PCI-Express Hardware

PCI-Express is rapidly gaining momentum in the PC and embedded systems industries.  The architecture provides a very high data bandwidth with fewer signals than PCI-X and a switch fabric architecture to reduce bottlenecks that a shared bus architecture has.  The PCI-Express cable specification is currently being ratified and this will be a huge leap forward.  The specification is using the IPass connectors from Molex.  The cable specification allows for a high data bandwidth connection between systems that are up to 7 m apart.  One huge potential application that I see is the use of the processing power of the PC in traditionally embedded applications.  There are off the shelf PCI-Express cable expansion adapter cards made by One Stop Systems.  These cards can plug into the PCI-Express slot of a PC and allow you to connect a cable between your embedded system hardware and the PC.  The adapter cards come both with and without redrivers in various PCI-Express widths (x4, x8).  The redriver chips are made by Pericom, and support programmable preemphasis and equalization.  One important reason that this type of architecture could catch on in embedded systems designs is less development time.  All the hardware for the processing power is off the shelf in the PC, software can be quickly created on the PC, and all major FPGA vendors are providing PCI-Express cores for their FPGAs to provide an interface to the embedded system hardware.  Xilinx and Lattice are both providing embedded hard cores for their current FPGA offerings, further reducing development cost and unit cost.

Update 11-10-2008

On an actual project a couple of years ago we had intended to use the One Stop Systems PCI-e cable expansion adapter card but had difficulty do to a bug in the Pericom redriver chips.  The redriver chips did not work with certain PCI-e devices, including the Altera PCI-e core.  The solution was to use a cable adapter card with a PCI-e bridge on it.  The downside of this architecture is that it adds the latency of one PCI-e bridge device in the communication path.  Cyclone Microsystems makes PCI-e hardware including large chassis switch fabrics that use PCI-e cable adapter cards that they also make.