null  null
US006600739B1
(12)
(54)
United States Patent
(10) Patent N0.:
Evans et al.
(45) Date of Patent:
75
6,324,605 B1 * 11/2001 Rafferty et al. ........... .. 710/100
SWITCHING AMONG A PLURALITY ()1?
6,415,343 B1 *
.
.
Kevin P‘ Grundy Fremont C
Craig B Owens ’San carlo’s CA
’
’
Sales
(57)
Subject to any disclaimer, the term of this
patent is extended or adjusted under 35
U.S.C. 154(b) by0 days.
(21) App1_ No; 09/327,214
_
Flled:
(51)
Int. Cl. .............................................. .. H04L 12/50
Jun- 7’ 1999
A switching device and method for selecting among a
plurality of hosts on a bus, such as a Universal Serial Bus
(USB). The switching device includes a ?rst hub to be
coupled to ?rst host controller and a second hub to be
coupled to second host controller. A ?rst selection device is
to be coupled to a ?rst peripheral device and the ?rst and
tively couple the ?rst peripheral device to one of the ?rst and
7
_
glslldcltl. iiiiii
1e
ABSTRACT
second hub devices. The ?rst selection device is to selec
(22)
( )
.
Primary Exammer—Ken Vanderpuye
(74) Attorney, Agent, or Firm—V. D. Duraiswamy; M. W.
(73) Assignee: Hughes Electronics Corporation, El
Segundo, CA (US)
Notice:
7/2002 Fensore et al. ........... .. 710/104
.
* cited by examiner
Inventors: Keith M. Evans, San Jose, CA US ;
'
(*)
Jul. 29, 2003
METHOD AND APPARATUS FOR
UNIVERSAL SERIAL BUS HOST DEVICES
( )
US 6,600,739 B1
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second host devices in res onse to a selection si nal. A
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selection device is to selectively couple the second periph
eral device to one of the ?rst and second host controllers in
References Cited
response to the selection signal. The selection signal is
US. PATENT DOCUMENTS
generated in response to one of the host controllers. During
the switching process among the host controllers and periph
eral devices, a cable disconnect and reconnect between the
5,784,581 A
6,064,554 A
7/1998
*
Hannah
-
5/2000 Kim .......................... .. 361/64
6,131,135 A * 10/2000 Abramson et a1.
710/126
6,308,239 B1 * 10/2001 Osakada et a1. .......... .. 710/131
CPU
-
18 Claims, 2 Drawing Sheets
:30
SELECT
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host Controllers and penpheral devlces 1S emulated‘
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213
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USB FUNCTION
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U88 FUNCTION
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U.S. Patent
Jul. 29, 2003
US 6,600,739 B1
Sheet 1 0f 2
103
USB HOST
119
USB FUNCTION
USB FUNCTION
USB FUNCTION
FIG. 1
(PRIOR ART)
U.S. Patent
Jul. 29, 2003
Sheet 2 0f 2
US 6,600,739 B1
2:50
SELECT
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CPU f
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CPU
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$332233“
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US 6,600,739 B1
1
2
METHOD AND APPARATUS FOR
SWITCHING AMONG A PLURALITY OF
UNIVERSAL SERIAL BUS HOST DEVICES
device and a second hub device to be coupled to a second
host device. The sWitching device also includes a ?rst
selection device coupled to a ?rst peripheral device and the
?rst and second hub devices. The ?rst selection device is to
selectively couple the ?rst peripheral device to one of the
?rst and second host devices in response to a selection
signal. The sWitching device also includes a second selection
device coupled to a second peripheral device and the ?rst
and second hub devices. The second selection device is to
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention generally relates to switching host
devices on a communications bus, and more speci?cally, the
present invention relates to sWitching host devices on a
10
Universal Serial Bus (USB).
2. Background Infommation
selectively couple the second peripheral device to said one
of the ?rst and second host devices in response to the
selection signal. Additional features and bene?ts of the
present invention Will become apparent from the detailed
description, ?gures and claims set forth beloW.
Various types of communications links and communica
tions protocols are used to interconnect devices and alloW
interconnected devices to communicate With one another. 15
BRIEF DESCRIPTION OF THE DRAWINGS
Communications links utiliZe different methods for control
ling the ?oW of instructions and data betWeen interconnected
The present invention is illustrated by Way of eXample
and not limitation in the accompanying ?gures.
devices. For example, one device may operate as a host
device of the communications link While other devices
operate as peripheral devices on the communications link. In
this con?guration, the host device may issue commands and
tokens on the communications link, Which permits the
FIG. 1 is an illustration of a block diagram of a host
device and a plurality of USB functions coupled together
through USB.
peripheral devices to communicate. If a particular peripheral
FIG. 2 is an illustration of one embodiment of a sWitching
device does not receive an appropriate command or token,
then the peripheral device does not transmit on the commu
device in accordance With the teachings of the present
invention.
25
nications link. Thus, a single host device controls the How of
DETAILED DESCRIPTION
commands and data on the communications link.
Another con?guration provides peer-to-peer interconnec
A method and an apparatus providing a USB sWitching
apparatus is disclosed. In the folloWing description numer
tions betWeen various devices on a communications link. In
this con?guration, the devices are not identi?ed as either a
ous speci?c details are set forth in order to provide a
host device or a peripheral device. Instead, each devices
capable of issuing commands and data on the communica
tions link Without requiring “permission” from another
device.
One particular system for interconnecting devices is pro
vided by the Universal Serial Bus (USB) standard. USB is
35
a useful system for connecting a series of peripheral devices
invention.
For illustration purposes, the present invention Will be
described as used in a Universal Serial Bus (USB) con?gu
ration. HoWever, those skilled in the art Will appreciate that
the present invention is applicable to any protocol or system
or USB functions to a computer. The USB utiliZes a USB
host controller contained Within a personal computer (PC) or
other computing device. The USB host controller operates as
the USB host device or master and controls other USB slave
devices or USB functions connected to the USB. To
illustrate, FIG. 1 is a block diagram illustrating a USB host
device 103 coupled to a plurality of USB functions 115, 117
and 119 through a USB hub 107. All data How on the USB
is controlled or monitored by the USB host device 103. The
USB host device 103 issues tokens and commands to the
for interconnecting various devices. Furthermore, the
45
present invention may be utiliZed With all variations and
extensions of USB, or the like.
The present invention is related to a system for providing
multiple host devices to be sWitched to control peripheral
devices over a communications link such as a USB.
attached USB functions 115, 117 and 119 giving permission
Therefore, peripheral devices may be shared by a plurality
of hosts in accordance With the teachings of the present
to transmit on the USB.
The USB speci?cation provides for a computer (eg a
personal computer) as the host device, issuing tokens and
commands to all USB functions. The USB speci?cation does
invention. In addition, if a primary host device on the
communications link is deactivated, a secondary host device
on the communications link may take control. Thus, periph
eral devices on the communications link Will continue to
not provide for USB functions that are shared among
multiple hosts. In addition, the USB speci?cation does not
address the issue of providing communications betWeen
thorough understanding of the present invention. It Will be
apparent, hoWever, to one having ordinary skill in the art that
the speci?c detail need not be employed to practice the
present invention. In other instances, Well-knoWn materials,
methods, procedures, components and circuits have not been
described in detail in order to avoid obscuring the present
55
have the ability to communicate.
Referring to FIG. 2, one embodiment of a communica
USB functions When a USB host controller is removed or is
tions link con?guration 201 is illustrated in accordance With
the teachings of the present invention. In one embodiment,
con?guration 201 includes USB devices. As illustrated, a
central processing unit (CPU) 230 is coupled to a USB host
not active (e.g. turned off). Thus, When a USB host device
is removed or deactivated, the USB functions 115, 117 and
119 are no longer able to communicate. Furthermore, the
USB speci?cation does not provide a system for sWitching
The present invention provides USB sWitching device
controller 203 and CPU 231 is coupled to USB host con
troller 205. In one embodiment, CPU 230 is coupled to USB
host controller 203 through a processor bus 233 and CPU
231 is coupled to USB host controller 205 through processor
bus 234. In one embodiment, USB host controllers 203 and
205 are implemented as combinations of hardWare, softWare
including a ?rst hub device to be coupled to a ?rst host
or ?rmWare. A doWnstream port of a USB host controller
control of the USB among USB host devices to enable a
USB function to be available to the particular USB host
device that needs to communicate With the USB function.
SUMMARY OF THE INVENTION
65
US 6,600,739 B1
3
4
203 is coupled to an upstream port of a USB hub 207. In one
embodiment, USB hub 207 is a root hub and is integrated
With the host system to provide one or more attachment
203 through the “0” upstream ports of selection devices 211
and 213, respectively. Therefore, USB functions 215 and
217 may continue to communicate even though primary
points to the USB. A doWnstream port of USB host control
ler 205 is coupled to an upstream port of a USB hub 209.
In one embodiment, doWnstream ports of USB hub 207
are coupled to upstream “0” ports of the selection devices
USB host controller 205 is deactivated.
To illustrate, USB function 215 in one embodiment may
be an Ethernet communications interface and USB function
217 may be a modem interface. In this illustration, assume
that USB host controller 205 has control of the USB
211 and 213, respectively. DoWnstream ports of USB hub
functions and acts as a bridge betWeen the tWo USB func
209 are coupled to upstream “1” ports of the selection
devices 211 and 213, respectively. A doWnstream port of
10
selection device 211 is coupled to an upstream port of a USB
function 215 and a doWnstream port of selection device 213
is coupled to an upstream port of USB function 217. In one
embodiment, USB functions 215 and 217 are devices that
may provide additional capabilities to a computer system,
tions. In accordance With the teachings of the present
invention, USB host controller 203 may be used to enable
the How of information in the event that USB host controller
205 is no longer able to act as a bridge betWeen the USB
functions. In one embodiment, if and When USB host
15
such as for eXample but not limited to an ISDN connection,
controller 203 detects through link 221 that USB host
controller 205 has been re-activated and may retake control
of the USB, select signal 223 is updated accordingly such
a digital joystick, speakers, a scanner, digital camera, etc.
that USB host controller relinquishes control of the USB.
As illustrated, CPU 230 in one embodiment generates a
select signal 223 coupled to selection devices 211 and 213.
In one embodiment, select signal 223 includes a bus having
In one embodiment, an asynchronous cable disconnect
from USB host controller 205 is emulated and an asynchro
n signals, Where n is greater than or equal to one. In one
nous cable reconnect to USB host controller 203 is emulated
embodiment, selection device 211 selectively couples USB
during the sWitching betWeen USB host controller 205 and
function 215 to either USB hub 207 or USB hub 209 in
203. In so doing, the doWnstream port of USB host control
ler 205 is presented With a USB disconnect state and the
doWnstream port of USB host controller 203 is presented
response to select signal 223. The selection device 213
selectively couples USB function 217 to either USB hub 207
or USB hub 209 in response to select signal 223. Thus, in
25
With a USB neW bus state. In one embodiment, after USB
host controller 203 is reconnected to take control of the
USB, USB host controller 203 issues a USB reset and
enumerates the bus. Thus, USB host controller 203 forces all
USB peripherals 215 and 217 to be reset and introduce
themselves over the bus according to the knoWn USB
one embodiment, USB functions 215 and 217 are selectively
coupled to either USB host controller 203 or USB host
controller 205 in response to select signal 223.
It is appreciated that the con?guration illustrated in FIG.
2 is provided for explanation purposes only and that there
protocol. Therefore, one embodiment of the present inven
may be additional USB host controllers and/or a greater or
feWer number of USB functions in accordance With the
teachings of the present invention.
During operation, assume that USB host controller 205
controls USB functions 215 and 217. In this example, USB
host controller 205 may be considered the primary host
device and USB host controller 203 may be considered the
secondary host device. As such, USB host controller 203
generates a select signal 223 via CPU 230 to enable USB
functions 215 and 217 to be coupled to USB host controller
205 through the “1” upstream ports of selection devices 211
and 213. Therefore, USB functions 215 and 217 may com
municate With one another through USB host controller 205.
Assume further that USB host controller 203 needs to
tion simulates USB peripherals 215 and 217 being physi
cally disconnected from USB host controller 205 and being
35
reconnected to USB host controller 203.
From the above description and draWings, it Will be
understood by those skilled in the art that the particular
embodiment shoWn and described are for purposes of illus
tration only and are not intended to limit the scope of the
invention. Those skilled in the art Will recogniZe that the
invention may be embodied in other speci?c forms Without
departing from the spirit or essential characteristics. Refer
ences to details of particular embodiments are not intended
45
to limit the scope of the claims.
What is claimed is:
1. A sWitching device, comprising:
control USB functions 215 and 217 or that USB host
controller 205 is deactivated or disconnected from USB hub
209. In a prior art USB con?guration, USB functions 215
a ?rst hub device coupled to a ?rst host device;
a second hub device coupled to a second host device;
a ?rst selection device coupled to a ?rst peripheral device
and 217 could not be controlled by USB host controller 203.
Moreover, USB functions 215 and 217 Would no longer be
and the ?rst and second hub devices, the ?rst selection
able to communicate over the USB if USB host controller is
device to selectively couple the ?rst peripheral device
deactivated, even though the peripheral devices may still be
active. HoWever, in one embodiment, secondary USB host
to one of the ?rst and second host devices in response
to a selection signal; and
a second selection device coupled to a second peripheral
controller 203 may take control of the USB bus.
In addition, USB host controller 203 may monitor the
status of primary USB host controller 205 over a link 221.
As illustrated, link 221 in one embodiment is a link betWeen
a USB function 232 and USB hub 209. USB function 232 is
coupled to CPU 230 and USB host controller 203 through
processor bus 233. When secondary USB host controller 203
detects that primary USB host controller 205 is no longer
available to control the USB, USB host controller 203 has
select signal 223 updated to take control of the USB. In
55
particular, select signal 223 is updated to alloW USB host
65
controller 203 to take control of the USB. In this case, USB
functions 215 and 217 are coupled to USB host controller
device and the ?rst and second hub devices, the second
selection device to selectively couple the second
peripheral device to said one of the ?rst and second host
devices in response to the selection signal.
2. The sWitching device described in claim 1 Wherein the
?rst host device is coupled to the second host device through
a link.
3. The sWitching device described in claim 1 Wherein the
selection signal is generated in response to the ?rst host
device.
4. The sWitching device described in claim 1 Wherein the
?rst and second peripheral devices are selectively coupled to
US 6,600,739 B1
6
5
12. The method described in claim 11 Wherein the step of
said one of the ?rst and second host devices through the ?rst
and second hub devices according to a Universal Serial Bus
presenting the upstream port of the USB peripheral device
the neW bus state is performed during the sWitching step.
(USB) protocol.
5. The sWitching device described in claim 2 Wherein the
?rst host device is further coupled to the second hub device
such that the link comprises the second hub device.
6. A method for sWitching betWeen a plurality of Univer
sal Serial Bus (USB) host devices from being coupled to a
13. The method described in claim 6 including the addi
tional step of issuing a USB reset command by the second
one of the USB host devices to the USB peripheral device
USB peripheral device, the method comprising the steps of:
tional step of latching a signal received by the upstream port
of the USB peripheral device.
generating a host select signal; and
sWitching an upstream port of the USB peripheral device
after the sWitching step.
14. The method described in claim 6 including the addi
10
15. A device adapted to be coupled to a Universal Serial
Bus (USB), comprising:
from being coupled to a doWnstream port of a ?rst USB
hub device to a doWnstream port of a second USB hub
device in response to the host select signal, Wherein a
?rst one of the USB host devices is coupled to an 15
upstream port of the ?rst USB hub device and a second
one of the USB host devices is coupled to an upstream
port of the second USB hub device.
7. The method described in claim 6 including the addi
tional step of coupling together the ?rst and second ones of
the USB host devices through a link.
8. The method described in claim 7 Wherein the host select
signal is generated in response to the ?rst one of the USB
host devices.
9. The method described in claim 7 Wherein the host select
signal is generated in response to the second one of the USB
host devices.
10. The method described in claim 6 Wherein the folloW
?rst selection device to selectively couple the ?rst USB
signal; and
a second selection device coupled to a second USB
25
selection signal.
tion signal is generated in response to the ?rst USB host
one of the USB host devices.
host devices a disconnect state; and
presenting the doWnstream port of the second one of the
USB host devices a neW bus state.
peripheral device and the ?rst and second USB hub
devices, the second selection device to selectively
couple the second USB peripheral device to said one of
the ?rst and second USB host devices in response to the
16. The device described in claim 15 Wherein the ?rst
USB host device is coupled to the second USB host device
through a link.
17. The device described in claim 15 Wherein the selec
one of the USB host devices; and
emulating an asynchronous cable reconnect to the second
presenting the doWnstream port of the ?rst one of the USB
device;
peripheral device to one of a ?rst USB host device and
a second USB host device in response to a selection
emulating an asynchronous cable disconnect from the ?rst
11. The method described in claim 6 Wherein the folloW
device;
a second USB hub device coupled to the second USB host
a ?rst selection device coupled to a ?rst USB peripheral
device and the ?rst and second USB hub devices, the
ing steps are performed during the sWitching step:
ing steps are performed during the sWitching step:
a ?rst USB hub device coupled to the ?rst USB host
35
device.
18. The device described in claim 16 Wherein the ?rst
USB host device is further coupled to the second USB hub
device such that the link comprises the second USB hub
device.
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