Systems await switched-fabric architectures

In designing embedded systems, developers have the choice of opting for a PCI-based system or a more-expensive VME-bus-based system.

Sep 1st, 2003

In designing embedded systems, developers have the choice of opting for a PCI-based system or a more-expensive VME-bus-based system. Whether you choose either one for a machine-vision or image-processing design, however, you will choose a shared bus system that has slowly evolved over the past two decades. In applications such as industrial control, medical imaging, instrumentation, and machine vision, open systems have become popular among systems integrators because of the relative ease with which off-the-shelf A/D boards, image-processing boards, CPU boards, display controllers, and I/O devices can be configured to make application-specific systems.

With standard parallel buses running out of steam for bandwidth-heavy applications, however, designers are looking to embrace high-speed switched-fabric architectures that resemble high-speed Ethernet interfaces. As serial switched interconnect infrastructure (or "switched-fabric") momentum builds, both VME and PCI houses are readying new standards and designs.

The VME International Trade Association (VITA; Fountain Hills, AZ, USA;, for example, has announced VITA 41, the first entry of a VME standard into switched-fabric technology. In the new specification, the form factor and the VME bus remain the same, but the switched-fabric pinouts and protocols are defined in complimentary standards, with 41.1 specifying Infiniband ( and 41.2 for Rapid IO ( Others such as StarFabric ( are planned for the near future, according to Melissa Heckman, an electrical engineer with Bustronic (Fremont, CA, USA;

On the PCI-replacement front, it is now likely that PCI Express (, formerly "NGIO," then "Arapahoe," and then "3GIO," will be the standard replacement for PCI. PCI Express currently runs at 2.5 Gbits/s over a x1 PCI Express lane in each direction, providing a total bandwidth of 16 Gbits/s in a 32-lane configuration with I/O attach points for graphics, IEEE 1394b, USB 2.0, InfiniBand, and Gigabit networking. Because of the lack of currently available image-processing or machine-vision boards for the VME bus, it is likely that PCI Express will become the next adopted standard.

According to Intel Corp. (Santa Clara, CA, USA;, this is likely to happen sometime next year. Whether this time frame is accurate remains a cause for speculation among many board vendors. Already, the semiconductor recession has placed many research projects on the back burner until market forces shake out whether specific standards will become ubiquitous. In the IEEE 1394b standard arena, for example, independent PHY and LINK ICs are still unavailable from Texas Instruments (Dallas, TX, USA; Rather than wait, many camera companies have implemented solutions using off-the-shelf parts coupled to gate arrays (see p. 95).

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