Interesting Spi Routing with Ice40 Fpgas
Posted2 months agoActiveabout 2 months ago
danielmangum.comTechstory
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FpgaIce40Spi Routing
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Fpga
Ice40
Spi Routing
The post explores an interesting SPI routing technique with iCE40 FPGAs, sparking a discussion about the design and usability of the FOMU/Fomu FPGA board.
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Nov 10, 2025 at 8:40 AM EST
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Nov 10, 2025 at 11:04 AM EST
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about 2 months ago
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That said, I never understood the appeal of the FOMU. It's cool that it fits in a USB port, but so little IO, there's not a lot I can think to do with it.
Has anyone heard of some cool projects that others have done with this hardware?
Or with a more conventional FPGA development board like Icebreaker:
https://1bitsquared.com/products/icebreaker
They exist at a price point where it’s an easy decision to pick one up on a whim and spend an evening installing the toolchain and building some little hello world tutorial.
I bought one for $25 back in 2018! What's going on here?
That obviously makes the FOMU a more reasonable starter purchase, but I'd still probably get an icebreacker for $80 (which I also have and love).
Fantastic little device! Relating to the post, I also happened to brick one erasing the Foboot bootloader by writing the flash beyond the limit (there was a bug regarding writing to addresses beyond max at the time, but then I was pushing the limit by abusing dfu-utils :) https://x.com/sylefeb/status/1391898565061001225 ). I tried to use the programming pads but at the time was lacking the skills and it ended in disaster (ripped pads...).
The code repo for the overall project is here: https://github.com/sylefeb/tinygpus
I have to agree with others that the "Fomu" design appears to be highly suboptimal. They could have given you a way better edge connector on the other side.
So difficult to get the directionality right and also enable a JTAG bus
Hate these parts for that reason