Embedded Domain Skill | Agent Skills

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<T, N>, arrays

Interrupt Safety

RULE: Shared state must be interrupt-safe
WHY: ISR can preempt at any time
RUST: Mutex<RefCell<T>> + 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<T, N>

"Need interrupt-safe state"
    ↓ m03-mutability: Mutex<RefCell<Option<T>>>
    ↓ 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<RefCell<Option<T>>> | | Fixed buffers | No heap | heapless::Vec<T, N> |

Code Pattern: Static Peripheral

#![no_std]
#![no_main]

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

static LED: Mutex<RefCell<Option<Led>>> = 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<T, N> | | ISR safety | Critical sections | Mutex<RefCell<T>> | | 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 |

Agent Skills: Embedded Domain

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