KeiSeiKit-1.0/_blocks/stack-embedded-stm32.md

STACK — Embedded Rust STM32 (embassy / cortex-m)

Rust-first by default. STM32H743 is a common reference MCU.

Crate skeleton:

#![no_std]
#![no_main]
use embassy_executor::Spawner;
use embassy_stm32::bind_interrupts;
use defmt_rtt as _;
use panic_probe as _;

HAL choice: embassy (async, preferred for new work) OR cortex-m-rt + HAL crates (if you need full sync control). Pick one per project; no mixing.

Memory budget (MANDATORY comment in Cargo.toml):

# STM32H743ZI — flash 2 MiB, RAM 1 MiB. Current: flash 312 KiB / RAM 84 KiB.

Update on every commit that moves size by > 4 KiB.

I/O rules:

• DMA for any transfer > 32 bytes (UART, SPI, I2C, ADC bursts). Polling in ISRs bricks latency.
• Interrupt priorities EXPLICIT via NVIC. Default 0 = highest — two handlers at priority 0 deadlock.
• NO heap allocations in ISRs. heapless::Vec / heapless::String only, with compile-time capacity.

Allocator: default is NO allocator (#![no_std] bare). If you add alloc, document why — usually avoidable with heapless.

Debug: defmt + probe-rs for logging. NEVER println! (no stdout).

Forbidden: alloc without justification; .unwrap() outside #[cfg(debug_assertions)]; interrupt handlers > 30 LOC (move logic to a task); DMA without 'static buffers (UB with stack buffers); flashing without probe-rs erase when changing memory map.