PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports

PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
ƒ PEX 8636 General Features
o 36-lane, 24-port PCIe Gen2 switch
- Integrated 5.0 GT/s SerDes
o 35 x 35mm2, 1156-ball FCBGA package
o Typical Power: 8.8 Watts
The ExpressLane™ PEX 8636 device offers Multi-Host PCI Express
switching capability enabling users to connect multiple hosts to their
respective endpoints via scalable, high bandwidth, non-blocking
interconnection to a wide variety of applications including
communications platforms. The PEX 8636 is well suited for fan-out,
aggregation, and peer-to-peer applications.
PEX 8636 Key Features
o Standards Compliant
- PCI Express Base Specification, r2.0
(backwards compatible w/ PCIe
- PCI Power Management Spec, r1.2
- Microsoft Vista Compliant
- Supports Access Control Services
- Dynamic link-width control
- Dynamic SerDes speed control
o High Performance
♦ performancePAK
9 Read Pacing (bandwidth throttling)
9 Multicast
9 Dynamic Buffer/FC Credit Pool
- Non-blocking switch fabric
- Full line rate on all ports
- Packet Cut-Thru with 200ns max packet
latency (x1 to x1)
- 2KB Max Payload Size
o Flexible Configuration
- Ports configurable as x1, x4, x8, x16
- Registers configurable with strapping
pins, EEPROM, I2C, or host software
- Lane and polarity reversal
- Compatible with PCIe 1.0a PM
o Multi-Host & Fail-Over Support
- Configurable Non-Transparent (NT) port
- Failover with NT port
- Up to Eight upstream/Host ports with
1+1 or N+1 failover to other upstream
o Quality of Service (QoS)
- Eight traffic classes per port
- Weighted round-robin source
port arbitration
o Reliability, Availability, Serviceability
♦ visionPAK
9 Per Port Performance Monitoring
ƒ Per port payload & header counters
9 SerDes Eye Capture
9 Error Injection and Loopback
- 3 Hot Plug Ports with native HP Signals
- All ports hot plug capable thru I2C
(Hot Plug Controller on every port)
- ECRC and Poison bit support
- Data Path parity
- Memory (RAM) Error Correction
- INTA# and FATAL_ERR# signals
- Advanced Error Reporting
- Port Status bits and GPIO available
• Per port error diagnostics
- JTAG AC/DC boundary scan
© PLX Technology,
Multi-Host Architecture
The PEX 8636 employs an enhanced version of PLX’s field tested PCIe
switch architecture, which allows users to configure the device in legacy
single-host mode or multi-host mode with up to Eight host ports capable of
1+1 (one active & one backup) or N+1 (N active & one backup) host failover.
This powerful architectural enhancement enables users to build PCIe based
systems to support high-availability, failover, redundant and clustered
High Performance & Low Packet Latency
The PEX 8636 architecture supports packet cut-thru with a maximum
latency of 200ns (x1 to x1). This, combined with large packet memory,
flexible common buffer/FC credit pool and non-blocking internal switch
architecture, provides full line rate on all ports for performance-hungry
applications such as servers and switch fabrics. The low latency enables
applications to achieve high throughput and performance. In addition to low
latency, the device supports a packet payload size of up to 2048 bytes,
enabling the user to achieve even higher throughput.
Data Integrity
The PEX 8636 provides end-to-end CRC (ECRC) protection and Poison bit
support to enable designs that require end-to-end data integrity. PLX also
supports data path parity and memory (RAM) error correction circuitry
throughout the internal data paths as packets pass through the switch.
Flexible Configuration
The PEX 8636’s 24 Ports can be
configured to lane widths of x1,
x4, x8 or x16. Flexible buffer
allocation, along with the device's
flexible packet flow control,
applications where more traffic
flows in the downstream, rather
than upstream, direction. Any port
can be designated as the upstream
port, which can be changed
dynamically. Figure 1 shows
some of the PEX 8636’s common
port configurations in legacy
Single-Host mode.
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PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
The PEX 8636 can also be configured in Multi-Host mode
where users can choose up to Eight ports as host/upstream
ports and assign a desired number of downstream ports to
each host. In Multi-Host mode, a virtual switch is created
for each host port and its associated downstream ports
inside the device. The traffic between the ports of a virtual
switch is completely isolated from the traffic in other
virtual switches. Figure 2 illustrates some configurations
of the PEX 8636 in Multi-Host mode where each ellipse
represents a virtual switch inside the device.
The PEX 8636
also provides
several ways to
configure its
registers. The
device can be
strapping pins,
I2C interface,
host software,
or an optional
allows for easy
debug during
the development phase, performance monitoring during
the operation phase, and driver or software upgrade.
Dual-Host & Failover Support
In Single-Host mode, the PEX 8636 supports a NonTransparent (NT) Port, which enables the
implementation of dualhost systems for
redundancy and host
failover capability. The
NT port allows systems
to isolate host memory
domains by presenting
the processor subsystem
as an endpoint rather
than another memory
system. Base address
registers are used to
translate addresses;
doorbell registers are used to send interrupts between the
address domains; and scratchpad registers (accessible by
both CPUs) allow inter-processor communication (see
Figure 3).
© PLX Technology,
Multi-Host & Failover Support
In Multi-Host mode, PEX 8636 can be configured with up
to Eight upstream host ports, each with its own dedicated
downstream ports. The device can be configured for 1+1
redundancy or N+1 redundancy. The PEX 8636 allows the
hosts to communicate their status to each other via special
door-bell registers. In failover mode, if a host fails, the
host designated for failover will disable the upstream port
attached to the failing host and program the downstream
ports of that host to its own domain. Figure 4a shows a two
host system in Multi-Host mode with two virtual switches
inside the device and Figure 4b shows Host 1 disabled
after failure and Host 2 having taken over all of Host 1’s
Hot Plug for High Availability
Hot plug capability allows users to replace hardware
modules and perform maintenance without powering down
the system. The PEX 8636 hot plug capability feature
makes it suitable for High Availability (HA)
applications. Four downstream ports include a Standard
Hot Plug Controller. If the PEX 8636 is used in an
application where one or more of its downstream ports
connect to PCI Express slots, each port’s Hot Plug
Controller can be used to manage the hot-plug event of its
associated slot. Every port on the PEX 8636 is equipped
with a hot-plug control/status register to support hot-plug
capability through external logic via the I2C interface.
SerDes Power and Signal Management
The PEX 8636 supports software control of the SerDes
outputs to allow optimization of power and signal strength
in a system. The PLX SerDes implementation supports
four levels of power – off, low, typical, and high. The
SerDes block also supports loop-back modes and
advanced reporting of error conditions, which enables
efficient management of the entire system.
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PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
The PEX 8636 is designed to be fully compliant with the
PCI Express Base Specification r2.0, and is backwards
compatible to PCI Express Base Specification r1.1 and
r1.0a. Additionally, it supports auto-negotiation, lane
reversal, and polarity reversal on its wide ports.
Furthermore, the PEX 8636 is tested for Microsoft Vista
compliance. All PLX switches undergo thorough
interoperability testing in PLX’s Interoperability Lab and
compliance testing at the PCI-SIG plug-fest.
Another PLX exclusive, visionPAK is a debug diagnostics
suite of integrated hardware and software instruments that
users can use to help bring their systems to market faster.
visionPAK features consist of Performance Monitoring,
SerDes Eye Capture, Error Injection, SerDes Loopback,
and more.
Exclusive to PLX, performancePAK is a suite of unique
and innovative performance features which allows PLX’s
Gen 2 switches to be the highest performing Gen 2
switches in the market today. The performancePAK
features consists of the Read Pacing, Multicast, and
Dynamic Buffer Pool.
Read Pacing
The Read Pacing feature allows users to throttle the
amount of read requests being made by downstream
devices. When a downstream device requests several long
reads back-to-back, the Root Complex gets tied up in
serving that downstream port. If that port has a narrow link
and is therefore slow in receiving these read packets from
the Root Complex, then other downstream ports may
become starved – thus, impacting performance. The Read
Pacing feature enhances performances by allowing for the
adequate servicing of all downstream devices.
Performance Monitoring
The PEX 8636’s real time performance monitoring allows
users to literally “see” ingress and egress performance on
each port as traffic passes through the switch using PLX’s
Software Development Kit (SDK). The monitoring is
completely passive and therefore has no affect on overall
system performance. Internal counters provide extensive
granularity down to traffic & packet type and even allows
for the filtering of traffic (i.e. count only Memory Writes).
SerDes Eye Capture
Users can evaluate their system’s signal integrity at the
physical layer using the PEX 8636’s SerDes Eye Capture
feature. Using PLX’s SDK, users can view the receiver
eye of any lane on the switch. Users can then modify
SerDes settings and see the impact on the receiver eye.
Figure 5 shows a screenshot of the SerDes Eye Capture
feature in the SDK.
The Multicast feature enables the copying of data (packets)
from one ingress port to multiple (up to 23) egress ports in
one transaction allowing for higher performance in dualgraphics, storage, security, and redundant applications,
among others. Multicast relieves the CPU from having to
conduct multiple redundant transactions, resulting in
higher system performance.
Dynamic Buffer Pool
The PEX 8636 employs a dynamic buffer pool for Flow
Control (FC) management. As opposed to a static buffer
scheme which assigns fixed, static buffers to each port,
PLX’s dynamic buffer allocation scheme utilizes a
common pool of FC Credits which are shared by other
ports. This shared buffer pool is fully programmable by the
user, so FC credits can be allocated among the ports as
needed. Not only does this prevent wasted buffers and
inappropriate buffer assignments, any unallocated buffers
remain in the common buffer pool and can then be used
for faster FC credit updates.
© PLX Technology,
Figure 5. SerDes Eye Capture
Error Injection & SerDes Loopback
Using the PEX 8636’s Error Injection feature, users can
inject malformed packets and/or fatal errors into their
system and evaluate a system’s ability to detect and
recover from such errors. The PEX 8636 also supports
Internal Tx, External Tx, Recovered Clock, and Recovered
Data Loopback modes.
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PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
Host Failover in Comms Control Plane
Suitable for host-centric as well as peer-to-peer traffic
patterns, the PEX 8636 can be configured for a wide
variety of form factors and applications.
Host Centric Fan-out in Control Plane
The PEX 8636, with its high port count, provides adequate
connectivity when used in host-centric applications. Figure
6 shows a control plane design where a single processor is
used to control a large number of proprietary ASICS,
FPGAs and/or other fabric interface chips. The upstream
port in this case can be programmed with a fat pipe, up to
x16, to the processor in order to sustain bandwidth
requirements from the downstream devices. Moreover,
each port in the PEX 8636 can independently support
2.5GT/s and/or 5.0GT/s devices.
The PEX 8636 can also be utilized in applications where
host failover is required. In the control plane application
below (Figure 8), an Active-Standby failover example is
shown. In this case, there is one active host which is
managing the endpoints during run-time. The PEX 8636
provides Non-Transparent functionality which can be
enabled on a single port. The Non-Transparent port allows
the Standby processor to communicate and exchange
status information with the primary processor without
interfering with the endpoints. When failover needs to
occur, system software configures the PEX 8636 so that
the upstream port is connected to the standby processor.
Figure 8. Failover using Non-Transparency
Figure 6. Host Centric Application
Multicast in Control Plane
The PEX 8636 implements Multicast as defined in the
PCIe Specification. It provides support for 64 multicast
groups and any port in the Switch can be the source port
for a multicast transaction. In a control plane application,
the multicast feature provides processor relief during
configuration and run-time by requiring the processor to
issue a single transaction and allowing the switch to
replicate that particular transaction to multiple destinations
as defined in the multicast group.
A second method for implementing failover is through the
Virtual Switch mode function. Figure 9 shows a control
plane application using the Virtual Switch mode. In these
example, two hosts may be active simultaneously and
controlling their own domains while exchange status
information through doorbell registers or I2C interface.
The devices can be programmed to trigger fail-over if the
heartbeat information is not provided. In the event of a
failure, the surviving device will reset the endpoints
connected to the failing processor and enumerate them in
its own domain without impacting the operation of
endpoints already in its domain.
Figure 8. Failover using Virtual Switch function
Figure 7. Multicast on PEX 8636
© PLX Technology,
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PEX 8636, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
Software Usage Model
From a system model viewpoint, each PCI Express port is
a virtual PCI to PCI bridge device and has its own set of
PCI Express configuration registers. It is through the
upstream port that the BIOS or host can configure the
other ports using standard PCI enumeration. The virtual
PCI to PCI bridges within the PEX 8636 are compliant to
the PCI and PCI Express system models. The
Configuration Space Registers (CSRs) in a virtual
primary/secondary PCI to PCI bridge are accessible by
type 0 configuration cycles through the virtual primary bus
interface (matching bus number, device number, and
function number).
Interrupt Sources/Events
The PEX 8636 switch supports the INTx interrupt message
type (compatible with PCI 2.3 Interrupt signals) or
Message Signaled Interrupts (MSI) when enabled.
Interrupts/messages are generated by PEX 8636 for hot
plug events, doorbell interrupts, baseline error reporting,
and advanced error reporting.
RDK provides everything that a user needs to get their
hardware and software development started.
Software Development Kit (SDK)
PLX’s Software Development Kit is available for
download at The software
development kit includes drivers, source code, and GUI
interfaces to aid in configuring and debugging the PEX
8636. For more information, please refer to the PEX 8636
RDK Product Brief.
Both performancePAK and visionPAK are supported by
PLX’s RDK and SDK, the industry’s most advanced
hardware- and software-development kits.
Product Ordering Information
Part Number
PEX8636-AA50BC F
PEX8636-16U1D BB
36-lane, 24-port PCI Express Switch,
Pb-Free (35x35mm2)
PEX 8636 Rapid Development Kit with
x16 Upstream and 20 x1 Downstream
PLX Technology, Inc. All rights reserved. PLX, the PLX logo, ExpressLane,
Read Pacing and Dual Cast are trademarks of PLX Technology, Inc. All other
product names that appear in this material are for identification purposes only
and are acknowledged to be trademarks or registered trademarks of their
respective companies. Information supplied by PLX is believed to be accurate
and reliable, but PLX assumes no responsibility for any errors that may appear in
this material. PLX reserves the right, without notice, to make changes in product
design or specification.
Visit for more information.
Figure 10. PEX8636-16U1D AIC RDK
Development Tools
PLX offers hardware and software tools to enable rapid
customer design activity. These tools consist of a hardware
module (PEX 8636 RDK), hardware documentation
(available at, and a Software
Development Kit (also available at
ExpressLane PEX 8636 RDK
The PEX 8636 RDK (see Figure 10) is a hardware module
containing the PEX 8636 which plugs right into your
system. The PEX 8636 RDK can be used to test and
validate customer software, or used as an evaluation
vehicle for PEX 8636 features and benefits. The PEX 8636
© PLX Technology,
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