Project Context (Auto-Injected)

Target configuration: !cat .cargo/config.toml 2>/dev/null || echo "No .cargo/config.toml found"

Embedded Domain

Layer 3: Domain Constraints

Domain Constraints → Design Implications Domain Rule Design Constraint Rust Implication No heap Stack allocation heapless, no Box/Vec No std Core only #![no_std] Real-time Predictable timing No dynamic alloc Resource limited Minimal memory Static buffers Hardware safety Safe peripheral access HAL + ownership Interrupt safe No blocking in ISR Atomic, critical sections Critical Constraints No Dynamic Allocation RULE: Cannot use heap (no allocator) WHY: Deterministic memory, no OOM RUST: heapless::Vec, arrays

Interrupt Safety RULE: Shared state must be interrupt-safe WHY: ISR can preempt at any time RUST: Mutex> + critical section

Hardware Ownership RULE: Peripherals must have clear ownership WHY: Prevent conflicting access RUST: HAL takes ownership, singletons

Trace Down ↓

From constraints to design (Layer 2):

"Need no_std compatible data structures" ↓ m02-resource: heapless collections ↓ Static sizing: heapless::Vec

"Need interrupt-safe state" ↓ m03-mutability: Mutex>> ↓ m07-concurrency: Critical sections

"Need peripheral ownership" ↓ m01-ownership: Singleton pattern ↓ m12-lifecycle: RAII for hardware

Layer Stack Layer Examples Purpose PAC stm32f4, esp32c3 Register access HAL stm32f4xx-hal Hardware abstraction Framework RTIC, Embassy Concurrency Traits embedded-hal Portable drivers Framework Comparison Framework Style Best For RTIC Priority-based Interrupt-driven apps Embassy Async Complex state machines Bare metal Manual Simple apps Key Crates Purpose Crate Runtime (ARM) cortex-m-rt Panic handler panic-halt, panic-probe Collections heapless HAL traits embedded-hal Logging defmt Flash/debug probe-run Design Patterns Pattern Purpose Implementation no_std setup Bare metal #![no_std] + #![no_main] Entry point Startup #[entry] or embassy Static state ISR access Mutex>> Fixed buffers No heap heapless::Vec Code Pattern: Static Peripheral

![no_std]

![no_main]

use cortex_m::interrupt::{self, Mutex}; use core::cell::RefCell;

static LED: Mutex>> = Mutex::new(RefCell::new(None));

[entry]

fn main() -> ! { let dp = pac::Peripherals::take().unwrap(); let led = Led::new(dp.GPIOA);

interrupt::free(|cs| {
    LED.borrow(cs).replace(Some(led));
});

loop {
    interrupt::free(|cs| {
        if let Some(led) = LED.borrow(cs).borrow_mut().as_mut() {
            led.toggle();
        }
    });
}

}

Common Mistakes Mistake Domain Violation Fix Using Vec Heap allocation heapless::Vec No critical section Race with ISR Mutex + interrupt::free Blocking in ISR Missed interrupts Defer to main loop Unsafe peripheral Hardware conflict HAL ownership Trace to Layer 1 Constraint Layer 2 Pattern Layer 1 Implementation No heap Static collections heapless::Vec ISR safety Critical sections Mutex Hardware ownership Singleton take().unwrap() no_std Core-only #![no_std], #![no_main] Related Skills When See Static memory m02-resource Interior mutability m03-mutability Interrupt patterns m07-concurrency Unsafe for hardware unsafe-checker