Embassy : Revolutionizing Embedded Systems With Rust And Asynchronous Programming

Embassy is the next-generation framework for embedded applications. Write safe, correct and energy-efficient embedded code faster, using the Rust programming language, its async facilities, and the Embassy libraries.

Documentation – API reference – Website – Chat

Rust + async Embedded

The Rust programming language is blazingly fast and memory-efficient, with no runtime, garbage collector or OS. It catches a wide variety of bugs at compile time, thanks to its full memory- and thread-safety, and expressive type system

Rust’s async/await allows for unprecedentedly easy and efficient multitasking in embedded systems. Tasks get transformed at compile time into state machines that get run cooperatively.

It requires no dynamic memory allocation, and runs on a single stack, so no per-task stack size tuning is required. It obsoletes the need for a traditional RTOS with kernel context switching, and is faster and smaller than one!

Batteries Included

• Hardware Abstraction Layers – HALs implement safe, idiomatic Rust APIs to use the hardware capabilities, so raw register manipulation is not needed.
  • The Embassy project maintains HALs for select hardware, but you can still use HALs from other projects with Embassy.
    • embassy-stm32, for all STM32 microcontroller families.
    • embassy-nrf, for the Nordic Semiconductor nRF52, nRF53, nRF91 series.
    • embassy-rp, for the Raspberry Pi RP2040 microcontroller.
    • esp-rs, for the Espressif Systems ESP32 series of chips.
      • Embassy HAL support for Espressif chips is being developed in the esp-rs/esp-hal repository.
      • Async WiFi, Bluetooth and ESP-NOW is being developed in the esp-rs/esp-wifi repository.
    • ch32-hal, for the WCH 32-bit RISC-V(CH32V) series of chips.
• Time that Just Works – No more messing with hardware timers. embassy_time provides Instant, Duration and Timer types that are globally available and never overflow.
• Real-time ready – Tasks on the same async executor run cooperatively, but you can create multiple executors with different priorities, so that higher priority tasks preempt lower priority ones. See the example.
• Low-power ready – Easily build devices with years of battery life. The async executor automatically puts the core to sleep when there’s no work to do. Tasks are woken by interrupts, there is no busy-loop polling while waiting.
• Networking – The embassy-net network stack implements extensive networking functionality, including Ethernet, IP, TCP, UDP, ICMP and DHCP. Async drastically simplifies managing timeouts and serving multiple connections concurrently.
• Bluetooth – The nrf-softdevice crate provides Bluetooth Low Energy 4.x and 5.x support for nRF52 microcontrollers. The embassy-stm32-wpan crate provides Bluetooth Low Energy 5.x support for stm32wb microcontrollers.
• LoRa – The lora-rs project provides an async LoRa and LoRaWAN stack that works well on Embassy.
• USB – embassy-usb implements a device-side USB stack. Implementations for common classes such as USB serial (CDC ACM) and USB HID are available, and a rich builder API allows building your own.
• Bootloader and DFU – embassy-boot is a lightweight bootloader supporting firmware application upgrades in a power-fail-safe way, with trial boots and rollbacks.

Sneak Peek

use defmt::info;
use embassy_executor::Spawner;
use embassy_time::{Duration, Timer};
use embassy_nrf::gpio::{AnyPin, Input, Level, Output, OutputDrive, Pin, Pull};
use embassy_nrf::Peripherals;

// Declare async tasks
#[embassy_executor::task]
async fn blink(pin: AnyPin) {
    let mut led = Output::new(pin, Level::Low, OutputDrive::Standard);

    loop {
        // Timekeeping is globally available, no need to mess with hardware timers.
        led.set_high();
        Timer::after_millis(150).await;
        led.set_low();
        Timer::after_millis(150).await;
    }
}

// Main is itself an async task as well.
#[embassy_executor::main]
async fn main(spawner: Spawner) {
    let p = embassy_nrf::init(Default::default());

    // Spawned tasks run in the background, concurrently.
    spawner.spawn(blink(p.P0_13.degrade())).unwrap();

    let mut button = Input::new(p.P0_11, Pull::Up);
    loop {
        // Asynchronously wait for GPIO events, allowing other tasks
        // to run, or the core to sleep.
        button.wait_for_low().await;
        info!("Button pressed!");
        button.wait_for_high().await;
        info!("Button released!");
    }
}

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