Electronic Design

96 Lane PCI Express Switch Supports Four Host Partitions

PLX Technology's latest Gen 3 PCI Express switches deliver lots of lanes and ports. They also allow these to be shared with up to four hosts providing a virtual switch environment. The new chips support non-transparent (NT) bridging ports that allow multiple hosts accessed to shared peripherals. Some processors are now supporting NT (see Fan-Out in Systems Using the Jasper Forest CPU) but switched-based NT allow any host to operate in a failover environment.

PLX Technology's PEX 8796 switch supports 96 lanes and 24 ports. The PEX 8780 supports 80 lanes and 20 ports while the PEX 8764 supports 64 lanes and 16 ports. All of the switches can handle up to four hosts that support two NT ports allowing dual failover configurations in a single switch (Fig. 1).


Figure 1. PLX Technology's PEX 8796 96-lane, 24-port switch handles up to four hosts, two that can support non-transparent (NT) bridging allowing fail-over support.

The switches can handle up to four host partitions and the I/O ports can be allocated to any host. The NT bridging support allows a host to take over the I/O of a failed host. This failover support is typically found in storage applications were redundant access to storage devices is needed. It can also be used in enbedded applications where high reliability is key.

All three switches support PCI Express Gen 3 that runs at 8 Gtransfers/s/lane. Latency is 150 ns. Fanout mode and virtual switch mode support is standard as is support for PCI Express multicast. PLX Technology enhancements include performancePAK and visionPAK diagnostics. PLX Technology's performancePAK supports packet cut-through with a maximum latency of 150 ns. The non-blocking architecture includes support for 2048 byte packets allowing full line rate performance.

The visionPAK diagnostics provide per port performance monitoring. It can capture SERDES eye width and height without external support. It supports error injection and it has a PCI Express packet generator tool.

Feature PEX 8760 PEX 8780 PEX8764
Lanes/ports 96/24 80/20 64/16
Root/hosts 4 4 4
Non-transparent ports 2 2 2
SSC clock isolation 24 20 16
Hot plug ports 6 5 4
Serial hot plug ports 18 15 12


The chips can be utilized in a range of configurations. For example, the PEX 8796 can support four x16 GPGPUs. All switches are delivered in a 35mm by 35mm package. Volume pricing starts at $150.

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