Modern embedded framework, using Rust and async.
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Timo Kröger b36337b3d2 Refactor bit search logic when no clock specified
Always search for a enable bit, even when no clock is specified in the
yaml. Try to derive the clock name from the register name.

This change picked up USART2 for stm32wle which was missing the clock.
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Embassy

Embassy is a project to make async/await a first-class option for embedded development. For more information and instructions to get started, click here.

Traits and types

embassy provides a set of traits and types specifically designed for async usage.

  • embassy::io: AsyncBufRead, AsyncWrite. Traits for byte-stream IO, essentially no_std compatible versions of futures::io.
  • embassy::traits::flash: Flash device trait.
  • embassy::time: Clock and Alarm traits. Std-like Duration and Instant.
  • More traits for SPI, I2C, UART async HAL coming soon.

Executor

The embassy::executor module provides an async/await executor designed for embedded usage.

  • No alloc, no heap needed. Task futures are statically allocated.
  • No "fixed capacity" data structures, executor works with 1 or 1000 tasks without needing config/tuning.
  • Integrated timer queue: sleeping is easy, just do Timer::after(Duration::from_secs(1)).await;.
  • No busy-loop polling: CPU sleeps when there's no work to do, using interrupts or WFE/SEV.
  • Efficient polling: a wake will only poll the woken task, not all of them.
  • Fair: a task can't monopolize CPU time even if it's constantly being woken. All other tasks get a chance to run before a given task gets polled for the second time.
  • Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks.

Utils

embassy::util contains some lightweight async/await utilities, mainly helpful for async driver development (signaling a task that an interrupt has occured, for example).

embassy-nrf

The embassy-nrf crate contains implementations for nRF 52 series SoCs.

  • uarte: UARTE driver implementing AsyncBufRead and AsyncWrite.
  • qspi: QSPI driver implementing Flash.
  • gpiote: GPIOTE driver. Allows awaiting GPIO pin changes. Great for reading buttons or receiving interrupts from external chips.
  • rtc: RTC driver implementing Clock and Alarm, for use with embassy::executor.

Examples

Examples are found in the examples/ folder seperated by the chip manufacturer they are designed to run on:

  • examples/nrf are designed to run on the nrf52840-dk board (PCA10056) but should be easily adaptable to other nRF52 chips and boards.
  • examples/rp are for the RP2040 chip.
  • examples/stm32 are designed for the STM32F429ZI chip but should be easily adaptable to other STM32F4xx chips.
  • examples/std are designed to run locally on your pc.

Running examples

  • Setup git submodules (needed for STM32 examples)
git submodule init
git submodule update
  • Install probe-run with defmt support.
cargo install probe-run
  • Run the example
cargo run --bin rtc_async

Minimum supported Rust version (MSRV)

Required nightly version is specified in the rust-toolchain.toml file. Nightly is required for:

  • generic_associated_types: for trait funcs returning futures.
  • type_alias_impl_trait: for trait funcs returning futures implemented with async{} blocks, and for static-executor.

Stable support is a non-goal until these features get stabilized.

Why the name?

EMBedded ASYnc! :)

License

This work is licensed under either of

at your option.