Over the last few months I’ve been looking at a number of low cost entry level FPGA development boards. The XuLa from XESS is one of those and also one that comes well recommended by other engineers. So in this blog post I will review how I think it compares to others in the sub $100 price range.
FPGAs tend to fall into one of two main manufactures, that being Altera and Xilinx. I’ve always been a Altera and Quartus person writing in VHDL - that's my background so was also interested to see what its was like to play on the other side with a Xilinx chip. The board that I have tested is the larger XuLA-200 which comes with the Spartan-3A (XC3S200A). Comparing this to Altera it’s similar to say a Cyclone II, both having around 4,000 logic cells. Not the biggest chips going, good starting point but some say these are not quite big enough. I’m a little undecided myself.
The board is supplied as a plan PCB with no extras. So that’s just the PCB, no connectors, cables or CD. I guess in a way the biggest issue I found was not having the two 20way connectors down the side. This meant I can’t ‘just’ plug it into a bread board or adaptor. I guess it gives you the choice but from the point of view of a new hobbyist means the soldering iron will have to come out before you can start to play. If you want the connectors and also jumpers you can buy these for a extra $9.
I’m normally also critical of not having a CD with files on them. Its again avalible for a extra $2 from Xess however I found the Xess web site far and above one of the best for support and finding downloads. Under thire product page you can find the manual as well as a ‘Learning FPGA’ guide that I’ll come back to. You will also find all the circuits as well as all the source code build details etc. These boards are supplied as open source and personally found that the level of detail way out weighted the lack of not having a CD with it all on.
The only thing I did have to source is the Xilinx ISE development environment. I can’t blame Xess for not supplying this on CD as they only make the Dev Kit. I would have however suggested to customer that while they are waiting for the XuLA board to turn up that they start downloading the IDE, not that its big or anything and took me me nearly two hours to install.
The rest of the XuLA hardware contains a Microchip PIC18 that handles USB to FPGA JTAG programming. The board also contains a EEPROM that you can store your configuration in and a SDRAM. The FPGA is clocked via the PIC at 12Mhz which may not be the 50Mhz some supply but fast enough in my view for 99% of applications. Anyway you can always use the internal PLL to pump this up in speed.
Using the PIC means that programming of the FPGA is not done via the IDE and the configuration is uploaded via a GXSLOAD program available from the website or on the CD. This was really easy to use compared to some I have seen. Just drag and drop the output file to the utility and this then allows programming directly to the FPGA and or to the EEPROM allowing the board to run standalone.
The PIC also adds other benefits other than just programming that you would get with say a FTDI chip. This is because Xess have supplied as I said all the code and also a really good example program that allows you to talk to your FPGA, via the PIC and JTAG interface to your PC. They even show you how to write and compile your own programmes on the PC side - nice touch. This takes allot of the headache away from figuring out how to do this - if you wanted to that is. The site also contains lots of other example code as well as one supplied by customers.
Now I said I wanted to come back and talk about the guides on programming and using the FPGA board. These are second to none as I found as I followed them word for word. There are no errors and the documents even throw in some errors for you to fix with guidance from the documents. This was very educational and extremely well explained. Everything from downloading licence files to the most complex examples was very well written and easy to follow.
I would have said that for $69 the XuLA is a little high on cost for it’s raw on the board features but as someone who has not used Xilinx before the support of the site and documents make up for this.
I also like the fact that this design plugs into a bread board and out of the others I have seen is the only one that will. Its just really easy to use and other than not coming with connectors, I would certainly follow other engineers in recommending. It’s a board for beginners and for the more advanced engineers that ‘just’ want a plug in solution.
If you would like to see the reviews of the other boards I have done then please follow the links below. In the coming weeks I’ll also be reviewing the Papilio One.
Paul (aka @monpjc)