My Contributions

Fork of: https://github.com/embassy-rs/embassy — async embedded framework for Rust.

I2C: Fix Slave Mode Hang in Blocking Mode (embassy-rs#6751)

The library uses a chip as an I2C slave in two modes - interrupt driven and another mode that just polls a status flag instead of using interrupts. In the original code, the I2C interrupts for both modes, even though blocking mode never installs a handler for them. Because the address match flag isn't clered automatically, a message on the bus would trigger the unhandled interrupts and due to this the I2C slave mode would hang and never recover.

#My Fix To fix this, I moved the interrupt setup so it only runs for the constructors that actually bind a handler, leaving the blocking mode untouched. I also noticed that there were two functions which could update the same interrupt enable bit at the same time without any synchronization which I fixed.

#Challenges I faced The blocking mode code path looked correct when you saw it independently. But, it was actually living one layer up. In setup logic shared both modes, so I had to trace the failure back through the constructors rather than the code which actually hung.

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Flash: Fix Bounds Check for Chips With Non-Contiguous Banks (embassy-rs#6700, closes #6258)

Flash on STM32 chips are split into two banks and this library's read/write bounds check assumed that they area always back to back in address space. On the STM32G473CB, it doesn't sit back to back. There is a gap between the banks so valid addresses in the second bank were being rejected as out of range, even though the lower level erase function could reach them without issue.

#To fix this: I changed the bounds check to validate against the chip's actual addressable memory span instead of assuming a contiguous layout.

#Challenges I faced: The person who reported it assumed the erase function itself was broken and had already worked around it with a manual register level implementation. The real bug was actually in the address validation.

I had to work through the chip's memory map to test that and prove it and to also let the managers know that the erase path didn't need any fix.

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Embassy

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, nRF54 and nRF91 series.
  • embassy-rp, for the Raspberry Pi RP2040 and RP23xx microcontrollers.
  • embassy-mspm0, for the Texas Instruments MSPM0 microcontrollers.
  • embassy-mcxa, for NXP's MCX-A series of microcontrollers.
  • esp-rs, for the Espressif Systems ESP32 series of chips.
    • Embassy HAL support for Espressif chips, as well as Async Wi-Fi, Bluetooth, and ESP-NOW, is being developed in the esp-rs/esp-hal repository.
  • ch32-hal, for the WCH 32-bit RISC-V(CH32V) series of chips.
  • mpfs-hal, for the Microchip PolarFire SoC.
  • py32-hal, for the Puya Semiconductor PY32 series of microcontrollers.
  • ra-hal, for the Renesas RA family of microcontrollers.

• 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 trouble crate provides a Bluetooth Low Energy 4.x and 5.x Host that runs on any microcontroller implementing the bt-hci traits (currently nRF52, nrf54, rp2040, rp23xx and esp32 and serial controllers are supported).
  • 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::{Peri, Peripherals};

// Declare async tasks
#[embassy_executor::task]
async fn blink(pin: Peri<'static, 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.into()).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!");
    }
}

Examples

Examples are found in the examples/ folder separated by the chip manufacturer they are designed to run on. For example:

• examples/nrf52840 run on the nrf52840-dk board (PCA10056) but should be easily adaptable to other nRF52 chips and boards.
• examples/nrf5340 run on the nrf5340-dk board (PCA10095).
• examples/stm32xx for the various STM32 families.
• examples/rp are for the RP2040 and RP235x chips.
• examples/mcxa run on the FRDM-MCXA266 board.
• examples/std are designed to run locally on your PC.

Running examples

• Install probe-rs following the instructions at https://probe.rs.
• Change directory to the sample's base directory. For example:

cd examples/nrf52840

• Ensure Cargo.toml sets the right feature for the name of the chip you are programming. If this name is incorrect, the example may fail to run or immediately crash after being programmed.

• Ensure .cargo/config.toml contains the name of the chip you are programming.

• Run the example

For example:

cargo run --release --bin blinky

For more help getting started, see Getting Started and Running the Examples.

Developing Embassy with Rust Analyzer-based editors

The Rust Analyzer is used by Visual Studio Code and others. Given the multiple targets that Embassy serves, there is no Cargo workspace file. Instead, the Rust Analyzer must be told of the target project to work with. In the case of Visual Studio Code, please refer to the .vscode/settings.json file's rust-analyzer.linkedProjectssetting.

Minimum supported Rust version (MSRV)

Embassy is guaranteed to compile on latest stable Rust. It might compile with older versions, but that may change in any new patch release.

Why the name?

EMBedded ASYnc! :)

License

Embassy is licensed under either of

• Apache License, Version 2.0 (LICENSE-APACHE or http://www.apache.org/licenses/LICENSE-2.0)
• MIT license (LICENSE-MIT or http://opensource.org/licenses/MIT)

at your option.

Contribution

Unless you explicitly state otherwise, any contribution intentionally submitted for inclusion in the work by you, as defined in the Apache-2.0 license, shall be dual licensed as above, without any additional terms or conditions.