# 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](https://github.com/Dirbaio/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 `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)

`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](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.