Merge #230

230: Make I2C compatible with multiple address sizes r=ryankurte a=eldruin

This adds I2C 7-bit and 10-bit address mode compatibility as roughly described [here](#147 (comment)).
Discussion issue: #147 

I have also added the `SevenBitAddress` as the default address mode to the traits so this is not even a breaking change.

Usage broken down per use case:
* **Device driver which only supports 7-bit addressing mode:**
       The driver looks exactly the same as now since the default address mode is 7-bit.

```rust
 impl<I2C, E> MyDriver<I2C>
 where I2C: i2c::Write<Error = E> {
   pub fn do_cool_stuff(&mut self) // ...
 }
 ```

* **Device driver which only supports 10-bit addressing mode:**
       The only difference to a 7-bit-address-only driver is one additional parameter in the I2C trait bound.
```rust
 impl<I2C, E> MyDriver<I2C>
 where I2C: i2c::Write<TenBitAddress, Error = E> {
   pub fn do_cool_stuff(&mut self) // ...
 }
 ```
 
* **Driver for device supporting both addressing modes:**
       Complexity can be abstracted away into additional internal traits which can handle the addressing stuff. Driver code stays clean.
       **This is nothing new**. We already do this on drivers for devices compatible with both I2C and SPI. No need for duplicated code.
       Here a real example: [usage](https://github.com/eldruin/bmi160-rs/blob/3af5637f1df047bb811a4885525cfbe8b44d8ede/src/device_impl.rs#L43), [traits](https://github.com/eldruin/bmi160-rs/blob/master/src/interface.rs)
  
 ```rust
 impl<DI, E> MyDriver<DI>
 where DI: WriteData<Error = E> {
   pub fn do_cool_stuff(&mut self) {} // ...
 }
 
 pub trait WriteData {
 // ...
 }
 
// it is also possible to just leave the `SevenBitAddress` type out here,
// since it is the default.
 impl<I2C, E> WriteData for I2cInterface<I2C, SevenBitAddress>
 where
     I2C: i2c::Write<SevenBitAddress, Error = E>,
 {
   // ...
 }
 
 impl<I2C, E> WriteData for I2cInterface<I2C, TenBitAddress>
 where
     I2C: i2c::Write<TenBitAddress, Error = E>,
 {
   // ...
 }
 ```
 
* **Bus controller impl supporting only 7-bit addressing mode:**
       Code stays almost the same, just adding one addressing mode parameter. Additionally, _if desired_:
    * 10-bit addressing can be software-emulated:
         Emulate by extending and copying payload in separate `TenBitAddress` implementation. Total flexibility to do whatever is necessary in this case since the code is independent.
    * 10-bit addressing cannot be software-emulated:
         Implementation does not offer implementation for `TenBitAddress` variant. The user gets a compilation error and everything is clear.
 
* **Bus controller impl supporting both addressing modes:**
       No problem. Two separate implementations guarantee as much flexibility as necessary. At the same time, sharing generic code is possible.
  
 Additional benefits: 
* No runtime performance cost 
* No runtime switching, duplicated code or panics for unsupported modes. 
* Consistent with what we do for code paths that can be determined statically by the compiler.
* To my taste elegant, simple and very descriptive.

See [here](#147 (comment)) for a comparison to other alternatives.

I have also sealed the trait.

## Proof
* A HAL implementation of both modes: [bitbang-hal](https://github.com/eldruin/bitbang-hal/tree/i2c-multi-address-mode). [code changes](eldruin/bitbang-hal@embedded-hal-1.0.0-alpha.1...eldruin:i2c-multi-address-mode)
* Drivers supporting only 7-bit addresses need **no changes**.
For demonstration purposes, explicitly including the `SevenBitAddress` would look like this: [OPT300x](https://github.com/eldruin/opt300x-rs/tree/i2c-multi-address-mode). [code changes](https://github.com/eldruin/opt300x-rs/compare/i2c-multi-address-mode).
This would be similar to the case of a 10-bit-only device driver.

Co-authored-by: Diego Barrios Romero <[email protected]>

Author: bors[bot]

CHANGELOG.md

@@ -8,8 +8,15 @@ and this project adheres to [Semantic Versioning](http://semver.org/).
 
 ## [Unreleased]
 
+### Added
+- 10-bit addressing mode for I2C traits.
+
 ### Changed
 
+- I2C addressing modes are now selected via an `AddressMode` type parameter.
+  The trait features implementations for marker types `SevenBitAddress` and
+  `TenBitAddress`. `SevenBitAddress` is the default mode so this is not a
+  breaking change.
 - The method `try_write` from the trait `blocking::i2c::WriteIter` trait
   has been renamed `try_write_iter` for consistency.
 - Updated `nb` dependency to version `1`.

src/blocking/i2c.rs

@@ -1,12 +1,119 @@
 //! Blocking I2C API
 //!
-//! Slave addresses used by this API are 7-bit I2C addresses ranging from 0 to 127.
+//! 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`.
 //!
-//! Operations on 10-bit slave addresses are not supported by the API yet (but applications might
-//! be able to emulate some operations).
+//! 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.
+//!
+//! ## Examples
+//!
+//! ### `embedded-hal` implementation for an MCU
+//! Here is an example of an embedded-hal implementation of the `Write` trait
+//! for both modes:
+//! ```
+//! # use embedded_hal::blocking::i2c::{SevenBitAddress, TenBitAddress, Write};
+//! /// I2C0 hardware peripheral which supports both 7-bit and 10-bit addressing.
+//! pub struct I2c0;
+//!
+//! impl Write<SevenBitAddress> for I2c0
+//! {
+//! #   type Error = ();
+//! #
+//!     fn try_write(&mut self, addr: u8, output: &[u8]) -> Result<(), Self::Error> {
+//!         // ...
+//! #       Ok(())
+//!     }
+//! }
+//!
+//! impl Write<TenBitAddress> for I2c0
+//! {
+//! #   type Error = ();
+//! #
+//!     fn try_write(&mut self, addr: u16, output: &[u8]) -> Result<(), Self::Error> {
+//!         // ...
+//! #       Ok(())
+//!     }
+//! }
+//! ```
+//!
+//! ### Device driver compatible only with 7-bit addresses
+//!
+//! For demonstration purposes the address mode parameter has been omitted in this example.
+//!
+//! ```
+//! # use embedded_hal::blocking::i2c::WriteRead;
+//! const ADDR: u8  = 0x15;
+//! # const TEMP_REGISTER: u8 = 0x1;
+//! pub struct TemperatureSensorDriver<I2C> {
+//!     i2c: I2C,
+//! }
+//!
+//! impl<I2C, E> TemperatureSensorDriver<I2C>
+//! where
+//!     I2C: WriteRead<Error = E>,
+//! {
+//!     pub fn read_temperature(&mut self) -> Result<u8, E> {
+//!         let mut temp = [0];
+//!         self.i2c
+//!             .try_write_read(ADDR, &[TEMP_REGISTER], &mut temp)
+//!             .and(Ok(temp[0]))
+//!     }
+//! }
+//! ```
+//!
+//! ### Device driver compatible only with 10-bit addresses
+//!
+//! ```
+//! # use embedded_hal::blocking::i2c::{TenBitAddress, WriteRead};
+//! const ADDR: u16  = 0x158;
+//! # const TEMP_REGISTER: u8 = 0x1;
+//! pub struct TemperatureSensorDriver<I2C> {
+//!     i2c: I2C,
+//! }
+//!
+//! impl<I2C, E> TemperatureSensorDriver<I2C>
+//! where
+//!     I2C: WriteRead<TenBitAddress, Error = E>,
+//! {
+//!     pub fn read_temperature(&mut self) -> Result<u8, E> {
+//!         let mut temp = [0];
+//!         self.i2c
+//!             .try_write_read(ADDR, &[TEMP_REGISTER], &mut temp)
+//!             .and(Ok(temp[0]))
+//!     }
+//! }
+//! ```
+
+use crate::private;
+
+/// Address mode (7-bit / 10-bit)
+///
+/// Note: This trait is sealed and should not be implemented outside of this crate.
+pub trait AddressMode: private::Sealed {}
+
+/// 7-bit address mode type
+pub type SevenBitAddress = u8;
+
+/// 10-bit address mode type
+pub type TenBitAddress = u16;
+
+impl AddressMode for SevenBitAddress {}
+
+impl AddressMode for TenBitAddress {}
 
 /// Blocking read
-pub trait Read {
+pub trait Read<A: AddressMode = SevenBitAddress> {
     /// Error type
     type Error;
 
@@ -28,11 +135,11 @@ pub trait Read {
     /// - `MAK` = master acknowledge
     /// - `NMAK` = master no acknowledge
     /// - `SP` = stop condition
-    fn try_read(&mut self, address: u8, buffer: &mut [u8]) -> Result<(), Self::Error>;
+    fn try_read(&mut self, address: A, buffer: &mut [u8]) -> Result<(), Self::Error>;
 }
 
 /// Blocking write
-pub trait Write {
+pub trait Write<A: AddressMode = SevenBitAddress> {
     /// Error type
     type Error;
 
@@ -52,11 +159,11 @@ pub trait Write {
     /// - `SAK` = slave acknowledge
     /// - `Bi` = ith byte of data
     /// - `SP` = stop condition
-    fn try_write(&mut self, address: u8, bytes: &[u8]) -> Result<(), Self::Error>;
+    fn try_write(&mut self, address: A, bytes: &[u8]) -> Result<(), Self::Error>;
 }
 
 /// Blocking write (iterator version)
-pub trait WriteIter {
+pub trait WriteIter<A: AddressMode = SevenBitAddress> {
     /// Error type
     type Error;
 
@@ -65,13 +172,13 @@ pub trait WriteIter {
     /// # I2C Events (contract)
     ///
     /// Same as `Write`
-    fn try_write_iter<B>(&mut self, address: u8, bytes: B) -> Result<(), Self::Error>
+    fn try_write_iter<B>(&mut self, address: A, bytes: B) -> Result<(), Self::Error>
     where
         B: IntoIterator<Item = u8>;
 }
 
 /// Blocking write + read
-pub trait WriteRead {
+pub trait WriteRead<A: AddressMode = SevenBitAddress> {
     /// Error type
     type Error;
 
@@ -99,14 +206,14 @@ pub trait WriteRead {
     /// - `SP` = stop condition
     fn try_write_read(
         &mut self,
-        address: u8,
+        address: A,
         bytes: &[u8],
         buffer: &mut [u8],
     ) -> Result<(), Self::Error>;
 }
 
 /// Blocking write (iterator version) + read
-pub trait WriteIterRead {
+pub trait WriteIterRead<A: AddressMode = SevenBitAddress> {
     /// Error type
     type Error;
 
@@ -118,7 +225,7 @@ pub trait WriteIterRead {
     /// Same as the `WriteRead` trait
     fn try_write_iter_read<B>(
         &mut self,
-        address: u8,
+        address: A,
         bytes: B,
         buffer: &mut [u8],
     ) -> Result<(), Self::Error>

src/lib.rs

@@ -700,3 +700,11 @@ pub mod serial;
 pub mod spi;
 pub mod timer;
 pub mod watchdog;
+
+mod private {
+    use crate::blocking::i2c::{SevenBitAddress, TenBitAddress};
+    pub trait Sealed {}
+
+    impl Sealed for SevenBitAddress {}
+    impl Sealed for TenBitAddress {}
+}