Catching the (PCIe) Bus

If you are trying to learn about FPGAs, there is only so far you can go with the usual blinking lights and VGA outputs. Eventually, you want to do something more. Although not terribly cheap, you can get FPGA boards in a PCIe form-factor and use them directly with PC software. Is it easy? Well, it isn’t flashing an LED, but there are tools to help. [Angelos Kyriakos] did a Master’s thesis on the very subject and used a project known as RIFFA to help with the task.

RIFFA (Reusable Integration Framework for FPGA Accelerators) is a simple framework for communicating data from a host CPU to an FPGA via a PCI Express bus. The framework requires a PCIe enabled workstation and an FPGA on a board with a PCIe connector. RIFFA supports Windows and Linux, Altera and Xilinx, with bindings for C/C++, Python, MATLAB, and Java. With proper design, RIFFA can transfer quite a bit of data in a short period of time between your computer and your FPGA.

Of course, the catch is finding a proper FPGA board, and these are not cheap. Also, RIFFA relies on the vendor’s PCIe endpoint block. In some cases, these are licensed with the development tool but in other cases, you’ll have to pay for that, too, so be sure you understand the situation with the FPGA and board you select.

Of course, RIFFA isn’t the only option. There are several PCIe cores on OpenCores, although your mileage may vary on what hardware support or how general-purpose or complete they are.

You can only hope the cost of hardware will come down. Right now the examples for RIFFA use a Xilinx board that goes for about $2,000. Numato has some boards in the $300-500 range. This board looks promising, although they don’t seem to be readily available in the United States, as far as we can tell. Speaking of outside the United States, there’s always Raggedstone. However, none of these boards are in the under $100 range, so be prepared to shell out some money.

Don’t let this put you off though. We’ve talked before about how you can do a lot with FPGAs with very little investment. Besides, you can talk to a PC without using the PCIe interface. Use serial, or Ethernet, or even SPI. It might not have the bandwidth, but it will be a lot cheaper.