These new switches feature the PLX-exclusive non-transparent (NT) port functionality. An NT port separates the address domains between the two hosts which in turn allows the switches’ dual virtual channels (VCs) to offer two separate data paths for the memory traffic (high and low priorities) with improved quality of service (QoS), regardless of the CPU single VC limitations. The two VCs benefit the designs by establishing dual buffer entities utilized to queue the PCIe packets thereby enhancing traffic performance. The traffic class (TC) specifies priorities for a given PCIe packet and takes advantage of two VCs by sending high- or low-priority TC assignments, as opposed to the same priority for all packets found on a single VC chip.
Another PLX-only feature, integrated spread spectrum clock (SSC) isolation, offers the capability for separating the clock domains of two systems. SSC isolation enables the designers the flexibility to develop products with the asynchronous clock sources, thus removing the necessity for a single clock source for all PCIe components in a system.
These new switches are supported by PLX’s visionPAK software design kit (SDK). This SDK is focused on getting the designs to market faster and adds the ability to access the internal data paths and state machines for debugging systems; a tool to measure receiver eye-width inside the device for validating signal integrity; a function to inject errors to check system behavior; loopback transmitter to debug data paths, and the capability for the packet performance/activity monitoring. Furthermore, fully integrated into the PEX 8617 and PEX 8613 is the new PLX performancePAK, which offers the designers additional functions to reach peak performance and incorporates Read Pacing to fairly assign host port bandwidth, along with Dynamic Buffer Allocation to absorb fluctuations in bandwidth demand.
As system requirements increase, the interconnect technology must not only keep pace in performance, but also increase in functionality, states Jim McGregor, chief technology strategist at In-Stat. PCI Express has become an essential element in system architectures and adding features like spread-spectrum-clock isolation and dual virtual channels adds a critical boost in performance while increasing the system flexibility for a wider range of applications.
Applications including dual-host/multi-host, host-failover/redundant systems and intelligent I/O modules will benefit from these new PLX switches, stated Krishna Mallampati, PLX marketing director of PCIe switch products. Every PLX Gen 2 device incorporates NT functionality, ten of which offer two VCs, and many designers have now come to expect integrated NT for their new designs in order to avoid the additional costs and performance loss of other solutions.
