SuperSpeed hub controller does not use the repeater-only model used for high-speed connectivity in
a USB 2.0 hub. This change allows multiple downstream devices to send asynchronous messages
simultaneously without data loss and for some traffic to be stored and delivered when it is directed
to downstream ports when the links are not in U0.
Figure 10-4 shows the high level packet signaling connectivity behavior for hubs in the upstream
and downstream directions. Later sections describe the hub internal buffering and connectivity in
more detail. A hub also has an Idle state, during which the hub makes no connectivity. When in
the Idle state, all of the hub’s ports (upstream plus downstream) are U1, U2 or in U0 receiving and
transmitting logical idles waiting for the start of the next packet.
Upstream
Port
Downstream Port
selected by
Route String
Downstream
Ports
Downstream
Connectivity
Upstream
Connectivity
Idle
(No Connectivity)
Enabled Port
Port not Enabled
U-143
Figure 10-4. Hub Signaling Connectivity
10-5
Universal Serial Bus 3.0 Specification, Revision 1.0
If a downstream facing port is enabled (i.e., in a state where it can propagate signaling through the
hub) and the hub detects the start of a packet on that port, the hub begins to store the packet header.
Connectivity is established in an upstream direction to the upstream facing port of that hub
whenever a valid header packet has been received on a downstream port. The hub transmits the
valid header packet received on the downstream port upstream, but not to any other downstream
facing ports. This means that when a device or a hub transmits a packet upstream, only those hubs
in a direct line between the transmitting device and the host will see the packet.
All packets except Isochronous Timestamp Packets are unicast in the downstream direction; hubs
operate using a direct connectivity model. This means that when the host or hub transmits a packet
downstream, only those hubs in a direct line between the host and recipient device will see the
packet. When a hub detects the start of a packet on its upstream facing port, the hub begins to store
the packet header. Whenever a valid header packet has been received on a hub upstream port, the
hub uses the Route String in the packet header packet and the hub depth value assigned when
enumerated to establish connectivity only to the port indicated. If the indicated port is not enabled,
it does not propagate packet signaling downstream. The hub shall silently drop a header packet that
is routed to a downstream port that is not enabled, a port with a link in U3, or a downstream port
that does not exist. The hub shall perform normal link level acknowledgement of the header packet
in these cases.
10.1.3.2
Routing Information
Packets received on the hub upstream port are routed based on information contained in a 20-bit
field (Route String) in the packet header. The route string is used in conjunction with a hub depth
value by the hub to identify the target port for a downstream directed packet. The hub depth value
is assigned by software using the Set Hub Depth request. The hub ignores the route string and
assumes all packets are routed directly to the hub until it enters the configured state. The hub’s
upstream port shall be represented by port number zero while the downstream ports shall begin
with port number one and count up sequentially. Whenever a hub controller responds to a packet
routed to the hub with a packet containing a route string or originates a packet (except for a packet
the hub is deferring) the hub shall set the route string to zero.
Figure 10-5 illustrates the use of route strings in an example topology with five levels of four port
USB 3.0 hubs. The hub depth value for each level of hub is illustrated in the figure. Each hub and
each device in the topology contains the route string that would be used to route a packet to that
device/hub. For each hub depth, the octet in the route string that determines the routing target at
that hub depth is shown in bold and a larger font size than the rest of the route string. The host root
port is not included in the 20-bit route string.
10-6
Hub, Host Downstream Port, and Device Upstream Port Specification
Host Root Port - Not Included in Route String
US Port 0
0x00000
Hub Depth 0
DS Port 1
DS Port 2
DS Port 3
DS Port 4
0x00002
0x00003
0x00004
US Port 0
0x00001
Hub Depth 1
DS Port 1
DS Port 2
0x00011
DS Port 3
DS Port 4
0x00031
0x00041
US Port 0
0x00021
Hub Depth 2
DS Port 1
DS Port 2
0x00121
0x00221
DS Port 3
DS Port 4
0x00421
US Port 0
0x00321
Hub Depth 3
DS Port 1
DS Port 2
DS Port 3
0x01321
0x02321
0x03321
DS Port 4
US Port 0
0x04321
Hub Depth 4
DS Port 1
DS Port 2
DS Port 3
DS Port 4
0x14321
0x24321
0x34321
0x44321
Peripheral Device
U-144
Figure 10-5. Route String Example
10-7
Universal Serial Bus 3.0 Specification, Revision 1.0
10.1.4
Resume Connectivity
Hubs exhibit different connectivity behaviors for upstream- and downstream-directed resume
signaling. A hub does not propagate resume signaling from its upstream facing port to any of its
downstream facing ports unless a downstream facing port is suspended and has received resume
signaling since it was suspended. Figure 10-6 illustrates hub upstream and downstream resume
connectivity.
Enabled Port
Port not Enabled
Suspended Port
U-145
Figure 10-6. Resume Connectivity
If a hub upstream port is suspended and the hub detects resume signaling from a suspended
downstream facing port, the hub propagates that signaling upstream and does not reflect that
signaling to any of the downstream facing ports (including the downstream port that originated
resume signaling). If a hub upstream port is not suspended and the hub detects resume signaling
from a suspended downstream facing port, the hub reflects resume signaling to the downstream
port. Note that software shall not initiate a transition to U3 on the upstream port of a hub unless it
has already initiated transitions to U3 on all enabled downstream ports. A detailed discussion of
resume connectivity appears in Section 10.8.
10.1.5
Hub Fault Recovery Mechanisms
Hubs are the essential USB component for establishing connectivity between the host and other
devices. It is vital that any connectivity faults be prevented if possible and detected in the unlikely
event they occur.
Hubs must also be able to detect and recover from lost or corrupted packets that are addressed to
the Hub Controller. Because the Hub Controller is, in fact, another USB device, it shall adhere to
the same rules as other USB devices, as described in Chapter 8.
10-8
Hub, Host Downstream Port, and Device Upstream Port Specification
10.1.6
Hub Header Packet Buffer Architecture
Figure 10-7 shows the logical representation of a typical header packet buffer implementation for a
SuperSpeed hub. Logically, a SuperSpeed hub has separate header packet buffers associated with
each port for both upstream and downstream traffic. When a hub receives a header packet on its
upstream port, it routes the header packet to the appropriate downstream header packet buffer for
transmission (unless the header packet is for the hub). When the hub receives a non-LMP header
packet on a downstream port, it routes the header packet to the upstream port header packet buffer
for transmission. Header packets are kept in the hub header packet buffers after transmission until
link level acknowledgement (LGOOD_n) for the header packet is received. This allows the hub to
retry the header packets if necessary to ensure that header packets are received correctly at the link
level. The header packet buffers also allow a hub to store the header packets until they can be
forwarded when the header packet is directed to a downstream link that is a low power link state.
Hubs store the header packet and deliver it once the link becomes active.
Traffic
Flow
US Port
US Port
Header
Buffer
Header
Buffer
Traffic
Flow
Header Router
Header Aggregater
Header
Buffer
Header
Buffer
Header
Buffer
Header
Buffer
Header
Buffer
Header
Buffer
Header
Buffer
Header
Buffer
DS Port 1
DS Port 2
DS Port 3
DS Port 4
DS Port 1
DS Port 2
DS Port 3
DS Port 4
U-146
Figure 10-7. Typical Hub Header Packet Buffer Architecture
10.1.6.1
Hub Data Buffer Architecture
US Port
DPP
2
DS Data
Buffer
US Data
Buffer
DPP
1
DPH2
DPH1
DS Port 1
DS Port 2
DS Port 3
DS Port 4
U-147
Figure 10-8. Hub Data Buffer Traffic
(Header Packet Buffer Only Shown for DS Port 1)
10-9
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure 10-8 shows the logical representation of the data buffer architecture in a typical SuperSpeed
hub. SuperSpeed hubs provide independent buffering for data packet payloads (DPP) in both the
upstream and downstream directions. The USB 3.0 Architecture allows concurrent transactions to
occur in both the upstream and downstream directions. In the figure, two data packets are in
progress in the downstream direction. The hub can store more than one data packet payload at the
same time. In rare occurrences where data packet payloads are discarded because buffering is
unavailable, the end-to-end protocol will recover by retrying the transaction. The isochronous
protocol does not include retries. However, discard errors are expected less frequently then bit
errors on the physical bus.
Note: Data packet headers are stored and handled in the same fashion as other header packet
packets using the header packet buffers. DPPs are handled using the separate data buffers.
10.2
10.2.1
Hub Power Management
Link States
The hub is required to support U0, U1, U2, and U3 on all ports (upstream and downstream).
10.2.2
Hub Downstream Port U1/U2 Timers
The hub is required to have inactivity timers for both U1 and U2 on each downstream port. The
timeout values are programmable and may be set by the host software. A timeout value of zero
means the timer is disabled. The default value for the U1/U2 timeouts is zero. The U1 and U2
timeout values for all downstream ports reset to the default state on PowerOn Reset or when the
hub upstream port is reset. The U1 and U2 timeout values for a downstream port reset to the
default values when the port receives a SetPortFeature request for a port reset. The downstream
port state machines presented in this chapter describe the specific operational rules when U1 and/or
U2 timeouts are enabled.
• Hub downstream ports shall accept U1 or U2 entry initiated by a link partner except when the
corresponding U1/U2 timeout is set to zero or there is pending traffic directed to the
downstream port.
• If a hub has received a valid packet on its upstream port that is routed to a downstream port, it
shall reject U1 or U2 link entry attempts on the downstream port until the packet has been
successfully transmitted. A hub may also reject U1 or U2 link entry attempts on downstream
ports if the hub is receiving a packet but has not determined the packet’s destination. A hub
implementation shall ensure no race condition exists where a header packet that has not been
deferred is queued for transmission on a downstream port with a link that is in U1, U2, or U3 or
is in the process of entering U1, U2, or U3.
• Hub downstream ports shall reject all U1 and U2 entry requests if the corresponding timeout is
set to zero.
• The hub inactivity timers for U1 and U2 shall not be reset by an Isochronous Timestamp
Packet.
10-10
Hub, Host Downstream Port, and Device Upstream Port Specification
10.2.3
Downstream/Upstream Port Link State Transitions
The hub shall evaluate the link power state of its downstream ports such that it propagates the
highest link state of any of its downstream ports to its upstream port when there is no pending
upstream traffic. U0 is the highest link state, followed by U1, then U2, then U3, then Rx.Detect,
and then SS.Disabled. If an upstream port link state transition would result in an upstream port link
state that has been disabled by software, the hub shall transition the upstream port link to the next
highest U-state that is enabled. The hub never automatically attempts to transition the hub
upstream port to U3.
The downstream port state machines presented in this chapter provide the specific timing
requirements for changing the upstream port link state in response to downstream port link state
changes.
The hub also shall initiate a link state transition on the appropriate downstream port whenever it
receives a packet that is routed to downstream port that is not in U0. The hub upstream port state
machines provided in this chapter provide the specific timing requirements for these transitions.
If enabled, port status change interrupts, e.g., due to a connect event on a downstream port, will
cause the upstream link to initiate a transition to U0.
10.3
Hub Downstream Facing Ports
The following sections provide a functional description of a state machine that exhibits the correct
required behavior for a downstream facing port.
Figure 10-9 is an illustration of the downstream facing port state machine. Each of the states is
described in Section 10.4.2. In the diagram below, some of the entry conditions into states are
shown without origin. These conditions have multiple origin states and the individual transitions
lines are not shown to simplify the diagram. The description of the entered state indicates from
which states the transition is applicable.
Note: For the root hub, the signals from the upstream facing port state machines are
implementation dependent.
10-11
Universal Serial Bus 3.0 Specification, Revision 1.0
SetPortFeature(PORT_LINK_STATE)
= SS.Disabled
ClearPortFeature (PORT_POWER)
Power Source Off
Over-Current
Upstream Port VBUS Off
Upstream Hub Port Link's Far End
Receiver Terminations Not Present
Upstream Port Reset
SetConfig(0)
DSPORT.Powered-off
DSPORT.Disabled
Link in SS.disabled (PLS = 4)
Link in SS.disabled (PLS = 4)
(PP = CCS = PR = PE = 0)
(PP = 1)
(CCS = PR = PE = 0)
Far end receiver terminations on
upstream hub port link present
Or Set Port Feature
(PORT_POWER)
Disconnect Detected
SetPortFeature(PORT_LINK_STATE)
= Rx.Detect
DSPORT.Disconnected
(Waiting for SS Connect)
st
1 LFPS
Timeout
DSPORT.Compliance
Link in Compliance Mode
(PLS = 10)
Link in Rx.Detect (PLS = 5)
(PP = 1)
(CCS = PR = PE = 0)
(PP = 1)
(CCS = PR = PE = 0)
Any Polling substate
times out
Connect Detected
Power Source On
OR Upstream VBUS Valid
DSPORT.Training
Link in Polling (PLS = 7)
Loopback exit LFPS
handshake successful
Loopback bit set
in received TS2
ordered sets
Link Transition from
Polling.Idle to U0
DSPORT.Loopback
Link in Loopback
(PLS = 11)
DSPORT.Enabled
(PP = 1)
(CCS = PR = PE = 0)
Loopback exit LFPS
handshake failed
(applies only if Downstream
Port is loopback master)
(PP = 1)
(CCS = PR = PLS = PE = 0)
Link in U0, U1, U2, or U3, or
Recovery (PLS = 0, 1, 2, 3, or 8)
Port Configuration Fails
(refer to Section 8.4.5)
(PP = CCS = PE = 1)
(PR = 0)
Any Polling substate
times out
DSPORT.Error
Link in SS.Inactive
(PLS = 6)
Reset Completes
Successfully
DSPORT.RESETTING
PLS Undefined
(PP = 1)
(CCS = PR = PE = 0)
(PP = CCS = PR = 1)
(PE = 0)
Link Exits
Recovery
After Timeout
U1 or U2 Exit Fails
Rx.Detect.Active
times out
Set Port Feature (PORT_RESET)
Set Port Feature (PORT_BH_RESET)
Port Status Field:
Notation Field Name
PP
PORT_POWER
CCS
PORT_CONNECTION
PR
PORT_RESET
PLS
PORT_LINK_STATE
PE
PORT_ENABLE
Note: GetPortStatus Requests will return
all zeros until a Set Configuration Request
for a non-zero config and a subsequent
Set Port Feature (PORT_POWER) request
have occurred for the port.
Note: Clear Port Feature
(PORT_ENABLED) and
Set Port Feature
(PORT_ENABLED) are
not used for SS Ports
U-148
Figure 10-9. Downstream Facing Hub Port State Machine
10-12
Hub, Host Downstream Port, and Device Upstream Port Specification
10.3.1
Hub Downstream Facing Port State Descriptions
10.3.1.1
DSPORT.Powered-off
The DSPORT.Powered-off state is a logical powered off state. The hub may still be required or
choose to provide VBUS for a downstream port in the DSPORT.Powered-off state. Detailed
requirements for presence of VBUS are covered later in this section.
A port shall transition into this state if any of the following situations occur:
• From any state when the hub receives a ClearPortFeature(PORT_POWER) request for this
port. In this case, power is only removed from the port if it would not impact the low-speed,
full-speed, or high-speed operation on any of the downstream ports on the hub and would not
impact SS operation on any ports other than the target port.
• From any state when local power is lost to the port or an over-current condition exists.
• From any state when VBUS is removed from the hub upstream port.
• From any state if the hub’s upstream port link transitions to the SS.Disabled state.
• From any state if the hub’s upstream port link has attempted eight consecutive Rx.Detect events
without detecting far-end receiver terminations.
• From any state if the hub upstream port receives a SetConfiguration(0) request. In this case the
downstream port remains in the DSPORT.Powered-off state regardless of other conditions until
the hub is reset or the hub upstream port receives a non-zero SetConfiguration request. After a
non-zero SetConfiguration request is received, the normal state machine rules apply.
A port will enter the DSPORT.Powered-off state due to an over-current condition on another port if
that over-current condition may have caused the power supplied to this port to drop below specified
limits for port.
If a hub was configured while the local power supply was present and then if local power is lost, the
hub shall place all ports in the Powered-off state if power remains to run the hub controller.
In the DSPORT.Powered-off state, the port's link is in the SS.Disabled state.
Table 10-1 shows the allowed state of VBUS for hub downstream ports for possible states of the hub
upstream port and logical port power for a downstream port. The table covers the case where the
hub has adequate power to provide power for the downstream ports (local power source is present).
For a hub that does not implement per port power control, all downstream ports that will be affected
by removing VBUS shall be in a state where power may be off (refer to Table 10-1) before the hub
removes VBUS.
Note: a hub may provide power to all its downstream ports all of the time to support applications
such as battery charging from a USB port.
10-13
Universal Serial Bus 3.0 Specification, Revision 1.0
Table 10-1. Downstream Port VBUS Requirements
Hub Upstream Port
Connection Status
SuperSpeed
Downstream Port
SuperSpeed Port
Power Off
(PORT_POWER = 0)
USB 2.0 Port Power On
(PORT_POWER = 1)
Downstream Port
SuperSpeed Port
Power On
(PORT_POWER = 1)
On*
On
May be off
Downstream Port
USB 2.0 and
SuperSpeed Port Power
Off (PORT_POWER = 0)
Downstream Port
USB 2.0 Port Power Off
(PORT_POWER = 0)
USB 2.0
On
May be off
May be off
SuperSpeed and USB 2.0
On
On
May be off
No VBUS
May be off
May be off
May be off
* If the hub upstream port is unable to connect on the USB 2.0 bus, the downstream port VBUS may be off in this state.
10.3.1.2
DSPORT.Disconnected (Waiting for SS Connect)
This is the default state when local power is valid (self-powered) or VBUS becomes valid (buspowered. A port transitions to this state in any of the following situations:
• From the DSPORT.Powered-off state when the hub receives a SetPortFeature(PORT_POWER)
request.
• From any state except the DSPORT.Powered-off state when the port detects a disconnect.
• From the DSPORT.Powered-off state when the hub upstream port’s link transitions from
Rx.Detect to the polling state.
• From the DSPORT.Resetting state when a port’s link times out from Rx.Detect.Active during a
reset.
• From the DSPORT.Disabled state when a SetPortFeature(PORT_LINK_STATE) Rx.Detext
request is received for the port.
• From the DSPORT.Resetting state if the port’s link times out from any Polling substate during
a reset.
• From the DSPORT.Training state if the port’s link times out from any Polling substate.
• From the DSPORT.Loopback state if the port’s link performs a successful LFPS handshake in
Loopback.Exit.
In this state, the port’s link shall be in the Rx.Detect state.
Note: The port’s link shall still perform connection detection normally from the Rx.Detect if the
hub upstream port’s link is in U3.
10.3.1.3
DSPORT.Training
A port transitions to this state from the DSPORT.Disconnected state when SuperSpeed far-end
receiver terminations are detected.
In this state, the port’s link shall be in the Polling state.
10-14
Hub, Host Downstream Port, and Device Upstream Port Specification
10.3.1.4
DSPORT.ERROR
A port shall transition to this state only when a SuperSpeed capable device is present and a serious
error condition occurred while attempting to operate the link.
A port transitions to this state in any of the following situations:
• From the DSPORT.Enabled state if the link enters recovery and times out without recovering.
• From the DSPORT.Resetting state if U1 or U2 exit fails.
• From the DSPORT.Loopback state if the port is the loopback master and the LFPS handshake
in Loopback.Exit fails.
• From DSPORT.Enabled if Port Configuration fails as described in Section 8.4.5.
In this state, the port’s link shall be in the SS.Inactive state.
10.3.1.5
DSPORT.Enabled
A port transitions to this state in any of the following situations:
• From the Training state when the port’s link successfully enters U0.
• From the DSPORT.Resetting state when a reset completes successfully.
A port in the DSPORT.Enabled state will propagate packets in both the upstream and the
downstream direction. When the hub downstream port first transitions to the DSPORT.Enabled
state after a power on or warm reset, it shall transmit a port configuration LMP as defined in
Section 8.4.5.
When the hub downstream port first transitions to the DSPORT.Enabled state after a power on
reset, the value for the U1 and U2 inactivity timers shall be reset to zero.
The link shall be in U0 when the enabled state is entered.
If the hub upstream port’s link is in U3 when the downstream port enters DSPORT.Enabled and the
hub is not enabled for remote wakeup, the downstream port shall initiate a transition to U3 on its
link within tDSPortEnabledToU3.
Section 10.4 provides a state machine that shows a functionally correct implementation for a
downstream port managing different link states within the DSPORT.Enabled state.
10.3.1.6
DSPORT.Resetting
A downstream port shall transition to the DSPORT.Resetting state when it receives a
SetPortFeature(PORT_RESET) or SetPortFeature(BH_PORT_RESET) request unless the port is in
the DSPORT.Powered-off or DSPORT.Disconnected state. If the downstream port is in the
DSPORT.Powered-off or DSPORT.Disconnected state and receives a SetPortFeature reset request,
the request is ignored. If the port state is DSPORT.Error when the SetPortFeature(PORT_RESET)
request or SetPortFeature(BH_PORT_RESET) is received, the port shall send a warm reset on the
downstream port link within tDSPortResetToLFPS. If the port state is DSPORT.Enabled and the
port’s link is in any state other than U3 when a SetPortFeature(PORT_RESET) request is received,
the port shall initiate a hot reset on the link within tDSPortResetToHotReset. If the port receives a
SetPortFeature(BH_PORT_RESET) request, the port shall initiate a warm reset on the link within
tDSPortResetToHotReset.
10-15
Universal Serial Bus 3.0 Specification, Revision 1.0
Note: If the port initiates a hot reset on the link and the hot reset TS1/TS2 handshake fails, a warm
reset is automatically tried. Refer to the Link Chapter for details on this process. The port stays in
the DSPORT.Resetting state throughout this process until the warm reset completes.
When the downstream port link enters Rx.Detect.Active during a warm reset, the hub shall start a
timer to count the time it is in Rx.Detect.Active. If this timer exceeds tTimeForResetError while
the link remains in Rx.Detect.active, the port shall transition to the DSPORT.Disconnected state.
10.3.1.7
DSPORT.Compliance
A port transitions to this state in any of the following situations:
• When the link enters the Compliance Mode state.
10.3.1.8
DSPORT.Loopback
A port transitions to this state in any of the following situations:
• From the DSPORT.Training state if the loopback bit is set in the received TS2 ordered sets.
In this state, the port’s link shall be in the Loopback state.
10.3.1.9
DSPORT.Disabled
A port transitions to this state when the port receives a SetPortFeature(PORT_LINK_STATE)
SS.Disabled request.
In this state, the port’s link shall be in the SS.Disabled state.
10.3.2
Disconnect Detect Mechanism
Disconnect detection mechanisms are covered in Section 7.5.
10.3.3
Labeling
USB system software uses port numbers to reference an individual port with a ClearPortFeature or
SetPortFeature request. If a vendor provides a labeling to identify individual downstream facing
ports, then each port connector shall be labeled with its respective port number. The port numbers
assigned to a specific port by the hub shall be consistent between the USB 2.0 hub and SuperSpeed
hub controller.
10.4
Hub Downstream Facing Port Power Management
The following sections provide a functional description of a state machine that exhibits correct link
power management behavior for a downstream facing port.
Figure 10-10 is an illustration of the downstream facing port power management state machine.
Each of the states is described in Section 10.4.2. In Figure 10-10, some of the entry conditions into
states are shown without origin. These conditions have multiple origin states and the individual
transitions lines are not shown so that the diagram can be simplified. The description of the entered
state indicates from which states the transition is applicable.
10-16
Hub, Host Downstream Port, and Device Upstream Port Specification
10.4.1
Downstream Facing Port PM Timers
Each downstream port maintains logical inactivity timers for keeping track of when U1 and U2
timeouts are exceeded. The U1 or U2 timeout values may be set by software with a
SetPortFeature(PORT_U1_TIMEOUT) or SetPortFeature(PORT_U2_TIMEOUT) command at any
time. The PM timers are reset to 0 every time a SetPortFeature(PORT_U1_TIMEOUT) or
SetPortFeature(PORT_U2_TIMEOUT) request is received. The timers shall be reset every time a
packet of any type except an isochronous timestamp packet is sent or received by the port’s link.
The U1 timer shall be accurate to +1/- 0 μs. The U2 timer shall be accurate to +500/-0 μs. Other
requirements for the timer are defined in the downstream port PM state machine descriptions.
10-17
Universal Serial Bus 3.0 Specification, Revision 1.0
Link Partner Initiates Transition
and U1 Timeout is not 0
Set Port Feature
(PORT_LINK_STATE) U0
U0 - U1
Transition
Rejected
Enabled - U0 Only
PM Timer Disabled
U1 Timeout 0 (Disabled)
U2 Timeout 0 (Disabled)
Set Port Feature
(U1 Timeout X)
Set Port Feature
(U2 Timeout Y)
Enabled U0 States
Enabled - U0 or U1
PM Timer Resets
U1 Timeout X (Enabled)
U2 Timeout 0 (Disabled)
U1 Timer = X
and X < FF
Attempt U0 - U1
Transition
Set Port Feature
(U2 Timeout Y)
U1 Timer = X
and X < FF
Set Port Feature
(U1 Timeout X)
Enabled - U0 or U2
PM Timer Resets
U1 Timeout 0 (Disabled)
U2 Timeout Y (Enabled)
Enabled - U0, U1, or U2
PM Timer Resets
U1 Timeout X (Enabled)
U2 Timeout Y (Enabled)
U2 Timer = Y
and Y < FF
U0 - U2
Transition
Rejected
U0 - U1
Transition
Accepted
U1
Attempt U0 - U2
Transition
Set Port Feature
(PORT_LINK_STATE) U0
OR
Device Initiates U0
Transition
OR
Upstream Hub Port
Receives Packet Routed
to Port
Set Port Feature
(PORT_LINK_STATE) U2
U2 Timer = Y
and Y ! = 0
and Y < FF
Link Partner Initiates Transition
and U2 Timeout is not 0
U0 - U2
Transition
Accepted
Appropriate
Enabled U0
State
Set Port Feature
(PORT_LINK_STATE) U0
OR
Device Initiates U0
Transition
OR
Upstream Hub Port
Receives Packet
Routed to Port
Appropriate
Enabled U0
State
U2
Set Port Feature
(PORT_LINK_STATE) U1
Set Port Feature
(PORT_LINK_STATE) U0
OR
Downstream Port Completes Device
Initiated Remote Wakeup Signaling
as Described in Section 10.1.4
From Any State
Set Port Feature
(PORT_LINK_STATE) U3
U3
Hub Upstream Port in U3
AND
Conn_RWEnable = 0
(Remote Wake Not Enabled for Connect)
U-149
Figure 10-10. Downstream Facing Hub Port Power Management State Machine
10-18
Hub, Host Downstream Port, and Device Upstream Port Specification
10.4.2
Hub Downstream Facing Port State Descriptions
10.4.2.1
Enabled U0 States
There are four enabled U0 states that differ only in the values that are configured for the U1 and U2
timeouts. The port behaves as follows for the various combinations of U1 and U2 timeout values:
U1_TIMEOUT = 0, U2_TIMEOUT = 0
• This is the default state before the hub has received any
SetPortFeature(PORT_U1/U2_TIMEOUT) requests for the port.
• The port’s link shall reject all U1 or U2 transition requests by the link partner.
• The PM timers may be disabled and the PM timer values shall be ignored.
• The port’s link shall not attempt to initiate transitions to U1 or U2.
U1_TIMEOUT = X > 0, U2_TIMEOUT = 0
• The port’s link shall reject all U2 transition requests by the link partner.
• The PM timers shall be reset when this state is entered and is active.
• The port’s link shall accept U1 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port.
• If the U1 timeout is 0xFF, the port shall be disabled from initiating U1 entry but shall accept
U1 entry requests by the link partner unless the hub has one or more packets/link commands to
transmit on the port.
• If the U1 timeout is not 0xFF and the U1 timer reaches X, the port’s link shall initiate a
transition to U1.
U1_TIMEOUT = 0, U2_TIMEOUT = Y > 0
• The port’s link shall reject all U1 transition requests by the link partner.
• The PM timers shall be reset when this state is entered and is active.
• The port’s link shall accept U2 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port.
• If the U2 timeout is 0xFF, the port shall be disabled from initiating U2 entry but shall accept
U2 entry requests by the link partner unless the hub has one or more packets/link commands to
transmit on the port.
• If the U2 timeout is not 0xFF and the U2 timer reaches Y, the port’s link shall initiate a direct
transition from U0 to U2. In this case, PORT_U2_TIMEOUT represents an amount of inactive
time in U0.
U1_TIMEOUT =X > 0, U2_TIMEOUT = Y > 0
• The PM timers are reset when this state is entered and is active.
• The port’s link shall accept U1 or U2 entry requests by its link partner unless the hub has one
or more packets/link commands to transmit on the port.
• If the U1 timeout is 0xFF, the port shall be disabled from initiating U1 entry but shall accept
U1 entry requests by the link partner unless the hub has one or more packets/link commands to
transmit on the port.
• If the U1 timeout is not 0xFF and the U1 timer reaches X, the port’s link shall initiate a
transition to U1.
10-19
Universal Serial Bus 3.0 Specification, Revision 1.0
•
If the U2 timeout is 0xFF, the port shall be disabled from initiating U2 entry but shall accept
U2 entry requests by the link partner unless the hub has one or more packets/link commands to
transmit on the port.
A port transitions to one of the Enabled U0 states (depending on the U1 and U2 Timeout values) in
any of the following situations:
• From any state if the hub receives a SetPortFeature(PORT_LINK_STATE) U0 request.
• From U1 if the link partner successfully initiates a transition to U0.
• From U2 if the link partner successfully initiates a transition to U0.
• From U1 if the hub successfully initiates a transition to U0 after receiving a packet routed to the
port.
• From U2 if the hub successfully initiates a transition to U0 after receiving a packet routed to the
port
• From an attempt to transition from the U0 to the U1 state if the downstream port’s link partner
rejects the transition attempt
• From an attempt to transition from the U0 to the U2 state if the downstream port’s link partner
rejects the transition attempt
• From U3 if the upstream port of the hub receives wakeup signaling and the hub downstream
port being transitioned received wakeup signaling while it was in U3.
• From U3 if the downstream port’s link partner initiated wake signaling and the upstream hub
port’s link is not in U3.
Note: Refer to Section 10.1.4 for details on cases where a downstream port’s link partner initiates
remote wakeup signaling.
10.4.2.2
Attempt U0 – U1 Transition
In this state, the port attempts to transition its link from the U0 state to the U1 state.
A port shall attempt to transition to the U1 state in any of the following situations:
• The U1 timer reaches the U1 timeout value.
• The hub receives a SetPortFeature(PORT_LINK_STATE) U1 request.
• The downstream port’s link partner initiates a U0-U1 transition.
If the transition attempt fails, the port returns to the appropriate enabled U0 state. However, if this
state was entered due to a SetPortFeature request, the port continues to attempt the U0-U1 transition
on its link.
Note: that the SetPortFeature request is typically only used for U1 entry for test purposes.
10.4.2.3
Attempt U0 – U2 Transition
In this state, the port attempts to transition the link from the U0 state to the U2 state.
A port shall attempt to transition to the U2 state in any of the following situations:
• The U2 timer reaches the U2 timeout value.
• The hub receives a SetPortFeature(PORT_LINK_STATE) U2 request.
• The downstream port’s link partner initiates a U0-U2 transition.
10-20
Hub, Host Downstream Port, and Device Upstream Port Specification
If the transition attempt fails, the port returns to the appropriate enabled U0 state. However, if this
state was entered due to a SetPortFeature request, the port continues to attempt the U0-U2
transition.
Note: that the SetPortFeature request is typically only used for U2 entry for test purposes.
10.4.2.4
Link in U1
Whenever a downstream port enters U1 and all downstream ports are now in the U1 or a lower
power state, the hub shall initiate a transition to U1 on the upstream port within
tHubPort2PortExitLat if the upstream port is enabled for U1.
The U2 timer is reset to zero and started when the Link enters U1.
If the U2 timeout is not 0xFF and the U2 timer reaches Y, the port’s link shall initiate a direct
transition from U1 to U2. In this case, PORT_U2_TIMEOUT represents an amount of time in U1.
Whenever a downstream port or its link partner initiates a transition from U1 to one of the Enabled
U0 states and the upstream port is not in U0, the hub shall initiate a transition to U0 on the
upstream port within tHubPort2PortExitLat of when the transition was initiated on the downstream
port. If the upstream port is in U0, it shall remain in U0 while the downstream port transitions to
U0.
10.4.2.5
Link in U2
The following rules apply when a downstream port enters U2:
• If all downstream ports are now in the U2 or a lower power state, the hub shall initiate a
transition to U2 on the upstream port within tHubPort2PortExitLat, if the upstream port is
enabled for U2. If U2 is not enabled on the upstream port, but U1 is enabled, the hub shall
initiate a transition to U1 with the same timing requirements.
• If all downstream ports are now in the U1 or lower power state, the hub shall initiate a
transition to U1 on the upstream port within tHubPort2PortExitLat, if the upstream port is
enabled for U1.
Whenever a downstream port or its link partner initiates a transition from U2 to one of the Enabled
U0 states and the hub upstream port is not in U0:
• If the hub upstream port’s link is in U2, the hub shall initiate a transition to U0 on the upstream
port’s link within tHubPort2PortExitLat of when the transition was initiated on the downstream
port.
• If the hub upstream port’s link is in U1, the hub upstream port shall initiate a transition to U0
within tHubPort2PortExitLat + U2DevExitLat-U1DevExitLat of when the transition was
initiated on the downstream port.
10.4.2.6
Link in U3
The following rules apply when a downstream port enters U3:
• If all downstream ports are now in the U2 or U3, the hub shall initiate a transition to the lowest
enabled power state above U3 on the upstream port within tHubPort2PortExitLat.
• If all downstream ports are now in the U1 or lower power state, the hub shall initiate a
transition to U1 on the upstream port within tHubPort2PortExitLat, if the upstream port is
enabled for U1.
10-21
Universal Serial Bus 3.0 Specification, Revision 1.0
Refer to Section 10.3.1.5 for a detailed description of the transition from Enabled – U0 Only to the
U3 state.
Note: If the upstream port of the hub receives a packet that is routed to a downstream port that is in
U3, the packet is silently dropped. The hub shall perform normal link level acknowledgement of
the header packet in this case.
10.5
Hub Upstream Facing Port
The following sections provide a functional description of a state machine that exhibits correct
behavior for a hub upstream facing port. These sections also apply to the upstream facing port on a
device unless exceptions are specifically noted. An upstream port shall only attempt to connect to
the SuperSpeed and USB 2.0 interfaces as described by the upstream port state machine in the
following sections.
Figure 10-11 is an illustration of the upstream facing port state machine. Each of the states is
described in Section 10.5.1. In Figure 10-11, some of the entry conditions into states are shown
without origin. These conditions have multiple origin states and the individual transitions lines are
not shown so that the diagram can be simplified. The description of the entered state indicates from
which states the transition is applicable.
10-22
Hub, Host Downstream Port, and Device Upstream Port Specification
VBUS Off
USPORT.Powered-off
Far End Receiver
Terminations Not Present
Link in SS.disabled
VBUS is Valid
USPORT.Powered On
Link in Rx.Detect
Far End Receiver
Terminations Present
Any Polling
substate
times out
LFPS Reset
Received
Training Initiated
Port Configuration Fails
(refer to Section 8.4.5)
USPORT.Training
Link in Polling
USPORT.ERROR
Link in SS.Inactive
Link Transitions from
Polling.Idle to U0
Training Successful
Link Exits Recovery
After Timeout
USPORT.Connected
Link in U0 or Recovery
Set Address
request received
Link Exits Recovery After Timeout
Reset Received
USPORT.Enabled
Link in U0, U1, U2, U3, or Recovery
Reset Received
U-150
Figure 10-11. Upstream Facing Hub Port State Machine
10.5.1
Upstream Facing Port State Descriptions
10.5.1.1
USPORT.Powered-off
The USPORT.Powered-off state is the default state for an upstream facing port.
A port shall transition into this state if any of the following situations occur:
• From any state when VBUS is removed.
• From any state if far-end receiver terminations are not detected.
• From the USPORT.Connected state if the Port Configuration process fails.
In this state, the port's link shall be in the SS.Disabled state.
10-23
Universal Serial Bus 3.0 Specification, Revision 1.0
10.5.1.2
USPORT.Powered-on
A port shall transition into this state in any of the following situations:
• From the USPORT.Powered-off state when VBUS becomes valid.
• From the USPORT.Error state when the link receives a warm reset.
• Form the USPORT.Connected state when the link receives any reset.
• From the USPORT.Enabled state when the link receives any reset.
• From the USPORT.Training state if the port’s link times out from any Polling substate.
In this state, the port’s link shall be in the Rx.Detect state. While in this state, if the USB 2.0
portion of the hub enters the suspended state, the total hub current draw from VBUS shall meet the
suspend current limit.
10.5.1.3
USPORT.Training
A port transitions to this state from the USPORT.Powered-on state when SuperSpeed far-end
receiver terminations are detected.
In this state, the port’s link shall be in the Polling state.
10.5.1.4
USPORT.Connected
A port transitions to this state from the USPORT.Training state when its link enters U0 from
Polling.Idle. In this state, the port’s link shall be in the U0 or Recovery states.
When the link enters U0 the port start the port configuration process as defined in 8.4.5.
The port may send link management packets or link commands but shall not transmit any other
packets except to respond to default control endpoint requests while in the USPORT.Connected
state.
10.5.1.5
USPORT.Error
A port transitions to this state when a serious error condition occurred while attempting to operate
the link. A port transitions to this state in any of the following situations:
• From the USPORT.Connected state if the link enters Recovery and times out without
recovering.
• From the USPORT.Enabled state if the link enters Recovery and times out without recovering.
In this state, the port’s link shall be in the SS.Inactive state.
A port exits the Error state only if a Warm Reset is received on the link.
10.5.1.6
USPORT.Enabled
A port transitions to this state from the USPORT.Connected state when a Set Address request is
received and the ACK TP response to the status stage of the Set Address has been sent and
successfully acknowledged at the link level.
In this state, the port’s link shall be in the U0, U1, U2, U3, or Recovery states.
The port may send any type of packet while in the USPORT.Enabled state.
The link shall be in U0 when the USPORT.Enabled state is entered.
10-24
Hub, Host Downstream Port, and Device Upstream Port Specification
10.5.2
Hub Connect State Machine
The following sections provide a functional description of a state machine that exhibits correct hub
behavior for when to connect on SuperSpeed or USB 2.0. For a hub the connection logic for
SuperSpeed and USB 2.0 are completely independent. The hub shall follow the USB 2.0
specification for connecting on USB 2.0. Figure 10-12 is an illustration of the hub connect state
machine for SuperSpeed. Each of the states is described in Section 10.5.2.1.
Link Training Timed Out
Powered-Off
VBUS Not Present
VBUS Valid
(and device local power
is valid if required)
Attempt SS Connect
Link in Rx.Detect
and/or Polling
SuperSpeed Link
transitions from
Polling.Configuration
to U0
Connected on SS
Link initially U0
Rx.Detect or Link
Training Timed Out
U-151
Figure 10-12. Hub Connect State Machine
10.5.2.1
Hub Connect State Descriptions
10.5.2.2
HCONNECT.Powered-off
The HCONNECT.Powered-off state is the default state for a hub device. A hub device shall
transition into this state if the following situation occurs:
• From any state when VBUS is removed.
In this state, the hub upstream port's link shall be in the SS.Disabled state.
10.5.2.3
HCONNECT.Attempt SS Connect
A hub shall transition into this state if any of the following situations occur:
• From the HCONNECT.Powered-off state when VBUS becomes valid (and local power is valid
if required).
• From the HCONNECT.Connected on SS state if Rx.Detect or Link Training time out.
In this state, the hub’s upstream port SuperSpeed link is in Rx.Detect or Polling.
10.5.2.4
HCONNECT.Connected on SS
A port shall transition into this state if the following situation occurs:
• From the PCONNECT.Attempt SS Connect when the link transitions from polling to U0.
In this state the hub’s upstream port SuperSpeed link is in U0, U1, U2, U3, Inactive, Rx.Detect,
Recovery, or Polling.
10-25
Universal Serial Bus 3.0 Specification, Revision 1.0
10.6
Upstream Facing Port Power Management
The following sections provide a functional description of a state machine that exhibits correct link
power management behavior for a hub upstream facing port.
Figure 10-13 is an illustration of the upstream facing port power management state machine. Each
of the states is described in Section 10.4.2. In Figure 10-13, some of the entry conditions into states
are shown without origin. These conditions have multiple origin states and the individual
transitions lines are not shown so that the diagram can be simplified. The description of the entered
state indicates from which states the transition is applicable.
If there is a status change on any downstream port, the hub shall initiate a transition on the
upstream port’s link to U0 if the upstream port is in U1 or U2.
If there is a status change on any downstream port and the hub upstream port’s link is in U3, the
hub behavior is specified by the current remote wakeup mask settings. Refer to Section 10.14.2.10
for more details.
10-26
Hub, Host Downstream Port, and Device Upstream Port Specification
Link Partner Initiates Transition
And No Pending Upstream
Traffic AND All Downstream
Ports Link States U1 or Lower
Force_Link_Pm_Accept is set
and the Link Partner Initiates a
Transition to U1
U0 - U1
Transition
Rejected
Enabled - U0 Only
PM Timer Disabled
U1 Enable 0 (Disabled)
U2 Enable 0 (Disabled)
ClearFeature(U1_Enable)
SetFeature(U1_Enable)
SetFeature
(U2_Enable)
Enabled - U0 or U1
PM Timer Disabled
U1 Enable 1 (Enabled)
U2 Enable 0 (Disabled)
ClearFeature
(U2_Enable)
Enabled U0 States
ClearFeature
(U2_Enable)
ClearFeature(U1_Enable)
SetFeature(U1_Enable)
Attempt U0 - U1
Transition
SetFeature
(U2_Enable)
Note: If the Link Partner initiates a
U1 or U2 transition and the
conditions to attempt the transition
are not met, the upstream port
rejects the request and stays in the
Enabled U0 state.
Enabled - U0 or U2
PM Timer Disabled
U1 Enable 0 (Disabled)
U2 Enable 1 (Enabled)
All Hub Downstream
Ports Link States
U1 or Lower
Enabled - U0, U1, or U2
PM Timer Disabled
U1 Enable 1 (Enabled)
U2 Enable 1 (Enabled)
All Hub
Downstream
Ports Link
States U1 or
Lower
All Hub Downstream Ports
Link States U2 or Lower
U1
PM Timer Resets
All Hub Downstream
Ports Link States
U2 or Lower
U0 - U2
Transition
Rejected
Attempt U0 - U2
Transition
Link Partner Initiates Transition
AND No Pending Upstream
Traffic AND All Downstream Port
Link States U2 or Lower
Appropriate
Enabled U0
State
Link Partner
Initiates
U0 Transition
OR
Hub Downstream
Port Link Initiates
U0 Transition
OR Status Change
on Downstream Port
U0 - U1
Transition
Accepted
Link Partner Initiates
U0 Transition
OR
Hub Downstream
Port Link Initiates
U0 Transition
OR
Status Change
on Downstream Port
OR
All Hub Downstream
Ports Link States U2 or
Lower and U2 is Enabled
U0 - U2
Transition
Accepted
PM Timer = U2
Inactivity Timeout
AND U2 Inactivity
Timeout NOT
(0 or FF) And All
Hub Downstream
Port Link States
U2 or Lower
Appropriate
Enabled U0
State
U2
Force_Link_Pm_Accept is set
and the Link Partner Initiates a
Transition to U2
Successful U3 Wakeup LFPS Handshake Initiated by Link Partner
OR
Status Change on Downstream Port or Local
Power Status Change and Wakeup Enabled
For Corresponding Status Change Type
Link Partner Initiates
Transition
U3
U-166
Figure 10-13. Upstream Facing Hub Port Power Management State Machine
10-27
Universal Serial Bus 3.0 Specification, Revision 1.0
10.6.1
Upstream Facing Port PM Timer
The hub upstream port maintains a logical PM timer for keeping track of when the U2 inactivity
timeout is exceeded. No standard U1 inactivity timeout is defined. The U2 inactivity timeout is set
when a U2 Inactivity Timeout LMP is received. The PM timer is reset when the hub upstream port
link enters U1. The PM timer shall be accurate to +500/-0 μs. Other requirements for the timer are
defined in the upstream port PM state machine descriptions.
10.6.2
Hub Upstream Facing Port State Descriptions
10.6.2.1
Enabled U0 States
There are four enabled U0 states that differ only in the U1 and U2 Enable settings. The following
rules apply globally to all Enabled U0 states:
• The upstream port shall not initiate a transition to U1 or U2 if there are pending packets to
transmit on the upstream port.
• The upstream port shall accept U1 or U2 transitions from the link partner if the
Force_LinkPM_Accept bit is set to one (refer to Section 8.4.2).
The port behaves as follows for the various combinations of U1 and U2 Enable values:
U1_ENABLE = 0, U2_ENABLE = 0
• This is the default state before the hub has received any SetFeature(U1/U2_ENABLE) requests.
• The PM timer may be disabled and the PM timer values shall be ignored.
• The port’s link shall accept U1 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port or one or more of the hub downstream ports has
a link in U0 or recovery.
• The port’s link shall accept U2 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port or one ore more of the hub downstream ports
has a link in U0, U1, or recovery.
• The port’s link shall not attempt to initiate transitions to U1 or U2.
U1_ENABLE = 1, U2_ENABLE = 0
• The port’s link shall not initiate a U2 transition.
• The port’s link shall accept all U2 entry requests by the link partner unless the hub has one or
more packets/link commands to transmit on the port or one or more of the hub downstream
ports has a link in U0, U1 or recovery.
• The port’s link shall accept U1 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port or one or more of the hub downstream ports has
a link in U0 or recovery.
• The PM timer may be disabled and the PM timer values shall be ignored.
• The port’s link shall initiate a transition to U1 if all the hub downstream ports are in U1 or a
lower link state.
U1_ENABLE = 0, U2_ENABLE = 1
• The port’s link shall not initiate a U1 transition.
10-28
Hub, Host Downstream Port, and Device Upstream Port Specification
•
•
•
•
The port’s link shall accept all U1 entry requests by the link partner unless the hub has one or
more packets/link commands to transmit on the port or one or more of the hub downstream
ports has a link in U0 or recovery.
The port’s link shall accept U2 entry requests by its link partner unless the hub has one or more
packets/link commands to transmit on the port or one ore more of the hub downstream ports
has a link in U0, U1, or recovery.
The PM timer may be disabled and the PM timer values shall be ignored.
The port’s link shall initiate a transition to U2 if all the hub downstream ports are in U2 or a
lower link state.
U1_ENABLE = 1, U2_ENABLE = 1
• The port’s link shall accept U1 or U2 entry requests by its link partner unless the hub has one or
more packets/link commands to transmit on the port.
•
•
⎯ A U1 entry request shall not be accepted if one or more of the hub downstream ports has a
link in U0 or recovery.
⎯ A U2 entry request shall not be accepted if one or more of the hub downstream ports has a
link in U1 or recovery.
The port’s link shall initiate a transition to U1 if all the hub downstream ports are in U1 or a
lower link state.
The PM timer may be disabled and the PM timer values shall be ignored.
A port transitions to one of the Enabled U0 states (depending on the U1 and U2 Enable values) in
any of the following situations:
• From U1 if the link partner successfully initiates a transition to U0.
• From U2 if the link partner successfully initiates a transition to U0.
• From U1 if there is a status change on a downstream port.
• From U2 if there is a status change on a downstream port.
• From U1 if a hub downstream port’s link initiates a transition to U0.
• From U2 if a hub downstream port’s link initiates a transition to U0.
• From an attempt to transition from the U0 to the U1 state if the upstream port’s link partner
rejects the transition attempt
• From an attempt to transition from the U0 to the U2 state if the upstream port’s link partner
rejects the transition attempt
• From U3 if the upstream port of the hub receives wakeup signaling.
• From U3 if there is a status change on a downstream port or a local power status change and
remote wakeup is enabled for the corresponding event type.
10.6.2.2
Attempt U0 – U1 Transition
In this state the port attempts to transition its link from the U0 state to the U1 state.
A port shall attempt to transition to the U1 state in any of the following situations:
• U1 entry is requested by the link partner and there is no pending traffic on the port and all the
hub downstream port’s links are in U1 or a lower state.
• All the hub downstream ports are in U1 or a lower link state and there is no pending traffic to
transmit on the upstream port and U1_ENABLE is set to one.
• U1 entry is requested by the link partner and Force_LinkPM_Accept bit is set.
10-29
Universal Serial Bus 3.0 Specification, Revision 1.0
If the transition attempt fails (an LXU is received or the link goes to recovery), the port returns to
the appropriate enabled U0 state.
10.6.2.3
Attempt U0 – U2 Transition
In this state, the port attempts to transition the link from the U0 state to the U2 state.
A port shall attempt to transition to the U2 state in any of the following situations:
• U2 entry is requested by the link partner and there is no pending traffic on the port and all the
hub downstream port’s links are in U2 or a lower state.
• All the hub downstream ports are in U2 or a lower link state and there is no pending traffic to
transmit on the upstream port and U2_ENABLE is set to one.
• U2 entry is requested by the link partner and Force_LinkPM_Accept bit is set.
If the transition attempt fails (an LXU is received or the link goes to recovery), the port returns to
the appropriate enabled U0 state.
10.6.2.4
Link in U1
The PM timer is reset when this state is entered and is active.
A port transitions to U1:
• After sending an LAU to accept a transition initiated by the link partner.
• After receiving an LAU from the link partner after initiating an attempt to transition the link
to U1
If the U2 inactivity timeout is not 0xFF or 0x00, and the PM timer reaches the U2 inactivity
timeout, the port’s link shall initiate a transition from U1 to U2.
10.6.2.5
Link in U2
The link is in U2.
A port transitions to U2:
• After sending an LAU to accept a transition initiated by the link partner.
• After receiving an LAU from the link partner after initiating an attempt to transition the link
to U2
10.6.2.6
Link in U3
The link is in U3.
A port transitions to U3:
• After sending an LAU to accept a transition initiated by the link partner.
10-30
Hub, Host Downstream Port, and Device Upstream Port Specification
10.7
Hub Header Packet Forwarding and Data Repeater
The Hub uses a store and forward model for header packets and a repeater model for data that
combined provide the following general functionality.
In the downstream direction:
• Validates header packets
• Sets up connection to selected downstream port
• Forwards header packets to downstream ports
• Forwards data payload to downstream port if present
• Sets up and tears down connectivity on packet boundaries
In the upstream direction:
• Validates header packets
• Sets up connection to upstream port
• Forwards header packets to the upstream port
• Forwards data packet payload to upstream port if present
• Sets up and tears down connectivity on packet boundaries
10.7.1
Hub Elasticity Buffer
There are no direct specifications for elasticity buffer behavior in a hub. However, note that a hub
must meet the requirements in Section 10.7.3 for the maximum variation in propagation delay for
header packets that are forwarded from the hub upstream port to a downstream port.
10.7.2
SKP Ordered Sets
A hub transmits SKP ordered sets, following the rules for all transmitters in Chapter 7, for all
transmissions.
10.7.3
Interpacket Spacing
When a hub originates or forwards packets, Data packet headers and data packet payloads shall be
sent contiguously at all times as required in Section 7.1.1.2.3.
When a hub forwards a header packet downstream and the downstream port link is in U0 when the
header packet is received on the hub upstream port the propagation delay variation shall not be
more than tPropagationDelayJitterLimit.
10.7.4
Header Packet Buffer Architecture
The specification does not require a specific architecture for the header packet buffers in a hub. An
example architecture that meets the functional requirements of this specification is shown in
Figure 10-14 and Figure 10-15 to illustrate the functional behavior of a hub. Figure 10-14 shows a
hub with a four header packet Rx buffer for the upstream port and a four header packet Tx buffer
for each of the downstream ports. Figure 10-15 shows a four header packet Rx buffer for each of
the downstream ports and a four header packet Tx buffer for the upstream port. The buffers shown
in Figure 10-14 and Figure 10-15 are independent physical buffers.
10-31
Universal Serial Bus 3.0 Specification, Revision 1.0
US Port
Rx Header
Buffer
Traffic
Flow
Header Router
Tx Header
Buffer
Tx Header
Buffer
Tx Header
Buffer
Tx Header
Buffer
DS Port 1
DS Port 2
DS Port 3
DS Port 4
U-152
Figure 10-14. Example Hub Header Packet Buffer Architecture - Downstream Traffic
US Port
Tx Header
Buffer
Traffic
Flow
Header Aggregater
Rx Header
Buffer
Rx Header
Buffer
Rx Header
Buffer
Rx Header
Buffer
DS Port 1
DS Port 2
DS Port 3
DS Port 4
U-153
Figure 10-15. Example Hub Header Packet Buffer Architecture - Upstream Traffic
The following lists functional requirements for a hub buffer architecture with the assumption in
each case that only the indicated port on the hub is receiving or transmitting header packets:
• A hub starting with all header packet buffers empty shall be able to receive at least eight header
packets directed to the same downstream port that is not in U0 before its upstream port runs out
of header packet flow control credits.
10-32
Hub, Host Downstream Port, and Device Upstream Port Specification
•
•
•
•
A hub that receives a header packet on its upstream port that is routed to a downstream port
shall immediately route the header packet to the appropriate downstream port header packet
buffer (if space in that buffer is available) regardless of the state of any other downstream port
header packet buffers or the state of the upstream port Rx header packet buffer. For example, a
hub Tx header packet buffer for downstream port 1 is full and the hub has three more header
packets routed to downstream port 1 in the hub upstream port Rx header packet buffer. If the
hub now receives a header packet routed to downstream port 2, it must immediately route the
header packet to the downstream port 2 Tx header packet buffer.
A hub starting with all header packet buffers empty shall be able to receive at least eight header
packets on the same downstream port directed for upstream transmission when the upstream
port is not in U0.
Header packets transmitted by a downstream port shall be transmitted in the order they were
received on the upstream port.
Header packets transmitted by an upstream port from the same downstream port shall be
transmitted in the order they were received on that downstream port.
Sections 10.7.6, 10.7.8, 10.7.10, and 10.7.12 provide detailed functional state machines for the
upstream and downstream port Tx and Rx header packet buffers in a hub implementation.
10-33
Universal Serial Bus 3.0 Specification, Revision 1.0
10.7.5
Upstream Facing Port Tx
This section describes the functional requirements of the upstream facing port Tx state machine.
No Link Commands in TX Queue
Link Command(s)
in TX Queue
TX IDLE
Entering U0
No Associated
Data Packet
TX Link Command
Link Command and a
SKP Ordered Set
(if required)
Transmitted
Header(s) and
No Link Commands
in TX Queue
Additional Link Commands
in TX Queue
TX Header
Header and a
SKP Ordered Set
(if required)
Transmitted
Associated Data Packet
TX Data
Data and required
SKP Ordered Set(s)
Transmitted
Downstream Port RX received DPPABORT
Ordered Set for data packet or exceeded
sDataSymbolsBabble without receiving a
DPPEND or DPPABORT Ordered Set
TX Data Abort
Data and required
SKP Ordered Set(s)
Transmitted
U-154
Figure 10-16. Upstream Facing Port Tx State Machine
10-34
Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.6
Upstream Facing Port Tx State Descriptions
An upstream port shall maintain a count of transmitted symbols.
10.7.6.1
Tx IDLE
In the Tx IDLE state, the upstream port transmitter is actively transmitting idle symbols. A port
shall transition to the Tx IDLE state in any of the following situations:
• From the Tx Data, Tx Data Abort, or Tx Header state after any required SKP ordered sets are
transmitted.
• From the Tx Link Command state after a link command is transmitted and there are no other
link commands awaiting transmission.
• As the default state when the link enters U0.
The transmitter shall transmit a LUP when required as described in Chapter 7.
When the transmitted symbol count reaches nSkipSymbolLimit, a SKP ordered set shall be
transmitted and the transmitted symbol count shall be reset to zero.
10.7.6.2
Tx Header
In the Tx Header state, the upstream port transmitter is actively transmitting a header packet.
Note: A hub shall not abort the transmission of a header packet with a DPPABORT ordered set.
A port shall transition to the Tx Header state in any of the following situations:
• From the Tx IDLE state when there are one or more header packets queued for transmission
and there are no link commands queued for transmission.
When the transmitted symbol count is greater than or equal to nSkipSymbolLimit at the end of
transmitting any header packet except a data packet header packet with a data packet payload, a
SKP ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
10.7.6.3
Tx Data
In the Tx Data state, the upstream port transmitter is actively transmitting a data packet payload.
After transmitting the end framing symbols for the data packet payload and required SKP ordered
sets, the port may remove the data packet payload from hub storage. A hub shall not retransmit a
DPP packet under any circumstances.
A port shall transition to the Tx Data state from the Tx Header state when there is a data packet
payload associated with the data packet header that was transmitted. The data packet payload
transmission shall begin immediately after transmission of the last symbol of the data packet
header.
At the end of transmitting a data packet payload that is not aborted:
• While the transmitted symbol count is greater than or equal to nSkipSymbolLimit ,a SKP
ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
• The sequence is repeated until the symbol count is less than nSkipSymbolLimit.
10-35
Universal Serial Bus 3.0 Specification, Revision 1.0
10.7.6.4
Tx Data Abort
In the Tx Data abort state, the upstream port transmitter aborts the normal transmission of a data
packet payload by transmitting DPPABORT ordered set and required SKP ordered sets. The port
then removes the data packet payload from hub storage.
A port shall transition to the Tx Data Abort state from the Tx Data state when the downstream port
receiving the data packet payload receives a DPPABORT ordered set or has received
sDataSymbolsBabble symbols without receiving a valid DPPEND ordered set or DPPABORT
ordered set.
At the end of transmitting a DPPABORT ordered set:
• While the transmitted symbol count is greater than or equal to nSkipSymbolLimit, a SKP
ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
• The sequence is repeated until the symbol count is less than nSkipSymbolLimit.
10.7.6.5
Tx Link Command
In the Tx Link Command state, the upstream port transmitter is actively transmitting a link
command. If multiple link commands are queued to be transmitted in the Tx Link Command state,
they shall be transmitted without a gap unless SKP ordered sets are transmitted.
A port shall transition to the Tx Link Command state in any of the following situations:
• From the Tx IDLE state when there are one or more link commands queued for transmission.
• From the Tx Link Command state when there are additional link commands queued for
transmission.
When the transmitted symbol count is greater than or equal to nSkipSymbolLimit at the end of
transmitting any link command, a SKP ordered set shall be transmitted and the transmitted symbol
count shall be reduced by nSkipSymbolLimit.
10-36
Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.7
Upstream Facing Port Rx
This section describes the functional requirements of the upstream facing port Rx state machine.
End Link
Command
RX Link Command
Process Link
Command
DPPEND or DPPABORT
Ordered Set Received or
sDataSymbolsBabble
exceeded without a DPPEND
or DPPABORT Ordered Set
Valid Start Link
Command Ordered
Set Received
RX Default
Entering U0
Valid
DPPSTART
Ordered Set
Received
RX Data
SKP Ordered Set
Received
Process
Header
Last Header
Symbol Received
Valid HPSTART
Ordered Set Received
RX Header
Compute CRC and
Check Route String
U-155
Figure 10-17. Upstream Facing Port Rx State Machine
10.7.8
Upstream Facing Port Rx State Descriptions
10.7.8.1
Rx Default
In the Rx Default state, the upstream port receiver is actively processing received symbols and
looking for DPPSTART ordered set, HPSTART ordered set, or LCSTART ordered set framing
symbols to begin receiving a packet or link command.
If a DPPStart ordered set is received that did not immediately follow a DPH, it is ignored and the
port receiver stays in the RX.Default state.
A port shall transition to the Rx Default state in any of the following situations:
• From the Rx Data state when a DPPEND ordered set or DPPABORT ordered set is received.
• From the Rx Header state when the last symbol in a header packet is received.
• From the Rx Data state when sDataSymbolsBabble is reached without receiving a DPPEND
ordered set or DPPABORT ordered set.
• After receiving a link command.
• As the default state when the link enters U0.
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10.7.8.2
Rx Data
In the Rx Data state, the upstream port receiver is actively processing received symbols and looking
for a DPPEND ordered set or DPPABORT ordered set. The receiver shall start a count of received
symbols from zero when entering this state. The first symbol counted is the first symbol after the
DPPSTART ordered set.
A port shall transition to the Rx Data state when it receives a valid DPPSTART ordered set.
When the port detects an error before the end of the DPP as defined in Section 7.2.4.1.6, it may
clear the data from its buffers only after it has transmitted the received DPP including the
DPPABORT ordered set on the appropriate downstream port. The hub shall transmit the valid
received symbols before the error for a data packet payload followed by a DPPABORT ordered set
on the appropriate downstream port when an error is detected. Note that this requirement applies
even when the hub detects an error before beginning to transmit the DPP on the hub downstream
port.
The hub shall have at least 1080 bytes of buffering for data packets received on the upstream port.
10.7.8.3
Rx Header
In the Rx header state, the upstream port receiver is actively processing received symbols until the
last header packet symbol is received. The receiver shall start a count of received symbols at zero
when entering this state. The first symbol counted is the first symbol after the HPSTART ordered
set.
A port shall transition to the Rx Header state when it receives a valid HPSTART ordered set.
The port shall finish validating CRC-16, the Link Control Word CRC-5, and check the route string
and header packet type within four symbol times after the last symbol of the header packet is
received.
Implementations may have to begin the CRC calculation as symbols are received and check the
route string before the header packet is verified to meet this requirement.
10.7.8.4
Process Header Packet
When the final symbol for a header packet is received the port shall perform all additional
processing necessary for the header packet. Any such processing shall not block the port from
immediately returning to the Rx Default state and continuing to process received symbols.
A port performs additional header packet processing in any of the following situations. The
additional processing steps in each situation are described.
• When the final header packet symbol is received in the Rx Header state and the header packet
CRC-16 and Link Control Word CRC-5 are determined to be valid, the appropriate LGOOD_n
link command is queued for transmission by the receiving port. Then if the upstream port Rx
header packet buffer has at least four free slots, the appropriate LCRD_x link command shall
be queued for transmission by the upstream port. Otherwise, the appropriate LCRD_x link
command shall be queued for transmission once the Rx header packet buffer slot used for the
header packet is available.
Note: A hub implementation could choose to provide more than four storage slots in an Rx
header packet buffer.
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Hub, Host Downstream Port, and Device Upstream Port Specification
⎯ If the header packet is routed to a downstream port that is not in U0 (and the header packet
is not an ITP):
1. The hub initiates U0 entry on the appropriate downstream port link. U0 entry shall be
initiated tDownLinkStateChange from when the hub received the route string of the
header packet.
2. The header packet is marked deferred (if it is not already marked deferred) and the
correct Link Control Word CRC-5 is re-calculated for modified header packet.
3. If the header packet was marked deferred in step 2, a deferred header packet including
the hub depth and correct CRC-5 is queued into the upstream port Tx header packet
buffer.
4. The header packet is queued for transmission on the appropriate downstream port.
5. If the header packet is a data packet header the corresponding data packet payload is
discarded.
⎯ If the header packet is routed to a downstream port that is in U0 or the header packet is an
ITP (in which case the processing below is done independently for each downstream port
with a link in U0):
1. If the downstream port Tx header packet buffer queue is not empty (there is at least one
header packet in the queue that has not been completely transmitted) or no link credit is
available for transmission on the downstream port, the header packet is marked delayed
and the correct Link Control Word CRC-5 is re-calculated for modified header packet.
2. The header packet is queued for transmission on the appropriate downstream port.
Note: If the queue for the appropriate downstream port is full, the header packet is queued
as soon as a space is available in the appropriate downstream port queue. The hub shall
still process subsequent header packets normally while a downstream port queue is full if
they are directed to a different downstream port.
⎯ If the header packet is an ITP:
1. The header packet is queued for transmission on each downstream port with a link in
U0
2. If the downstream port Tx header packet buffer queue is not empty (there is at least one
header packet in the queue that has not been completely transmitted) or no link credit is
available for transmission on the downstream port, the header packet is marked delayed
and the correct Link Control Word CRC-5 is re-calculated for modified header packet.
Note: If the queue for the appropriate downstream port is full, the header packet is queued
as soon as a space is available in the appropriate downstream port queue. The hub shall
still process subsequent header packets normally while a downstream port queue is full if
they are directed to a different downstream port.
⎯ If the header packet is not routed to a downstream port:
1. The header packet is processed.
2. The header packet is removed from the RX header packet buffer.
3. A response to the header packet is queued for transmission if required.
⎯ If the header packet is routed to a disabled or nonexistent downstream port:
1. The header packet is removed from the RX header packet buffer.
2. The header packet is silently discarded.
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
When the final header packet symbol is received in the Rx header packet state and either the
header packet CRC-16 or Link Control Word CRC-5 is determined to be invalid.
⎯ The header packet is removed from the Rx header packet buffer.
⎯ An LBAD link command is queued for transmission by the upstream port.
Note: All subsequent header packets are silently discarded until a retry of the invalid header
packet is received.
10.7.8.5
Rx Link Command
In the Rx Link Command state, the upstream port receiver is actively processing received symbols
and looking for the end of a link command (second instance of link command word).
A port transitions to the Rx Link Command state when it receives a valid LCSTART ordered set.
10.7.8.6
Process Link Command
Once the final symbol for a link command is received, the port shall perform all additional
processing necessary for the link command. Any such processing shall not block the port from
immediately returning to the Rx Default state and continuing to process received symbols.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.9
Downstream Facing Port Tx
This section describes the functional requirements of the downstream facing port Tx state machine.
No Link Commands in TX Queue
Link Command(s)
in TX Queue
TX IDLE
Entering U0
No Associated
Data Packet
TX Link Command
Link Command and a
SKP Ordered Set
(if required)
Transmitted
Header(s) and
No Link Commands
in TX Queue
Additional Link Commands
in TX Queue
TX Header
Header and a
SKP Ordered Set
(if required)
Transmitted
Associated Data Packet
TX Data
Data and required
SKP Ordered Set(s)
Transmitted
Upstream Port RX received a DPPABORT
Ordered Set for data packet or exceeded
sDataSymbolsBabble without receiving a
DPPEND or DPPABORT Ordered Set
TX Data Abort
Data and required
SKP Ordered Set(s)
Transmitted
U-156
Figure 10-18. Downstream Facing Port Tx State Machine
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.7.10
Downstream Facing Port Tx State Descriptions
A downstream port shall maintain a count of transmitted symbols.
10.7.10.1
Tx IDLE
In the Tx IDLE state, the downstream port transmitter is actively transmitting idle symbols. A port
shall transition to the TX IDLE state in any of the following situations:
• From the Tx Data, Tx Data Abort, or Tx Header state after the last required SKP ordered set is
transmitted.
• From the Tx Link Command state after a link command is transmitted and there are no other
link commands awaiting transmission.
• As the default state when the link enters U0.
When the transmitted symbol count reaches nSkipSymbolLimit a SKP ordered set shall be
transmitted and the transmitted symbol count shall be reset to zero.
10.7.10.2
Tx Header
In the Tx Header state, the downstream port transmitter is actively transmitting a header packet.
Note: A hub shall not abort the transmission of a header packet with a DPPABORT ordered set.
A port shall transition to the Tx Header state in any of the following situations:
• From the Tx IDLE state when there are one or more header packets queued for transmission
and there are no link commands queued for transmission.
When the transmitted symbol count is greater than or equal to nSkipSymbolLimit at the end of
transmitting any header packet except a data packet header packet with a data packet payload, a
SKP ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
10.7.10.3
Tx Data
In the Tx Data state, the downstream port transmitter is actively transmitting a data packet payload.
After transmitting the end framing symbols for the data packet payload and required SKP ordered
sets the port may remove the data packet payload from hub storage. A hub shall not retransmit a
data packet payload packet under any circumstances.
A port shall transition to the Tx Data state from the Tx Header state when there is a data packet
payload associated with the data packet header packet that was transmitted. The data packet
payload transmission shall begin immediately after transmission of the last symbol of the data
packet header packet.
At the end of transmitting a data packet payload that is not aborted:
• While the transmitted symbol count is greater than or equal to nSkipSymbolLimit, a SKP
ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
• The sequence is repeated until the symbol count is less than nSkipSymbolLimit.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.10.4
Tx Data Abort
In the Tx Data abort state, the downstream port transmitter aborts the normal transmission of a data
packet payload by transmitting DPPABORT ordered set framing symbols and required SKP
ordered sets. The port then removes the data packet payload from hub storage.
A port transitions to the Tx Data Abort state from the Tx Data state when the upstream port
receiving the data packet payload receives a DPPABORT ordered set or has received
sDataSymbolsBabble symbols without receiving a valid DPPEND ordered set or DPPABORT
ordered set.
At the end of transmitting a DPPABORT ordered set:
• While the transmitted symbol count is greater than or equal to nSkipSymbolLimit, a SKP
ordered set shall be transmitted and the transmitted symbol count shall be reduced by
nSkipSymbolLimit.
• The sequence is repeated until the symbol count is less than nSkipSymbolLimit.
10.7.10.5
Tx Link Command
In the Tx Link Command state, the downstream port transmitter is actively transmitting a link
command. If multiple link commands are queued to be transmitted in the Tx Link Command state,
they shall be transmitted without a gap unless SKP ordered sets are transmitted.
A port shall transition to the Tx Link Command state in any of the following situations:
• From the Tx IDLE state when there are one or more link commands queued for transmission.
• From the Tx Link Command state when there are additional link commands queued for
transmission.
When the transmitted symbol count is greater than or equal to nSkipSymbolLimit at the end of
transmitting any link command, a SKP ordered set shall be transmitted and the transmitted symbol
count shall be reduced by nSkipSymbolLimit.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.7.11
Downstream Facing Port Rx
This section describes the functional requirements of the downstream facing port Rx state machine.
End Link
Command
RX Link Command
Process Link
Command
DPPEND or DPPABORT
Ordered Set Received or
sDataSymbolsBabble
exceeded without a DPPEND
or DPPABORT Ordered Set
Valid Start Link
Command Ordered
Set Received
RX Default
Entering U0
Valid
DPPSTART
Ordered Set
Received
RX Data
SKP Ordered Set
Received
Process
Header
Last Header
Symbol Received
Valid HPSTART
Ordered Set Received
RX Header
Compute CRC and
Check Route String
U-157
Figure 10-19. Downstream Facing Port Rx State Machine
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.12
Downstream Facing Port Rx State Descriptions
10.7.12.1
Rx Default
In the Rx Default state, the downstream port receiver is actively processing received symbols and
looking for DPPSTART ordered set, HPSTART ordered set, or LCSTART ordered set framing
symbols to begin receiving a packet or link command.
If a DPPStart ordered set is received that did not immediately follow a DPH, it is ignored and the
port receiver stays in the RX.Default state.
A port shall transition to the Rx IDLE state in any of the following situations:
• From the Rx Data state when a DPPEND ordered set or DPPABORT ordered set is received.
• From the Rx Header state when the last symbol of a header packet is received.
• From the Rx Data state when sDataSymbolsBabble is reached without receiving a DPPEND
ordered set or DPPSTART ordered set.
• After receiving a link command.
• As the default state when the link enters U0.
10.7.12.2
Rx Data
In the Rx Data state the downstream port receiver is actively processing received symbols and
looking for a DPPEND ordered set, or DPPSTART ordered set. The receiver shall start a count of
received symbols at zero when entering this state. The first symbol counted is the first symbol after
the DPPSTART ordered set.
A port shall transition to the Rx Data state when it receives a valid DPPSTART ordered set.
When a downstream port detects an error before the end of the DPP as defined in Section 7.2.4.1.6
port it may clear the data from its buffers only after it has transmitted the received DPP including
the DPPABORT ordered set on the upstream port. The hub shall transmit the valid received
symbols before the error for a data packet payload followed by a DPPABORT ordered set on its
upstream port when an error is detected on the downstream port. Note that this requirement applies
even when the hub detects an error before beginning to transmit the data payload packet on the hub
upstream port.
The hub shall have at least 1080 bytes of shared buffering for data packets received on all
downstream ports.
10.7.12.3
Rx Header
In the Rx header state, the downstream port receiver is actively processing received symbols until
the last header packet symbol is received. The receiver shall start a count of received symbols at
zero when entering this state. The first symbol counted is the first symbol after the HPSTART
ordered set.
A port shall transition to the Rx Header state when it receives a valid HPSTART ordered set.
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Universal Serial Bus 3.0 Specification, Revision 1.0
The port shall finish validating the CRC-16 and the Link Control Word CRC-5 and check the
header packet type within four symbol times after the last symbol of the header packet is received.
Note: Implementations may have to begin the CRC calculation as symbols are received to meet
this requirement.
10.7.12.4
Process Header
When the final symbol for a header packet is received, the port shall perform all additional
processing necessary for the header packet. Any such processing shall not block the port from
immediately returning to the Rx Default state and continuing to process received symbols.
A port performs additional header packet processing in any of the following situations. The
additional processing steps in each situation are described.
• When the final header packet symbol is received in the Rx header state and the header packet
CRC-16 and Link Control Word CRC-5 are determined to be valid, the appropriate LGOOD_n
link command is queued for transmission by the receiving port and:
1. The header packet is queued for transmission on the upstream port.
If the queue for the upstream port is full, the header packet is queued as soon as a space is
available in the upstream port queue. The hub shall still process subsequent header packets
normally while the upstream port queue is full. If header packets have been received on
more than one downstream port or are queued to be sent by the hub controller when a space
becomes available in the upstream port header packet queue, the hub shall prioritize a nondata packet header over a data packet header packet if one is waiting at the front of a
downstream queue or from the hub controller. Otherwise, the arbitration algorithm the hub
uses is not specified.
Note: These arbitration requirements only apply across multiple downstream ports and the
hub controller. For a single source (downstream port or hub controller), packets must be
transmitted in the ordered received or generated.
•
2. If the downstream port Rx header buffer has at least four free slots, the appropriate
LCRD_x link command is queued for transmission by the downstream port. Otherwise, the
appropriate LCRD_x link command is queued for transmission once the Rx header buffer
slot used for the header packet is available.
When the final header packet symbol is received in the Rx header state and either the header
CRC-16 or Link Control Word CRC-5 is determined to be invalid:
⎯ The header packet is removed from the Rx header buffer.
⎯ An LBAD link command is queued for transmission by the downstream port.
⎯ Note: All subsequent header packets are silently discarded until a retry of the invalid
header packet is received.
10.7.12.5
Rx Link Command
In the Rx Link Command state, the downstream port receiver is actively processing received
symbols and looking for the end of a link command (second instance of link command word).
A port shall transition to the Rx Link Command state when it receives a valid LCSTART ordered
set.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.7.12.6
Process Link Command
Once the final symbol for a link command is received, the port shall perform all additional
processing necessary for the link command. Any such processing shall not block the port from
immediately returning to the Rx.Default state and continuing to process received symbols.
10.7.13
SuperSpeed Packet Connectivity
The SuperSpeed hub packet repeater/forwarder must reclock the packets in both directions.
Reclocking means that the repeater extracts the data from the received stream and retransmits the
stream using its own local clock.
10.8
Suspend and Resume
Hubs must support suspend and resume both as a USB device and in terms of propagating suspend
and resume signaling. Global suspend/resume refers to the entire bus being suspended or resumed
without affecting any hub’s downstream facing port states; selective suspend/resume refers to a
downstream facing port of a hub being suspended or resumed without affecting the hub state.
SuperSpeed hubs only support selective suspend and resume. They do not support global suspend
and resume. Selective suspend/resume is implemented via requests to a hub. Device-initiated
resume is called remote-wakeup.
The hub follows the same suspend requirements as a SuperSpeed device on its upstream facing
port.
When a hub downstream port link is in the U3 state, the following requirements apply to the hub if
it receives wakeup signaling from its link partner on that downstream port:
• If the hub upstream port’s link is not in U3, the hub shall drive remote wakeup signaling on the
downstream link where the wakeup signaling was received in
tHubDriveRemoteWakeDownstream.
• If the hub upstream port’s link is in U3, the hub shall drive wakeup signaling on its upstream
port in tHubPropRemoteWakeUpstream.
When a hub upstream port’s link is in the U3 state and it receives wakeup signaling from its link
partner on the hub upstream port’s link, the hub shall automatically drive remote wakeup to any
downstream ports that are in U3 and have received remote wakeup signaling since entering U3.
When the hub receives a SetPortFeature(PORT_LINK_STATE) U0 for a downstream port with a
link in U3, the hub shall drive remote wakeup signaling on the link in
tHubDriveRemoteWakeDownstream.
10.9
Hub Upstream Port Reset Behavior
Reset signaling to a hub is defined only in the downstream direction, which is at the hub's upstream
facing port. The reset signaling mechanism required of the hub is described in Chapter 6.
A suspended hub shall interpret the start of reset as a wakeup event; it shall be awake and have
completed its reset sequence by the end of reset signaling.
After completion of a Warm Reset, the entire hub returns to the default state.
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Universal Serial Bus 3.0 Specification, Revision 1.0
After completion of a Hot Reset, the hub returns to the default state except port configuration
information is maintained for the upstream port.
10.10 Hub Port Power Control
Self-powered hubs may have power switches that control delivery of power to downstream facing
ports but it is not required. A hub with power switches can switch power to all ports as a
group/gang, to each port individually, or have an arbitrary number of gangs of one or more ports.
A hub indicates whether or not it supports power switching by the setting of the Logical Power
Switching Mode field in wHubCharacteristics. If a hub supports per-port power switching, then
the power to a port is turned on or off as specified in Table 10-1. If a hub supports ganged power
switching, then the power to all ports in a gang is turned on when power is required to be on for any
port in the gang. The power to a gang is not turned off unless all ports in a gang are in a state that
allows power to be removed as specified in Table 10-1. The power to a port is not turned on by a
SetPortFeature(PORT_POWER) if both C_HUB_LOCAL_POWER and Local Power Status (in
wHubStatus) are set to one at the time when the request is executed and the PORT_POWER feature
would be turned on. A hub that supports charging applications may keep power on at other times.
Refer to Section 10.3.1.1 for more details on allowed behavior for a hub that supports charging
applications.
Although a self-powered hub is not required to implement power switching, the hub shall support
the Powered-off state for all ports. Additionally, the hub shall implement the PortPwrCtrlMask (all
bits set to one) even though the hub has no power switches that can be controlled by the USB
system software.
For a hub with no power switches, bPwrOn2PwrGood shall be set to zero.
10.10.1
Multiple Gangs
A hub may implement any number of power and/or over-current gangs. A hub that implements
more than one over-current and/or power switching gang shall set both the Logical Power
Switching Mode and the Over-current Reporting Mode to indicate that power switching and overcurrent reporting are on a per port basis (these fields are in wHubCharacteristics). Also, all bits in
PortPwrCtrlMask shall be set to one.
When an over-current condition occurs on an over-current protection device, the over-current is
signaled on all ports that are protected by that device. When the over-current is signaled, all the
ports in the group are placed in the DSPORT.Powered-off state, and the
C_PORT_OVER_CURRENT field is set to one on all the ports. When port status is read from any
port in the group, the PORT_OVER_CURRENT field will be set to one as long as the over-current
condition exists. The C_PORT_OVER_CURRENT field shall be cleared in each port individually.
When multiple ports share a power switch, setting PORT_POWER on any port in the group will
cause the power to all ports in the group to turn on. It will not, however, cause the other ports in
that group to leave the DSPORT.Powered-off state. When all the ports in a group are in the
DSPORT.Powered-off state or the hub is not configured, the power to the ports is turned off.
If a hub implements both power switching and over-current, it is not necessary for the over-current
groups to be the same as the power switching groups.
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Hub, Host Downstream Port, and Device Upstream Port Specification
If an over-current condition occurs and power switches are present, then all power switches
associated with an over-current protection circuit shall be turned off. If multiple over-current
protection devices are associated with a single power switch, then that switch will be turned off
when any of the over-current protection circuits indicates an over-current condition.
10.11 Hub Controller
The Hub Controller is logically organized as shown in Figure 10-20.
Upstream Connection
Status
Change
Endpoint
Endpoint 0:
Configuration
Information
Port 1
Port N
Port 2
Port 3
U-158
Figure 10-20. Example Hub Controller Organization
10.11.1
Endpoint Organization
The Hub Class defines one additional endpoint beyond the default control pipe, which is required
for all hubs: the Status Change endpoint. This endpoint has the maximum burst size set to one.
The host system receives port and hub status change notifications through the Status Change
endpoint. The Status Change endpoint is an interrupt endpoint. If no hub or port status change bits
are set, then the hub returns an NRDY when the Status Change endpoint receives an IN (via and
ACK TP) request. When a status change bit is set, the hub will send an ERDY TP to the host. The
host will subsequently ask the Status Change endpoint for the data, which will indicate the entity
(hub or port) with a change bit set. The USB system software can use this data to determine which
status registers to access in order to determine the exact cause of the status change interrupt.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.11.2
Hub Information Architecture and Operation
Figure 10-21 shows how status, status change, and control information relate to device states. Hub
descriptors and Hub/Port Status and Control are accessible through the default control pipe. The
Hub descriptors may be read at any time. When a hub detects a change on a port or when the hub
changes its own state, the Status Change endpoint transfers data to the host in the form specified in
Section 10.11.4.
Hub or port status change bits can be set because of hardware or software events. When set, these
bits remain set until cleared directly by the USB system software through a ClearPortFeature()
request or by a hub reset. While a change bit is set, the hub continues to report a status change
when the Status Change endpoint is read until all change bits have been cleared by the USB system
software.
Status Information
(static)
s
tu
ta es
l S ng
Al ha
C
Host Software
(e.g., Hub Driver)
Change Information
(due to hardware
events)
Har
dwa
re E
ven
ts
Hardware Events
Change Device
State
Device
Control
Control Information
(change device state)
Software Device
Control
U-159
Figure 10-21. Relationship of Status, Status Change, and Control Information
to Device States
The USB system software uses the interrupt pipe associated with the Status Change endpoint to
detect changes in hub and port status.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.11.3
Port Change Information Processing
Hubs report a port's status through port commands on a per-port basis. The USB system software
acknowledges a port change by clearing the change state corresponding to the status change
reported by the hub. The acknowledgment clears the change state for that port so future data
transfers to the Status Change endpoint do not report the previous event. This allows the process to
repeat for further changes (see Figure 10-22).
Begin
Host requests Interrupt Pipe notification for Status Change Information
Send ERDY
when data
available
Hub
Sends an
NRDY TP
No
Change Data
Available?
Yes
Interrupt Pipe returns Hub and Port Status Change Change Bitmap
Interrupt Pipe notification retired
System Software reads Hub or Port Status (for affected ports)
Any Changed
State?
Yes
Accumulate change information
System software clears
corresponding change state
No
System software processes accumulated change information
Re-initialize Interrupt Pipe notification for Status Change endpoint
Return to beginning
U-160
Figure 10-22. Port Status Handling Method
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.11.4
Hub and Port Status Change Bitmap
The Hub and Port Status Change Bitmap, shown in Figure 10-23, indicates whether the hub or a
port has experienced a status change. This bitmap also indicates which port(s) have had a change in
status. The hub returns this value on the Status Change endpoint. Hubs report this value in byteincrements. For example, if a hub has six ports, it returns a byte quantity, and reports a zero in the
invalid port number field locations. The USB system software is aware of the number of ports on a
hub (this is reported in the hub descriptor) and decodes the Hub and Port Status Change Bitmap
accordingly. The hub reports any changes in hub status in bit zero of the Hub and Port Status
Change Bitmap.
The Hub and Port Status Change Bitmap size is two bytes. Hubs report only as many bits as there
are ports on the hub. A USB 3.0 hub may have no more than nMaxHubPorts.
N
2
1
0
Port N change detected
Port 2 change detected
Port 1 change detected
Hub change detected
U-161
Figure 10-23. Hub and Port Status Change Bitmap
10-52
Hub, Host Downstream Port, and Device Upstream Port Specification
Any time any of the Status Changed bits are non-zero, an ERDY is returned (if an NRDY was
previously sent) notifying the host that the Hub and Port Status Change Bitmap has changed.
Figure 10-24 shows an example creation mechanism for hub and port change bits.
Per-Port Logic
Port N
Change
Detect Logic
Logical OR
Change
Information
Hub and Port Status Change Bitmap
N
U-162
Figure 10-24. Example Hub and Port Change Bit Sampling
10.11.5
Over-current Reporting and Recovery
USB devices shall be designed to meet applicable safety standards. Usually, this will mean that a
self-powered hub implements current limiting on its downstream facing ports. If an over-current
condition occurs, it causes a status and state change in one or more ports. This change is reported
to the USB system software so that it can take corrective action.
A hub may be designed to report over-current as either a port or a hub event. The hub descriptor
field wHubCharacteristics is used to indicate the reporting capabilities of a particular hub (refer to
Section 10.13.2.1). The over-current status bit in the hub or port status field indicates the state of
the over-current detection when the status is returned. The over-current status change bit in the
Hub or Port Change field indicates if the over-current status has changed.
When a hub experiences an over-current condition, it shall place all affected ports in the
DSPORT.Powered-off state. If a hub has per-port power switching and per-port current limiting,
an over-current condition on one port may still cause the power on another port to fall below
specified minimums. In this case, the affected port is placed in the DSPORT.Powered-off state and
C_PORT_OVER_CURRENT is set for the port, but PORT_OVER_CURRENT is not set. If the
hub has over-current detection on a hub basis, then an over-current condition on the hub will cause
all ports to enter the DSPORT.Powered-off state. However, in this case, neither
C_PORT_OVER_CURRENT nor PORT_OVER_CURRENT is set for the affected ports.
Host recovery actions for an over-current event should include the following:
1. Host gets change notification from hub with over-current event.
2. Host extracts appropriate hub or port change information (depending on the information in the
change bitmap).
3. Host waits for over-current status bit to be cleared to 0.
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Universal Serial Bus 3.0 Specification, Revision 1.0
4. Host cycles power to on for all of the necessary ports (e.g., issues a
SetPortFeature(PORT_POWER) request for each port).
5. Host re-enumerates all affected ports.
10.11.6
Enumeration Handling
The hub device class commands are used to manipulate its downstream facing port state. When a
device is attached, the device attach event is detected by the hub and reported on the Status Change
endpoint. The host will accept the status change report and may request a
SetPortFeature(PORT_RESET) on the port. The Get_Status(PORT) request invoked by the host
will return a PORT_SUPER_SPEED indication that the downstream facing port is operating at
SuperSpeed.
When the device is detached from the port, the port reports the status change through the Status
Change endpoint. Then the process is ready to be repeated on the next device attach detect.
10.12 Hub Configuration
Hubs are configured through the standard USB device configuration commands. A hub that is not
configured behaves like any other device that is not configured with respect to power requirements
and addressing. A hub is required to power its downstream ports based on several factors,
including whether the hub supports power switching and charging applications. Refer to
Section 10.3.1.1 for details on when a hub is required to provide power to downstream ports.
Configuring a hub enables the Status Change endpoint. Part of the configuration process is setting
the hub depth which is used to compute an index (refer to Section 10.14.2.8) into the Route String
(refer to Section 8.9). The hub depth is used to derive the offset into the Route String (in a TP or
DP) that the hub shall use to route packets received on its upstream port. The USB system software
may then issue commands to the hub to switch port power on and off at appropriate times.
The USB system software examines hub descriptor information to determine the hub’s
characteristics. By examining the hub’s characteristics, the USB system software ensures that
illegal power topologies are not allowed by not powering on the hub’s ports if doing so would
violate the USB power topology. The device status and configuration information can be used to
determine whether the hub can be used in a given topology. Table 10-2 summarizes the
information and how it can be used to determine the current power requirements of the hub.
Table 10-2. Hub Power Operating Mode Summary
10-54
Explanation
MaxPower
bmAttributes
(Self Powered)
Hub
Device Status
(Self Power)
0
0
N/A
N/A
This is an illegal combination.
0
1
0
N/A
A device which is only self-powered, but does not have
local power, cannot connect to the bus and communicate.
Configuration Descriptor
Hub, Host Downstream Port, and Device Upstream Port Specification
Explanation
MaxPower
bmAttributes
(Self Powered)
Hub
Device Status
(Self Power)
0
1
1
Self-powered only hub and local power supply is good.
Hub status also indicates local power good. Hub
functionality is valid anywhere depth restriction is not
violated.
>0
0
N/A
Bus-powered only hub. Downstream facing ports may
not be powered unless allowed in current topology. Hub
device status reporting self-powered is meaningless if
bmAttributes.self-powered is zero.
>0
1
0
This hub is capable of both self- and bus-powered
operating modes. It is currently only available as a buspowered hub.
>0
1
1
This hub draws power from both the bus and its local
power supply. It is currently available as a self-powered
hub.
Configuration Descriptor
A self-powered hub has a local power supply, but may optionally draw one unit load from its
upstream connection. This allows the interface to function when local power is not available (refer
to Section 7.2.1.2). When local power is removed (either a hub-wide over-current condition or
local supply is off), a hub of this type remains in the Configured state but transitions all ports
(whether removable or non-removable) to the Powered-off state. While local power is off, all port
status and change information read as zero and all SetPortFeature() requests are ignored (request is
treated as a no-operation). The hub will use the Status Change endpoint to notify the USB system
software of the hub event (refer to Section 10.11.4 for details on hub status).
The MaxPower field in the configuration descriptor is used to report to the system the maximum
power the hub will draw from VBUS when the configuration is selected. The external devices
attaching to the hub will report their individual power requirements.
A compound device may power both the hub electronics and the permanently attached devices from
VBUS. The entire load may be reported in the hubs' configuration descriptor with the permanently
attached devices each reporting self-powered, with zero MaxPower in their respective configuration
descriptors.
A bus powered hub shall be able to supply any power not used by the hub electronics or
permanently attached devices for the selected configuration to the exposed downstream ports. The
hub shall be able to provide the power with any split across the exposed downstream ports (i.e., if
the hub can provide 600 mA to two exposed downstream ports, it must be able to provide 450 mA
to one and 150 mA to the other, 300 mA to each, etc.).
Note: Software shall ensure that at least 150 mA is available for each exposed downstream port on
a bus powered hub.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.13 Descriptors
Hub descriptors are derived from the general USB device framework. Hub descriptors describe a
hub device and the ports on that hub. The host accesses hub descriptors through the hub’s default
control pipe.
The USB specification (refer to Chapter 8) defines the following descriptors:
• Device Level Descriptors
• Configuration
• Interface
• Endpoint
• String (optional)
The hub class defines additional descriptors (refer to Section 10.13.2). In addition, vendor-specific
descriptors are allowed in the USB device framework. Hubs support standard USB device
commands as defined in Chapter 8.
A hub is the only device that is allowed to function at high-speed and SuperSpeed at the same time.
This specification only defines the descriptors a hub shall report when it is operating in SuperSpeed
mode.
Note that a SuperSpeed hub shall always support the Get Descriptor (BOS) (refer to Section 9.6.2)
in both SuperSpeed and non-SuperSpeed modes.
10.13.1
Standard Descriptors for Hub Class
The hub class pre-defines certain fields in standard USB descriptors. Other fields are either
implementation-dependent or not applicable to this class.
A hub has a device descriptor with a bDeviceProtocol field set to 3 and an interface descriptor with
a bInterfaceProtocol field set to 0.
Hub Descriptors in SuperSpeed Mode
Device Descriptor (SuperSpeed information)
10-56
bLength
18
bDescriptorType
1
bcdUSB
300H
bDeviceClass
HUB_CLASSCODE (9)
bDeviceSubClass
0
bDeviceProtocol
3
bMaxPacketSize0
9
bNumConfigurations
1
Hub, Host Downstream Port, and Device Upstream Port Specification
BOS Descriptor
bLength
5
bDescriptorType
BOS Descriptor type
wTotalLength
44
bNumDeviceCaps
3
USB 2.0 Extension
bLength
7
bDescriptorType
1
bDevCapabilityType
2
bmAttributes
2
SuperSpeed USB Device Capability
bLength
12
bDescriptorType
DEVICE CAPABILITY Descriptor
type
bDevCapabilityType
3
bmAttributes
Implementation-dependent
wSpeedsSupported
12
bFunctionalitySupport
8
bU1DevExitLat
Implementation-dependent
wU2DevExitLat
Implementation-dependent
wReserved
0
ContainerID
bLength
20
bDescriptorType
1
bDevCapabilityType
4
bReserved
0
ContainerID
Implementation-dependent
10-57
Universal Serial Bus 3.0 Specification, Revision 1.0
Configuration Descriptor (SuperSpeed information)
bLength
9
bDescriptorType
2
wTotalLength
31
bNumInterfaces
1
bConfigurationValue
X
iConfiguration
Y
bmAttributes
Z
bMaxPower
The maximum amount of bus power the hub
will consume in this configuration
Interface Descriptor
bLength
9
bDescriptorType
4
bInterfaceNumber
0
bAlternateSetting
0
bNumEndpoints
1
bInterfaceClass
HUB_CLASSCODE (9)
bInterfaceSubClass
0
bInterfaceProtocol
0
iInterface
I
Endpoint Descriptor (for Status Change Endpoint)
bLength
7
bDescriptorType
5
bEndpointAddress
Implementation-dependent; Bit 7:
Direction = In(1)
bmAttributes
Transfer Type = Interrupt (19)
wMaxPacketSize
2
bInterval
255 (maximum allowable interval)
Endpoint Companion Descriptor (for Status Change Endpoint)
10-58
bLength
6
bDescriptorType
48
bMaxBurst
0
bmAttributes
0
Hub, Host Downstream Port, and Device Upstream Port Specification
10.13.2
Class-specific Descriptors
10.13.2.1
Hub Descriptor
Table 10-3 outlines the various fields contained in the hub descriptor.
Table 10-3. SuperSpeed Hub Descriptor
Offset
Field
Size
Description
0
bDescLength
1
Number of bytes in this descriptor, including this byte. (12 bytes)
1
bDescriptorType
1
Descriptor Type, value: 2AH for SuperSpeed hub descriptor
2
bNbrPorts
1
Number of downstream facing ports that this hub supports. The
maximum number of ports of ports a hub can support is 15.
3
wHubCharacteristics
2
D1...D0: Logical Power Switching Mode
00:
Ganged power switching (all ports’ power at once)
01:
Individual port power switching
1X:
Reserved
D2:
Identifies a Compound Device
0:
Hub is not part of a compound device.
1:
Hub is part of a compound device.
D4...D3: Over-current Protection Mode
00:
Global Over-current Protection. The hub reports overcurrent as a summation of all ports’ current draw, without
a breakdown of individual port over-current status.
01:
Individual Port Over-current Protection. The hub reports
over-current on a per-port basis. Each port has an overcurrent status.
1X:
No Over-current Protection. This option is allowed only for
bus-powered hubs that do not implement over-current
protection.
D15...D5: Reserved
5
bPwrOn2PwrGood
1
Time (in 2-ms intervals) from the time the power-on sequence begins
on a port until power is good on that port. The USB system software
uses this value to determine how long to wait before accessing a
powered-on port. This value is set to zero if power-switching is not
supported by the hub.
6
bHubContrCurrent
1
Maximum current requirements of the Hub Controller electronics
when the hub is operating on both USB 2.0 and SuperSpeed
expressed in units of aCurrentUnit (i.e., 50 = 50* aCurrentUnit mA).
Note that the encoding of this field is different if the encoding used is
the USB 2.0 specification for USB 2.0 hubs. A USB 3.0 hub shall
report the current requirements when it is only operating on USB 2.0
(not SuperSpeed) in the USB 2.0 hub descriptor.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Offset
Field
Size
Description
7
bHubHdrDecLat
1
Hub Packet Header Decode Latency.
Worst case latency for hubs whose upstream link is in U0 to decode
the header of a downstream flowing TP or DP packet and initiate a
transition to U0 on the relevant downstream port. The time is
measured from receipt of the last symbol of the header packet by the
upstream port until the hubs starts LFPS on the intended downstream
port.
This field is used to calculate the total path exit latency through a
hub.
The following are permissible values:
Value
Meaning
00H
Much less than 0.1 µs.
01H
0.1 µs
02H
0.2 µs
03H
0.3 µs
04H
0.4 µs
05H –
FFH
Reserved
8
wHubDelay
2
This field defines the average delay in nanoseconds a hub introduces
on downstream flowing header packets that it receives before
forwarding them when both its upstream link and the downstream link
on which it forwards the packet are in the U0 state and no Link
Commands are in flight. The time is measured from receipt of the
last symbol of the packet by the upstream port until the downstream
port sends the first framing symbol of the packet.
10
DeviceRemovable
2
Indicates if a port has a removable device attached. This field is
reported on byte-granularity. Within a byte, if no port exists for a
given location, the bit field representing the port characteristics shall
be 0.
Bit value definition:
0B - Device is removable.
1B - Device is non-removable.
This is a bitmap corresponding to the individual ports on the hub:
Bit 0: Reserved for future use
Bit 1: Port 1
Bit 2: Port 2
....
Bit n: Port n (implementation-dependent, up to a maximum of
15 ports)
10-60
Hub, Host Downstream Port, and Device Upstream Port Specification
10.14 Requests
10.14.1
Standard Requests
Hubs have tighter constraints on request processing timing than specified in Section 9.2.6 for
standard devices because they are crucial to the “time to availability” of all devices attached to the
USB. The worst case request timing requirements are listed below (they apply to both Standard
and Hub Class requests):
• Completion time for requests with no data stage: 50 ms
• Completion times for standard requests with data stage(s):
⎯ Time from setup packet to first data stage: 50 ms
⎯ Time between each subsequent data stage: 50 ms
⎯ Time between last data stage and status stage: 50 ms
Because hubs play such a crucial role in bus enumeration, it is recommended that hubs average
response times be less than 5 ms for all requests.
Table 10-4 outlines the various standard device requests.
Table 10-4. Hub Responses to Standard Device Requests
bRequest
Hub Response
CLEAR_FEATURE
Standard
GET_CONFIGURATION
Standard
GET_DESCRIPTOR
Standard
GET_INTERFACE
Undefined. Hubs are allowed to support only one interface.
GET_STATUS
Standard
SET_ADDRESS
Standard
SET_CONFIGURATION
Standard
SET_DESCRIPTOR
Optional
SET_FEATURE
Standard
SET_INTERFACE
Undefined. Hubs are allowed to support only one interface.
SET_ISOCH_DELAY
Standard
SET_SEL
Standard
SYNCH_FRAME
Undefined. Hubs are not allowed to have isochronous endpoints.
Optional requests that are not implemented shall return a STALL in the Data stage or Status stage
of the request.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.14.2
Class-specific Requests
The hub class defines requests to which hubs respond, as outlined in Table 10-5. Table 10-6
defines the hub class request codes. All requests in the table below except SetHubDescriptor() are
mandatory.
Table 10-5. Hub Class Requests
Request
bmRequestType
bRequest
wValue
wIndex
wLength
Data
ClearHubFeature
00100000B
CLEAR_FEATURE
Feature Selector
Zero
Zero
None
ClearPortFeature
00100011B
CLEAR_FEATURE
Feature Selector
Port
Zero
None
GetHubDescriptor
10100000B
GET_DESCRIPTOR
Descriptor Type
and Descriptor
Index
Zero or
Language
ID
Descriptor
Length
Descriptor
GetHubStatus
10100000B
GET_STATUS
Zero
Zero
Four
Hub Status
and Change
Status
GetPortStatus
10100011B
GET_STATUS
Zero
Port
Four
Port Status
and Change
Status
GetPortErrorCount
10000000B
GET_PORT_ERR_
COUNT
Zero
Port
Two
Number of
Link Errors
on this port
SetHubDescriptor
00100000B
SET_DESCRIPTOR
Descriptor Type
and Descriptor
Index
Zero or
Language
ID
Descriptor
Length
Descriptor
SetHubFeature
00100000B
SET_FEATURE
Feature Selector
Zero
Zero
None
SetHubDepth
00100000B
SET_HUB_DEPTH
Hub Depth
Zero
Zero
None
SetPortFeature
00100011B
SET_FEATURE
Feature Selector
Selector,
Timeout,
Port
Zero
None
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Hub, Host Downstream Port, and Device Upstream Port Specification
Table 10-6. Hub Class Request Codes
bRequest
Value
GET_STATUS
0
CLEAR_FEATURE
1
RESERVED (used in previous specifications for GET_STATE)
2
SET_FEATURE
3
RESERVED
4-5
GET_DESCRIPTOR
6
SET_DESCRIPTOR
7
RESERVED (used in USB 2.0 specification)
8-11
SET_HUB_DEPTH
12
GET_PORT_ERR_COUNT
13
Table 10-7 gives the valid feature selectors for the hub class. Refer to Section 10.14.2.4 and
Section 10.14.2.6 for a description of the features.
Table 10-7. Hub Class Feature Selectors
Feature Selector
Recipient
Value
C_HUB_LOCAL_POWER
Hub
0
C_HUB_OVER_CURRENT
Hub
1
PORT_CONNECTION
Port
0
PORT_OVER_CURRENT
Port
3
PORT_RESET
Port
4
PORT_LINK_STATE
Port
5
PORT_POWER
Port
8
C_PORT_CONNECTION
Port
16
C_PORT_OVER_CURRENT
Port
19
C_PORT_RESET
Port
20
RESERVED (used in USB 2.0 specification)
Port
21
PORT_U1_TIMEOUT
Port
23
PORT_U2_TIMEOUT
Port
24
C_PORT_LINK_STATE
Port
25
C_PORT_CONFIG_ERROR
Port
26
PORT_REMOTE_WAKE_MASK
Port
27
BH_PORT_RESET
Port
28
C_BH_PORT_RESET
Port
29
FORCE_LINKPM_ACCEPT
Port
30
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.14.2.1
Clear Hub Feature
This request resets a value reported in the hub status.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00100000B
CLEAR_FEATURE
Feature Selector
Zero
Zero
None
Clearing a feature disables that feature; refer to Table 10-7 for the feature selector definitions that
apply to the hub as a recipient. If the feature selector is associated with a status change, clearing
that status change acknowledges the change. This request format is used to clear either the
C_HUB_LOCAL_POWER or C_HUB_OVER_CURRENT features.
It is a Request Error if wValue is not a feature selector listed in Table 10-7 or if wIndex or wLength
are not as specified above.
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.2
Clear Port Feature
This request resets a value reported in the port status.
bmRequestType
bRequest
wValue
wIndex
00100011B
CLEAR_FEATURE
Feature Selector
Selector
Port
wLength
Data
Zero
None
The port number shall be a valid port number for that hub, greater than zero. The port field is
located in bits 7..0 of the wIndex field.
Clearing a feature disables that feature or starts a process associated with the feature; refer to
Table 10-7 for the feature selector definitions. If the feature selector is associated with a status
change, clearing that status change acknowledges the change. This request format is used to clear
the following features:
• PORT_POWER
• C_PORT_CONNECTION
• C_PORT_RESET
• C_PORT_OVER_CURRENT
• C_PORT_LINK_STATE
• C_PORT_CONFIG_ERROR
• C_BH_PORT_RESET
Clearing the PORT_POWER feature causes the port to be placed in the DSPORT.Powered-off state
and may, subject to the constraints due to the hub’s method of power switching, result in power
being removed from the port. When in the DSPORT.Powered-off state, the only requests that are
valid when this port is the recipient are Get Port Status (refer to Section 10.14.2.6) and Set Port
Feature (PORT_POWER) (refer to Section 10.14.2.10).
Clearing the FORCE_LINKPM_ACCEPT feature causes the port to de-assert the
Force_LinkPM_Accept bit in Set Link Function LMPs. If the Force_LinkPM_Accept bit is not
asserted on the port, the hub shall treat this request as a functional no-operation.
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Hub, Host Downstream Port, and Device Upstream Port Specification
It is a Request Error if wValue is not a feature selector listed in Table 10-7, if wIndex specifies a
port that does not exist, or if wLength is not as specified above. It is not an error for this request to
try to clear a feature that is already cleared (the hub shall treat this as a functional no-operation).
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.3
Get Hub Descriptor
This request returns the hub descriptor.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10100000B
GET_DESCRIPTOR
Descriptor Type
and Descriptor
Index
Zero
Descriptor
Length
Descriptor
The GetDescriptor() request for the hub class descriptor follows the same usage model as that of the
standard GetDescriptor() request (refer to Chapter 9). The standard hub descriptor is denoted by
using the value bDescriptorType defined in Section 10.13.2.1. All hubs are required to implement
one hub descriptor, with descriptor index zero.
If wLength is larger than the actual length of the descriptor, then only the actual length is returned.
If wLength is less than the actual length of the descriptor, then only the first wLength bytes of the
descriptor are returned; this is not considered an error even if wLength is zero.
It is a Request Error if wValue or wIndex are other than as specified above.
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.4
Get Hub Status
This request returns the current hub status and the states that have changed since the previous
acknowledgment.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10100000B
GET_STATUS
Zero
Zero
Four
Hub Status
and Change
Status
The first word of data contains the wHubStatus field (refer to Table 10-8). The second word of
data contains the wHubChange field (refer to Table 10-9).
It is a Request Error if wValue, wIndex, or wLength are other than as specified above.
If the hub is not configured, the hub's response to this request is undefined.
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Universal Serial Bus 3.0 Specification, Revision 1.0
Table 10-8. Hub Status Field, wHubStatus
Bit
0
Description
Local Power Source: This is the source of the local power supply.
This field indicates whether hub power (for other than the SIE) is being provided by an external source or from
the USB. This field allows the USB system software to determine the amount of power available from a hub
to downstream devices.
0 = Local power supply good
1 = Local power supply lost (inactive)
1
Over-current:
If the hub supports over-current reporting on a hub basis, this field indicates that the sum of all the ports’
current has exceeded the specified maximum and all ports have been placed in the Powered-off state. If the
hub reports over-current on a per-port basis or has no over-current detection capabilities, this field is always
zero. The hub shall only report over-current if it is physically unable to meet the sum of all ports’ current
draws. For more details on over-current protection, refer to the USB 2.0 Specification, Section 7.2.1.2.1.
0 = No over-current condition currently exists.
1 = A hub over-current condition exists.
2-15
Reserved
There are no defined feature selector values for these status bits and they can neither be set nor
cleared by the USB system software.
Table 10-9. Hub Change Field, wHubChange
Bit
Description
0
Local Power Status Change (C_HUB_LOCAL_POWER): This field indicates that a change has occurred in
the hub’s Local Power Source field in wHubStatus.
This field is initialized to zero when the hub receives a bus reset.
0 = No change has occurred to Local Power Status.
1 = Local Power Status has changed.
1
Over-Current Change (C_HUB_OVER_CURRENT): This field indicates if a change has occurred in the OverCurrent field in wHubStatus.
This field is initialized to zero when the hub receives a bus reset.
0 = No change has occurred to the Over-Current Status.
1 = Over-Current Status has changed.
2-15
Reserved
Hubs may allow setting of these change bits with SetHubFeature() requests in order to support
diagnostics. If the hub does not support setting of these bits, it shall either treat the
SetHubFeature() request as a Request Error or as a functional no-operation. When set, these bits
may be cleared by a ClearHubFeature() request. A request to set a feature that is already set or to
clear a feature that is already clear has no effect and the hub shall treat this as a functional nooperation.
10-66
Hub, Host Downstream Port, and Device Upstream Port Specification
10.14.2.5
Get Port Error Count
This request returns the number of link errors detected by the hub on the port indicated by wIndex.
This value is reset to zero whenever the device goes through a Reset (refer to Section 7.3) or at
power up.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10000000B
GET_PORT_ERR_COUNT
Zero
Port
Two
Number of
Link Errors
The port number shall be a valid port number for that hub, greater than zero.
It is a Request Error if wValue or wLength are other than as specified above or if wIndex specifies a
port that does not exist.
If the hub is not configured, the behavior of the hub in response to this request is undefined.
10.14.2.6
Get Port Status
This request returns the current port status and the current value of the port status change bits.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
10100011B
GET_STATUS
Zero
Port
Four
Port Status
and Change
Status
The port number shall be a valid port number for that hub, greater than zero.
The first word of data contains the wPortStatus field (refer to Table 10-10). The second word of
data contains the wPortChange field (refer to Table 10-11).
The bit locations in the wPortStatus and wPortChange fields correspond in a one-to-one fashion
where applicable.
It is a Request Error if wValue or wLength are other than as specified above or if wIndex specifies a
port that does not exist.
If the hub is not configured, the behavior of the hub in response to this request is undefined.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.14.2.6.1
Port Status Bits
Table 10-10. Port Status Field, wPortStatus
Bit
Description
0
Current Connect Status (PORT_CONNECTION): This field reflects whether or not a device is currently
connected to this port.
1
Meaning
No device is present
1
A device is present on this port
Port Enabled/Disabled: This field indicates whether the port is enabled. Ports can be disabled by either a fault
condition (disconnect event or other fault condition) or by the USB system software.
Value
Meaning
0
Port is disabled
1
Port is enabled
2
Reserved
3
Over-current (PORT_OVER_CURRENT): If the hub reports over-current conditions on a per-port basis, this field
indicates that the current drain on the port exceeds the specified maximum.
4
5-8
10-68
Value
0
Value
Meaning
0
No over-current condition exists on this port
1
An over-current condition exists on this port
Reset (PORT_RESET): This field is set when the host wishes to reset the attached device. It remains set until
the reset signaling is turned off by the hub.
Value
Meaning
0
Reset signaling not asserted
1
Reset signaling asserted
Port Link State (PORT_LINK_STATE): This field reflects the current state of the link attached to this port. A new
state is not reflected until the link state transition to that state is complete.
Value
Meaning
0x00
Link is in the U0 State
0x01
Link is in the U1 State
0x02
Link is in the U2 State
0x03
Link is in the U3 State
0x04
Link is in the SS.Disabled State
0x05
Link is in the Rx.Detect State
0x06
Link is in the SS.Inactive State
0x07
Link is in the Polling State
0x08
Link is in the Recovery State
0x09
Link is in the Hot Reset State
0xA
Link is in the Compliance Mode State
0xB
Link is in the Loopback State
0xC-0xF
Reserved
Hub, Host Downstream Port, and Device Upstream Port Specification
Bit
Description
9
Port Power (PORT_POWER): This field reflects a port’s logical, power control state. Because hubs can
implement different methods of port power switching, this field may or may not represent whether power is
applied to the port. The device descriptor reports the type of power switching implemented by the hub.
10-12
13-15
Value
Meaning
0
This port is in the Powered-off state
1
This port is not in the Powered-off state
Negotiated speed of the SuperSpeed Device Attached to this port (PORT_SPEED): This field is valid only if a
device is attached.
Value
Meaning
0
5 Gbps
1
Reserved
2
Reserved
3
Reserved
4
Reserved
5
Reserved
6
Reserved
7
Reserved
Reserved
PORT_CONNECTION
This bit is set to one when the port in the DSPORT.Enabled or DSPORT.Resetting or
DSPORT.Error state and is set to zero otherwise.
SetPortFeature(PORT_CONNECTION) and ClearPortFeature(PORT_CONNECTION) requests
shall not be used by the USB system software and shall be treated as no-operation requests by hubs.
PORT_ENABLE
This bit is set to one when the downstream port is in the DSPORT.Enabled state and is set to zero
otherwise.
Note that the USB 2.0 ClearPortFeature (PORT_ENABLE) request is not supported by SuperSpeed
hubs and cannot be used by USB system software to disable a port.
PORT_OVER_CURRENT
This bit is set to one while an over-current condition exists on the port and set to zero otherwise.
If the voltage on this port is affected by an over-current condition on another port, this bit is set to
one and remains set to one until the over-current condition on the affecting port is removed. When
the over-current condition on the affecting port is removed, this bit is set to zero.
Over-current protection is required on self-powered hubs (it is optional on bus-powered hubs) as
outlined in Section 10.10.
The SetPortFeature(PORT_OVER_CURRENT) and ClearPortFeature(PORT_OVER_CURRENT)
requests shall not be used by the USB system software and may be treated as no-operation requests
by hubs.
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Universal Serial Bus 3.0 Specification, Revision 1.0
PORT_RESET
This bit is set to one while the port is in the DSPORT.Resetting state. This bit is set to zero in all
other downstream port states.
A SetPortFeature(PORT_RESET or BH_PORT_RESET) request will initiate the
DSPORT.Resetting state if the conditions in Section 10.3.1.6 are met.
The ClearPortFeature(PORT_RESET) request shall not be used by the USB system software and
may be treated as a no-operation request by hubs.
PORT_LINK_STATE
This field reflects the current state of the link.
The SetPortFeature(PORT_LINK_STATE) request may be issued by the USB system software at
any time but will have an effect only as specified in Section 10.14.2.10.
The ClearPortFeature(PORT_LINK_STATE) requests shall not be used by the USB System
software and may be treated as no-operation requests by hubs.
PORT_POWER
This bit reflects the current logical power state of a port. This bit is implemented on all ports
whether or not actual port power switching devices are present.
While this bit is zero, the port is in the DSPORT.Powered-off state. Similarly, anything that causes
this port to go to the DSPORT.Powered-off state will cause this bit to be set to zero.
A SetPortFeature(PORT_POWER) will set this bit to one unless both C_HUB_LOCAL_POWER
and Local Power Status (in wHubStatus) are set to one in which case the request is treated as a
functional no-operation.
PORT_SPEED
This value in this field is only valid when the PORT_ENABLE bit is set to one. A value of zero in
this field indicates that the SuperSpeed device attached to this port is operating at 5 Gbps. All other
values in this field are reserved.
This field can only be read by USB system software.
10.14.2.6.2
Port Status Change Bits
Port status change bits are used to indicate changes in port status bits that are not the direct result of
requests. Port status change bits can be cleared with a ClearPortFeature() request or by a hub reset.
Hubs may allow setting of the status change bits with a SetPortFeature() request for diagnostic
purposes. If a hub does not support setting of the status change bits, it may either treat the request
as a Request Error or as a functional no-operation. Table 10-11 describes the various bits in the
wPortChange field.
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Hub, Host Downstream Port, and Device Upstream Port Specification
Table 10-11. Port Change Field, wPortChange
Bit
Description
0
Connect Status Change (C_PORT_CONNECTION): Indicates a change has occurred in the port’s Current
Connect Status. The hub device sets this field as described in Section 10.3.1.
Value
Meaning
0
No change has occurred to Current Connect status
1
Current Connect status has changed
1-2
Reserved
3
Over-Current Indicator Change (C_PORT_OVER_CURRENT): This field applies only to hubs that report overcurrent conditions on a per-port basis (as reported in the hub descriptor).
Value
Meaning
0
No change has occurred to Over-Current Indicator
1
Over-Current Indicator has changed
If the hub does not report over-current on a per-port basis, then this field is always zero.
4
5
6
7
8-15
Reset Change (C_PORT_RESET): This field is set when reset processing for any type of reset on this port is
complete.
Value
Meaning
0
No change
1
Reset complete
BH Reset Change (C_BH_PORT_RESET): This field is set when a warm reset processing on this port is
complete
Value
Meaning
0
No change
1
Reset complete
Port Link State Change (C_PORT_LINK_STATE): This field is set when the port link status has changed as
described below.
Value
Meaning
0
No change
1
Link Status has changed
Port Config Error (C_PORT_CONFIG_ERROR): This field is set when the port fails to configure its link partner.
Value
Meaning
0
Port Link Configuration was successful
1
Port Link Configuration was unsuccessful
Reserved
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Universal Serial Bus 3.0 Specification, Revision 1.0
C_PORT_CONNECTION
This bit is set to one when the PORT_CONNECTION bit changes because the hub port
downstream port successfully completed training and transitioned to the DSPORT.Enabled state.
This bit shall be set to zero by a ClearPortFeature(C_PORT_CONNECTION) request.
C_PORT_OVER_CURRENT
This bit is set to one when the PORT_OVER_CURRENT bit changes from zero to one or from one
to zero. This bit is also set if the port is placed in the DSPORT.Powered-off state due to an overcurrent condition on another port.
This bit shall be set to zero by a ClearPortFeature(C_PORT_OVER_CURRENT) request or while
logical port power is off and when the port is in the DSPORT.Powered-off state.
C_PORT_RESET
This bit is set to one when the port transitions from the DSPORT.Resetting state to the
DSPORT.Enabled state for any type of reset.
This bit shall be set to zero by a ClearPortFeature(C_PORT_RESET) request, or while logical port
power is off.
C_PORT_BH_RESET
This bit is set to one when the port transitions from the DSPORT.Resetting state to the
DSPORT.Enabled state for a Warm Reset only.
This bit shall be cleared by a ClearPortFeature(C_PORT_BH_RESET) request, or while logical
port power is off.
C_PORT_LINK_STATE
This bit is set to one when the port’s link completes a transition from the U3 state to the U0 state as
a result of a SetPortFeature(Port_Link_State) request or completes a transition from any of the
U-states to SS.Inactive. This bit is not set to one due to transitions from U3 to U0 as a result of
remote wakeup signaling received on a downstream facing port.
This bit will be cleared by a ClearPortFeature(C_PORT_LINK_STATE) request, or while logical
port power is off.
C_PORT_CONFIG_ERROR
This bit is set to one if the link connected to the port could not be successfully configured, e.g. if
two downstream only capable ports are connected to each other or if the link configuration could
not be completed. In addition, the port shall transition to the DSPORT.Disabled state when this
occurs.
This bit will be cleared by a ClearPortFeature(C_PORT_CONFIG_ERROR) request, or while
logical port power is off.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.14.2.7
Set Hub Descriptor
This request overwrites the hub descriptor.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00100000B
SET_DESCRIPTOR
Descriptor
Type and
Descriptor
Index
Zero
Descriptor
Length
Descriptor
The SetDescriptor request for the hub class descriptor follows the same usage model as that of the
standard SetDescriptor request (refer to the framework chapter). The standard hub descriptor is
denoted by using the value bDescriptorType defined in Section 10.13.2.1. All hubs are required to
implement one hub descriptor with descriptor index zero.
This request is optional. This request writes data to a class-specific descriptor. The host provides
the data that is to be transferred to the hub during the data transfer phase of the control transaction.
This request writes the entire hub descriptor at once.
Hubs shall buffer all the bytes received from this request to ensure that the entire descriptor has
been successfully transmitted from the host. Upon successful completion of the bus transfer, the
hub updates the contents of the specified descriptor.
It is a Request Error if wIndex is not zero or if wLength does not match the amount of data sent by
the host. Hubs that do not support this request respond with a STALL during the Data stage of the
request.
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.8
Set Hub Feature
This request sets a value reported in the hub status.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00100000B
SET_FEATURE
Feature
Selector
Zero
Zero
None
Setting a feature enables that feature; refer to Table 10-7 for the feature selector definitions that
apply to the hub as recipient. Status changes may not be acknowledged using this request.
It is a Request Error if wValue is not a feature selector listed in Table 10-7 or if wIndex or wLength
are not as specified above.
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.9
Set Hub Depth
This request sets the value that the hub uses to determine the index into the Route String Index for
the hub.
bmRequestType
bRequest
wValue
wIndex
wLength
Data
00100000B
SET_HUB_DEPTH
Hub Depth
Zero
Zero
None
wValue has the value of the Hub Depth. The Hub Depth left shifted by two is the offset into the
Route String that identifies the lsb of the Route String Port Field for the hub.
It is a Request Error if wValue is greater than 4 or if wIndex or wLength are not as specified above.
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Universal Serial Bus 3.0 Specification, Revision 1.0
If the hub is not configured, the hub's response to this request is undefined.
10.14.2.10
Set Port Feature
This request sets a value reported in the port status.
bmRequestType
bRequest
wValue
wIndex
00100011B
SET_ FEATURE
Feature
Selector
Selector or
Timeout
Value
Port
wLength
Data
Zero
None
or
Remote Wake
Mask
The port number shall be a valid port number for that hub, greater than zero. The port number is in
the least significant byte (bits 7..0) of the wIndex field. The most significant byte of wIndex is zero,
except when the feature selector is PORT_U1_TIMEOUT or PORT_U2_TIMEOUT or
PORT_LINK_STATE or PORT_REMOTE_WAKE_MASK.
Setting a feature enables that feature or starts a process associated with that feature; see Table 10-7
for the feature selector definitions that apply to a port as a recipient. Status change may not be
acknowledged using this request. Features that can be set with this request are:
• PORT_RESET
• BH_PORT_RESET
• PORT_POWER
• PORT_U1_TIMEOUT
• PORT_U2_TIMEOUT
• PORT_LINK_STATE
• PORT_REMOTE_WAKE_MASK
When the feature selector is PORT_U1_TIMEOUT, the most significant byte (bits 15..8) of the
wIndex field specifies the Timeout value for the U1 inactivity timer. Refer to Section 10.4.2.1 for a
detailed description of how the U1 inactivity timer value is used.
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Hub, Host Downstream Port, and Device Upstream Port Specification
The following are permissible values:
Table 10-12. U1 Timeout Value Encoding
Value
Description
00H
Zero (Default)
01H
1 µs
02H
2 µs
03H
3 µs
…
…
7FH
127 µs
80H-FEH
Reserved
FFH
Infinite
When the feature selector is PORT_U2_TIMEOUT, the most significant byte (bits 15..8) of the
wIndex field specifies the Timeout value for the U2 inactivity timer. The port’s link shall send an
LMP to its link partner with the specified timeout value after receiving a Set Port Feature request
with the PORT_U2_TIMEOUT feature selector. Refer to Section 10.4.2.1 for a detailed
description of how the U2 inactivity timer value is used.
The following are permissible values:
Table 10-13. U2 Timeout Value Encoding
Value
Description
00H
Zero (Default)
01H
256 µs
02H
512 µs
03H
768 µs
…
…
FEH
65.024 ms
FFH
Infinite
Note: Software shall not enable the U2 timeout for a downstream port that is connected to a hub.
Inconsistent link states could result if the timeout is enabled.
When the feature selector is PORT_LINK_STATE, the most significant byte (bits 15..8) of the
wIndex field specifies the U state the host software wants to put the link connected to the port into.
This request is only valid when the PORT_ENABLE bit is set and the PORT_LINK_STATE is not
set to SS.Disabled, Rx.Detect or SS.Inactive except as noted below:
• If the value is 0, then the hub shall transition the link to U0 from any of the U states.
• If the value is 1, then host software wants to transition the link to the U1 State. The hub shall
attempt to transition the link to U1 from U0. If the link is in any state other than U0 when a
request is received with a value of 1, the behavior is undefined.
• If the value is 2, then the host software wants to transition the link to the U2 State. The hub
shall attempt to transition the link to U2 from U0. If the link is in any state other than U0 when
a request is received with a value of 2, the behavior is undefined.
• If the value is 3, then host software wants to selectively suspend the device connected to this
port. The hub shall transition the link to U3 from any of the other U states using allowed link
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Universal Serial Bus 3.0 Specification, Revision 1.0
•
•
•
state transitions. If the port is not already in the U0 state, then it shall transition the port to the
U0 state and then initiate the transition to U3. While this state is active, the hub does not
propagate downstream-directed traffic to this port, but the hub will respond to resume signaling
from the port.
If the value is 4 (SS.Disabled), the hub shall transition the link to SS.Disabled. The request is
valid at all times when the value is 4. The downstream port shall transition to the
DSPORT.Disabled state after this request is received.
If the value is 5 (Rx.Detect), the hub shall transition the link to Rx.Detect. This request is only
valid when the downstream port is in the DSPORT.Disabled state. If the link is in any other
state when a request is received with this value, the behavior is undefined. The downstream
port shall transition to the DSPORT.Disconnected state after this request is received.
The hub shall respond with a Request Error if it sees any other value in the upper byte of the
wIndex field.
When the feature selector is PORT_REMOTE_WAKE_MASK, the most significant byte
(bits 15..8) of the wIndex field specifies the conditions that would cause the hub to signal a remote
wake event on its upstream port. The encoding for the port remote wake mask is given below:
Table 10-14. Downstream Port Remote Wake Mask Encoding
Bit
Description
0
Conn_RWEnable
1
2
3-7
10-76
Value
Meaning
0
The hub is disabled from signaling a remote wakeup due to a connect
event on this port; connect events that occur during suspend must still be
detected and reported after the resume process has completed (due to
some other event) as a C_PORT_CONNECTION port status change.
1
The hub is enabled to signal a remote wakeup due to a connect event on
the port.
Disconn_RWEnable
Value
Meaning
0
The hub is disabled from signaling a remote wakeup due to a disconnect
event on this port; disconnect events that occur during suspend must still
be detected and reported after the resume process has completed (due to
some other event) as a C_PORT_CONNECTION port status change.
1
The hub is enabled to signal a remote wakeup due to a disconnect event
on the port.
OC_RWEnable
Value
Meaning
0
The hub is disabled from signaling a remote wakeup due to an overcurrent event on this port; over-current events that occur during suspend
must still be detected and reported after the resume process has
completed (due to some other event) as a C_PORT_OVER_CURRENT
port status change. Note that a hub that does not support per-port over
current detection/reporting will signal remote-wakeup for an over-current
event unless all ports have OC-RWEnable set to 0.
1
The hub is enabled to signal a remote wakeup due to an over-current
event on the port.
These bits are reserved and must be set to zero.
Hub, Host Downstream Port, and Device Upstream Port Specification
Note that after power on or after the hub is reset, the remote wake mask is set to zero (i.e., the mask
is enabled).
The hub shall meet the following requirements:
• If the port is in the Powered-off state, the hub shall treat a SetPortFeature(PORT_RESET)
request as a functional no-operation.
• If the port is not in the Enabled state, the hub shall treat a
SetPortFeature(PORT_LINK_STATE) U3 request as a functional no-operation.
• If the port is not in the Powered-off state, the hub shall treat a SetPortFeature(PORT_POWER)
request as a functional no-operation.
• If the port is not in the Enabled state, the hub shall treat a
SetPortFeature(FORCE_LINKPM_ACCEPT) request as a functional no-operation.
When the feature selector is BH_PORT_RESET, the hub shall initiate a warm reset (refer to
Section 7.3) on the port that is identified by this command. The state of the port after this reset
shall be the same as the state after a SetPortFeature(PORT_RESET). On completion of a
BH_PORT_RESET, the hub shall set the C_BH_PORT_RESET field to one in the PortStatus for
this port.
It is a Request Error if wValue is not a feature selector listed in Table 10-7, if wIndex specifies a
port that does not exist, or if wLength is not as specified above.
If the hub is not configured, the hub's response to this request is undefined.
10.15 Host Root (Downstream) Ports
The root ports of a USB 3.0 host have similar functional requirements to the downstream ports of a
USB 3.0 hub. This section summarizes which requirements also apply to the root port of a host and
identifies any additional or different requirements.
A host root port shall follow the requirements for a downstream facing hub port in Section 10.2
except for Section 10.2.3.
A host root port shall follow the requirements for a downstream facing hub port in Section 10.3
with the following exceptions and additions:
• None of the transitions and/or transition conditions based on the state of the hub upstream port
apply to a root port.
• A host shall have control mechanisms in the host interface that allow software to achieve
equivalent behavior to hub downstream port behavior in response to SetPortFeature or
ClearPortFeature requests documented in Section 10.3.
• A host shall implement port status bits consistent with the downstream port state descriptions in
Section 10.3.
• A host is required to provide a mechanism to correlate each USB 2.0 port with any SuperSpeed
port that shares the same physical connector. Note that this is similar to the requirement for
USB 3.0 hubs in Section 10.3.3.
A host root port shall follow the requirements for a downstream facing hub port in Section 10.4
with the same general exceptions already noted in this section.
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Universal Serial Bus 3.0 Specification, Revision 1.0
A host shall implement port status bits through the host interface that are equivalent to all port
status bit definitions in this chapter.
A host shall have mechanisms to achieve equivalent control over its root ports as provided by the
SetPortFeature, ClearPortFeature, and GetPortStatus requests documented in this chapter.
10.16 Peripheral Device Upstream Ports
The upstream port of a peripheral device has similar functional requirements to the upstream port of
a USB 3.0 hub. This section summarizes which requirements also apply to the upstream port of a
peripheral device and identifies any additional or different requirements.
10.16.1
Peripheral Device Upstream Ports
A peripheral device shall follow the requirements for an upstream facing hub port in Section 10.5
with the following exceptions and additions:
• A peripheral device shall not attempt to connect on the USB 2.0 interface when the port is in
the USPORT.Connected state.
• A peripheral device shall not attempt to connect on the USB 2.0 interface unless the port has
entered the USPORT.Powered-off state and VBUS is still present as shown in Figure 10-11.
• If a device is connected on the USB 2.0 interface and it receives a USB 2.0 bus reset, the device
shall enter the USPORT.Powered-On state within tCheckSuperSpeedOnReset time.
• After a USB 2.0 reset, if the SuperSpeed port enters the USPORT.Training state, the device
shall disconnect on the USB 2.0 interface within tUSB2SwitchDisconnect time.
A device shall follow the requirements for an upstream facing hub port in Section 10.6 with the
following exceptions and additions:
• None of the conditions related to downstream port apply.
• A peripheral device initiates transitions to U1 or U2 when otherwise allowed based on vendor
specific algorithms.
10.16.2
Peripheral Device Connect State Machine
The following sections provide a functional description of a state machine that exhibits correct
peripheral device behavior for when to connect on SuperSpeed or USB 2.0. Figure 10-25 is an
illustration of the peripheral device connect state machine.
10-78
Hub, Host Downstream Port, and Device Upstream Port Specification
VBUS Not Valid
Rx.Detect or Link
Training Timed Out
Connected on
USB 2.0
pull-up applied
Not Connected
on SS Link
is SS.Disabled
Rx.Detect or Link
Training Timed Out
Powered-Off
VBUS Not Present
Link in SS.Disabled
VBUS Valid
(and device local
power is valid
if required)
Attempt SS Connect
Link in Rx.Detect
and/or Polling
USB 2.0 Reset
Received
Connected on
USB 2.0 and
Attempting
SS Connection
Link transitions from
Polling to U0
Link transitions from Polling to U0
USB 2.0 Connection Removed
Connected on SS
Link in U0 initially
Not Connected
on USB 2.0
Link in Rx.Detect
or Polling
Rx.Detect or Link
Training Timed Out
U-163
Figure 10-25. Peripheral Device Connect State Machine
10.16.2.1
PCONNECT.Powered-off
The PCONNECT.Powered-off state is the default state for a peripheral device. A peripheral device
shall transition into this state if any of the following situations occur:
• From any state when VBUS is removed.
In this state, the port's link shall be in the SS.Disabled state and the USB 2.0 pull-up is not applied.
10.16.2.2
PCONNECT.Attempt SS Connect
A port shall transition into this state if any of the following situations occur:
• From the PCONNECT.Powered-off state when VBUS becomes valid (and local power is valid
if required).
In this state, the SuperSpeed link is in Rx.Detect or Polling and the USB 2.0 pull-up is not applied.
10.16.2.3
PCONNECT.Connected on SS
A port shall transition into this state if any of the following situations occur:
• From the PCONNECT.Attempt SS Connect when the link transitions from polling to U0.
• From the PCONNECT.Connected on USB 2.0 state when the SS link transitions from polling
to U0.
In this state, the SuperSpeed link is in U0, U1, U2, U3, Inactive, Rx.Detect, Recovery, or Polling
and the USB 2.0 pull-up is not applied.
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Universal Serial Bus 3.0 Specification, Revision 1.0
10.16.2.4
PCONNECT.Connected on USB 2.0
A port shall transition into this state if any of the following situations occur:
• From the PCONNECT.Attempt SS Connect, PCONNECT.Connected on SS, or
PCONNECT.Connected on USB 2.0 Attempting SS states if any Rx.Detect or Polling substate
times out.
In this state, the SuperSpeed link is in SS.Disabled and the USB 2.0 pull-up is applied.
10.16.2.5
PCONNECT.Connected on USB 2.0 and Attempting SS Connection
A port shall transition into this state if any of the following situations occur:
• From the PCONNECT.Connected on USB 2.0 state when a USB 2.0 reset is received.
In this state, the SuperSpeed link is in Rx.Detect or Polling and the USB 2.0 pull-up is applied.
While in this state, a device shall remove USB 2.0 pull-up if the SuperSpeed link transitions from
polling to U0.
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Hub, Host Downstream Port, and Device Upstream Port Specification
10.17 Hub Chapter Parameters
Table 10-15 includes a complete list of the parameters used in the hub chapter.
Table 10-15. Hub Parameters
Name
Description
Min
Max
Units
tDownLinkStateChange
Time from receiving the route string of a header
packet directed to a downstream port that is in a
low power link state to initiating a return to U0 on
the downstream link.
The number of symbols in a data packet payload
after the DPPSTART ordered set without and
Data Packet Payload ending frame ordered set or
DPPABORT ordered set that shall cause a device
to detect the packet is invalid.
Time from start of remote wakeup signaling on the
downstream port a hub to when the hub must
propagate the remote wakeup signaling on its
upstream port if the upstream port link is in U3.
Time from receiving a
SetPortFeature(PORT_LINK_STATE) U0 for a
downstream port with a link in U3 to driving
remote wakeup signaling on the link.
Time from a downstream port’s link initiating a
U-state change to when a hub must initiate a
U-state change on the upstream port’s link (when
required).
Unit for reporting the current draw of hub
controller circuitry in the hub descriptor.
Maximum number of ports on a USB 3.0 hub.
If the downstream port link remains in
RxDetect.active for this length of time during a
warm reset, the reset is considered to have failed.
Time from when a device (not a hub) detects a
USB 2.0 bus reset to when the device port must
enter the USPORT.Powered-On state.
Time from when a device (not a hub) enters
USPORT.Training to when the device must
disconnect on the USB 2.0 interface if the device
is connected on USB 2.0.
Variation from the minimum time between when
the last symbol of a header packet routed to a
downstream port with a link in U0 is received on a
hub upstream port and when the first symbol of
the header packet is transmitted on the hub
downstream port.
ITP propagation shall meet
tPropagationDelayJitterLimit for all downstream
ports that transmit the ITP.
Average number of symbols between transmitted
SKP ordered sets.
0
100
ns
1030
N/A
symbols
0
1
ms
0
1000
ns
0
1
μs
4
mA
100
15
200
Ports
ms
0
1
ms
0
1
ms
-0
+8
ns
354
354
Symbols
sDataSymbolsBabble
tHubPropRemoteWakeUpstream
tHubDriveRemoteWakeDownstream
tHubPort2PortExitLat
aCurrentUnit
nMaxHubPorts
tTimeForResetError
tCheckSuperSpeedOnReset
tUSB2SwitchDisconnect
tPropagationDelayJitterLimit
nSkipSymbolLimit
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10-82
11
Interoperability and Power Delivery
This chapter defines interoperability and power delivery requirements for USB 3.0. Areas covered
include USB 3.0 host and device support for USB 2.0 operation, and USB 3.0 VBUS power
consumption limits.
Table 11-1 lists the compatibility matrix for USB 3.0 and USB 2.0. The implication of identifying
a host port as supporting USB 3.0 is that both hardware and software support for USB 3.0 is in
place; otherwise the port shall only be identified as a USB 2.0 port.
Table 11-1. USB 3.0 and USB 2.0 Interoperability
USB Host Port
USB 2.0
USB 3.0
USB Device Capability
Connected Mode
USB 2.0
USB 2.0 high-speed, full-speed, or low-speed
USB 3.0
USB 2.0 high-speed or full-speed
USB 2.0
USB 2.0 high-speed, full-speed, or low-speed
USB 3.0
USB 3.0 SuperSpeed
It should be noted that USB 3.0 devices are not required to be backward compatible with USB 1.1
host ports although supporting full-speed and low-speed modes are allowed.
11.1
USB 3.0 Host Support for USB 2.0
USB 3.0-capable ports on hosts shall also support USB 2.0 operation in order to enable backward
compatibility with USB 2.0 devices. It should be noted, however, that USB 3.0-capable hosts are
not required to support USB 3.0 operation on all of the ports available on the host, i.e., some
USB 3.0-capable hosts may have a mix of USB 2.0-only and USB 3.0-capable ports.
To address the situation where a USB 3.0 device is connected to a USB 2.0-only port on a USB 3.0capable host, after establishing a USB 2.0 high-speed connection with the device, it is
recommended that the host inform the user that the device will support SuperSpeed operation if it is
moved to a USB 3.0-capable port on the same host. If a USB 3.0 device is connected to a USB 3.0capable host via a USB 2.0 hub, it is recommended that the host inform the user that the device will
support SuperSpeed operation if it is moved to an appropriate host port or if the hub is replaced
with a USB 3.0 hub.
When a USB 3.0 hub is connected to a host’s USB 3.0-capable port, both USB 3.0 SuperSpeed and
USB 2.0 high-speed bus connections shall be allowed to connect and operate in parallel. There is
no requirement for a USB 3.0-capable host to support multiple parallel connections to peripheral
devices.
The USB 2.0 capabilities of a USB 3.0 host shall be designed to the USB 2.0 specification and shall
meet the USB 2.0 compliance requirements.
11-1
Universal Serial Bus 3.0 Specification, Revision 1.0
11.2
USB 3.0 Hub Support for USB 2.0
All ports, both upstream and downstream, on USB 3.0 hubs shall support USB 2.0 operation in
order to enable backward compatibility with USB 2.0 devices.
When another USB 3.0 hub is connected in series with a USB 3.0 hub, both SuperSpeed and
USB 2.0 high-speed bus connections shall be allowed to connect and operate in parallel. There is
no requirement for a USB 3.0 hub to support multiple parallel connections to peripheral devices.
Within a USB 3.0 hub, both the SuperSpeed and USB 2.0 hub devices shall implement in the hub
framework a common standardized ContainerID to enable software to identify the physical
relationship of the hub devices. The ContainerID descriptor is a part of the BOS descriptor set.
The USB 2.0 capabilities of a USB 3.0 hub shall be designed to the USB 2.0 specification and shall
meet the USB 2.0 compliance requirements.
11.3
USB 3.0 Device Support for USB 2.0
In most cases, backward compatible operation at USB 2.0 signaling is supported by USB 3.0
devices in order that higher capability devices are still useful with lesser capable hosts and hubs.
For product installations where support for USB 3.0 operation can be independently assured
between the device and the host, such as internal devices that are not user accessible, device support
for USB 2.0 may not be necessary. USB 3.0 device certification requirements require support for
USB 2.0 for all user attached devices.
For any given USB 3.0 peripheral device within a single physical package, only one USB
connection mode, either SuperSpeed or a USB 2.0 speed but not both, shall be established for
operation with the host.
Peripheral devices may implement in the device framework a common standardized ContainerID to
enable software to identify all of the functional components of a specific device and independent of
which speed bus it appears on. All devices within a compound device that support ContainerID
shall return the same ContainerID.
The USB 2.0 capabilities of a USB 3.0 device shall be designed to the USB 2.0 specification and
shall meet the USB 2.0 compliance requirements.
11.4
Power Distribution
This section describes the USB 3.0 power distribution specification. Note that the USB 2.0 power
distribution requirements still apply when a USB 3.0 device is operating at high-speed, full-speed,
or low-speed.
11-2
Interoperability and Power Delivery
11.4.1
Classes of Devices and Connections
USB 3.0 provides power over two connectors: the Standard-A connector and the Powered-B
connector. The following sections focus on the power delivery requirements for the Standard-A
connector.
The power source and sink requirements of different device classes can be simplified with the
introduction of the concept of a unit load. A unit load for SuperSpeed has been redefined to be
150 mA. The number of unit loads a device can draw is an absolute maximum, not an average over
time. A device may be either low-power at one unit load or high-power, consuming up to six unit
loads. All devices default to low-power when first powered. The transition to high-power is under
software control. It is the responsibility of software to ensure adequate power is available before
allowing devices to consume high-power.
The USB supports a range of power sourcing and power consuming agents; these include the
following:
• Root port hubs: Are directly attached to the USB Host Controller. Hub power is derived
from the same source as the Host Controller. Systems that obtain operating power externally,
either AC or DC, must be capable of supplying at least six unit loads to each port. Such ports
are called high-power ports. Battery-powered systems may supply either one or six unit loads.
Ports that can supply only one unit load are termed low-power ports.
• Self-powered hubs: Power for the internal functions and downstream facing ports does not
come from VBUS. However, the USB interface of the hub may draw up to one unit load from
VBUS on its upstream facing port to allow the interface to function when the remainder of the
hub is powered down. Hubs that obtain operating power externally (not from VBUS) must
supply six unit loads to each port.
• Low-power bus-powered devices: All power to these devices comes from VBUS. They may
draw no more than one unit load at any time.
• High-power bus-powered devices: All power to these devices comes from VBUS. They must
draw no more than one unit load upon power-up and may draw up to six unit loads after being
configured.
• Ports may support the USB Charging Specification.
• Self-powered devices: May draw up to one unit load from VBUS to allow the USB interface to
function when the remainder of the function is powered down. All other power comes from an
external (not from VBUS) source.
No device shall supply (source) current on VBUS at its upstream facing port at any time. From
VBUS on its upstream facing port, a device may only draw (sink) current. Devices must also ensure
that the maximum operating current drawn by a device is one unit load until configured.
11-3
Universal Serial Bus 3.0 Specification, Revision 1.0
11.4.1.1
Self-powered Hubs
Self-powered hubs have a local power supply that furnishes power to any non-removable functions
and to all downstream facing ports, as shown in Figure 11-1. Power for the Hub Controller,
however, may be supplied from the upstream VBUS (a “hybrid” powered hub) or the local power
supply. The advantage of supplying the Hub Controller from the upstream supply is that
communication from the host is possible even if the device’s power supply remains off. This
makes it possible to differentiate between a disconnected and an unpowered device. If the hub
draws power for its upstream facing port from VBUS, it may not draw more than one unit load.
Upstream VBUS
1 unit load (max)
Regulator
Downstream
Data Ports
Hub Controller
Upstream
Data Port
Local Power
Supply
Regulator
Non-removable
Function
On/Off
Current Limit
6 unit loads/port
Downstream VBUS
Current Limit
U-059
Figure 11-1. Compound Self-powered Hub
The maximum number of ports that can be supported is limited by the capability of the local VBUS
supply.
11.4.1.1.1
Over-current Protection
The host and all self-powered hubs must implement over-current protection for safety reasons, and
the hub must have a way to detect the over-current condition and report it to the USB software.
Should the aggregate current drawn by a gang of downstream facing ports exceed a preset value,
the over-current protection circuit removes or reduces power from all affected downstream facing
ports. The over-current condition is reported through the hub to the Host Controller, as described in
Section 10.14.2. The preset value cannot exceed 5.0 A and must be sufficiently higher than the
maximum allowable port current or time delayed such that transient currents (e.g., during power up
or dynamic attach or reconfiguration) do not trip the over-current protector. If an over-current
condition occurs on any port, subsequent operation of the USB is not guaranteed, and once the
condition is removed, it may be necessary to reinitialize the bus as would be done upon power-up.
The over-current limiting mechanism must be resettable without user mechanical intervention.
11-4
Interoperability and Power Delivery
Polymeric PTCs and solid-state switches are examples of methods that can be used for over-current
limiting.
11.4.1.2
Low-power Bus-powered Devices
A low-power device is one that draws up to one unit load from the USB cable when operational.
Figure 11-2 shows a typical bus-powered, low-power device, such as a mouse. Low-power
regulation can be integrated into the device silicon. Low-power devices must be capable of
operating with input VBUS voltages as low as 4.00 V, measured at the plug end of the cable.
Upstream
Data Port
Function
Upstream VBUS
1 unit load (max)
Regulator
U-060
Figure 11-2. Low-power Bus-powered Function
11.4.1.3
High-power Bus-powered Devices
A device is defined as being high-power if, when fully powered, it draws over one but no more than
six unit loads from the USB cable. A high-power device requires staged switching of power. It
must first come up in a reduced power state of less than one unit load. At bus enumeration time, its
total power requirements are obtained and compared against the available power budget. If
sufficient power exists, the remainder of the device may be powered on. High-power devices shall
be capable of operating with an input voltage as low as 4.00 V. They must also be capable of
operating at full power (up to six unit loads) with an input voltage of 4.00 V measured at the device
side of the B-series receptacle.
A typical high-power device is shown in Figure 11-3. The device’s electronics have been
partitioned into two sections. The device controller contains the minimum amount of circuitry
necessary to permit enumeration and power budgeting. The remainder of the device resides in the
function block.
Upstream
Data Port
Function
Controller
Function
On/Off
1 unit load
(max)
Upstream VBUS
6 unit loads (max)
Regulator
U-061
Figure 11-3. High-power Bus-powered Function
11-5
Universal Serial Bus 3.0 Specification, Revision 1.0
11.4.1.4
Self-powered Devices
Figure 11-4 shows a typical self-powered device. The device controller is powered either from the
upstream bus via a low-power regulator or from the local power supply. The advantage of the
former scheme is that it permits detection and enumeration of a self-powered device whose local
power supply is turned off. The maximum upstream power that the device controller can draw is
one unit load, and the regulator block must implement inrush current limiting. The amount of
power that the device block may draw is limited only by the local power supply. Because the local
power supply is not required to power any downstream bus ports, it does not need to implement
current limiting, soft start, or power switching.
Upstream
Data Port
Function
Controller
Upstream VBUS
1 unit load (max)
Regulator
Local Power
Supply
Function
Regulator
U-062
Figure 11-4. Self-powered Function
11.4.2
Steady-State Voltage Drop Budget
The steady–state voltage drop budget is derived from the following assumptions:
• The nominal 5 V ± 5% source (host or hub) is 4.75 V to 5.25 V.
• The voltage supplied at the connector of hub or root ports shall be between 4.45 V to 5.25 V.
• The maximum voltage drop (for detachable cables) between the A-series plug and B-series plug
on VBUS is 171 mV.
• The maximum current for the calculations is 0.9 A.
• The maximum voltage drop for all cables between upstream and downstream on GND is
171 mV.
• The maximum voltage drop for all mated connectors is 27 mV.
• All hubs and peripheral devices shall be able to provide configuration information with as little
as 4.00 V at the device end of their B-series receptacle. Both low and high-power devices need
to be operational with this minimum voltage.
Figure 11-5 shows the minimum allowable voltages. Note that under transient conditions, the
supply at the device can drop to 3.67 V for a brief moment.
11-6
Interoperability and Power Delivery
Function
Host or Powered Hub
4.450 V
4.423 V
4.225 V
4.252 V
4.000 V
0.027 V
0.000 V
0.198 V
0.225 V
U-063
Figure 11-5. Worst-case Voltage Drop Topology (Steady State)
Note: the following assumptions were used in Figure 11-5:
• 3 meter cable assembly with A-series and B-series plugs
• #22AWG wire used for power and ground (0.019 Ω/foot)
• A-series and B-series plug/receptacle pair have a contact resistance of 30 mΩ
• Wire ~380 mΩ series resistance
• IR Drop at device = (((2 * 30 mΩ) + 190 mΩ) * 900 mA) * 2 or 0.450 V
Host
Device
RT
RC
RW
RC
RT
RC
RW
RC
+5 V
Power
Supply
Gnd
U-064
Figure 11-6. Worst-case Voltage Drop Analysis Using Equivalent Resistance
Rt
Host Trace Resistance:
0.167 Ω
Rc
Mated Connector Resistance:
0.030 Ω
Rw
Cable Resistance:
0.190 Ω
11-7
Universal Serial Bus 3.0 Specification, Revision 1.0
11.4.3
Power Control During Suspend/Resume
All USB devices may draw up to 2.5 mA during suspend. When configured, bus-powered
compound devices may consume a suspend current of up to 12.5 mA. This 12.5 mA budget
includes 2.5 mA suspend current for the internal hub plus 2.5 mA suspend current for each port on
that internal hub having attached internal functions, up to a maximum of four ports. When
computing suspend current, the current from VBUS through the bus pull-up and pull-down resistors
must be included.
While in the Suspend state, a device may briefly draw more than the average current. The
amplitude of the current spike cannot exceed the device power allocation 150 mA (or 900 mA). A
maximum of 1.0 second is allowed for an averaging interval. The average current cannot exceed
the average suspend current limit (ICCS, see Table 11-2) during any 1.0-second interval. The profile
of the current spike is restricted so the transient response of the power supply (which may be an
efficient, low-capacity, trickle power supply) is not overwhelmed. The rising edge of the current
spike must be no more than 100 mA/μs. Downstream facing ports must be able to absorb the 900
mA peak current spike and meet the voltage droop requirements defined for inrush current during
dynamic attach. Figure 11-7 illustrates a typical example profile for an averaging interval.
ICONFIGURED(max)
Edge rate must
not exceed
100 mA/µs
Current
Spike
ICCS
Averaging Interval
I, current
0 mA
Time
U-065
Figure 11-7. Typical Suspend Current Averaging Profile
Devices are responsible for handling the bus voltage reduction due to the inductive and resistive
effects of the cable. When a hub is in the Suspend state, it must still be able to provide the
maximum current per port (six unit loads per port for self-powered hubs). This is necessary to
support remote wakeup-capable devices that will power-up while the remainder of the system is
still suspended. Such devices, when enabled to do remote wakeup, must drive resume signaling
upstream within 10 ms of starting to draw the higher, non-suspend current. Devices not capable of
remote wakeup must not draw the higher current when suspended.
When devices wakeup, either by themselves (remote wakeup) or by seeing resume signaling, they
must limit the inrush current on VBUS. The device must have sufficient on-board bypass
capacitance or a controlled power-on sequence such that the current drawn from the hub does not
exceed the maximum current capability of the port at any time while the device is waking up.
11-8
Interoperability and Power Delivery
11.4.4
Dynamic Attach and Detach
The act of plugging or unplugging a hub or peripheral device must not affect the functionality of
another device on other segments of the network. Unplugging a device will stop any transactions in
progress between that device and the host. However, the hub or root port to which this device was
attached will recover from this condition and will alert the host that the port has been disconnected.
11.4.4.1
Inrush Current Limiting
When a peripheral device or hub is plugged into the network, it has a certain amount of on-board
capacitance between VBUS and ground. In addition, the regulator on the device may supply current
to its output bypass capacitance and to the device as soon as power is applied. Consequently, if no
measures are taken to prevent it, there could be a surge of current into the device which might pull
the VBUS on the hub below its minimum operating level. Inrush currents can also occur when a
high-power device is switched into its high-power mode. This problem must be solved by limiting
the inrush current and by providing sufficient capacitance in each hub to prevent the power
supplied to the other ports from going out of tolerance. An additional motivation for limiting
inrush current is to minimize contact arcing, thereby prolonging connector contact life.
The maximum droop possible in the hub VBUS is 330 mV. In order to meet this requirement, the
following conditions must be met:
• The maximum load (CRPB) that can be placed at the downstream end of a cable is 10 μF in
parallel with as small as a 27 Ω resistance. The 10 μF capacitance represents any bypass
capacitor directly connected across the VBUS lines in the device plus any capacitive effects
visible through the regulator in the device. The 27 Ω resistance represents one unit load of
current drawn by the device during connect.
• If more bypass capacitance is required in the device, then the device must incorporate some
form of VBUS surge current limiting, such that it matches the characteristics of the above load.
• The hub downstream facing port VBUS power lines must be bypassed (CHPB) with no less than
120 μF of low-ESR capacitance per hub. Standard bypass methods should be used to minimize
inductance and resistance between the bypass capacitors and the connectors to reduce droop.
The bypass capacitors themselves should have a low dissipation factor to allow decoupling at
higher frequencies.
The upstream facing port of a hub is also required to meet the above requirements.
A high-power bus-powered device that is switching from a lower power configuration to a higher
power configuration must not cause droop > 330 mV on the VBUS at its upstream hub. The device
can meet this by ensuring that changes in the capacitive load it presents do not exceed 10 μF.
11-9
Universal Serial Bus 3.0 Specification, Revision 1.0
11.4.4.2
Dynamic Detach
When a device is detached from the network with power flowing in the cable, the inductance of the
cable will cause a large flyback voltage to occur on the open end of the device cable. This flyback
voltage is not destructive. Proper bypass measures on the hub ports will suppress any coupled
noise. This will require some low capacitance, very low inductance bypass capacitors on each hub
port connector. The flyback voltage and the noise it creates are also moderated by the bypass
capacitance on the device end of the cable. Also, there must be some minimum capacitance on the
device end of the cable to ensure that the inductive flyback on the open end of the cable does not
cause the voltage on the device end to reverse polarity. A minimum of 1.0 μF is recommended for
bypass across VBUS.
11.4.5
VBUS Electrical Characteristics
Table 11-2. DC Electrical Characteristics
Parameter
Symbol
Conditions
Min.
Max.
Units
5.25
V
Supply Voltage:
Port (downstream connector)
VBUS
4.45
Port (upstream connector)
VBUS
4.0
V
High-power Hub Port (out)
ICCPRT
900
mA
Low-power Hub Port (out)
ICCUPT
150
mA
High-power Peripheral Device (in)
ICCHPF
900
mA
Low-power Peripheral Device (in)
ICCLPF
150
mA
Unconfigured Device (in)
ICCINIT
150
mA
ICCS
2.5
mA
Supply Current:
Suspended High-power Device
11.4.6
Powered-B Connector
The Powered-B connector was defined to allow devices such as printers to connect to and power
devices such as Wireless USB adapters. This improves usability by eliminating the need for an
external power supply (e.g., “wall-wart”) to power the adapter.
The Powered-B receptacle shall meet the following electrical requirements:
• The Powered-B receptacle shall supply 5 V ± 10% over the entire load range (0-1 A).
• The Powered-B receptacle shall be capable of supplying 1 A.
• The Powered-B receptacle shall implement over-current protection for safety reasons.
• The Powered-B receptacle shall deliver full power whenever the device is turned on or in
standby.
• A device that exposes a Powered-B receptacle shall operate as a low-power device.
• A device that is powered (in whole or in part) by a Powered-B receptacle shall not expose any
Standard-A ports
11-10
Interoperability and Power Delivery
Note: Power distribution defined in this chapter applies to the devices with the Powered-B
connector. The cable assembly has to deliver VBUS to the device’s USB interface via the VPWR
and GND pins of the Powered-B connector.
11.4.7
Wire Gauge Table
Table 11-3 is a table of VBUS/Gnd wire gauges showing the relationship between gauge and
maximum length in order to achieve the previously cited voltage drop values. The user should note
that these lengths are the maximum length possible to meet the voltage drop budget, thus gauges
smaller and lengths greater than the table values will fail to deliver the expected voltage value.
Table 11-3. VBUS/Gnd Wire Gauge vs. Maximum Length
American Stranded Wire Gauge
(AWG) on VBUS/Gnd
Ohms Per 100 Meters
(Maximum)
Maximum Cable Length
(Meters)
28
23.20
0.8
26
14.60
1.3
24
9.09
2.0
22
5.74
3.0
20
3.58
5.3
11-11
Universal Serial Bus 3.0 Specification, Revision 1.0
11-12
A
Symbol Encoding
Table A-1 shows the byte-to-Symbol encodings for data characters. Table A-2 shows the Symbol
encodings for the Special Symbols. RD- and RD+ refer to the Running Disparity of the Symbol
sequence on a per-Lane basis.
Table A-1. 8b/10b Data Symbol Codes
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D0.0
00
000 00000
100111 0100
011000 1011
D1.0
01
000 00001
011101 0100
100010 1011
D2.0
02
000 00010
101101 0100
010010 1011
D3.0
03
000 00011
110001 1011
110001 0100
D4.0
04
000 00100
110101 0100
001010 1011
D5.0
05
000 00101
101001 1011
101001 0100
D6.0
06
000 00110
011001 1011
011001 0100
D7.0
07
000 00111
111000 1011
000111 0100
D8.0
08
000 01000
111001 0100
000110 1011
D9.0
09
000 01001
100101 1011
100101 0100
D10.0
0A
000 01010
010101 1011
010101 0100
D11.0
0B
000 01011
110100 1011
110100 0100
D12.0
0C
000 01100
001101 1011
001101 0100
D13.0
0D
000 01101
101100 1011
101100 0100
D14.0
0E
000 01110
011100 1011
011100 0100
D15.0
0F
000 01111
010111 0100
101000 1011
D16.0
10
000 10000
011011 0100
100100 1011
D17.0
11
000 10001
100011 1011
100011 0100
D18.0
12
000 10010
010011 1011
010011 0100
D19.0
13
000 10011
110010 1011
110010 0100
D20.0
14
000 10100
001011 1011
001011 0100
D21.0
15
000 10101
101010 1011
101010 0100
D22.0
16
000 10110
011010 1011
011010 0100
D23.0
17
000 10111
111010 0100
000101 1011
D24.0
18
000 11000
110011 0100
001100 1011
D25.0
19
000 11001
100110 1011
100110 0100
D26.0
1A
000 11010
010110 1011
010110 0100
D27.0
1B
000 11011
110110 0100
001001 1011
D28.0
1C
000 11100
001110 1011
001110 0100
D29.0
1D
000 11101
101110 0100
010001 1011
D30.0
1E
000 11110
011110 0100
100001 1011
D31.0
1F
000 11111
101011 0100
010100 1011
A-1
Universal Serial Bus 3.0 Specification, Revision 1.0
A-2
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D0.1
20
001 00000
100111 1001
011000 1001
D1.1
21
001 00001
011101 1001
100010 1001
D2.1
22
001 00010
101101 1001
010010 1001
D3.1
23
001 00011
110001 1001
110001 1001
D4.1
24
001 00100
110101 1001
001010 1001
D5.1
25
001 00101
101001 1001
101001 1001
D6.1
26
001 00110
011001 1001
011001 1001
D7.1
27
001 00111
111000 1001
000111 1001
D8.1
28
001 01000
111001 1001
000110 1001
D9.1
29
001 01001
100101 1001
100101 1001
D10.1
2A
001 01010
010101 1001
010101 1001
D11.1
2B
001 01011
110100 1001
110100 1001
D12.1
2C
001 01100
001101 1001
001101 1001
D13.1
2D
001 01101
101100 1001
101100 1001
D14.1
2E
001 01110
011100 1001
011100 1001
D15.1
2F
001 01111
010111 1001
101000 1001
D16.1
30
001 10000
011011 1001
100100 1001
D17.1
31
001 10001
100011 1001
100011 1001
D18.1
32
001 10010
010011 1001
010011 1001
D19.1
33
001 10011
110010 1001
110010 1001
D20.1
34
001 10100
001011 1001
001011 1001
D21.1
35
001 10101
101010 1001
101010 1001
D22.1
36
001 10110
011010 1001
011010 1001
D23.1
37
001 10111
111010 1001
000101 1001
D24.1
38
001 11000
110011 1001
001100 1001
D25.1
39
001 11001
100110 1001
100110 1001
D26.1
3A
001 11010
010110 1001
010110 1001
D27.1
3B
001 11011
110110 1001
001001 1001
D28.1
3C
001 11100
001110 1001
001110 1001
D29.1
3D
001 11101
101110 1001
010001 1001
D30.1
3E
001 11110
011110 1001
100001 1001
D31.1
3F
001 11111
101011 1001
010100 1001
D0.2
40
010 00000
100111 0101
011000 0101
D1.2
41
010 00001
011101 0101
100010 0101
D2.2
42
010 00010
101101 0101
010010 0101
D3.2
43
010 00011
110001 0101
110001 0101
D4.2
44
010 00100
110101 0101
001010 0101
D5.2
45
010 00101
101001 0101
101001 0101
D6.2
46
010 00110
011001 0101
011001 0101
D7.2
47
010 00111
111000 0101
000111 0101
Symbol Encoding
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D8.2
48
010 01000
111001 0101
000110 0101
D9.2
49
010 01001
100101 0101
100101 0101
D10.2
4A
010 01010
010101 0101
010101 0101
D11.2
4B
010 01011
110100 0101
110100 0101
D12.2
4C
010 01100
001101 0101
001101 0101
D13.2
4D
010 01101
101100 0101
101100 0101
D14.2
4E
010 01110
011100 0101
011100 0101
D15.2
4F
010 01111
010111 0101
101000 0101
D16.2
50
010 10000
011011 0101
100100 0101
D17.2
51
010 10001
100011 0101
100011 0101
D18.2
52
010 10010
010011 0101
010011 0101
D19.2
53
010 10011
110010 0101
110010 0101
D20.2
54
010 10100
001011 0101
001011 0101
D21.2
55
010 10101
101010 0101
101010 0101
D22.2
56
010 10110
011010 0101
011010 0101
D23.2
57
010 10111
111010 0101
000101 0101
D24.2
58
010 11000
110011 0101
001100 0101
D25.2
59
010 11001
100110 0101
100110 0101
D26.2
5A
010 11010
010110 0101
010110 0101
D27.2
5B
010 11011
110110 0101
001001 0101
D28.2
5C
010 11100
001110 0101
001110 0101
D29.2
5D
010 11101
101110 0101
010001 0101
D30.2
5E
010 11110
011110 0101
100001 0101
D31.2
5F
010 11111
101011 0101
010100 0101
D0.3
60
011 00000
100111 0011
011000 1100
D1.3
61
011 00001
011101 0011
100010 1100
D2.3
62
011 00010
101101 0011
010010 1100
D3.3
63
011 00011
110001 1100
110001 0011
D4.3
64
011 00100
110101 0011
001010 1100
D5.3
65
011 00101
101001 1100
101001 0011
D6.3
66
011 00110
011001 1100
011001 0011
D7.3
67
011 00111
111000 1100
000111 0011
D8.3
68
011 01000
111001 0011
000110 1100
D9.3
69
011 01001
100101 1100
100101 0011
D10.3
6A
011 01010
010101 1100
010101 0011
D11.3
6B
011 01011
110100 1100
110100 0011
D12.3
6C
011 01100
001101 1100
001101 0011
D13.3
6D
011 01101
101100 1100
101100 0011
D14.3
6E
011 01110
011100 1100
011100 0011
D15.3
6F
011 01111
010111 0011
101000 1100
A-3
Universal Serial Bus 3.0 Specification, Revision 1.0
A-4
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D16.3
70
011 10000
011011 0011
100100 1100
D17.3
71
011 10001
100011 1100
100011 0011
D18.3
72
011 10010
010011 1100
010011 0011
D19.3
73
011 10011
110010 1100
110010 0011
D20.3
74
011 10100
001011 1100
001011 0011
D21.3
75
011 10101
101010 1100
101010 0011
D22.3
76
011 10110
011010 1100
011010 0011
D23.3
77
011 10111
111010 0011
000101 1100
D24.3
78
011 11000
110011 0011
001100 1100
D25.3
79
011 11001
100110 1100
100110 0011
D26.3
7A
011 11010
010110 1100
010110 0011
D27.3
7B
011 11011
110110 0011
001001 1100
D28.3
7C
011 11100
001110 1100
001110 0011
D29.3
7D
011 11101
101110 0011
010001 1100
D30.3
7E
011 11110
011110 0011
100001 1100
D31.3
7F
011 11111
101011 0011
010100 1100
D0.4
80
100 00000
100111 0010
011000 1101
D1.4
81
100 00001
011101 0010
100010 1101
D2.4
82
100 00010
101101 0010
010010 1101
D3.4
83
100 00011
110001 1101
110001 0010
D4.4
84
100 00100
110101 0010
001010 1101
D5.4
85
100 00101
101001 1101
101001 0010
D6.4
86
100 00110
011001 1101
011001 0010
D7.4
87
100 00111
111000 1101
000111 0010
D8.4
88
100 01000
111001 0010
000110 1101
D9.4
89
100 01001
100101 1101
100101 0010
D10.4
8A
100 01010
010101 1101
010101 0010
D11.4
8B
100 01011
110100 1101
110100 0010
D12.4
8C
100 01100
001101 1101
001101 0010
D13.4
8D
100 01101
101100 1101
101100 0010
D14.4
8E
100 01110
011100 1101
011100 0010
D15.4
8F
100 01111
010111 0010
101000 1101
D16.4
90
100 10000
011011 0010
100100 1101
D17.4
91
100 10001
100011 1101
100011 0010
D18.4
92
100 10010
010011 1101
010011 0010
D19.4
93
100 10011
110010 1101
110010 0010
D20.4
94
100 10100
001011 1101
001011 0010
D21.4
95
100 10101
101010 1101
101010 0010
D22.4
96
100 10110
011010 1101
011010 0010
D23.4
97
100 10111
111010 0010
000101 1101
Symbol Encoding
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D24.4
98
100 11000
110011 0010
001100 1101
D25.4
99
100 11001
100110 1101
100110 0010
D26.4
9A
100 11010
010110 1101
010110 0010
D27.4
9B
100 11011
110110 0010
001001 1101
D28.4
9C
100 11100
001110 1101
001110 0010
D29.4
9D
100 11101
101110 0010
010001 1101
D30.4
9E
100 11110
011110 0010
100001 1101
D31.4
9F
100 11111
101011 0010
010100 1101
D0.5
A0
101 00000
100111 1010
011000 1010
D1.5
A1
101 00001
011101 1010
100010 1010
D2.5
A2
101 00010
101101 1010
010010 1010
D3.5
A3
101 00011
110001 1010
110001 1010
D4.5
A4
101 00100
110101 1010
001010 1010
D5.5
A5
101 00101
101001 1010
101001 1010
D6.5
A6
101 00110
011001 1010
011001 1010
D7.5
A7
101 00111
111000 1010
000111 1010
D8.5
A8
101 01000
111001 1010
000110 1010
D9.5
A9
101 01001
100101 1010
100101 1010
D10.5
AA
101 01010
010101 1010
010101 1010
D11.5
AB
101 01011
110100 1010
110100 1010
D12.5
AC
101 01100
001101 1010
001101 1010
D13.5
AD
101 01101
101100 1010
101100 1010
D14.5
AE
101 01110
011100 1010
011100 1010
D15.5
AF
101 01111
010111 1010
101000 1010
D16.5
B0
101 10000
011011 1010
100100 1010
D17.5
B1
101 10001
100011 1010
100011 1010
D18.5
B2
101 10010
010011 1010
010011 1010
D19.5
B3
101 10011
110010 1010
110010 1010
D20.5
B4
101 10100
001011 1010
001011 1010
D21.5
B5
101 10101
101010 1010
101010 1010
D22.5
B6
101 10110
011010 1010
011010 1010
D23.5
B7
101 10111
111010 1010
000101 1010
D24.5
B8
101 11000
110011 1010
001100 1010
D25.5
B9
101 11001
100110 1010
100110 1010
D26.5
BA
101 11010
010110 1010
010110 1010
D27.5
BB
101 11011
110110 1010
001001 1010
D28.5
BC
101 11100
001110 1010
001110 1010
D29.5
BD
101 11101
101110 1010
010001 1010
D30.5
BE
101 11110
011110 1010
100001 1010
D31.5
BF
101 11111
101011 1010
010100 1010
A-5
Universal Serial Bus 3.0 Specification, Revision 1.0
A-6
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D0.6
C0
110 00000
100111 0110
011000 0110
D1.6
C1
110 00001
011101 0110
100010 0110
D2.6
C2
110 00010
101101 0110
010010 0110
D3.6
C3
110 00011
110001 0110
110001 0110
D4.6
C4
110 00100
110101 0110
001010 0110
D5.6
C5
110 00101
101001 0110
101001 0110
D6.6
C6
110 00110
011001 0110
011001 0110
D7.6
C7
110 00111
111000 0110
000111 0110
D8.6
C8
110 01000
111001 0110
000110 0110
D9.6
C9
110 01001
100101 0110
100101 0110
D10.6
CA
110 01010
010101 0110
010101 0110
D11.6
CB
110 01011
110100 0110
110100 0110
D12.6
CC
110 01100
001101 0110
001101 0110
D13.6
CD
110 01101
101100 0110
101100 0110
D14.6
CE
110 01110
011100 0110
011100 0110
D15.6
CF
110 01111
010111 0110
101000 0110
D16.6
D0
110 10000
011011 0110
100100 0110
D17.6
D1
110 10001
100011 0110
100011 0110
D18.6
D2
110 10010
010011 0110
010011 0110
D19.6
D3
110 10011
110010 0110
110010 0110
D20.6
D4
110 10100
001011 0110
001011 0110
D21.6
D5
110 10101
101010 0110
101010 0110
D22.6
D6
110 10110
011010 0110
011010 0110
D23.6
D7
110 10111
111010 0110
000101 0110
D24.6
D8
110 11000
110011 0110
001100 0110
D25.6
D9
110 11001
100110 0110
100110 0110
D26.6
DA
110 11010
010110 0110
010110 0110
D27.6
DB
110 11011
110110 0110
001001 0110
D28.6
DC
110 11100
001110 0110
001110 0110
D29.6
DD
110 11101
101110 0110
010001 0110
D30.6
DE
110 11110
011110 0110
100001 0110
D31.6
DF
110 11111
101011 0110
010100 0110
D0.7
E0
111 00000
100111 0001
011000 1110
D1.7
E1
111 00001
011101 0001
100010 1110
D2.7
E2
111 00010
101101 0001
010010 1110
D3.7
E3
111 00011
110001 1110
110001 0001
D4.7
E4
111 00100
110101 0001
001010 1110
D5.7
E5
111 00101
101001 1110
101001 0001
D6.7
E6
111 00110
011001 1110
011001 0001
D7.7
E7
111 00111
111000 1110
000111 0001
Symbol Encoding
Data Byte
Name
Data Byte Value
(hex)
Bits HGF EDCBA
(binary)
Current RD- abcdei
fghj(binary)
Current RD+ abcdei
fghj (binary)
D8.7
E8
111 01000
111001 0001
000110 1110
D9.7
E9
111 01001
100101 1110
100101 0001
D10.7
EA
111 01010
010101 1110
010101 0001
D11.7
EB
111 01011
110100 1110
110100 1000
D12.7
EC
111 01100
001101 1110
001101 0001
D13.7
ED
111 01101
101100 1110
101100 1000
D14.7
EE
111 01110
011100 1110
011100 1000
D15.7
EF
111 01111
010111 0001
101000 1110
D16.7
F0
111 10000
011011 0001
100100 1110
D17.7
F1
111 10001
100011 0111
100011 0001
D18.7
F2
111 10010
010011 0111
010011 0001
D19.7
F3
111 10011
110010 1110
110010 0001
D20.7
F4
111 10100
001011 0111
001011 0001
D21.7
F5
111 10101
101010 1110
101010 0001
D22.7
F6
111 10110
011010 1110
011010 0001
D23.7
F7
111 10111
111010 0001
000101 1110
D24.7
F8
111 11000
110011 0001
001100 1110
D25.7
F9
111 11001
100110 1110
100110 0001
D26.7
FA
111 11010
010110 1110
010110 0001
D27.7
FB
111 11011
110110 0001
001001 1110
D28.7
FC
111 11100
001110 1110
001110 0001
D29.7
FD
111 11101
101110 0001
010001 1110
D30.7
FE
111 11110
011110 0001
100001 1110
D31.7
FF
111 11111
101011 0001
010100 1110
A-7
Universal Serial Bus 3.0 Specification, Revision 1.0
Table A-2.
8b/10b Special Character Symbol Codes
Data Byte
Name
Data Byte Value
Bits HGF EDCBA
Current RD - abcdei
fghj
Current RD +
abcdei fghj
K28.0
1C
000 11100
001111 0100
110000 1011
K28.1
3C
001 11100
001111 1001
110000 0110
K28.2
5C
010 11100
001111 0101
110000 1010
K28.3
7C
011 11100
001111 0011
110000 1100
K28.4
9C
100 11100
001111 0010
110000 1101
K28.5
BC
101 11100
001111 1010
110000 0101
K28.6
DC
110 11100
001111 0110
110000 1001
K28.7
FC
111 11100
001111 1000
110000 0111
K23.7
F7
111 10111
111010 1000
000101 0111
K27.7
FB
111 11011
110110 1000
001001 0111
K29.7
FD
111 11101
101110 1000
010001 0111
K30.7
FE
111 11110
011110 1000
100001 0111
Note: Only a small fraction of the possible K-characters are defined in this table. Any K-character
that decodes to a value that is not in Table A-2 shall be returned as Decode_Error_Substitution
(K28.4). Refer to Section 6.3.4 and Table 6-1 for more information.
A-8
B
Symbol Scrambling
B.1
Data Scrambling
The following subroutines encode and decode an 8-bit value contained in “inbyte” with the LFSR.
This is presented as one example only; there are many ways to obtain the proper output. This
example demonstrates how to advance the LFSR eight times in one operation and how to XOR the
data in one operation. Many other implementations are possible but they must all produce the same
output as that shown here.
The following algorithm uses the “C” programming language conventions, where “<<” and “>>”
represent the shift left and shift right operators, “>” is the compare greater than operator, and “^” is
the exclusive or operator, and “&” is the logical “AND” operator.
/*
this routine implements the serial descrambling algorithm in parallel form
for the LSFR polynomial: x^16+x^5+x^4+x^3+1
this advances the LSFR 8 bits every time it is called
this requires fewer than 25 xor gates to implement (with a static register)
The XOR required to advance 8 bits/clock is:
0
1
2
3
4
5
6
7
8
9 10
bit
8
9
10
11
8
12
9
8
13
10
9
8
14
11
10
9
15
12
11
10
0
13
12
11
1
14
13
12
2
15
14
13
11
12
13
14
15
3
4
5
6
7
15
14
15
The serial data is just the reverse of the upper byte:
0
1
2
3
4
5
6
7
15 14 13 12 11 10
9
8
bit
*/
B-1
Universal Serial Bus 3.0 Specification, Revision 1.0
int scramble_byte(int inbyte)
{
static
static
static
static
int i,
int scrambit[16];
int bit[16];
int bit_out[16];
unsigned short lfsr = 0xffff; // 16 bit short for polynomial
outbyte;
if (inbyte == COMMA)
{
lfsr = 0xffff;
return (COMMA);
}
// if this is a comma
if (inbyte == SKIP)
return (SKIP);
// don't advance or encode on skip
// reset the LFSR
// and return the same data
for (i=0; i<16;i++)
// convert LFSR to bit array for legibility
bit[i] = (lfsr >> i) & 1;
for (i=0; i<8; i++)
// convert byte to be scrambled for legibility
scrambit[i] = (inbyte >> i) & 1;
// apply the xor to the data
if (! (inbyte & 0x100) &&
// if not a KCODE, scramble the data
! (TrainingSequence == TRUE)) // and if not in the middle of
{
// a training sequence
scrambit[0] ^= bit[15];
scrambit[1] ^= bit[14];
scrambit[2] ^= bit[13];
scrambit[3] ^= bit[12];
scrambit[4] ^= bit[11];
scrambit[5] ^= bit[10];
scrambit[6] ^= bit[9];
scrambit[7] ^= bit[8];
}
B-2
Symbol Scrambling
// Now advance the LFSR 8 serial clocks
bit_out[ 0] = bit[ 8];
bit_out[ 1] = bit[ 9];
bit_out[ 2] = bit[10];
bit_out[ 3] = bit[11] ^ bit[ 8];
bit_out[ 4] = bit[12] ^ bit[ 9] ^ bit[ 8];
bit_out[ 5] = bit[13] ^ bit[10] ^ bit[ 9] ^ bit[ 8];
bit_out[ 6] = bit[14] ^ bit[11] ^ bit[10] ^ bit[ 9];
bit_out[ 7] = bit[15] ^ bit[12] ^ bit[11] ^ bit[10];
bit_out[ 8] = bit[ 0] ^ bit[13] ^ bit[12] ^ bit[11];
bit_out[ 9] = bit[ 1] ^ bit[14] ^ bit[13] ^ bit[12];
bit_out[10] = bit[ 2] ^ bit[15] ^ bit[14] ^ bit[13];
bit_out[11] = bit[ 3]
^ bit[15] ^ bit[14];
bit_out[12] = bit[ 4]
^ bit[15];
bit_out[13] = bit[ 5];
bit_out[14] = bit[ 6];
bit_out[15] = bit[ 7];
lfsr = 0;
for (i=0; i <16; i++) // convert the LFSR back to an integer
lfsr += (bit_out[i] << i);
outbyte = 0;
for (i= 0; i<8; i++) // convert data back to an integer
outbyte += (scrambit[i] << i);
return outbyte;
}
/*
NOTE THAT THE DESCRAMBLE ROUTINE IS IDENTICAL TO THE SCRAMBLE ROUTINE
this routine implements the serial descrambling algorithm in parallel form
this advances the lfsr 8 bits every time it is called
this uses fewer than 25 xor gates to implement (with a static register)
The XOR tree is the same as the scrambling routine
*/
B-3
Universal Serial Bus 3.0 Specification, Revision 1.0
int unscramble_byte(int inbyte)
{
static int descrambit[8];
static int bit[16];
static int bit_out[16];
static unsigned short lfsr = 0xffff;
int outbyte, i;
if (inbyte == COMMA)
{
lfsr = 0xffff;
return (COMMA);
}
if (inbyte == SKIP)
return (SKIP);
// 16 bit short for polynomial
// if this is a comma
// reset the LFSR
// and return the same data
// don't advance or encode on skip
for (i=0; i<16;i++)
// convert the LFSR to bit array for legibility
bit[i] = (lfsr >> i) & 1;
for (i=0; i<8; i++)
// convert byte to be de-scrambled for legibility
descrambit[i] = (inbyte >> i) & 1;
// apply the xor to the data
if (! (inbyte & 0x100) &&
// if not a KCODE, scramble the data
! (TrainingSequence == TRUE)) // and if not in the middle of
{
// a training sequence
descrambit[0] ^= bit[15];
descrambit[1] ^= bit[14];
descrambit[2] ^= bit[13];
descrambit[3] ^= bit[12];
descrambit[4] ^= bit[11];
descrambit[5] ^= bit[10];
descrambit[6] ^= bit[9];
descrambit[7] ^= bit[8];
}
B-4
Symbol Scrambling
// Now advance the LFSR 8 serial clocks
bit_out[ 0] = bit[ 8];
bit_out[ 1] = bit[ 9];
bit_out[ 2] = bit[10];
bit_out[ 3] = bit[11] ^ bit[ 8];
bit_out[ 4] = bit[12] ^ bit[ 9] ^ bit[ 8];
bit_out[ 5] = bit[13] ^ bit[10] ^ bit[ 9] ^ bit[ 8];
bit_out[ 6] = bit[14] ^ bit[11] ^ bit[10] ^ bit[ 9];
bit_out[ 7] = bit[15] ^ bit[12] ^ bit[11] ^ bit[10];
bit_out[ 8] = bit[ 0] ^ bit[13] ^ bit[12] ^ bit[11];
bit_out[ 9] = bit[ 1] ^ bit[14] ^ bit[13] ^ bit[12];
bit_out[10] = bit[ 2] ^ bit[15] ^ bit[14] ^ bit[13];
bit_out[11] = bit[ 3]
^ bit[15] ^ bit[14];
bit_out[12] = bit[ 4]
^ bit[15];
bit_out[13] = bit[ 5];
bit_out[14] = bit[ 6];
bit_out[15] = bit[ 7];
lfsr = 0;
for (i=0; i <16; i++) // convert the LFSR back to an integer
lfsr += (bit_out[i] << i);
outbyte = 0;
for (i= 0; i<8; i++) // convert data back to an integer
outbyte += (descrambit[i] << i);
return outbyte;
}
The initial 16-bit values of the LFSR for the first 128 LFSR advances following a reset are listed
below:
00
08
10
18
20
28
30
38
40
48
50
58
60
68
70
78
0, 8
FFFF
4E79
7D09
E055
E5AF
2BA4
345F
5C7C
CB84
29D7
F207
F927
2E04
9019
E8D6
5AA3
1, 9
E817
761E
02E5
40E0
BA3D
A2A3
5B54
70FC
9743
D1D1
1102
3081
027E
0610
C228
AF6A
2, A
0328
1466
E572
EE40
248A
B8D2
5853
F6F0
5CBF
C069
01A9
85B0
7E72
1096
3AB2
70C7
3, B
284B
6574
673D
54BE
8DC4
CBF8
5F18
E6E6
B3FC
7BC0
A939
AC5D
79AE
9590
B70A
CDF0
4, C
4DE8
7DBD
34CF
B334
D995
EB43
14B7
F376
E47B
CB73
2351
478C
A501
8FCD
129F
E3D5
5, D
E755
B6E5
CB54
2C7B
85A1
5763
B474
603B
6E04
6043
566B
82EF
1A7D
D0E7
9CE2
C0AB
6, E
404F
FDA6
4743
7D0C
BD5D
6E7F
6CD4
3260
0C3E
4A60
6646
F3F2
7F2A
F650
FC3C
B9C0
7, F
4140
B165
4DEF
07E5
4425
773E
DC4C
64C2
3F2C
6FFA
4FF6
E43B
2197
46E6
2B5C
D9C1
B-5
Universal Serial Bus 3.0 Specification, Revision 1.0
An 8-bit value of 0 repeatedly encoded with the LFSR after reset produces the following
consecutive 8-bit values:
00
00 FF
10 BE
20 A7
30 2C
40 D3
50 4F
60 74
70 17
80 8B
90 7C
A0 DA
B0 68
C0 31
D0 0B
E0 88
F0 84
100 4F
110 56
120 8B
B-6
01
17
40
5D
DA
E9
88
40
43
0D
D1
31
D5
C5
5E
14
01
AC
61
D6
02
C0
A7
24
1A
3A
80
7E
5C
8E
CF
72
38
ED
DA
F5
A0
60
63
86
03
14
E6
B1
FA
CD
95
9E
ED
5C
A8
C5
84
CF
62
4F
01
B6
20
57
04
B2
2C
9B
28
27
C4
A5
48
33
1C
A0
DD
91
BA
8B
83
79
6A
B2
05
E7
D3
A1
2D
76
6A
58
39
98
12
D7
00
64
5B
C8
49
D6
97
AA
06
02
E2
BD
36
30
66
FE
3F
77
EE
93
CD
6E
AB
56
67
62
4A
1A
07
82
B2
22
3B
FC
F2
84
D4
AE
41
0E
18
3D
DF
CB
EE
B7
38
80
08
72
07
D4
3A
94
9F
09
5A
2D
C2
DC
9E
FE
59
D3
3E
43
05
18
09
6E
02
45
0E
8B
0C
60
F5
AC
3F
AF
CA
E8
B7
10
2A
E7
E5
DC
0A
28
77
1D
6F
03
A1
08
0E
0B
38
A4
30
29
7D
42
8B
E5
DD
BA
0B
A6
2A
D3
67
DE
35
A9
B3
3E
7A
55
59
04
37
63
A4
2A
68
FC
0C
BE
CD
D7
CF
D3
E2
F1
C7
DA
0D
E7
4C
CF
5E
04
76
40
0D
03
0D
6D
34
EA
06
06
41
0B
03
0B
69
F0
75
6C
E3
8A
AF
2C
78
A3
0E
BF
BE
76
4C
52
CF
6F
9D
42
F4
72
1B
FC
1A
B4
14
6E
4C
4B
0F
8D
E0
EE
26
F6
27
62
9B
7A
01
16
77
C4
C6
F7
D5
7A
53
30
C
Power Management
This appendix offers a system level overview of USB 3.0’s power management features and
capabilities. The following topics are also included:
• Examples of how end to end low power link state exit latencies are calculated
• A discussion of device-initiated link power management policies
• An example device implementation for Latency Tolerance Messaging
• System power considerations for SuperSpeed versus High Speed device interfaces
C.1
SuperSpeed Power Management Overview
The SuperSpeed architecture has been defined with platform power efficiency as a primary
objective. Some of the key power efficiency enhancements include:
• Elimination of continuous device polling
• Elimination of broadcast packet transmission through hubs
• Introduction of link power management states enabling aggressive power savings when idle
• Host and device initiated transition to low power states
• Device and individual Function level suspend capabilities enabling devices to remove power
from all, or only those portions of their circuitry that are not in use
C.1.1
Link Power Management
Link power management enables a link to be placed into a lower power state when the link partners
are idle. The longer a pair of link partners remain idle, the deeper the power savings that can be
achieved by progressing from U0 (link active) to U1 (link standby with fast exit), to U2 (link
standby with slower exit), and finally to U3 (suspend).
After being configured by software, the U1 and U2 link states are entered and exited via hardware
autonomous control. Hardware autonomous transitions for the U1 and U2 link states enable faster
response times. This, in turn, translates to better power savings when entering a power saving state,
and less impact on the operational state when exiting. The U3 link state however is entered only
under software control, typically after a software inactivity timeout, and is exited either by software
(host initiated exit) or hardware (remote wakeup). The U3 link state is directly coupled to the
device’s suspend state (refer to Section C.1.4).
C-1
Universal Serial Bus 3.0 Specification, Revision 1.0
C.1.1.1
Summary of Link States
Table C-1 provides a summary characterization of the SuperSpeed link states.
Table C-1. Link States and Characteristics Summary
Link
State
Description
Characteristics
State
Transition
Initiator
Device
Clock Gen
On/Off
Typical Exit
Latency
Range
U0
Link active
Link operational state
N/A
U1
Link idle – fast
exit
Rx and Tx circuitry quiesced
Hardware
1
U2
Link idle –
slower exit
Clock generation circuitry may
additionally be quiesced
Hardware
1
U3
Link suspend
Interface (e.g., Physical Layer)
power may be removed
Entry: Software
only
On
N/A
On or Off
μs
On or Off
μs – ms
Off
ms
2
Exit: Hardware or
Software
Notes:
1. It is possible, under system test conditions, to instrument software initiated U1 and U2 state transitions.
2. From a power efficiency perspective it is desirable for devices to turn off their clock generation circuitry (e.g.,
their PLL) during the U2 link state.
C.1.1.2
U0 – Link Active
U0 is the fully operational, link active state. Packets of any type may be communicated over a link
that is in the U0 State.
C.1.1.3
U1 – Link Idle with Fast Exit
U1 is a power saving state this is characterized by fast transition time back to the U0 State. Note
that the predominant latency, when transitioning from the U1 Æ U0 state is imposed by the time
that is required to achieve symbol lock between the two link partners.
C.1.1.3.1
U1 Entry
Either link partner for a given link can request a transition to the U1 link state. All downstream
ports (hub or root ports) track inactivity using an inactivity timer mechanism. When a port’s
inactivity timer expires, if enabled, it requests transition to the U1 state. Upstream ports may also
initiate U1 entry based on device specific policies.
When a port initiates U1 entry, its link partner may either accept or reject the request. The link
level U0 Æ U1 transition process consists of one port transmitting an LGO_U1 link command, and
its link partner responding with either an LAU (accept the request) or an LXU (reject the request)
link command.
The most typical reason for rejecting a U1 transition request would be because the requesting port’s
link partner has some activity which will shortly require a packet transmission. Downstream ports
would also reject a U1 transition request if not enabled to accept U1 transition requests. Rejection
of a U1 transition request by an upstream port simply resets and restarts the requesting link
partner’s inactivity timer.
C-2
Power Management
System software configures and then enables each device to initiate U1 entry. The primary
programming parameters involved in setting up hardware autonomous link state management
include:
U1DevExitLat – Parameter used by devices to report their maximum U1 to U0 exit latency (refer to
Chapter 9 for details).
PORT_U1_TIMEOUT – Sets the value for the downstream port’s U1 inactivity timer. When
specifying a value between the range 0x01-0xFE it also enables the downstream port to send U1
entry transition requests to its link partner (refer to Chapter 10 for details).
U1_Enable – Enables an upstream port to initiate requests for transition into U1 (refer to Chapter 9
for details).
The U1_Enable feature controls whether that particular upstream port may initiate U1 entry.
Regardless of whether the upstream port is enabled for U1 entry initiation or not, it still responds to
requests for U1 entry from its link partner, either accepting or rejecting the transition request.
The following table illustrates the relationship between the downstream timeout and the upstream
U1_Enable to configure the platform for any combination of port link state management. For
example, if U1_Enable is enabled, and PORT_U1_TIMEOUT is set to FFH, then only the upstream
port may initiate requests for transition to U1.
PORT_U1_TIMEOUT
U1_Enable
Initiating Port
01H-FEH
Disabled
Downstream Port only
FFH
Enabled
Upstream Port only
01H-FEH
Enabled
Either Port
0H or FFH
Disabled
Neither Port
For detailed information regarding the specifics of the U1 entry process, refer to Chapter 7 of this
specification.
C.1.1.3.2
Exiting the U1 State
There are two ways to exit the U1 state. The link can return to the active U0 state or it can
transition into a deeper power savings state (U2).
Transitioning from U1 Æ U0
Either link partner can initiate a transition from U1 Æ U0. This transition is normally initiated
when a packet needs to be transmitted, such as an IN message from the host, or an ERDY message
from a device. The transition process is initiated by first signaling a Low Frequency Periodic
Signaling (LFPS) handshake. This is followed by link recovery and training sequences. Refer to
Chapter 6 and 7 respectively.
Transitioning from U1 Æ U2
This transitions the link to an even lower power state and is triggered by a second inactivity timer
(U2 inactivity timer). When a link enters U1, this starts the U2 inactivity timer. If the U2 inactivity
timer expires while the link is still in U1, then both link partners transition silently from U1 Æ U2
without additional bus activity. The next sections discuss this in more detail.
C-3
Universal Serial Bus 3.0 Specification, Revision 1.0
C.1.1.4
U2 – Link Idle with Slow Exit
The purpose of the U2 link state is to use less power than the U1 state, however at the cost of
increased exit latency. For example, clock generation circuitry may be quiesced in order to save
additional power in comparison with U1. Under some implementation-specific circumstances, this
may not make sense. For example, a hub may share one PLL across all of its ports so the PLL
cannot be quiesced unless all of its ports are in U2.
The primary parameters involved in configuring a port for U2 link transitions include:
U2DevExitLat – Parameter used by devices to report their maximum U2 to U0 exit latency (refer to
Chapter 9 for details).
PORT_U2_TIMEOUT – Sets the value of a downstream port’s U2 inactivity timer. When
specified with a value in the range 0x01-0xFE it also enables the downstream port to initiate U2
entry transition requests to its link partner (refer to Chapter 10 for details).
U2_Enable – Enables an upstream port to initiate requests for transitions into U2 (refer to
Chapter 9 for details).
The U2_Enable feature controls whether an upstream port may initiate U2 entry from U0.
Regardless of whether the upstream port is enabled for U2 entry initiation or not, it still responds to
requests for U2 entry from its link partner, either accepting or rejecting the transition request.
The following table illustrates the relationship between the downstream timeout and the upstream
U2_Enable to configure the platform for any combination of port link state management. For
example, if U2_Enable is enabled, and PORT_U2_TIMEOUT is set to FFH, then only the upstream
port may initiate requests for transition to U2.
PORT_U2_TIMEOUT
U2_Enable
Initiating Port
01H-FEH
Disabled
Downstream Port only
FFH
Enabled
Upstream Port only
01H-FEH
Enabled
Either Port
0H or FFH
Disabled
Neither Port
Transitioning from U1 Æ U2
U2 is typically entered directly from U1 as mentioned earlier. The U2 inactivity timer starts when a
link enters U1, and when the U2 inactivity timer expires both link partners silently transition from
U1 Æ U2.
Both link partners must be configured with the same U2 inactivity timeout value. This is done by
first having software program the U2 inactivity timeout in the downstream port. The downstream
port then sends an LMP containing the U2 inactivity timeout value to its link partner. Any changes
to this value on the downstream port are also updated with the link partner in the same manner
(refer to Chapter 10).
Note that U2 inactivity timer synchronization between link partners can never be perfect so there
can be brief periods of time where one port is in U2 while its link partner is still in U1. However
given that the U1 Æ U0 and U2 Æ U0 state transition processes are compatible with one another
this corner condition is handled cleanly.
C-4
Power Management
Transitioning directly to U2 from U0
A downstream port can be configured for direct, hardware autonomous transition from U0 Æ U2
by programming its U1 inactivity timer to zero while programming its U2 inactivity timer with a
non-zero value in the range 0x01- 0xFE. In this case, when the U2 inactivity timer expires, the
downstream port initiates U2 entry from U0.
When a port initiates U2 entry from U0, its link partner may either accept or reject the request. The
link level U0 Æ U2 transition process consists of one port transmitting an LGO_U2 Link
Command, and its link partner responding with either an LAU (accept the request) or an LXU
(reject the request) Link Command.
Exiting U2
Exiting U2 can only result in a link state transition to U0. Either link partner can initiate U2 exit,
which is initiated when a packet needs to be transmitted. The exit process is similar to that of a U1
Æ U0 transition, consisting of a Low Frequency Periodic Signaling handshake followed by link
recovery and training.
C.1.1.5
U3 – Link Suspend
The U3 state is a deep power saving state where portions of device power may be removed, except
as needed to perform the following functions:
• For upstream ports in devices and hubs:
⎯ Warm Reset signaling detection
⎯ Wakeup signaling detection (for host initiated wakeup)
⎯ Wakeup signaling transmission (for remote wakeup capable devices)
• For downstream ports in hubs and hosts:
⎯ Warm Reset generation
⎯ Disconnect event detection
⎯ Wakeup signaling detection (for remote wakeup)
⎯ Wakeup signaling transmission (for host initiated wakeup)
The purpose of U3 is to minimize power consumption during device or system suspend.
VBUS remains active during U3. Any power rail switching by devices is implementation specific
and beyond the scope of this specification.
Entering the U3 State
U3 entry may only be initiated by the host (refer to Chapter 10 for details). Software typically
implements an inactivity timeout for the purpose of placing a function into suspend following a
long period of inactivity.
When a downstream port initiates a U3 entry request, its link partner is not allowed to reject it. The
downstream port sends an LGO_U3 Link Command, and its link partner responds with an LAU
Link Command (refer to Chapter 7 for details).
C-5
Universal Serial Bus 3.0 Specification, Revision 1.0
Exiting the U3 State
The only legitimate link state transition from U3 is U3 Æ U0, and either link partner can initiate it.
Host software initiates U3 exit on a downstream port by issuing a
SetPortFeature(PORT_LINK_STATE) request to the desired downstream port. Upstream ports
(e.g., upstream port of a hub, or a peripheral device), initiate U3 exit in response to a remote
wakeup event. An example of this would be an incoming Wake on LAN packet for a USB attached
network interface device. The exit process consists of a Low Frequency Periodic Signaling (LFPS)
handshake followed by link recovery and training.
Device Initiated U3 Exit
If the exit was initiated by a device, the specific function within the device that initiated the wakeup
would follow up the LFPS triggered transition to U0 by sending a Function Wake device
notification packet to the host.
Host initiated U3 Exit
For host initiated U3 exit, the LFPS handshake process allows devices up to 20 ms to complete,
allowing sufficient time for a device to turn on a switched power rail if implemented (refer to
Chapter 6 for details).
The software interface associated with U3 consists of a set of port controls and function controls.
The port controls, e.g., initiating U3 on a hub downstream port, are described in Section C.1.2.3.
The function controls, e.g., enabling a function (device) for remote wakeup, are described in
Section C.1.4.1.
C.1.2
Link Power Management for Downstream Ports
Hubs play several critical roles in link power management. They perform the following functions:
• Coordinate the upstream port link power management state with that of their downstream ports.
• Handle packet deferral, where the hub tells the host that a packet was sent to a downstream port
that is not currently in U0.
• Provide inactivity timers on downstream ports to initiate U1 and U2 entry.
C.1.2.1
Link State Coordination and Management
A hub monitors its downstream ports’ link states and keeps its upstream port in the lowest power
link state it can without allowing it to be in a lower power state than any of its downstream ports.
The intent for this policy is to ensure that the path to the host, (i.e., the upstream port), is as active
as the most active of its downstream ports.
When a device initiates a transition from a low power state back to U0 on a hub downstream port,
the hub begins transitioning its upstream port to U0 immediately, in parallel with the downstream
port.
For packets traveling downstream, hubs must first receive the packet, determine which of its
downstream ports the packet is targeted at, and then only initiate a transition to U0 for that
particular downstream port.
USB 3.0 hubs use a unicast packet transmission model and this improves the power efficiency of
the platform in every instance where a hub is deployed.
C-6
Power Management
C.1.2.2
Packet Deferring
Packet deferring is a mechanism that enables efficient bus utilization while supporting aggressive
link power management. Packet deferring achieves this by enabling a hub to respond on behalf of a
downstream device whose link is in a low power state. This allows the host to make forward
progress while the device is brought back to the active state.
Hub’s Role in Packet Deferring
After receiving a header packet from the host and detecting a packet deferring condition, the hub
informs the host of this by sending a deferred header packet back to the host. The hub also sends
the original header packet to the device, with the deferred field asserted, once it is brought back to
the U0 state. The host treats this deferred header packet as it would receipt of an NRDY, and so is
then free to initiate transfers with other devices’ endpoints instead of waiting for the sleeping link to
return to U0 (refer to Chapter 10 for details).
Device’s Role in Packet Deferring
When a device receives an IN or an OUT header packet with the deferred field asserted, it prepares
for the transfer, sends an ERDY to the host when ready, and keeps its link in U0 until the transfer
occurs.
The host ultimately responds to the ERDY by rescheduling the original transfer.
C.1.2.3
Software Interface
The software interface for downstream port power management consists of the following port
controls and status fields:
• PORT_LINK_STATE feature and port status field
• PORT_REMOTE_WAKE_MASK feature
• C_PORT_LINK_STATE port status change bit
• PORT_U1_TIMEOUT feature
• PORT_U2_TIMEOUT feature
The PORT_LINK_STATE
This feature is used to request a link state change from any current U-state to any next U-state. In a
normal operating environment, this feature is used solely to request U0 Æ U3 and U3 Æ U0
transitions. It can be used for test purposes though, to request other state transitions.
The PORT_REMOTE_WAKE_MASK
This feature is used to mask each remote wakeup event that might be originated at a downstream
port.
Note that if remote wake notifications for connect, disconnect, or over current events are disabled,
these events are still captured and reported as port status change events after the host or hub is
resumed.
C_PORT_LINK_STATE
This flag is used to signal completion of a transition from U3 Æ U0. Specifically, assertion of this
flag results from a host initiated wakeup on a downstream port.
C-7
Universal Serial Bus 3.0 Specification, Revision 1.0
Once the C_PORT_LINK_STATE flag is set, a port status change event is sent to system software
indicating that the downstream port and its link partner have completed the transition to the U0
state.
Note that C_PORT_LINK_STATE is not asserted in the event of a remote wakeup. As discussed
previously, in the event of a Remote Wakeup the associated function sends the host a Function
Wake device notification packet.
PORT_U1_TIMEOUT
This feature is used to enable and disable U1 entry on downstream ports. It also specifies the U1
inactivity timeout value.
Timeout
Value
U1 Transition Capabilities
U1 Transition Initiation
00H
U1 transitions disabled; will not initiate or accept link partner
requests
n/a
01H-FEH
U1 transitions enabled; port will initiate and accept link partner
requests
Following timer expiration using
specified Timeout Value
FFH
U1 transition initiation disabled; will accept transition requests
from its link partner
n/a
PORT_U2_TIMEOUT
This feature is used to enable and disable U2 on downstream ports, and also to set an inactivity
timeout for initiating a transition to U2.
Timeout
Value
U2 Transition Capabilities
U2 Transition Initiation
00H
U2 transitions disabled; will not initiate or accept link partner
requests
n/a
01H-FEH
U2 transitions enabled; port will initiate and accept link partner
requests
Following timer expiration using
specified Timeout Value
FFH
Direct U1 Æ U2 transition is disabled; will accept U2 transition
requests (if current link state is U0) from its link partner
n/a
Other hub port controls can impact link power management behavior, e.g., the PORT_RESET
feature, but are not covered here (refer to Chapter 10 for details).
C.1.3
Other Link Power Management Support Mechanisms
C.1.3.1
Packets Pending Flag
Devices may use the Packets Pending flag (refer to Chapter 8) to help decide when to place their
link in a low power state. The Packets Pending flag provides an indication of whether the host
controller has any additional packets to transfer on the schedule associated with a given endpoint.
When there are no more packets pending for all endpoints on a device, the device may place its link
in a low power state immediately.
C-8
Power Management
C.1.3.2
Support for Isochronous Transfers
If a link is in a low power state when an isochronous transfer is scheduled, the latency to transition
to U0 from source to destination could potentially delay the transfer beyond its subscribed
isochronous service interval.
To ensure that isochronous service contract guarantees are satisfied, a SuperSpeed mechanism
(Ping) has been defined to bring all paths between the host and an isochronous endpoint to U0 as a
routine step in servicing isochronous endpoints.
The host controller, with sufficient information to know how long any given path might take to
become fully active, factors this link path exit latency into its isochronous service scheduler and
uses the Ping protocol to ensure that the links are brought to a fully active state in time to meet the
isochronous service contract.
The ping process consists of the following:
• The host sends a PING packet to a device.
• Hubs route the PING packet toward the targeted device.
• The device responds to the PING packet by sending a PING_RESPONSE packet to the host.
• The device keeps its link in U0 until it receives a subsequent packet from the host.
After sending a PING packet to one device and prior to receiving a PING_RESPONSE packet, the
host may transfer data with other devices. Much like the Packet Deferring mechanism, the Ping
mechanism enables efficient bus utilization while at the same time supporting significant power
savings.
C.1.3.3
Support for Interrupt Transfers
If any links between the host and a scheduled interrupt endpoint are in a low power state, the
latency to transition the end to end pathway to U0 could potentially delay the transfer beyond the
subscribed interrupt service interval. A host controller, possessing knowledge of link path exit
latency between itself and any given device within the link hierarchy, is able to schedule interrupt
transfers far enough in advance to compensate for these latencies.
C.1.4
Device Power Management
Device power management is directed primarily under software control, with various hardware
mechanisms to support it. Device power management consists of some function level mechanisms
plus some device and hub mechanisms.
C.1.4.1
Function Suspend
A function may be placed into function suspend independent of other functions using the
FUNCTION_SUSPEND feature. The FUNCTION_SUSPEND feature is also used to enable
function remote wakeup (refer to Chapter 9 for details).
If a composite device has at least one of its functions in suspend while other functions remain
active, i.e., the device’s upstream port is not in U3, a mechanism is needed for a suspended function
to signal a remote wakeup. This is done with the Function Wake device notification packet (refer
to Chapter 8 for details).
C-9
Universal Serial Bus 3.0 Specification, Revision 1.0
C.1.4.2
Device Suspend
Device suspend is a device-wide state entered and exited intrinsically as a result of a device’s
upstream port entering and exiting the U3 state. A device may be transitioned into device suspend
regardless of the function suspend state of any function within the device.
Devices may implement a switched power rail and remove power from large portions of the device
while in suspend. Some device state information must be retained in a persistent state during
suspend (refer to Chapter 9 for details).
C.1.4.3
Host Initiated Suspend
Suspending a Device
The host transitions a device into the suspend state according to the following sequence:
• Enable remote wakeup, if needed
• A SetPortFeature(PORT_LINK_STATE, U3) request is issued to the downstream port of
which the targeted device is its link partner.
• The downstream port initiates U3 entry by sending an LGO_U3 link command.
• The device sends an LAU link command (acceptance is non-negotiable).
• The downstream port sends an LPMA link command.
• Both link partners transition their transmitters to electrical idle and enter the U3 state (refer to
Chapter 7 for details).
Suspending the USB Link Hierarchy
A link hierarchy of devices and hubs is placed into suspend on a device by device basis under host
software control. First, all peripheral devices in the hierarchy are placed into suspend. Then the
hubs connected to the peripheral devices are placed into suspend. This is repeated all the way up
the hierarchy until reaching the root ports of the USB hierarchy.
Note that by using the same technique a select subset of a given USB link hierarchy could be
suspended rather then the whole of it if so desired.
C-10
Power Management
C.1.4.4
Host Initiated Wake from Suspend
Host initiated wake from suspend (U3 Æ U0) of an individual device, group of devices, or of the
entire link hierarchy is accomplished using the same repetitive process, one link at a time.
Figure C-1 illustrates the Host initiated Wake Sequence.
System Wakeup
Event Occurs
Host Sets
PORT_LINK_STATE
to U0 for Next Hub
Downstream Port
(in Path to Device)
that is in U3
Downstream Port
Initiates U3 Exit
Link transitions
to U0
Hub Sends
C_PORT_LINK_STATE
Port Status Change
Interrupt to Host
Yes
Downstream Port
Connected to
Another Hub?
No
Wakeup Process
is Complete
U-067
Figure C-1. Flow Diagram for Host Initiated Wakeup
C.1.4.5
Device Initiated Wake from Suspend
A device initiated transition from suspend (U3 Æ U0) follows the sequence outlined below:
1. The device transmits LFPS wakeup signaling to its link partner.
2. The LFPS signaling is propagated upstream until it reaches the root hub or a hub that is not in
U3. This hub is referred to as the Controlling Hub.
3. The Controlling Hub then automatically reflects LFPS wakeup signaling on the downstream
port which had received (from the opposite direction) the wakeup signaling.
4. Each hub in the direct path to the remote wakeup device propagates the wakeup signaling
downstream on the hub downstream port that had received wakeup signaling. As the wakeup
signaling is propagated downstream, each link completes the LFPS handshake and transitions
to U0 (refer to Chapters 6 and 7 for details).
5. After all of the links between the Controlling Hub and the remote wakeup device transition to
U0, the function within the remote wakeup device that had originated the remote wakeup sends
a Function Wake device notification packet to the host. This in turn causes a software
interrupt, and in the service of this interrupt the function suspend state is cleared for that
function.
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C.1.5
Platform Power Management Support
The Latency Tolerance Message (LTM) feature allows a platform to make dynamic tradeoffs
between power and performance. It enables this, in cooperation with devices, without imposing
additional cost.
The LTM protocol enables USB devices to inform the host how long they can tolerate lack of
service before experiencing unintended side effects. Each device provides this information in the
form of a Best Effort Latency Tolerance (BELT) value. A given device’s BELT value is derived
considering all configured endpoints, typically conforming to the endpoint with the lowest latency
tolerance.
LTM provides the ability for a device to dynamically change its BELT value to more accurately
reflect, for example, long periods of anticipated idle time. The platform can potentially take
advantage of this insight and, along with other system-related information, conserve more energy at
the system level without running the risk of unintended side effects.
C.1.5.1
System Exit Latency and BELT
A device’s reported BELT value has to comprehend not only its own intrinsic design
characteristics, such as its internal buffering, but also factor in other associated end to end latencies
between itself and the host. These would include other latencies associated with the time required
to awaken sleeping links, the number of hubs between the device and the host, host processing
time, packet propagation delays, etc. The system provides the device with additional system
latency information, through the SET_SEL request, such that the device’s intrinsic BELT value can
be adjusted downward to account for these other factors. Refer to Chapter 8 for detailed LTM
specification and to Chapter 9 for specification details regarding the SET_SEL request.
Device implementation determines the total latency that a device can tolerate. The primary factors
are the amount of data that the device is required to produce or consume, and the amount of
buffering on the device. The total device latency tolerance must be allocated among different
system components.
Figure C-2 illustrates the total latency a device may experience within the context of LTM. The
latency is the sum of parameters t1, t2, t3, and t4:
t1: the time to transition all links in the path to the host to U0 when the transition is initiated
by the device
t2: the time for the ERDY to traverse the interconnect hierarchy from the device to the host
t3: the time for the host to consume the ERDY and transmit a response to that request
t4: the time for the response to traverse the interconnect hierarchy from the host to the device
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Host
t3
t1 + t2
Interconnect
Hierarchy
(zero to five hubs)
t4
SuperSpeed Device
U-167
Figure C-2. Device Total Intrinsic Latency Tolerance
Devices may calculate their BELT value by subtracting U1SEL or U2SEL (refer to the SET_SEL
request in Chapter 9) from their total intrinsic latency tolerance. If the device allows its link to
enter U2, then the device calculates its BELT by subtracting U2SEL from its total intrinsic latency
tolerance. If the device does not allow its link to enter U2 but does allow its link to enter U1, then
the device calculates its BELT by subtracting U1SEL from its total intrinsic latency tolerance.
U1SEL and U2SEL are calculated and programmed by host software. Example calculations for t1
are provided in Section C.2. For LTM purposes t2 and t4 should be calculated by host software as
follows:
• For t2, a hub may delay forwarding the ERDY by up to one maximum packet size
(approximately 2.1 μs including framing) when there is a transfer in progress. Each additional
hub will delay forwarding the ERDY by up to approximately 250 ns to transfer the packet. The
value of t2 is determined as follows:
⎯ If there are zero hubs in the direct path between the device and the host, then t2 is zero
•
⎯ If there are one or more hubs in the direct path between the device and the host, then t2 is
approximately 2.1 μs + 250 ns * (number of hubs – 1)
For t4, a hub may delay forwarding a packet by up to approximately 250 ns. The value of t4 is
approximately 250 ns times the number of hubs in the direct path between the device and the
host).
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C.2
Calculating U1 and U2 End to End Exit Latencies
This section provides examples of how to calculate the exit latency (i.e., time to transition from a
non-U0 state to a U0 state) spanning the end to end path between a device and the host. Examples
are given for both device initiated exit and host initiated exit.
Figure C-3 depicts a SuperSpeed hierarchy and calls out the relevant parameters used in the
calculations that follow.
Host
U1DEL,
U2DEL
RP1
RP2
Link1
Link2
UP
U1DEL,
U2DEL
Dev1
Hub1
Descriptors:
U1DEL=
bU1DevExitLat
UP
U1DEL,
U2DEL,
HHDL
DP1
DP2
Link3
Dev2
U2DEL=
bU2DevExitLat
HHDLbHubHdrDecLat
(Hub Header
Decode Latency)
UP
U1DEL,
U2DEL
RP = Root Port
UP = Upstream Port
DP = Downstream Port
U-075
Figure C-3. Host to Device Path Exit Latency Calculation Examples
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C.2.1
Device Connected Directly to Host
C.2.1.1
Host Initiated Transition
In this example, a peripheral device (Dev1) and a host controller root port (RP1) are link partners
communicating over a link (Link1).
Host
U1DEL,
U2DEL
RP1
RP2
Link1
Link2
UP
U1DEL,
U2DEL
Dev1
Hub1
Descriptors:
U1DEL=
bU1DevExitLat
UP
U1DEL,
U2DEL,
HHDL
DP1
DP2
Link3
Dev2
U2DEL=
bU2DevExitLat
HHDLbHubHdrDecLat
(Hub Header
Decode Latency)
UP
U1DEL,
U2DEL
RP = Root Port
UP = Upstream Port
DP = Downstream Port
U-057
Figure C-4. Device Connected Directly to a Host
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U1 Æ U0 Transition Latency
The host initiates the transition by transmitting LFPS. At this point, both link partners’ transitions
from U1 Æ to U0 are executed in parallel.
The exit latency is characterized by the largest of the two device exit latencies: Dev1:U1DEL
and RP1:U1DEL
U2 Æ U0 Transition Latency
In this example it is assumed that at least one of the link partners (e.g., the RP1) is enabled for U2.
The host initiates the transition by transmitting LFPS. At this point both link partners execute
transition from U2 Æ to U0 in parallel.
The exit latency is characterized by the largest of the two device exit latencies: Dev1:U2DEL
and RP1:U2DEL
C.2.1.2
Device Initiated Transition
These transition latencies are the same as for the host initiated cases.
• U1 End to End Exit Latency is the larger of Dev1:U1DEL and RP1:U1DEL
• U2 End to End Exit Latency is the larger of Dev1:U2DEL and RP1:U2DEL
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C.2.2
Device Connected Through a Hub
In this example a peripheral device (Dev2) is connected to one of a hub’s downstream ports (DP2)
via a link (Link3), which in turn is connected to a host controller’s root port (RP2) via a link
(Link2).
Host
U1DEL,
U2DEL
RP1
RP2
Link1
UP
U1DEL,
U2DEL
Link2
Dev1
Hub1
Descriptors:
U1DEL=
bU1DevExitLat
UP
U1DEL,
U2DEL,
HHDL
DP1
DP2
HHDLbHubHdrDecLat
(Hub Header
Decode Latency)
Link3
Dev2
U2DEL=
bU2DevExitLat
UP
U1DEL,
U2DEL
RP = Root Port
UP = Upstream Port
DP = Downstream Port
U-058
Figure C-5. Device Connected Through a Hub
C.2.2.1
Host Initiated Transition
U1 Æ U0 Transition Latency
This example highlights the end to end latency incurred when transitioning both Link2 and Link3
from U1 Æ U0. For the purposes of this example, it is assumed that all link partners are enabled
for U1, and that both Link2 and Link3 are currently in the U1 state.
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Figure C-6 shows the chronological sequence of events. Following the figure is a more detailed
description of each stage of the multi-hop link state transition.
Link3_EL
HSD
Link2_EL
HHDL
Time
Host Initiates
U1 Exit
Link2 Completes
U0 Entry
Hub1: DP2
Initiates U1 Exit
Link3 Completes
U0 Entry
U-076
Figure C-6. Downstream Host to Device Path Exit Latency with Hub
1. The host is prepared to send a packet to Dev2, however it first needs to bring Link2 out of U1
before it is able to send the packet. The host begins the process by transmitting LFPS on RP2
to Hub1’s upstream port (UP) which then starts both link partners transitioning in parallel
towards U0. This latency is characterized by the larger of RP2:U1DEL and Hub1:U1DEL
2. Once the Link2 partners are in U0, the host sends its packet targeting Dev2 over Link2 where it
then needs to be routed to Link3. This incurs the latency associated with the Hub having to
parse the packet header to determine the target downstream port for the packet. This latency is
characterized by the hub parameter HHDL.
3. The final hop requires Hub1:DP2 to signal LFPS over Link3 at which point the final
component of the end to end latency is executed by the Link3 partners in parallel. This final
ingredient to the end to end latency is characterized by the larger of Hub1:U1DEL and
Dev2_UP:U1DEL.
The total latency for end to end link transition to U0 can be summarized as:
Max(RP2:U1DEL, Hub1:U1DEL) + HSD + HUB1:HHDL + Max(Hub1:U1DEL, Dev2_UP:U1DEL)
U2 Æ U0 Transition Latency
This example highlights the end to end latency incurred when transitioning both Link2 and Link3
from U2 Æ U0. For the purposes of this example it is assumed that all link partners are enabled for
U2 and that both Link2 and Link3 are currently in the U2 state.
1. The host is prepared to send a packet to Dev2, however it first needs to bring Link2 out of U2
before it is able to send the packet. The host begins the process by transmitting LFPS to
Hub1:UP which then starts both link partners transitioning in parallel towards U0. This latency
is characterized by the larger of RP2:U2DEL and Hub1:U2DEL.
2. Once the Link2 partners are in U0 the host sends its packet targeting Dev2 over Link2 where it
then needs to be routed to Link3. This incurs the latency associated with the Hub having to
parse the packet header to determine the target downstream port for the packet. This latency is
characterized by the hub parameter HHDL.
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3. The final hop requires Hub1:DP2 to signal LFPS over Link3 at which point the final
component of the end to end latency is executed by the Link3 partners in parallel. This final
ingredient to the end to end latency is characterized by the larger of Hub1:U2DEL and
Dev2_UP:U2DEL.
The total exit latency for end to end link transition to U0 can be summarized as:
Max(RP2:U2DEL, Hub1:U2DEL) + HSD + Hub1:HHDL + Max(Hub1:U2DEL, Dev2_UP:U2DEL)
C.2.2.2
Device Initiated Transition
This section provides some examples for calculating end to end exit latencies for device initiated
exit.
U1 Æ U0 Transition Latency
This example highlights the end to end latency incurred when transitioning both Link2 and Link3
from U1 Æ U0. For the purposes of this example it is assumed that all link partners are enabled for
U1 and that both Link2 and Link3 are currently in the U1 state.
Figure C-7 depicts the end to end link state transition in chronological order. Following the figure a
more detailed description of the sequence is provided.
Link2_EL
Link3_EL
tHubPort2PortU1EL
Time
Dev2
Initiates
U1 Exit
Hub1: UP
Initiates U1 Exit
Link3
Completes
U0 Entry
Link2 Completes
U0 Entry
U-077
Figure C-7. Upstream Device to Host Path Exit Latency with Hub
1. Dev2 is prepared to send a packet upstream to the host. However, it first needs to bring Link3
out of U1 and back to U0 before it is able to send the packet. Dev2 begins the process by
transmitting LFPS to Hub1:DP2 which then starts both link partners transitioning in parallel
towards U0. The Link3 exit latency (Link3_EL) is characterized by the larger of
Dev2_UP:U1DEL and Hub1_DP2:U1DEL.
2. After a latency of tPort2PortU1EL, the time it takes the hub to determine that one of its
downstream ports is awakening, the hub then begins signaling LFPS on Link2 to initiate
transition of the Link2 partners (hub’s upstream port and host controller root port RP2 ) to U0.
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3. The last component of the end to end exit latency is characterized by the larger of
Hub1_UP:U1DEL and RP2:U1DEL which represents the Link2 exit latency (Link2_EL).
End to end exit latency = Max(Link3_EL, (Link2_EL + tHubPort2PortU1ExitLat))
U2 Æ U0 Transition Latency
This example highlights the end to end latency incurred when transitioning both Link2 and Link3
from U2 Æ U0. For the purposes of this example it is assumed that all link partners are enabled for
U2 and that both Link2 and Link3 are currently in the U2 state.
1. Dev2 is prepared to send a packet upstream to the host. However, it first needs to bring Link3
out of U2 and back to U0 before it is able to send the packet. Dev2 begins the process by
transmitting LFPS to Hub1:DP2 which then starts both link partners transitioning in parallel
towards U0. The Link3 exit latency (Link3_EL) is characterized by the larger of
Dev2_UP:U2DEL and Hu1b_DP2:U2DEL.
2. After a latency of tPort2PortU2EL, the time it takes the hub to determine that one of its
downstream ports is awakening, the hub then begins signaling LFPS on Link2 to initiate
transition of the Link2 partners (hub’s upstream port and host controller root port RP2 ) to U0.
3. The last component of the end to end exit latency is characterized by the larger of
Hub1_UP:U2DEL and RP2:U2DEL which represents the Link2 exit latency (Link2_EL).
End to end exit latency = Max(Link3_EL, Link2_EL + tHubPort2PortU2EL)
C.3
Device-Initiated Link Power Management Policies
Power savings resulting from the effective use of link power management can have a significant
impact on system power consumption. For example, without using link power management, the
average battery life of a typical notebook computer could be decreased by as much as 15%.
Both devices and downstream ports can initiate U1 and U2 entry.
• Downstream ports have inactivity timers used to initiate U1 and U2 entry. Downstream port
inactivity timeouts are programmed by system software.
• Devices may have additional information available that they can use to decide to initiate U1 or
U2 entry more aggressively than inactivity timers.
This section describes policies for devices to initiate U1 or U2.
C.3.1
Overview and Background Information
Devices can save significant power by initiating U1 or U2 more aggressively rather than waiting for
downstream port inactivity timeouts. For example, an isochronous device may substantially
increase U1 residency by initiating U1 upon completion of isochronous transfers within each
service interval.
Devices can use the following information to help determine when to initiate U1 or U2 due to
endpoint idle conditions:
• The type of device endpoints and related flags (refer to Chapter 8)
⎯ Packets Pending flag, used with bulk endpoints
⎯ End of Burst flag, used with interrupt endpoints
⎯ Last Packet flag, used with isochronous endpoints
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Power Management
•
•
•
Protocol level endpoint flow control conditions, e.g., an endpoint having sent an NRDY
Device class and device implementation
U1 and U2 device-to-host exit latencies
U1 and U2 device-to-host exit latencies are the total latency to transition all links in the path
between the device and the host to U0, when exit is initiated by the device. The device may assume
a device-to-host exit latency based on the worst case exit latency (device connected five hubs deep).
The device may alternatively use the device-to-host exit latency provided with the U1PEL and
U2PEL fields of the SET_SEL request (refer to Chapter 9).
C.3.2
Entry Conditions for U1 and U2
A device should initiate U1 or U2 when idle conditions are met for all its endpoints. A device
typically initiates U1. However, if a device is able to determine that its link will not be needed for a
long time, then the device may be able to initiate U2. For example, WiFi has a protocol where its
radio may be shut off for long periods, e.g., 100 ms, and since the link is not needed during this
time it may be placed in U2.
A device should initiate U2 if it is able to determine its link is not needed for a period of time that
exceeds the U2 device-to-host exit latency (plus an appropriate guard band). The device should
initiate U1 in all other cases.
Devices should consider the device-to-host exit latency when determining whether to initiate U1
and U2 entry. The host-to-device exit latency and the device-to-host exit latency are both
considered by host software when determining whether to enable U1 or U2 on each link. Devices
are enabled to initiate U1 and U2 with the U1_Enable and U2_Enable feature selectors (refer to
Chapter 9).
The following subsections offer recommendations for determining when an endpoint is idle, or does
not need to use the link for a known period, based on endpoint type. Idle conditions may be
determined in other implementation specific ways.
C.3.2.1
Control Endpoints
A control endpoint is idle when all of the following conditions are met:
• Device is in the configured state
• Device is not in the midst of a control transfer
• Either an NRDY was sent, or the Packets Pending flag was set to zero in the last ACK packet
received from the host
• Device does not have a pending ERDY
C.3.2.2
Bulk Endpoints
A bulk endpoint is idle when both of the following conditions are met:
• Either an NRDY was sent, or the Packets Pending flag was set to zero in the last ACK packet
received from the host
• Device does not have a pending ERDY
Some devices can also determine that their link is not needed for a known period of time. For
example, a mass storage device may need to spin up a spindle to service a request. Since the spin
up time can be hundreds of milliseconds, the device should place its link in U2.
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After a device has sent an ERDY associated with a bulk endpoint, the link should be kept in U0
until the host sends a request in response to the ERDY (or until the tERDYTimeout occurs, refer to
Section 8.13).
C.3.2.3
Interrupt Endpoints
An interrupt endpoint is idle when both of the following conditions are met:
• Either an NRDY was sent, or the Packets Pending flag was set to zero in the last ACK packet
received from the host.
• Device does not have a pending ERDY.
After a device has sent an ERDY associated with an interrupt endpoint, the link should be kept in
U0 until the host sends a request in response to the ERDY (or until the tERDYTimeout occurs) in
order to achieve the subscribed interrupt service latency. However, when all transfers for a given
service interval have been completed, the endpoint will not need the link until the next service
interval. The device may be able to place its link in U1 or U2 during this time. The End of Burst
flag can be used to determine when all transfers for a given service interval are completed. Note
that hosts are required to initiate interrupt transfers far enough ahead of a transfer window to meet
subscribed service requirements.
C.3.2.4
Isochronous Endpoints
An isochronous endpoint is idle when all transfers for a given service interval have been completed,
as indicated by the Last Packet flag. The endpoint will not need the link until the next service
interval. Note that the host is required to send a PING packet far enough ahead of a transfer
window to meet subscribed service requirements.
C.3.2.5
Devices That Need Timestamp Packets
When a device needs timestamp information, it needs to ensure that its link is in U0 when the next
bus interval boundary is reached in order to receive a timestamp packet. If the device’s link is not
in U0, it should transition to U0 prior to the next bus interval boundary. The device must track
when the bus interval boundary will occur. The device initiates a transition to U0 a period of time
before the bus interval boundary occurs, where the period of time is the device-to-host link exit
latency.
C.4
Latency Tolerance Message (LTM) Implementation
Example
Computer systems typically maintain a high state of readiness to service devices even when the
computer system is idle. LTM supports a mechanism for a system to reduce its state of readiness
with the cooperation of USB 3.0 devices. This may result in substantial system power savings
without requiring additional cost to devices.
This section provides a device implementation example for LTM support. This example is based
on a model using two device Latency Tolerance states, an active state and an idle state. Each state
has a different Best Effort Latency Tolerance (BELT).
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In the following subsections, first a description of BELT and its relationship to overall system exit
latency is given. This is followed by a description of a device state machine implementation
example.
C.4.1
Device State Machine Implementation Example
This section describes an example of a typical device implementation. It assumes the device
implementation supports both U1 and U2 in conjunction with LTM.
In this example, two device Latency Tolerance states (LT-states) are defined:
• LT-idle state: the device is idle and can tolerate a larger latency from the system (this is the
default state).
• LT-active state: the device has determined a need to perform data transfers with the host and
wants a shorter latency from the system.
A state machine is illustrated in Figure C-8.
Device Becomes Idle
LT-idle
LT-active
Device Determines
Need for Data Transfer
U-168
Figure C-8. LT State Diagram
The device described by this implementation example is designed to accommodate the worst case
value for U1SEL during LT-active, and the worst case value for U2SEL during LT-idle.
The following device design goals are to be met:
• Design for a minimum LTM BELT of 1 ms when in LT-idle
• Design for a minimum LTM BELT of 125 μs when in LT-active
C.4.1.1
LTM-Idle State BELT
The device determines its LT-idle state BELT value by subtracting U2SEL from the total latency it
can tolerate. To achieve a minimum LT-idle state BELT of 1 ms, the total latency the device must
be able to tolerate is 1 ms plus the worst case value for U2SEL, or a total of approximately 3.1 ms
(refer to Section C.1.5.1). The worst case U2SEL is based on a worst case device-to-host U2 exit
latency of 2.053 ms for t1 (2.047 ms device exit latency plus 1 μs for each of five hubs), plus 0.003
ms for t2, plus 0.001 ms for t4, plus some guard band.
For system implementations where U2SEL is less than its worst case value, the device reports a
BELT value larger than 1 ms.
C.4.1.2
LTM-Active State BELT
The device determines its LT-active state BELT value by subtracting U1SEL from the total latency
it can tolerate. To achieve a minimum LT-active state BELT of 125 μs, the total latency the device
must be able to tolerate is 125 μs plus the maximum value for U1SEL, or a total of approximately
145 μs. The worst case U1SEL is based on a worst case device-to-host U1 exit latency of 15 μs for
t1 (10 μs device exit latency plus 1 μs for each of five hubs), plus 3.1 μs for t2, plus 1.3 μs for t4,
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plus some guard band. This assumes the device will not allow its link to enter U2 prior to changing
its state to LT-idle. If the device will allow its link to enter U2 when in LT-active, then the total
latency the device must be able to tolerate is 125 μs plus the worst case value for U2SEL.
For system implementations where U1SEL is less than its worst case value, the device reports a
BELT value larger than 125 μs.
C.4.1.3
Transitioning Between LT-States
When a device transitions between LT-states, the device sends an LTM Transaction Packet (TP)
with an updated BELT. The device should send all BELT updates as soon as possible after a
change in LT-state.
C.4.1.3.1
Transitioning From LT-idle to LT-active
Devices transition from LT-idle to LT-active when the device determines that a bulk or interrupt
data transfer needs to occur. Some examples are given below:
• The host initiates a bulk OUT transfer with the Packets Pending flag asserted to a flash drive
device. As a result of receiving this OUT request, the device transitions to LT-active and sends
an updated BELT to the host.
• The host initiates a bulk IN transfer with the Packets Pending flag asserted to a hard disk drive
device with is spindle currently spun down and the requested data not in a cache on the hard
disk drive. As a result of receiving this IN request, the device determines that a bulk data
transfer has been initiated by the host. However, the device will service the IN request after its
spindle spins up, which may take substantially longer than the last reported BELT. The device
may delay transitioning to LT-active. When the device determines that the spindle will
complete its spin up within the last reported BELT, the device transitions to LT-active and
sends an updated BELT to the host.
• A Network Interface Controller device begins receiving data on its network interface that
requires a bulk IN data transfer with the host. As a result of receiving data on its network
interface, the device transitions to LT-active, begins to transition its link to U0 (if not already in
U0), and sends both an ERDY and an updated BELT to the host.
• A multi-touch Human Interface Device is set up with an interrupt endpoint. When human input
is detected the device transitions to LT-active, begins transitioning its link to U0 (if not already
in U0), and sends both an ERDY and an updated BELT to the host.
In some cases, a transition from LT-idle to LT-active is not appropriate even though the device
needs to transmit to the host. For example:
• The host sends a GetStatus request to a device. Since it is a control transfer and not a bulk or
an interrupt transfer, the device remains in the LT-idle state.
When the device transitions from LT-idle to LT-active, the device sends an LTM TP with a BELT
of at least tBELTmin.
C.4.1.3.2
Transitioning From LT-active to LT-idle
When a device determines that it is idle, it transitions from LT-active to LT-idle. The method used
in this example for device idle detection is based on U2 entry. When the device is in LT-active, the
device transitions to LT-idle just prior to when its link will enter U2.
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In preparation for a transition from U0 to U2, a device in LT-active should perform the following
actions:
1. The device transitions to LT-idle.
2. The device sends an LTM with a BELT value of at least tBELTdefault.
3. The device initiates a transition to U2 from U0.
In preparation for a transition from U1 to U2, a device in LT-active should perform the following
actions:
1. The device transitions its link to U0 prior to U2 entry.
2. The device transitions to LT-idle.
3. The device sends an LTM with a BELT value of at least tBELTdefault.
4. The device initiates a transition to U2 from U0.
In the latter case, since the device must transition its link to U0 prior to U2 entry, the device must
detect the U2 inactivity timer expiration enough in advance to avoid the possibility that its link
partner will have already transitioned from U1 directly to U2. For example, the device may initiate
a transition to U0 1 μs before the U2 inactivity timer expires.
C.4.2
Other Considerations
The following are additional considerations associated with device support of LTM:
• The BELT represents a latency tolerance for an entire peripheral device. The BELT value must
be aggregated across all endpoints within the device, including all functions within a composite
device. The smallest BELT value across all endpoints should be selected. For LTM purposes,
isochronous endpoints are ignored when determining the BELT value.
• If LTM is supported by a device, LTM should be disabled prior to placing the device into
suspend (refer to the PORT_LINK_STATE feature selector in Chapter 10). Devices send an
updated LTM when LTM is enabled, or immediately before LTM is disabled, as defined in
Chapter 8. Disabling LTM in this way ensures that a suspended device does not keep the
system in a high state of readiness, wasting power.
C.5
SuperSpeed vs. High Speed Power Management
Considerations
Some devices may operate well with a High Speed (480 Mbps) interface, but can substantially
reduce system power consumption if implemented with a SuperSpeed interface. In addition to
device power consumption, system power consumption should be considered when selecting the
interface for a new device design.
When a device is actively transferring data, system components are also transferring that data. For
some systems, the power consumption of system components is much larger than a USB device’s
contribution to the system’s power consumption.
Under typical circumstances, the faster the data transfer completes, the faster system components
can return to a low power state. Transferring data faster can save power, on average, over time.
Examples of system components include a Host Controller, a DRAM controller, DRAM
components, a microprocessor with a cache that needs to snoop DRAM accesses, etc.
C-25
Universal Serial Bus 3.0 Specification, Revision 1.0
Figure C-9 illustrates a sample device that has an average data transfer rate of 20 MBps when
actively in use. The figure shows the system power consumption when the device is operating in
SuperSpeed mode and also in High Speed mode.
System Power
High Speed
Data Transfers
PSS-ACTIVE
PHS-ACTIVE
PIDLE
SuperSpeed
Data Transfers
Time
System Power During SuperSpeed Data Transfer
System Power During High Speed Data Transfer
U-169
Figure C-9. System Power during SuperSpeed and High Speed Device Data Transfers
When no data transfer is taking place the system power consumption is PIDLE. PIDLE is
approximated to be the same in both SuperSpeed and High Speed modes. Link power management
considerations are ignored for simplicity of illustration.
When a data transfer is taking place, the system power is PSS-ACTIVE and PHS-ACTIVE for SuperSpeed
and High Speed modes respectively. The difference between PSS-ACTIVE and PHS-ACTIVE is due to the
physical layer interface power of the device and its link partner (no hubs present).
Data transfers complete roughly ten times faster in SuperSpeed mode than in High Speed mode.
This causes the average system power in High Speed mode to be much larger than the average
system power in SuperSpeed mode. The difference in average system power may be as high as
50% during a data transfer. This can have a major impact on the battery life of mobile systems.
C-26
D
Example Packets
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
000_0001b
Reserved
000_0000_0000b
Reserved
00000b
NumP
00001b
Type
00100b
Reserved
0000b
Ept Num
0000b
D
0
Rsvd
000b
SubType
0011b
Reserved
000_0000_0000_0000_0000_0000_0000b
Link Control Word
0 0 001b
000b
11110b
8 7 6 5 4 3 2 1 0
Reserved
0000_0000_0000_0000_0000b
CRC-16
010b
10001111b
01001110b
U-164
Figure D-1. Sample ERDY Transaction Packet
31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 16 15 14 13 12 11 10 9
Device Address
000_0100b
Data Length
0000_0000_0000_1001b
Rsvd
0000b
01011b
PP
1
8 7 6 5 4 3 2 1 0
Type
01000b
Routing String
0000_0000_0000_0010_0001b
S
0
Rsvd
000b
Ept Num
0001b
D EOB R
0 1 0
Seq Num
00010b
Reserved
000_0000_0000_0000_0000_0000_0000b
Link Control Word
0 0 010b
000b
CRC-16
001b
00011000b
11101101b
Byte 3
0111_0110b
Byte 2
0101_0100b
Byte 1
0011_0010b
Byte 0
0001_0000b
Byte 7
1111_1110b
Byte 6
1101_1100b
Byte 5
1011_1010b
Byte 4
1001_1000b
0110_0010b
CRC32
1111_0011b
1000_1011b
Byte 8
0001_0000b
CRC32
0000_0111b
U-165
Figure D-2. Sample Data Packet
D-1
Universal Serial Bus 3.0 Specification, Revision 1.0
D-2
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