PEX 8747, PCI Express Gen 3 Switch, 48 Lanes, 5 Ports

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10/20/2010, Version 1.0

Figure 3. Dual Graphics Fan-Out

GPU1

GPU2

PEX 8747

x16

x16

x16

CPU

CPU

CPU

CPU

Figure 5. Dual Graphics with

nication

Peer-to-Peer Commu

GPU1

GPU2

PEX 8747

x16

x16

x16

CPU

CPU

CPU

CPU

traffic scripts for system bring-up and debug. Fully

integrated into the PEX 8747, the Packet Generator proves

to be a very convenient on-chip debug tool. Furthermore,

the Packet Generator can be used to create PCIe traffic to

test and debug other devices on the system.

Error Injection & SerDes Loopback

Using the PEX 8747’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 8747 also supports

Internal Tx, External Tx, Recovered Clock, and Recovered

Data Loopback modes.

Applications

Suitable for host-centric as well as peer-to-peer traffic

patterns, the PEX 8747 can be configured for a variety of

graphics applications.

Dual-GPU Fan-out

In a graphics fan-out application (see Figure 3), the PEX

8747 drives a dual-output display. The PEX 8747 will fan

out to two Graphics Modules (shown as

GPUs in the Figures) via the two x16

downstream ports while the x16

upstream port links to the Root

Complex. Each graphics module

drives its own monitor. Increasing

memory and bandwidth requirements

have put a strain on local GPU

memory. The PEX 8747 allows

for highly efficient data transfers

over the PCI Express bus,

allowing the Graphics Module

to utilize the system memory

and render it as if it were local

graphics memory. In a fan-out

application such as this one,

each Graphics Module drives

its own output.

Quad-GPU Fan-Out

For Quad-GPU applications using four GPUs to drive four

separate displays, users can take advantage of the PEX

8747’s four x8 downstream ports. Mid-range to low-end

systems that may not require the bandwidth provided by a

x16 Link can instead take advantage of the PEX 8747’s x8

Links and fan-out to up to four display units. Figure 4

illustrates a graphics system which uses four x8 links to

fan-out to four display units.

x8

x16

x8

GPU1

GPU1

GPU2

GPU2

x8

x8

CPU

CPU

CPU

CPU

PEX 8747

Figure 4. Quad Graphics Fan-Out

Dual-GPU w/ Peer-to-Peer Communication

High resolution 3D graphics applications can take full

advantage of the PEX 8747. Applications such as high-

resolution gaming, high resolution scientific use, and

image processing can benefit from the performance of the

PEX 8747 switch.

Figure 2 illustrates the use of the device in

a high resolution gaming application where

two Graphics Modules (GPUs) drive a

single monitor for the ultimate gaming

experience. The upstream x16 port links

to the Root Complex and the two

downstream ports connect to the GPUs.

The peer-to-peer support of the PEX

8747 allows the two GPUs to

communicate with each other for

maximum performance.

In this example, the two GPUs divide the

screen into a checkerboard pattern. In

Figure 5, the screen is divided into white

frames and blue frames, with one

GPU managing the white frames

and the other managing the blue frames. This mode of

operation is referred to as Supertiling, and is generally the

most efficient because it evenly divides the processing and

graphics rendering workload across the two GPUs. This

usage model calls for heavy peer-to-peer communication

between the two GPUs. The PEX 8747 can also support

dual-graphics solutions running in Scissor, or Alternate

Frame-Rate (AFR) modes. In each of these modes, the

processing and graphics rendering workload is shared by

the GPUs, and therefore requires a great amount of peer-

to-peer communication between the GPUs to monitor each

other’s progress and execution.