Rust Embedded

---
name: rust-embedded
description: "Rust for embedded systems"
category: embedded
tags: [rust, embedded, microcontroller, no-std, arm, risc-v]
models: [sonnet, opus]
version: 1.0.0
created: 2026-05-14
updated: 2026-09-29
---
# Rust Embedded

> Develop embedded systems firmware with Rust for safety, performance, and modern tooling.

## Quick Start
```rust
//! Blinky example for STM32 microcontroller
#![no_std]
#![no_main]

use cortex_m_rt::entry;
use panic_halt as _;
use stm32f4xx_hal::{
    pac,
    prelude::*,
    timer::Timer,
};
use embedded_hal::digital::OutputPin;

#[entry]
fn main() -> ! {
    // Get peripherals
    let dp = pac::Peripherals::take().unwrap();
    let cp = cortex_m::Peripherals::take().unwrap();

    // Configure clocks
    let rcc = dp.RCC.constrain();
    let clocks = rcc.cfgr.sysclk(48.MHz()).freeze();

    // Configure LED pin (PC13 on many STM32 boards)
    let gpioc = dp.GPIOC.split();
    let mut led = gpioc.pc13.into_push_pull_output();

    // Configure timer
    let mut timer = Timer::syst(cp.SYST, 1.Hz(), &clocks);

    // Blink loop
    loop {
        led.set_high().unwrap();
        timer.wait(); // 1 second delay
        led.set_low().unwrap();
        timer.wait();
    }
}
```

```toml
# .cargo/config.toml — Cross-compilation target
[target.thumbv7em-none-eabihf]
runner = "gdb-multiarch"
rustflags = ["-C", "link-arg=-Tlink.x", "-C", "linker=arm-none-eabi-gcc"]

[build]
target = "thumbv7em-none-eabihf"
```

```rust
// Embedded HAL traits — abstraction for portability
use embedded_hal::{
    blocking::delay::DelayMs,
    digital::OutputPin,
    spi::SpiDevice,
};

fn control_display<D: DelayMs<u32>, P: OutputPin>(
    delay: &mut D,
    reset: &mut P,
) {
    reset.set_low().unwrap();
    delay.delay_ms(10);
    reset.set_high().unwrap();
    delay.delay_ms(100);
}
```

## Key Concepts
`#![no_std]` enables bare-metal code without the standard library. The Embedded HAL provides portable hardware abstraction. `cortex-m-rt` handles vector table and startup. Use probe-rs for flashing and debugging.

## When to Use
- Firmware for ARM Cortex-M, RISC-V microcontrollers
- IoT sensor nodes and actuators
- Safety-critical embedded systems
- Replacing C/C++ with memory-safe Rust

## Step-by-Step
1. Pick the board/target: install `rustup target add thumbv7em-none-eabihf` for Cortex-M4F or the RISC-V equivalent.
2. Configure the linker: add `.cargo/config.toml` with `rustflags` (link.x) and default build target.
3. Scaffold a `no_std` crate: use `#![no_std]` + `#![no_main]`, add `cortex-m-rt` for startup and a panic handler.
4. Get a HAL: enable `stm32f4xx_hal` (or `nrf-hal`, `esp-hal`) peripheral features matching the chip.
5. Flash & debug: use `probe-rs`/`cargo embed` (or `openocd + gdb-multiarch`) with the target config.
6. Verify on device: blink an LED, then exercise a sensor/UART; check binary size with `cargo size`.

## Examples
```rust
// Read a button and toggle an LED via embedded-hal traits
#![no_std]
#![no_main]
use cortex_m_rt::entry;
use panic_halt as _;
use stm32f4xx_hal::{pac, prelude::*, gpio::Edge};
use embedded_hal::digital::{InputPin, OutputPin};

#[entry]
fn main() -> ! {
    let dp = pac::Peripherals::take().unwrap();
    let rcc = dp.RCC.constrain();
    let clocks = rcc.cfgr.sysclk(48.MHz()).freeze();
    let gpioa = dp.GPIOA.split(&clocks);
    let gpioc = dp.GPIOC.split();

    let mut led = gpioc.pc13.into_push_pull_output();
    let btn = gpioa.pa0.into_pull_up_input();

    loop {
        if btn.is_low().unwrap() {
            led.set_high().unwrap();
        } else {
            led.set_low().unwrap();
        }
        cortex_m::asm::delay(100_000);
    }
}
```
```bash
# Build, flash, and inspect the binary
cargo build --release
cargo size --release
cargo embed --release   # flashes via probe-rs using the target config
```

## Best Practices
- Use `no_std` crates for bare-metal targets.
- Keep memory and stack usage bounded and profiled.
- Use interrupts and DMA for I/O; avoid busy polling.
- Pin toolchain and target for reproducible builds.
- Test on hardware with a CI runner or QEMU.
- Use a RTOS (RTIC/embassy) for concurrency.

## Troubleshooting
- Link errors: check target triple and memory layout.
- Stack overflow: increase stack or profile usage.
- Flaky interrupts: check priorities and critical sections.
- No output: verify the UART config and baud rate.

## Validation
1. `cargo build --target thumbv7em-none-eabihf` compiles without std
2. Firmware flashes to device and runs (LED blinks)
3. UART/sensor output matches expected values
4. Binary size fits within target flash memory