pex-8647 PLX, pex-8647 Datasheet - Page 2

• Manufacturer Part Number: pex-8647
• Description: 48-lane, 3-port Pci Express Gen 2 5.0 Gt/s Switch, 27 X 27mm Fcbga
• Manufacturer: PLX

SerDes Power and Signal Management
The PEX 8647 supports software control of the SerDes
outputs to allow for the 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.
Interoperability
The PEX 8647 is designed to be fully compliant with the
PCI Express Base Specification r2.0. Additionally, it
supports auto-negotiation, lane reversal, and polarity
reversal. Furthermore, the PEX 8647 is tested for
Microsoft Vista compliance testing. All PLX switches
undergo thorough interoperability testing in PLX’s
Interoperability Lab and compliance testing at the
PCI-SIG plug-fest.
Applications
Targeted at high-end graphics applications, the
PEX 8647 supports host-centric as well as peer-to-peer
traffic patterns.
Graphics Fan-out
In a graphics fan-out application (see
Figure 1), the PEX 8647 drives a
dual-output display. The PEX 8647
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 8647 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.
Figure 1. Dual Graphics Fan-Out
GPU1
GPU1
GPU1
GPU1
x16
PEX 8647
PEX 8647
Complex
Complex
Complex
Complex
Root
Root
Root
Root
CPU
CPU
CPU
CPU
x16
GPU2
GPU2
GPU2
GPU2
x16
Dual Graphics with Peer-to-Peer
Communication
High resolution 3D graphics applications can take full
advantage of the PEX 8647 three port configuration.
Applications such as high-resolution gaming, high
resolution scientific use, and image processing can
benefit from the performance of the PEX 8647 switch.
Figure 2 illustrates the use of the device in a high
resolution gaming application where two Graphics
Modules 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
Graphics Modules. The peer-to-peer support of the
PEX 8647 allows the two Graphics Modules to
communicate with each other for maximum
performance.
In this example, the two Graphics Modules divide the
screen into a checkerboard pattern. In Figure 2, 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 Graphics Modules.
This usage model calls for
heavy peer-to-peer
communication between
the two Graphics Modules.
The PEX 8647 can also
support dual-graphics
solutions running in
scissor, or alternate frame-
rate modes. In each of
these modes, the
processing and graphics
rendering workload is
shared by the Graphics
Modules, and therefore
requires a great amount of peer-to-peer communication
between the Graphics Modules to monitor each o
progress and execution.
Figure 2. Dual Graphics with
Peer-to-Peer Communication
GPU1
GPU1
GPU1
GPU1
x16
PEX 8647
PEX 8647
Complex
Complex
Complex
Complex
Root
Root
Root
Root
CPU
CPU
CPU
CPU
x16
ther’s
GPU2
GPU2
GPU2
GPU2
x16