Embassy

Embassy is a project to make async/await a first-class option for embedded development.

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::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 with timers

The embassy::executor module provides an async/await executor based on static-executor.

• No alloc, no heap needed. Task futures are statically allocated.
• Integrated timer queue allows simple sleeping: Timer::after(Duration::from_ticks(64000)).await;.
• Suitable for low-power operation. Using interrupts or WFE/SEV ensures the CPU sleeps when there's no work to do. No busy-loop polling.
• Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks.
• Compatible with RTIC (example coming soon).

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.

Running the examples

Examples are for the nRF52840 chip but should be easily adaptable to other nRF52 chips.

GPIO pins are set up for the nrf52840-dk board (PCA10056)

• Install probe-run with defmt support.

cargo install --git https://github.com/knurling-rs/probe-run --branch main --features defmt

• Run the example

cargo run --bin rtc_async

Minimum supported Rust version (MSRV)

rustc 1.48.0-nightly (1fd5b9d51 2020-09-20)

Any recent nightly should work. 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

• 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.