> The ZPU is a small CPU in two ways: it takes up very little resources and the architecture itself is small.
It would have been nice if they had tried a quantitative comparison with the Risc-V RV32I to support this claim. That would also allow them to showcase the design choices and trade offs that make this project interesting. As it is, there's not much information of this kind to be gained from the README...
It would. If they had a Time Machine. ZPU is over a decade and a half old… Back from from when we called RISC-V just "MIPS"
But since you asked. It IS small. The smallest sane RV32 core I can find is PicoRV, which uses 750-2000 LUS[1]. SERV [2] does claim to only need 440 LUTs, but its performance (most instrs take over 32 cycles) makes even ZPU seem speedy... The ZPU uses 442 LUTs[3].
[1] https://github.com/YosysHQ/picorv32
SERV is a fair comparison, since it's architected for 4LUTs and I suspect the synthesis results come from iCE40 tools.
I have a contender in the "very small" space, too [1], although I don't claim it's as mature or complete as SERV. (If Minimax was excluded from your post on the basis of insanity, I'm OK with that.)
I did play with the ZPU quite a bit 8 or 9 years ago, and forked the ZPU Small variant to create ZPUFlex [0]. I borrowed a number of ideas from ZPU when I created my own CPU Project, EightThirtyTwo [1], some years later.
[0] https://github.com/robinsonb5/ZPUFlex [1] https://github.com/robinsonb5/EightThirtyTwo