Add error traits for communication interfaces

Author: eldruin

CHANGELOG.md

@@ -11,6 +11,10 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 - Added `IoPin` trait for pins that can change between being inputs or outputs
   dynamically.
 - Added `Debug` to all spi mode types.
+- `Error` traits for SPI, I2C and Serial traits. The error types used in those must
+  implement these `Error` traits, which implies providing a conversion to a common
+  set of error kinds. Generic drivers using these interfaces can then convert the errors
+  to this common set to act upon them.
 
 ### Changed
 - Swap PWM channel arguments to references

src/fmt.rs

@@ -3,7 +3,8 @@
 //! TODO write example of usage
 use core::fmt::{Result, Write};
 
-impl<Word, Error> Write for dyn crate::serial::nb::Write<Word, Error = Error> + '_
+impl<Word, Error: crate::serial::Error> Write
+    for dyn crate::serial::nb::Write<Word, Error = Error> + '_
 where
     Word: From<u8>,
 {

src/i2c.rs

@@ -26,13 +26,13 @@
 //! Here is an example of an embedded-hal implementation of the `Write` trait
 //! for both modes:
 //! ```
-//! # use embedded_hal::i2c::{SevenBitAddress, TenBitAddress, blocking::Write};
+//! # use embedded_hal::i2c::{ErrorKind, SevenBitAddress, TenBitAddress, blocking::Write};
 //! /// I2C0 hardware peripheral which supports both 7-bit and 10-bit addressing.
 //! pub struct I2c0;
 //!
 //! impl Write<SevenBitAddress> for I2c0
 //! {
-//! #   type Error = ();
+//! #   type Error = ErrorKind;
 //! #
 //!     fn write(&mut self, addr: u8, output: &[u8]) -> Result<(), Self::Error> {
 //!         // ...
@@ -42,7 +42,7 @@
 //!
 //! impl Write<TenBitAddress> for I2c0
 //! {
-//! #   type Error = ();
+//! #   type Error = ErrorKind;
 //! #
 //!     fn write(&mut self, addr: u16, output: &[u8]) -> Result<(), Self::Error> {
 //!         // ...
@@ -101,6 +101,58 @@
 
 use crate::private;
 
+/// I2C error
+pub trait Error: core::fmt::Debug {
+    /// Convert error to a generic I2C error kind
+    ///
+    /// By using this method, I2C errors freely defined by HAL implementations
+    /// can be converted to a set of generic I2C errors upon which generic
+    /// code can act.
+    fn kind(&self) -> ErrorKind;
+}
+
+/// I2C error kind
+///
+/// This represents a common set of I2C operation errors. HAL implementations are
+/// free to define more specific or additional error types. However, by providing
+/// a mapping to these common I2C errors, generic code can still react to them.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[non_exhaustive]
+pub enum ErrorKind {
+    /// An unspecific bus error occurred
+    Bus,
+    /// The arbitration was lost, e.g. electrical problems with the clock signal
+    ArbitrationLoss,
+    /// A bus operation was not acknowledged, e.g. due to the addressed device not being available on
+    /// the bus or the device not being ready to process requests at the moment
+    NoAcknowledge,
+    /// The peripheral receive buffer was overrun
+    Overrun,
+    /// A different error occurred. The original error may contain more information.
+    Other,
+}
+
+impl Error for ErrorKind {
+    fn kind(&self) -> ErrorKind {
+        *self
+    }
+}
+
+impl core::fmt::Display for ErrorKind {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::Bus => write!(f, "An unspecific bus error occurred"),
+            Self::ArbitrationLoss => write!(f, "The arbitration was lost"),
+            Self::NoAcknowledge => write!(f, "A bus operation was not acknowledged"),
+            Self::Overrun => write!(f, "The peripheral receive buffer was overrun"),
+            Self::Other => write!(
+                f,
+                "A different error occurred. The original error may contain more information"
+            ),
+        }
+    }
+}
+
 /// Address mode (7-bit / 10-bit)
 ///
 /// Note: This trait is sealed and should not be implemented outside of this crate.
@@ -119,12 +171,12 @@ impl AddressMode for TenBitAddress {}
 /// Blocking I2C traits
 pub mod blocking {
 
-    use super::{AddressMode, SevenBitAddress};
+    use super::{AddressMode, Error, SevenBitAddress};
 
     /// Blocking read
     pub trait Read<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Reads enough bytes from slave with `address` to fill `buffer`
         ///
@@ -150,7 +202,7 @@ pub mod blocking {
     /// Blocking write
     pub trait Write<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Writes bytes to slave with address `address`
         ///
@@ -174,7 +226,7 @@ pub mod blocking {
     /// Blocking write (iterator version)
     pub trait WriteIter<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Writes bytes to slave with address `address`
         ///
@@ -189,7 +241,7 @@ pub mod blocking {
     /// Blocking write + read
     pub trait WriteRead<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Writes bytes to slave with address `address` and then reads enough bytes to fill `buffer` *in a
         /// single transaction*
@@ -224,7 +276,7 @@ pub mod blocking {
     /// Blocking write (iterator version) + read
     pub trait WriteIterRead<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Writes bytes to slave with address `address` and then reads enough bytes to fill `buffer` *in a
         /// single transaction*
@@ -258,7 +310,7 @@ pub mod blocking {
     /// This allows combining operations within an I2C transaction.
     pub trait Transactional<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Execute the provided operations on the I2C bus.
         ///
@@ -285,7 +337,7 @@ pub mod blocking {
     /// This allows combining operation within an I2C transaction.
     pub trait TransactionalIter<A: AddressMode = SevenBitAddress> {
         /// Error type
-        type Error;
+        type Error: Error;
 
         /// Execute the provided operations on the I2C bus (iterator version).
         ///

src/lib.rs

@@ -143,23 +143,17 @@
 //! // convenience type alias
 //! pub type Serial1 = Serial<USART1>;
 //!
-//! /// Serial interface error
-//! pub enum Error {
-//!     /// Buffer overrun
-//!     Overrun,
-//!     // omitted: other error variants
-//! }
 //!
 //! impl hal::serial::nb::Read<u8> for Serial<USART1> {
-//!     type Error = Error;
+//!     type Error = hal::serial::ErrorKind;
 //!
-//!     fn read(&mut self) -> nb::Result<u8, Error> {
+//!     fn read(&mut self) -> nb::Result<u8, Self::Error> {
 //!         // read the status register
 //!         let isr = self.usart.sr.read();
 //!
 //!         if isr.ore().bit_is_set() {
 //!             // Error: Buffer overrun
-//!             Err(nb::Error::Other(Error::Overrun))
+//!             Err(nb::Error::Other(Self::Error::Overrun))
 //!         }
 //!         // omitted: checks for other errors
 //!         else if isr.rxne().bit_is_set() {
@@ -173,14 +167,14 @@
 //! }
 //!
 //! impl hal::serial::nb::Write<u8> for Serial<USART1> {
-//!     type Error = Error;
+//!     type Error = hal::serial::ErrorKind;
 //!
-//!     fn write(&mut self, byte: u8) -> nb::Result<(), Error> {
+//!     fn write(&mut self, byte: u8) -> nb::Result<(), Self::Error> {
 //!         // Similar to the `read` implementation
 //!         # Ok(())
 //!     }
 //!
-//!     fn flush(&mut self) -> nb::Result<(), Error> {
+//!     fn flush(&mut self) -> nb::Result<(), Self::Error> {
 //!         // Similar to the `read` implementation
 //!         # Ok(())
 //!     }
@@ -326,12 +320,11 @@
 //! use embedded_hal as hal;
 //! use hal::nb;
 //!
-//! use hal::serial::nb::Write;
-//! use ::core::convert::Infallible;
+//! use hal::serial::{ErrorKind, nb::Write};
 //!
 //! fn flush<S>(serial: &mut S, cb: &mut CircularBuffer)
 //! where
-//!     S: hal::serial::nb::Write<u8, Error = Infallible>,
+//!     S: hal::serial::nb::Write<u8, Error = ErrorKind>,
 //! {
 //!     loop {
 //!         if let Some(byte) = cb.peek() {
@@ -396,9 +389,9 @@
 //! # }
 //! # struct Serial1;
 //! # impl hal::serial::nb::Write<u8> for Serial1 {
-//! #   type Error = Infallible;
-//! #   fn write(&mut self, _: u8) -> nb::Result<(), Infallible> { Err(::nb::Error::WouldBlock) }
-//! #   fn flush(&mut self) -> nb::Result<(), Infallible> { Err(::nb::Error::WouldBlock) }
+//! #   type Error = ErrorKind;
+//! #   fn write(&mut self, _: u8) -> nb::Result<(), Self::Error> { Err(::nb::Error::WouldBlock) }
+//! #   fn flush(&mut self) -> nb::Result<(), Self::Error> { Err(::nb::Error::WouldBlock) }
 //! # }
 //! # struct CircularBuffer;
 //! # impl CircularBuffer {

src/serial/blocking.rs

@@ -7,7 +7,7 @@
 /// Write half of a serial interface (blocking variant)
 pub trait Write<Word> {
     /// The type of error that can occur when writing
-    type Error;
+    type Error: crate::serial::Error;
 
     /// Writes a slice, blocking until everything has been written
     ///

src/serial/mod.rs

@@ -2,3 +2,58 @@
 
 pub mod blocking;
 pub mod nb;
+
+/// Serial error
+pub trait Error: core::fmt::Debug {
+    /// Convert error to a generic serial error kind
+    ///
+    /// By using this method, serial errors freely defined by HAL implementations
+    /// can be converted to a set of generic serial errors upon which generic
+    /// code can act.
+    fn kind(&self) -> ErrorKind;
+}
+
+/// Serial error kind
+///
+/// This represents a common set of serial operation errors. HAL implementations are
+/// free to define more specific or additional error types. However, by providing
+/// a mapping to these common serial errors, generic code can still react to them.
+#[derive(Debug, Copy, Clone, Eq, PartialEq, Ord, PartialOrd, Hash)]
+#[non_exhaustive]
+pub enum ErrorKind {
+    /// The peripheral receive buffer was overrun.
+    Overrun,
+    /// Received data does not conform to the peripheral configuration.
+    /// Can be caused by a misconfigured device on either end of the serial line.
+    FrameFormat,
+    /// Parity check failed.
+    Parity,
+    /// Serial line is too noisy to read valid data.
+    Noise,
+    /// A different error occurred. The original error may contain more information.
+    Other,
+}
+
+impl Error for ErrorKind {
+    fn kind(&self) -> ErrorKind {
+        *self
+    }
+}
+
+impl core::fmt::Display for ErrorKind {
+    fn fmt(&self, f: &mut core::fmt::Formatter<'_>) -> core::fmt::Result {
+        match self {
+            Self::Overrun => write!(f, "The peripheral receive buffer was overrun"),
+            Self::Parity => write!(f, "Parity check failed"),
+            Self::Noise => write!(f, "Serial line is too noisy to read valid data"),
+            Self::FrameFormat => write!(
+                f,
+                "Received data does not conform to the peripheral configuration"
+            ),
+            Self::Other => write!(
+                f,
+                "A different error occurred. The original error may contain more information"
+            ),
+        }
+    }
+}

src/serial/nb.rs

@@ -6,7 +6,7 @@
 /// This can be encoded in this trait via the `Word` type parameter.
 pub trait Read<Word> {
     /// Read error
-    type Error;
+    type Error: crate::serial::Error;
 
     /// Reads a single word from the serial interface
     fn read(&mut self) -> nb::Result<Word, Self::Error>;
@@ -15,7 +15,7 @@ pub trait Read<Word> {
 /// Write half of a serial interface
 pub trait Write<Word> {
     /// Write error
-    type Error;
+    type Error: crate::serial::Error;
 
     /// Writes a single word to the serial interface
     fn write(&mut self, word: Word) -> nb::Result<(), Self::Error>;

src/spi/blocking.rs

@@ -7,7 +7,7 @@
 /// Blocking transfer
 pub trait Transfer<W> {
     /// Error type
-    type Error;
+    type Error: crate::spi::Error;
 
     /// Writes and reads simultaneously. The contents of `words` are
     /// written to the slave, and the received words are stored into the same
@@ -18,7 +18,7 @@ pub trait Transfer<W> {
 /// Blocking write
 pub trait Write<W> {
     /// Error type
-    type Error;
+    type Error: crate::spi::Error;
 
     /// Writes `words` to the slave, ignoring all the incoming words
     fn write(&mut self, words: &[W]) -> Result<(), Self::Error>;
@@ -27,7 +27,7 @@ pub trait Write<W> {
 /// Blocking write (iterator version)
 pub trait WriteIter<W> {
     /// Error type
-    type Error;
+    type Error: crate::spi::Error;
 
     /// Writes `words` to the slave, ignoring all the incoming words
     fn write_iter<WI>(&mut self, words: WI) -> Result<(), Self::Error>
@@ -50,7 +50,7 @@ pub enum Operation<'a, W: 'static> {
 /// as part of a single SPI transaction
 pub trait Transactional<W: 'static> {
     /// Associated error type
-    type Error;
+    type Error: crate::spi::Error;
 
     /// Execute the provided transactions
     fn exec<'a>(&mut self, operations: &mut [Operation<'a, W>]) -> Result<(), Self::Error>;