Is it planned to support both rv32imac and bare rv32i without these extensions?

[Plaque-fcc]

Hi!

I'm quite new to the development of such things, but after me constantly mentioning MicroPython here and there on different devices, my friend said that he wants to give it a try.
He's very good at Python, but all that he currently has is a j2me-enabled phone, a rv32i emulator in Java for j2me, and a QEMU setup. Building it is on my part.

Could someone please explain what to isolate and where to separate to make mpy-cross (presumably we need changes there) support rv32i with or without various extensions? Appreciate any help.

[Plaque-fcc]

Can actually have it with these additions:
https://github.com/Plaque-fcc/micropython/tree/qemu-rv32i

Standalone commits:
01_commit-3fcf4e8.txt
00_commit-88ae530.txt

[Plaque-fcc]

More from my friend: https://github.com/orgs/micropython/discussions/15980

[agatti]

Both extensions are required for the native/viper code emitters to work. If you don't need that then you can probably change the makefiles to use plain rv32i and explicitly disable MICROPY_EMIT_RV32.

For the M extension, one of the operations needed to generate code for is in fact multiplication. You can replace the implementation of ASM_MUL_REG_REG in py/asmrv32.h with an emitter for a series of shifts and additions. Unless there's a hardware RV32-based platform MicroPython runs on that doesn't support the M extension, I'd say that such a thing won't probably show up in the codebase.

The C extension requirement has a similar background: the first iteration of the native code generator only supported I and M extensions, but after some discussion then the C extension was made a requirement. The only real hardware platform MicroPython ran on that supported RV32 at the time (ESP32C3) has an IMC-enabled core, so it made sense to use that.

Making the C extension optional isn't that difficult, it's just a matter of placing the right ifdefs in py/asmrv32.c. However the same remark about seeing such a change merged in still applies. Technically the same can be said about the I extension too, as some RV32E MCUs do exist, but none of them run MicroPython (as far as I know).