[cliffordvienna]

PicoRV32 (https://github.com/cliffordwolf/picorv32) and ORCA (https://github.com/VectorBlox/orca) are two RISC-V implementations that nicely fit in ~2000 iCE40 LUTs. UCB-BAR V-Scale (https://github.com/ucb-bar/vscale) fits in ~4000 iCE40 LUTs.