Flexible Port Configuration

The lane width for each port can be individually configured

through auto-negotiation, hardware strapping, upstream

software configuration, or through an optional EEPROM.

The PEX 8508 supports a large number of port configurations.

For example, if you are using the PEX 8508 in a fan-out

application, you may configure the upstream port as x4 and

the downstream ports as four x1 ports or two x2. In a peer-to-

peer switch aggregation application you can configure four x2

ports. Figure 1 show most common port configurations.

Figure 1. Common 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 8508 hot-plug capability and Advanced Error

Reporting features makes it suitable for High Availability

(HA) applications. Each port includes a Standard Hot-Plug

Controller. If the PEX 8508 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. Furthermore, its

upstream port is a hot-plug client, allowing it to be used on

hot-pluggable adapter cards, backplanes and fabric

modules.

Fully Compliant Power Management

For applications that require power management, the

PEX 8508 devices support both link (L0, L0s, L1, L2/L3

Ready, L2 and L3) and device (D0 and D3hot) power

management states, in compliance with the PCI Express power

management specification. Vaux, Wake# and Beacon support

the wakeup protocol from the D3cold state.

SerDes Power and Signal Management

The PEX 8508 supports software control of the SerDes

outputs to allow 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 debug and

management of the entire system.

Flexible Virtual Channel Arbitration

The PEX 8508 switch supports fixed priority and Round

Robin arbitration schemes for up to two virtual channels. This

allows fine tuning of Quality of Service, efficient use of

packet buffers and the system bandwidth.

Applications

Suitable for host-centric as well as Intelligent I/O applications

the PEX 8508 can be configured for a wide variety of form

factors and applications.

Processor Isolation for Redundancy

The PEX 8508 switch, with its low latency, Hot-Plug, and

NTB capability, allows users to isolate processors in multi-

host or failover applications.

Figure 2. Processor Isolation

Figure 2 shows two server boards. The PCI Express switch is

used to prevent the backup host from enumerating and

configuring portions of the primary host system. In addition,

non transparent ports provide doorbell and mailbox registers

for inter-processor communications. The backup processor

will monitor heartbeat messages from the primary system and

upon failure take over as the primary host.

PEX 8508 has very low latency, under 150ns, to assist in a

rapid failover to the backup system. Here only one PEX 8508

switch is required with the one non transparent port but to

maintain identical board layouts, each board shown has a

PEX 8508 switch. This application can be generalized to

where each compute or storage or I/O board would include a

PEX 8508 to isolate each processor domain.

Adapter Card Aggregation

The number and variety of PCI Express native-mode devices

is growing quickly. As these devices become mainstream it

will be necessary to create multifunction and multi-port

adapter cards with PCI Express capability.