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# Embassy
Embassy is a project to make async/await a first-class option for embedded development.
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## Traits and types
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`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` .
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- More traits for SPI, I2C, UART async HAL coming soon.
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## Executor
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The `embassy::executor` module provides an async/await executor designed for embedded usage.
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- No `alloc` , no heap needed. Task futures are statically allocated.
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- 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.
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- Creating multiple executor instances is supported, to run tasks with multiple priority levels. This allows higher-priority tasks to preempt lower-priority tasks.
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## 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
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The `embassy-nrf` crate contains implementations for nRF 52 series SoCs.
- `uarte` : UARTE driver implementing `AsyncBufRead` and `AsyncWrite` .
- `qspi` : QSPI driver implementing `Flash` .
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- `gpiote` : GPIOTE driver. Allows `await` ing 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)
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Only recent nighly supported. Nightly is required for:
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- `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` .
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Stable support is a non-goal until these features get stabilized.
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## Why the name?
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EMBedded ASYnc! :)
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## License
This work is licensed under either of
- Apache License, Version 2.0 ([LICENSE-APACHE](LICENSE-APACHE) or
http://www.apache.org/licenses/LICENSE-2.0)
- MIT license ([LICENSE-MIT](LICENSE-MIT) or http://opensource.org/licenses/MIT)
at your option.
