Embassy is a powerful framework for building asynchronous embedded applications in Rust. Embassy focuses on safety, performance, and efficiency makes it an excellent choice for latency-sensitive systems. This guide provides junior and mid-level engineers with a comprehensive understanding of using Embassy to develop embedded software in Rust. We’ll outline ten essential steps, each accompanied by examples, to help you get started effectively.

Step 1: Understand the Embassy Architecture

Principle Consideration

Embassy’s architecture revolves around a lightweight, async runtime designed for embedded systems. It employs cooperative multitasking, allowing tasks to yield execution to enable concurrency without traditional preemptive scheduling. This is ideal for low-powered devices. You can also tie interrupts and events to asynchronous tasks - enabling an intuitive workflow.

Embassy’s hardware support focuses on one of Rust’s core advantages: making impossible/dangerous states unrepresentable in software, transforming many common runtime errors into compilation errors - reducing debugging time.

Example

Understanding the core components—such as tasks, executors, and the async-await syntax—is essential.

Implementation

1. Executors: Embassy uses an executor to run async tasks. Familiarize yourself with how it manages task scheduling and execution.

2. Task Definition: Tasks are defined with async fn, allowing for non-blocking code.

   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       spawner.spawn(async {
           // Your asynchronous task here
       }).unwrap();
   }
   

3. Example Code:

   use embassy_executor::Spawner;
   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       spawner.spawn(async {
           loop {
               // Your task logic here
           }
       }).unwrap();
   }
   

Step 2: Set Up Your Development Environment

Principle Consideration

A proper development environment is crucial for successful embedded development. This includes installing Rust, setting up the target, and managing dependencies.

Example

You’ll need to configure your Rust toolchain for embedded development.

Implementation

1. Toolchain Installation: Install Rust using rustup and ensure you’re using the nightly version for async support (Embassy works best with the nightly toolchain):

   rustup install nightly
   rustup default nightly
   

2. Adding Targets: Add the target architecture for your embedded device (e.g., ARM Cortex-M):

   rustup target add thumbv6m-none-unknown
   

3. Cargo.toml Configuration: Define your dependencies in Cargo.toml:

   [dependencies]
   embassy = "0.3"
   embassy-nrf = "0.3" # For nRF devices
   

Step 3: Select the Target Microcontroller

Principle Consideration

Selecting the right microcontroller is critical for ensuring that the hardware capabilities align with your application requirements.

Example

For a project using the nRF52 series, Embassy provides specific libraries for interaction.

Implementation

1. Microcontroller Research: Investigate the features of potential microcontrollers, focusing on GPIO, UART, I2C, and ADC.

2. Use Embassy HAL: Leverage the Hardware Abstraction Layer for your specific microcontroller:

   [dependencies]
   embassy-nrf = "0.3"
   

3. Example Code for GPIO:

   use embassy_nrf::gpio::{Output, Level};
   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       let led = Output::new(p0.p0_13, Level::Low);
       led.set_high().unwrap();
   }
   

Step 4: Write Asynchronous Code

Principle Consideration

Asynchronous programming is central to Embassy’s model, allowing for efficient I/O operations without blocking the CPU.

Example

Use async and await syntax to write non-blocking tasks. Avoid blocking for long periods of time - it will stall the execution of other tasks.

Implementation

1. Define Asynchronous Tasks: Tasks can perform operations like sensor readings or communication without blocking:

   async fn read_sensor() -> f32 {
       // Simulate an asynchronous sensor read
       42.0
   }
   

2. Execute the Task:

   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       let sensor_value = read_sensor().await;
       println!("Sensor value: {}", sensor_value);
   }
   

Step 5: Handle Interrupts and Events

Principle Consideration

Efficient handling of hardware interrupts is crucial for responsive embedded systems. Embassy’s architecture simplifies this through its event model. One of Embassy’s core strengths is easily tying interrupts and hardware events to a task-based model, leading to intuitive domain-driven code design.

Example

You can set up event-driven programming to respond to interrupts efficiently.

Implementation

1. Set Up Interrupts: Use the embassy::interrupt module to manage interrupts:

   use embassy_nrf::interrupt;
   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       // Configure interrupt
       interrupt::enable(p0.p0_12);
   }
   

2. Asynchronous Interrupt Handler:

   #[interrupt]
   fn GPIO() {
       // Handle GPIO interrupt
       spawner.spawn(async {
           // React to the interrupt
       }).unwrap();
   }
   

Step 6: Use Timers and Delays

Principle Consideration

Timers are essential for scheduling tasks and creating non-blocking delays.

Example

Embassy provides straightforward APIs to work with timers.

Implementation

1. Timer Setup: Utilize Embassy’s timer capabilities to create delays.

   use embassy_time::{Timer, Duration};
   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       let timer = Timer::new();
       loop {
           timer.delay(Duration::from_secs(1)).await;
           // Code to execute after delay
       }
   }
   

2. Multiple Timers: You can manage multiple tasks with different timing requirements.

   spawner.spawn(async {
       loop {
           timer.delay(Duration::from_secs(5)).await;
           // Execute every 5 seconds
       }
   }).unwrap();
   

Step 7: Implement Communication Protocols

Principle Consideration

Asynchronous communication protocols like UART, I2C, and SPI are vital in embedded systems. Embassy supports these through specific libraries.

Example

Use Embassy’s APIs to implement UART communication.

Implementation

1. Set Up UART: Configure the UART interface for asynchronous communication:

   use embassy_nrf::uart::{Uart, Config};
   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       let config = Config::default();
       let uart = Uart::new(p0.p0_0, p0.p0_1, config);
       let mut buf = [0u8; 32];
       uart.read(&mut buf).await.unwrap();
   }
   

2. Send Data: Use the UART interface to send data asynchronously:

   uart.write(b"Hello, UART!\n").await.unwrap();
   

Step 8: Manage Power Consumption

Principle Consideration

Power efficiency is critical, especially in battery-operated devices. Implementing strategies for low power consumption is essential.

Example

Use sleep modes and efficient task scheduling to minimize energy usage.

Implementation

1. Sleep Functionality: Implement low-power modes effectively.

   use embassy_nrf::power::PowerManager;
   async fn low_power_sleep() {
       let pm = PowerManager::new();
       pm.sleep();
   }
   

2. Incorporate Sleep into Main Loop:

   #[embassy_executor::main]
   async fn main(spawner: Spawner) {
       loop {
           low_power_sleep().await; // Sleep between tasks
           // Perform necessary tasks
       }
   }
   

Step 9: Testing and Debugging

Principle Consideration

Testing and debugging are crucial in embedded development to ensure reliability and performance.

Example

Utilize Rust’s built-in testing framework along with debugging tools for effective testing.

Implementation

1. Unit Tests: Write tests to verify your code’s functionality:

   #[cfg(test)]
   mod tests {
       use super::*;
       #[test]
       fn test_sensor_read() {
           let value = read_sensor();
           assert_eq!(value, 42.0);
       }
   }
   

2. Debugging Tools: Use GDB or other tools to debug your application:

   rust-gdb target/thumbv6m-none-unknown/release/your_project
   

Step 10: Prepare for Deployment

Principle Consideration

Deploying embedded software involves compiling your application and programming it onto the microcontroller.

Example

Use tools to build and flash your application.

Implementation

1. Build Artifacts: Compile your project for the target architecture:

   cargo build --release --target thumbv6m-none-unknown
   

2. Flashing: Use a flashing tool like cargo-embed or nrfjprog to upload your firmware to the device:

   cargo embed --target thumbv6m-none-unknown --release
   

   Or for nrfjprog:

   nrfjprog --program target/thumbv6m-none-unknown/release/your_project.hex --chiperase --reset
   

3. Post-Deployment Testing: After flashing, perform checks to ensure that your application runs as expected.

Conclusion

Using Embassy for embedded Rust development provides a modern approach to building efficient, asynchronous applications. By following these ten steps, you’ll be equipped to create reliable, high-performance embedded systems that leverage the unique features of Rust and the Embassy framework.

Summary of Steps

1. Understand the Architecture of Embassy: Familiarize yourself with the task model and executor.
2. Set Up Your Development Environment: Properly configure your Rust toolchain and project dependencies.
3. Select Your Target Microcontroller: Choose a microcontroller that meets your project’s requirements.
4. Write Asynchronous Code: Use async/await to manage non-blocking tasks effectively.
5. Handle Interrupts and Events: Implement responsive interrupt handling with Embassy’s event model.
6. Use Timers and Delays: Manage timing for tasks using Embassy’s asynchronous timer APIs.
7. Implement Communication Protocols: Use Embassy’s APIs to set up UART, I2C, or SPI communication.
8. Manage Power Consumption: Implement low-power modes and strategies to maximize efficiency.
9. Testing and Debugging: Write tests and use debugging tools to ensure code reliability.
10. Prepare for Deployment: Build and flash your application to the target hardware.

By mastering these steps, engineers can effectively harness the power of Embassy and Rust to build robust and efficient embedded systems, ultimately leading to better performance and reliability in production environments.