Flexible Port Configurations
The PEX 8608 supports the port configurations as shown in
figure 1 below. The figure shows an 8-port configuration, a 5-
port configuration as well as a 2-port configuration.
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 debug and management of
the entire system.
Port and Virtual Channel (VC) Arbitration
The PEX 8608 switch supports hardware fixed and Weighted
Round-Robin (WRR) Ingress Port Arbitration. This allows
fine tuning of Quality of Service and efficient use of packet
buffers for better system performance. The PEX 8608 also
supports WRR VC arbitration scheme between the two virtual
channels.
Applications
Suitable for
fan-out, control plane applications, embedded
systems
as well as
intelligent I/O and host isolation
applications,
PEX 8608 can be configured for a wide variety
of form factors and applications.
Figure 1. Port Configurations
Hot-Plug for High Availability
Hot-Plug capability allows users to replace hardware modules
and perform maintenance without powering down the system.
The PEX 8608 Hot-Plug capability feature makes it suitable
for
High Availability (HA) applications.
If the PEX 8608 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 8608 is equipped with
a Hot-Plug control/status register to support Hot-Plug
capability through external logic via the I
2
C interface
.
Fan-Out
The PEX 8608 switch, with its high port count and flexible
configurations, allows user specific tuning to a variety of
host-
centric as well as peer-to-peer applications.
Control
Processor
Memory
PCIe
PCIe
FPGA
PCIe
PCIe
PEX 8608
PEX 8311
DSP
PCI
Dual Cast
The PEX 8608 supports Dual Cast, a feature which allows for
the copying of data (e.g. packets) from one ingress port to two
egress ports allowing for higher performance in storage,
security, and mirroring applications.
PEX 8112
Read Pacing
The Read Pacing feature allows users to throttle the amount of
read requests being made by downstream devices. In the case
where a downstream device requests several long reads back-
to-back, the Root Complex gets tied up in serving this
downstream port. If this 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 by intelligent handling of read requests.
Figure 2. Fan-in/out Usage
Figure 2 shows a typical
fan-out
design, where the processor
provides a PCI Express link that needs to be fanned into a
larger number of smaller ports for a variety of I/O functions,
each with different bandwidth requirements.
In this example, the PEX 8608 would typically have a 1-lane
upstream port, and as many as 7 downstream ports. The
downstream ports provide x1 PCI Express connectivity to the
endpoints. With its eight ports, the PEX 8608 can provide fan-
out connectivity to up to seven PCI Express devices. The
figure also shows how some of the ports can be bridged to
provide
PCI slots or Generic devices
through the use of the
PEX 8311 and PEX 8112 PCIe
bridging devices.
SerDes Power and Signal Management
The PEX 8608 provides low power capability that is fully
compliant with the PCI Express power management
specification. In addition, the SerDes physical links can be
turned off when unused for even lower power. The PEX 8608
supports
software control
of the
SerDes outputs
to allow
optimization of power and signal strength in a system. The
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