pymcu-arm

ARM (Cortex-M) support for the PyMCU compiler: LLVM-IR codegen backend + LLVM toolchain driver.

Unlike the AVR/PIC/RISC-V backends, this backend does not emit assembly directly. It lowers PyMCU's architecture-agnostic IR (.mir) to LLVM IR text (.ll) and hands it to LLVM — so register allocation, instruction selection, the AAPCS calling convention, and all optimization passes are done by LLVM.

Currently supported targets:

Target	Triple	CPU
RP2040 (Raspberry Pi Pico)	thumbv6m-none-eabi	cortex-m0plus

The codegen is chip-agnostic: only -mtriple/-mcpu change per target.

Pipeline

pymcuc --emit-ir        →  firmware.mir    (target-agnostic IR, 32-bit pointers)
pymcuc-arm (this pkg)   →  firmware.ll     (LLVM IR text)
LLVM toolchain          →  opt → llc → ld.lld → llvm-objcopy
                            + generic boot2 (crc32) + crt0  →  firmware.bin

The flat flash image (firmware.bin, boot2 at offset 0) is what the RP2040Sharp emulator's PicoSimulation.LoadFlash(...) consumes in the integration tests.

Installation

pip install pymcu-arm

LLVM tools are resolved (in order) from the pymcu-arm-toolchain wheel cache, common system install paths (/opt/homebrew/opt/llvm/bin, /usr/lib/llvm/bin), or PATH. A system LLVM (brew install llvm lld / apt install llvm lld) also works with no extra package.

Layout

src/python/pymcu/backend/rp2040/    backend plugin — wraps pymcuc-arm
src/python/pymcu/toolchain/rp2040/  LLVM toolchain driver (opt → firmware.bin)
src/csharp/lib/                     Rp2040BackendProvider + Targets/RP2040/Rp2040LlvmCodeGen
src/csharp/cli/                     pymcuc-arm runner CLI
src/runtime/                        generic boot2 (crc32), crt0, rp2040.ld linker script

Status

Alpha. MVP scope: single-core (core0), GPIO + UART0. No GC / exceptions / float yet.