domain-embedded

# 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