Add asynchronous versions of most embedded-hal traits using GATs

CHANGELOG.md

@@ -10,6 +10,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 ### Added
 - Added `IoPin` trait for pins that can change between being inputs or outputs
   dynamically.
+- Added `futures` module that contains asynchronous traits (using currently unstable GATs) for I2C, RNG, Serial, SPI, digital pins, and delays. These traits are behind the feature flag `unstable-futures`. The `futures` module currently needs Rust nightly and it is not included in `embedded-hal`'s SemVer guarantees. We may release breaking changes in any patch release. If you use this module, please use an `=1.x.x` crate version specification.
 
 ### Changed
 - Swap PWM channel arguments to references

Cargo.toml

@@ -15,6 +15,11 @@ readme = "README.md"
 repository = "https://github.com/rust-embedded/embedded-hal"
 version = "1.0.0-alpha.4" # remember to update html_root_url
 
+[features]
+# Enabling this feature enables the `futures` module using generic associated types (GATs), which are still unstable.
+# Therefore, this feature requires compiling on nightly.
+unstable-futures = []
+
 [dependencies]
 nb = "1"
 

src/futures/delay.rs

@@ -0,0 +1,36 @@
+//! Asynchronous Delays
+//!
+//! # What's the difference this trait and the `timer::CountDown` trait?
+//!
+//! The `Delay` trait provides an asynchronous delay abstraction and it's meant to be used either
+//! to build higher-level abstractions like I/O timeouts or by itself.
+
+use core::{future::Future, time::Duration};
+
+/// Asynchronously wait a duration of time.
+///
+/// # Example
+/// ```rust
+/// # use embedded_hal::futures::delay::Delay;
+/// use core::time::Duration;
+///
+/// async fn wait_100_micros<D: Delay>(timer: &D) {
+///     timer.delay(Duration::from_micros(100))
+///         .await
+///         .expect("failed to await on timer");
+/// }
+/// ```
+pub trait Delay {
+    /// Enumeration of `Delay` errors.
+    type Error;
+
+    /// The future returned from `delay`.
+    type DelayFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that will resolve when `duration` has passed.
+    /// It is not guaranteed that _exactly_ `duration` will pass, but it will
+    /// be `duration` or longer.
+    fn delay<'a>(&'a mut self, duration: Duration) -> Self::DelayFuture<'a>;
+}

src/futures/digital.rs

@@ -0,0 +1,121 @@
+//! Asynchronous digital I/O
+//!
+//! # Examples
+//! ```rust
+//! # use embedded_hal::futures::digital::AsyncInputPin;
+//! //! Asynchronously wait until the `ready_pin` becomes high.
+//! async fn wait_until_ready<P>(ready_pin: &P)
+//! where
+//!     P: WaitFor,
+//! {
+//!     ready_pin
+//!         .wait_for_high()
+//!         .await
+//!         .expect("failed to await input pin")
+//! }
+//! ```
+//!
+//! ```rust,ignore
+//! # use embedded_hal::futures::digital::WaitForHigh;
+//! # use embedded_hal::futures::delay::Delay;
+//! use core::time::Duration;
+//!
+//! //! Wait until the `ready_pin` is high or timeout after 1 millisecond.
+//! //! Returns true if the pin became high or false if it timed-out.
+//! async fn wait_until_ready_or_timeout<P, D>(ready_pin: &P, delay: &mut D) -> bool
+//! where
+//!     P: WaitForHigh,
+//!     D: Delay,
+//! {
+//!     futures::select_biased! {
+//!         x => ready_pin.wait_for_high() => {
+//!             x.expect("failed to await input pin");
+//!             true
+//!         },
+//!         _ => delay.delay(Duration::from_millis(1)) => false, // ignore the error
+//!     }
+//! }
+//! ```
+
+use core::future::Future;
+
+/// Asynchronously wait for a pin to be high.
+pub trait WaitForHigh {
+    /// Enumeration of errors.
+    type Error;
+
+    /// The future returned by the `wait_for_high` function.
+    type Fut<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that resolves when this pin _is_ high. If the pin
+    /// is already high, the future resolves immediately.
+    ///
+    /// # Note for implementers
+    /// The pin may have switched back to low before the task was run after
+    /// being woken. The future should still resolve in that case.
+    fn wait_for_high<'a>(&'a mut self) -> Self::Fut<'a>;
+}
+
+/// Asynchronously wait for a pin to be low.
+pub trait WaitForLow {
+    /// Enumeration of errors.
+    type Error;
+
+    /// The future returned by `wait_for_low`.
+    type Fut<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that resolves when this pin _is_ low. If the pin
+    /// is already low, the future resolves immediately.
+    ///
+    /// # Note for implementers
+    /// The pin may have switched back to high before the task was run after
+    /// being woken. The future should still resolve in that case.
+    fn wait_for_low<'a>(&'a mut self) -> Self::Fut<'a>;
+}
+
+/// Wait for a rising edge (transition from low to high).
+pub trait WaitForRisingEdge {
+    /// Enumeration of errors.
+    type Error;
+
+    /// The future returned from `wait_for_rising_edge`.
+    type Fut<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that resolves when this pin transitions from low to high.
+    fn wait_for_rising_edge<'a>(&'a mut self) -> Self::Fut<'a>;
+}
+
+/// Wait for a falling edge (transition from high to low).
+pub trait WaitForFallingEdge {
+    /// Enumeration of errors.
+    type Error;
+
+    /// The future returned from `wait_for_falling_edge`.
+    type Fut<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that resolves when this pin transitions from high to low.
+    fn wait_for_falling_edge<'a>(&'a mut self) -> Self::Fut<'a>;
+}
+
+/// Wait for any edge (transition from low to high OR high to low).
+pub trait WaitForAnyEdge {
+    /// Enumeration of errors.
+    type Error;
+
+    /// The future returned from `wait_for_any_edge`.
+    type Fut<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Returns a future that resolves when this pin undergoes any transition, e.g.
+    /// low to high OR high to low.
+    fn wait_for_any_edge<'a>(&'a mut self) -> Self::Fut<'a>;
+}

src/futures/i2c.rs

@@ -0,0 +1,117 @@
+//! Async I2C API
+//!
+//! This API supports 7-bit and 10-bit addresses. Traits feature an `AddressMode`
+//! marker type parameter. Two implementation of the `AddressMode` exist:
+//! `SevenBitAddress` and `TenBitAddress`.
+//!
+//! Through this marker types it is possible to implement each address mode for
+//! the traits independently in `embedded-hal` implementations and device drivers
+//! can depend only on the mode that they support.
+//!
+//! Additionally, the I2C 10-bit address mode has been developed to be fully
+//! backwards compatible with the 7-bit address mode. This allows for a
+//! software-emulated 10-bit addressing implementation if the address mode
+//! is not supported by the hardware.
+//!
+//! Since 7-bit addressing is the mode of the majority of I2C devices,
+//! `SevenBitAddress` has been set as default mode and thus can be omitted if desired.
+
+pub use crate::blocking::i2c::{AddressMode, SevenBitAddress, TenBitAddress};
+use core::future::Future;
+
+/// Async read
+pub trait Read<A: AddressMode = SevenBitAddress> {
+    /// Error type
+    type Error;
+    /// The future associated with the `read` method.
+    type ReadFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Reads enough bytes from slave with `address` to fill `buffer`
+    ///
+    /// # I2C Events (contract)
+    ///
+    /// ``` text
+    /// Master: ST SAD+R        MAK    MAK ...    NMAK SP
+    /// Slave:           SAK B0     B1     ... BN
+    /// ```
+    ///
+    /// Where
+    ///
+    /// - `ST` = start condition
+    /// - `SAD+R` = slave address followed by bit 1 to indicate reading
+    /// - `SAK` = slave acknowledge
+    /// - `Bi` = ith byte of data
+    /// - `MAK` = master acknowledge
+    /// - `NMAK` = master no acknowledge
+    /// - `SP` = stop condition
+    fn read<'a>(&'a mut self, address: A, read: &'a mut [u8]) -> Self::ReadFuture<'a>;
+}
+
+/// Async write
+pub trait Write<A: AddressMode = SevenBitAddress> {
+    /// Error type
+    type Error;
+    /// The future associated with the `write` method.
+    type WriteFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Writes bytes to slave with address `address`
+    ///
+    /// # I2C Events (contract)
+    ///
+    /// ``` text
+    /// Master: ST SAD+W     B0     B1     ... BN     SP
+    /// Slave:           SAK    SAK    SAK ...    SAK
+    /// ```
+    ///
+    /// Where
+    ///
+    /// - `ST` = start condition
+    /// - `SAD+W` = slave address followed by bit 0 to indicate writing
+    /// - `SAK` = slave acknowledge
+    /// - `Bi` = ith byte of data
+    /// - `SP` = stop condition
+    fn write<'a>(&'a mut self, address: A, write: &'a [u8]) -> Self::WriteFuture<'a>;
+}
+
+/// Async write + read
+pub trait WriteRead<A: AddressMode = SevenBitAddress> {
+    /// Error type
+    type Error;
+    /// The future associated with the `write_read` method.
+    type WriteReadFuture<'a>: Future<Output = Result<&'a [u8], Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Writes bytes to slave with address `address` and then reads enough bytes to fill `read` *in a
+    /// single transaction*. The returned buffer is the initialized `read` buffer.
+    ///
+    /// # I2C Events (contract)
+    ///
+    /// ``` text
+    /// Master: ST SAD+W     O0     O1     ... OM     SR SAD+R        MAK    MAK ...    NMAK SP
+    /// Slave:           SAK    SAK    SAK ...    SAK          SAK I0     I1     ... IN
+    /// ```
+    ///
+    /// Where
+    ///
+    /// - `ST` = start condition
+    /// - `SAD+W` = slave address followed by bit 0 to indicate writing
+    /// - `SAK` = slave acknowledge
+    /// - `Oi` = ith outgoing byte of data
+    /// - `SR` = repeated start condition
+    /// - `SAD+R` = slave address followed by bit 1 to indicate reading
+    /// - `Ii` = ith incoming byte of data
+    /// - `MAK` = master acknowledge
+    /// - `NMAK` = master no acknowledge
+    /// - `SP` = stop condition
+    fn write_read<'a>(
+        &'a mut self,
+        address: A,
+        write: &'a [u8],
+        read: &'a mut [u8],
+    ) -> Self::WriteReadFuture<'a>;
+}

src/futures/mod.rs

@@ -0,0 +1,9 @@
+//! Asynchronous APIs
+//!
+//! This traits use `core::future::Future` and generic associated types.
+
+pub mod delay;
+pub mod digital;
+pub mod i2c;
+pub mod serial;
+pub mod spi;

src/futures/serial.rs

@@ -0,0 +1,42 @@
+//! Serial interface
+
+use core::future::Future;
+
+/// Read half of a serial interface
+///
+/// Some serial interfaces support different data sizes (8 bits, 9 bits, etc.);
+/// This can be encoded in this trait via the `Word` type parameter.
+pub trait Read<Word> {
+    /// Read error
+    type Error;
+
+    /// The future associated with the `read` method.
+    type ReadFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Reads words from the serial interface into the supplied slice.
+    fn read<'a>(&'a mut self, read: &'a mut [Word]) -> Self::ReadFuture<'a>;
+}
+
+/// Write half of a serial interface
+pub trait Write<Word> {
+    /// Write error
+    type Error;
+
+    /// The future associated with the `write` method.
+    type WriteFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// The future associated with the `flush` method.
+    type FlushFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+        Self: 'a;
+
+    /// Writes a single word to the serial interface
+    fn write<'a>(&'a mut self, word: Word) -> Self::WriteFuture<'a>;
+
+    /// Ensures that none of the previously written words are still buffered
+    fn flush<'a>(&'a mut self) -> Self::FlushFuture<'a>;
+}