PEX8749, PCI Express Gen 3 Switch, 48 Lanes, 18 Ports
The PEX8749 can also be configured in Multi-Host mode
Multi-Host & Failover Support
where users can choose up to six 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 PEX8749 in Multi-Host mode where each ellipse
represents a virtual switch inside the device.
In Multi-Host mode, PEX8749 can be configured with up
to six upstream host ports, each with its own dedicated
downstream ports. The device can be configured for 1+1
redundancy or N+1 redundancy. The PEX8749 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 Multi-Host 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.
x8
x8
x8 x4 x4
The PEX8749
also provides
several ways to
configure its
registers. The
device can be
configured
PEX 8749
PEX 8749
3 x8
2 x4
2 x8 2 x4 2 x4
3 x2s 2 x4s
through
4 x4s
strapping pins,
I2C interface,
host software, or
an optional
PEX 8749
PEX 8749
serial EEPROM.
This allows for
easy debug
Hot-Plug for High Availability
Hot-plug capability allows users to replace hardware
modules and perform maintenance without powering down
the system. The PEX8749 hot plug capability feature
makes it suitable for High Availability (HA)
8 x4s
9 x2s 4 x4s
Figure 2. Multi-Host Port Configurations
during the
development phase, performance monitoring during the
operation phase, and driver or software upgrade.
applications. Three downstream ports include a Standard
Hot Plug Controller. If the PEX8749 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 PEX8749 is equipped
with a hot-plug control/status register to support hot-plug
capability through external logic via the I2C interface.
Dual-Host & Failover Support
In Single-Host mode, the PEX8749 supports 2 Non-
Transparent (NT) Ports,
Primary Host
Primary Host
Secondary Host
Secondary Host
which enables the
CPU
CPU
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
Root
Complex
SerDes Power and Signal Management
The PEX8749 provides low power capability that is fully
compliant with the PCIe power management specification
and supports software control of the SerDes outputs to
allow optimization of power and signal strength in a
system. Furthermore, the SerDes block supports loop-back
modes and advanced reporting of error conditions,
which enables efficient management of the entire system.
NT
PEX 8749
Non-Transparent
Port
End
Point
End
Point
End
Point
subsystem
as an endpoint rather
than another memory
Figure 3. Non-Transparent Port
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).
Interoperability
The PEX8749 is designed to be fully compliant with the
PCI Express Base Specification r3.0, and is backwards
compatible to PCI Express Base Specification r2.0, r1.1,
© PLX Technology, www.plxtech.com
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22Aug11, version 1.0
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