[FastFT]

Hardware compatible doesn’t mean very much in this case. It’s a different ISA so you’ll need a different tool chain and recompilation (possibly rewrite given that assembly is very common in deeply embedded processors). It’ll also have different LUT usage, etc.

[tails4e]

It means it's designed as a direct drop in replacent for a traditional microblaze ISA code..sure software must be recompiled, but hardware interfaces match what was there before for peripheral access, debug, instruction offload, etc. This makes the transition to using RISC-v much more seamless if you were already using microblaze