First ever FPGA CPU built using open source tools?
First ever FPGA CPU built using open source tools? launched on July 27, 2015 with 13 votes, #1,649 of 4,208 launches that month and more than 75% of that year's launches. The site was still online in September 2026, 11 years on.
In plain words
J1a is a minimal 16-bit CPU written in Verilog that runs on Lattice FPGAs using open source IceStorm tools. It fits on the iCEstick evaluation board with 8K of RAM and executes SwapForth, a complete interactive Forth development environment. The project demonstrates that FPGA designs can be synthesized and programmed using fully open source toolchains without proprietary software, making it relevant for hardware developers and FPGA enthusiasts interested in open tools.
written from the facts on this page · September 2026
From the sources
Project IceStorm aims to reverse engineer some Lattice FPGAs, and provides a working tool chain for synthesizing designs and downloading them into the hardware. The J1a CPU is a minimal 16-bit Verilog CPU, fits easily on the Lattice HX20-1K on the Lattice iCEstick evaluation board . After some help from the people at project IceStorm, it is now buildable using the IceStorm tools. The J1a is a simplified variant of the original J1 . The modifications from the original J1 are: The board has 8K of RAM, and runs SwapForth, a small but complete interactive Forth development environment. SwapForth takes about 5K of the available RAM, and includes a full native compiler, the ANS standard CORE…from excamera.com
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