PEX8796, PCI Express Gen3 Switch, 96 Lanes, 24 Ports

PEX8796, PCI Express Gen3 Switch, 96 Lanes, 24 Ports
PEX8796 General Features
o 96-lane, 24-port PCIe Gen3 switch
- Integrated 8.0 GT/s SerDes
o 35 x 35mm2, 1156-ball FCBGA package
o Typical Power: 18.6 Watts
 PEX8796 Key Features
o Standards Compliant
- PCI Express Base Specification, r3.0
(compatible w/ PCIe r1.0a/1.1 & 2.0)
- PCI Power Management Spec, r1.2
- Microsoft Windows Logo Compliant
- Supports Access Control Services
- Dynamic link-width control
- Dynamic SerDes speed control
o High Performance
 performancePAK
 Multicast
 Dynamic Buffer/FC Credit Pool
- Non-blocking switch fabric
- Full line rate on all ports
- Cut-Thru with 150ns max packet latency
- 2KB Max Payload Size
o Multi-Host & Fail-Over Support
- 2 Configurable Non-Transparent ports
- Failover with Non-Transparent port
- Up to 4 upstream/Host ports with 1+1 or
N+1 failover to other upstream ports
o Quality of Service (QoS)
- Traffic Class Queuing
- Eight traffic classes per port
- Weighted round-robin source
port arbitration
o Reliability, Availability, Serviceability
 visionPAK
 Per Port Performance Monitoring
 SerDes Eye Capture
 PCIe Packet Generator
 Error Injection and Loopback
- 6 Hot-Plug port with native HP Signals
- All ports Hot-Plug capable thru I2C
- SSC Isolation on up to 24 ports
- ECRC and Poison bit support
- Data Path parity
- Memory (RAM) Error Correction
- Advanced Error Reporting
- Port Status bits and GPIO available
- JTAG AC/DC boundary scan
The ExpressLaneTM PEX8796 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 servers, storage
systems, and communications platforms. The PEX8796 is well suited for
fan-out, aggregation, and peer-to-peer applications.
Multi-Host Architecture
The PEX8796 employs an enhanced architecture, which allows users to
configure the device in legacy single-host mode or multi-host mode with up
to four 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 systems.
High Performance & Low Packet Latency
The PEX8796 architecture supports packet cut-thru with a maximum
latency of 150ns (x16 to x16). 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 PEX8796 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 PEX8796’s 24 ports can be configured to lane
widths of x4, x8, or x16. Flexible buffer allocation,
along with the device's flexible packet flow
control, maximizes throughput for 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
PEX8796’s common port configurations in legacy
Single-Host mode.
The PEX8796 can also be configured in Multi-Host mode where users can
choose up to four 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 PEX8796 in Multi-Host mode where each ellipse
represents a virtual switch inside the device.
© PLX Technology,
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PEX8796, PCI Express Gen3 Switch, 96 Lanes, 24 Ports
The PEX8796 also
provides several ways to
configure its registers.
The device can be
configured through
strapping pins, I2C
interface, host software,
or an optional serial
EEPROM. This 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 PEX8796 supports a NonTransparent (NT) Port, which enables the
implementation of dual-host 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).
Multi-Host & Failover Support
In Multi-Host mode, PEX8796 can be configured with
up to four upstream host ports, each with its own
dedicated downstream ports. The device can be
configured for 1+1 redundancy or N+1 redundancy. The
PEX8796 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 MultiHost 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 end-points.
© PLX Technology,
Host 1
Host 2
Host 1
PEX 8796
Host 2
PEX 8796
Figure 4a. Multi-Host
Figure 4b. Multi-Host Fail-Over
Hot-Plug for High Availability
Hot plug capability allows users to replace hardware
modules and perform maintenance without powering
down the system. The PEX8796 Hot-Plug capability
feature makes it suitable for High Availability (HA)
applications. Four downstream ports include a Standard
Hot Plug Controller. If the PEX8796 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 PEX8796 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 PEX8796 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.
The PEX8796 is designed to be fully compliant with the
PCI Express Base Specification r3.0, and is backwards
compatible to PCI Express Base Specification r1.1 and
r1.0a. Additionally, it supports auto-negotiation, lane
reversal, and polarity reversal. Furthermore, the
PEX8796 is tested for Microsoft Windows Logo
compliance. All PLX switches undergo thorough
interoperability testing in PLX’s Interoperability Lab
and compliance testing at the PCI-SIG plug-fest.
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PEX8796, PCI Express Gen3 Switch, 96 Lanes, 24 Ports
Exclusive to PLX, performancePAK is a suite of unique
and innovative performance features which allows
PLX’s Gen 3 switches to be the highest performing Gen
3 switches in the market today. The performancePAK
features consists of Multicast, and Dynamic Buffer Pool.
SSC Isolation
The PEX8796 employs a multi-clock domain which
allows the user to terminate Spread Spectrum Clock
enabled domains. Terminating the SSC clock removes
the need to pass a common clock across a backplane.
The PEX8796 supports SSC isolation on all of its ports.
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.
Performance Monitoring
The PEX8796’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 PEX8796’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.
Figure 5. SerDes Eye Capture
Error Injection & SerDes Loopback
Using the PEX8796’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 PEX8796 also supports
Internal Tx, External Tx, Recovered Clock, and
Recovered Data Loopback modes.
Suitable for host-centric as well as peer-to-peer traffic
patterns, the PEX8796 can be configured for a wide
variety of form factors and applications.
Host Centric Fan-out
The PEX8796, with its symmetric or asymmetric lane
configuration capability, allows user-specific tuning to a
variety of host-centric applications. Figure 6 shows a
server design where, in a quad or multi processor
system, users can assign endpoints/slots to CPU cores to
distribute the system load. The packets directed to
different CPUs will go to different (user assigned)
PEX8796 upstream ports, allowing better queuing and
load balancing capability for higher performance.
PEX 8796
PCIe Gen1 Gen2, and Gen3 slots
Figure 6. Host Centric Dual Upstream
© PLX Technology,
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PEX8796, PCI Express Gen3 Switch, 96 Lanes, 24 Ports
Multi-Host Systems
In multi-host mode, the PEX8796 can support up to four
hosts at once. By creating four virtual switches, the
PEX8796 allows four hosts to fan-out to their respective
endpoints. This reduces the number of switches required
for fan-out, saving precious board space and power. In
Figure 7, the PEX8796 is being shared by four different
CPU cores (hosts) on three servers, with each CPU core
running its own applications (I/Os). The PEX8796
assigns the endpoints to the appropriate host and isolates
them from the other hosts. In Figure 7, the endpoints are
assigned to the CPU core of the same color.
PEX 8796
PEX 8796
Figure 7. Multi-Host System
Figure 9. Host Fail-Over
High-End Graphics Systems
The PEX8796’s 96 lanes can come in handy for highend graphics systems, such as high-resolution gaming
and medical imaging applications, employing two or
more GPUs alongside multiple endpoints. Figure 8a
shows a dual-graphics system where the PEX8796 is
being used to fan-out to two GPUs using x16 links and
numerous (up to 16) endpoints using x4 and x8 links.
Figure 8b, shows an ultra-gaming system using the
PEX8796 to fan-out to four GPUs via x16 links. In both
examples, two x16 upstream ports are being used. Using
PEX8796’s multi-host capabilities, two separate virtual
hierarchies can be created, assigning GPUs & endpoints
to a particular CPU core via the x16 upstream ports.
© PLX Technology,
x4 & x8
PEX 8796
Host Failover
The PEX8796 can also be utilized in applications where
host failover is required. In the below application
(Figure 9), 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 CPU and enumerate them in its
own domain without impacting the operation of
endpoints already in its domain.
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PEX8796, PCI Express Gen3 Switch, 96 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 PEX8796 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 PEX8796 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 PEX8796 for hot
plug events, doorbell interrupts, baseline error reporting,
and advanced error reporting.
Development Tools
PLX offers hardware and software tools to enable rapid
customer design activity. These tools consist of a
hardware module (PEX8796 RDK), hardware
documentation (available at, and a
Software Development Kit (also available at
validate customer software, or used as an evaluation
vehicle for PEX8796 features and benefits. The
PEX8796 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
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
PEX8796-AB80BI G
96-Lane, 24-Port PCI Express Gen 3
Switch, Pb-Free (35x35mm2)
PEX8796 Rapid Development Kit
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.
ExpressLane PEX8796 RDK
The PEX8796 RDK is a baseboard RDK containing the
PEX8796 and multiple PCIe slots for connecting
endpoints. The PEX8796 RDK can be used to test and
© PLX Technology,
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