PEX 8625, PCI Express Gen 2 Switch, 36 Lanes, 24 Ports
Applications
Host Failover in Comms Control Plane
The PEX 8625 can also be utilized in applications where
Suitable for host-centric as well as peer-to-peer traffic
patterns, the PEX 8625 can be configured for a wide
variety of form factors and applications.
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 8625
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 8625 so that
the upstream port is connected to the standby processor.
Host Centric Fan-out in Control Plane
The PEX 8625, 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 8625 can independently support
2.5GT/s and/or 5.0GT/s devices.
Figure 8. Failover using Non-Transparency
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 6. Host Centric Application
Multicast in Control Plane
The PEX 8625 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.
Figure 8. Failover using Virtual Switch function
Figure 7. Multicast on PEX 8625
© PLX Technology, www.plxtech.com
Page 4 of 5
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