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Since introducing the ctx pointer, the handler is now two words, so setting it can race with the interrupt firing. On race it's possible for the new handler to be alled with the old ctx pointer or viceversa. Rather than documenting this, it's better to split the function in two to make it obvious to the user that it's not atomic. The user can use a critical section, or disable/enable the interrupt to avoid races if this is a concern.
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, essentiallyno_stdcompatible versions offutures::io.embassy::flash: Flash device trait.embassy::time:ClockandAlarmtraits. Std-likeDurationandInstant.- 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 implementingAsyncBufReadandAsyncWrite.qspi: QSPI driver implementingFlash.gpiote: GPIOTE driver. Allowsawaiting GPIO pin changes. Great for reading buttons or receiving interrupts from external chips.rtc: RTC driver implementingClockandAlarm, for use withembassy::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-runwith 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)
Only recent nighly supported. Nightly is required for:
generic_associated_types: for trait funcs returning futures.type_alias_impl_trait: for trait funcs returning futures implemented withasync{}blocks, and forstatic-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.