Zylin ZPU: The worlds smallest 32 bit CPU with GCC toolchain

Re:Zylin ZPU: The worlds smallest 32 bit CPU with GCC toolchain by dmitrygr on Friday April 14, 2023 @02:53AM (#35566343)

> It would have been nice if they had tried a quantitative comparison with the Risc-V RV32I

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

[2] https://github.com/olofk/serv

[3] https://opencores.org/projects/zpu

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Re:Zylin ZPU: The worlds smallest 32 bit CPU with GCC toolchain by gsmecher on Friday April 14, 2023 @11:56AM (#35570966)

Note that you can't compare LUT4 results (ZPU @ 440 LUTs) against LUT6 results (PicoRV32 @ 750 LUTs). The ZPU is remarkably small, and it's a bigger gap than a direct comparison shows.

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.)

[1] https://github.com/gsmecher/minimax

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