J1a system on a Lattice ICESTICK40

June 22, 2016 | FPGA | By: Mark VandeWettering

Long time readers of this blog might remember that I received a Gameduino board designed by James Bowman. I used it to construct ANGST, an Arduino and Gameduino satellite tracking project. James did all the heavy lifting: the Gameduino uses a Xilinx FPGA to implement an Arduino shield that can generate graphics and sounds. To do so, it actually implements a “soft processor”, a very simple CPU core designed to execute the Forth Programming Language. I enjoyed goofing around with it, but it’s been sitting in a box for quite a while.

A couple months ago, I remember hearing about an interesting project called Project IceStorm. One of the things that has kept me from tinkering with FPGAs is that the development environments are proprietary and big. Really big. Wrapping my head around them just didn’t seem like fun. But Project Icestorm tries to apply open source methodology to FPGA programming. They reverse engineered the bitstream used by a simple family of FPGAs made by Lattice Semiconductor. The result is a complete set of tools to code logic designs in Verilog, compile, place, route and download them to a Lattice FPGA board. What’s doubly cool is that James took the core of his J1a processor and adapted it for a very cheap Lattice IceStick development board. Compared to some other FPGA boards, the Lattice ICE40 chips are pretty limited, but the J1a is a pretty good fit, and now with Project IceStorm, you can compile and download directly to the board, and have a small Forth base system running without any extra hardware.

I went ahead an ordered one of the boards, and following the instructions on James’ website, I went ahead and built the code and successfully installed in on my $21 ICESTICK. Initially, I had some trouble running the LED blink test: three of the leds worked fine, but two wouldn’t seem to light. Eventually, I tried updating the “yosys” software and recompiling it, and after that, it worked as expected. I’ve never done any Verilog programming before, but having this setup seems to make it seem more tractable than it has before. I’m dusting off the largely unused Verilog books I have on my shelf, and am thinking of trying something simple like a digital clock as my first try. I suspect I’ll outgrow the ICESTICK pretty quickly, but until I do, I bet I am going to learn a lot.

James does a better job describing his system than I could, so here’s a link to his video and his page describing the system. Thanks to Ken Boak for also drawing my attention to this project.

James’ page on J1a SwapForth