Draft: alternate ManagedCS trait

src/spi/blocking.rs

@@ -15,6 +15,7 @@ pub trait Transfer<Word = u8>: ErrorType {
     fn transfer(&mut self, read: &mut [Word], write: &[Word]) -> Result<(), Self::Error>;
 }
 
+#[cfg(conflicting)]
 impl<T: Transfer<Word>, Word: Copy> Transfer<Word> for &mut T {
     fn transfer(&mut self, read: &mut [Word], write: &[Word]) -> Result<(), Self::Error> {
         T::transfer(self, read, write)
@@ -29,6 +30,7 @@ pub trait TransferInplace<Word: Copy = u8>: ErrorType {
     fn transfer_inplace(&mut self, words: &mut [Word]) -> Result<(), Self::Error>;
 }
 
+#[cfg(conflicting)]
 impl<T: TransferInplace<Word>, Word: Copy> TransferInplace<Word> for &mut T {
     fn transfer_inplace(&mut self, words: &mut [Word]) -> Result<(), Self::Error> {
         T::transfer_inplace(self, words)
@@ -44,6 +46,7 @@ pub trait Read<Word: Copy = u8>: ErrorType {
     fn read(&mut self, words: &mut [Word]) -> Result<(), Self::Error>;
 }
 
+#[cfg(conflicting)]
 impl<T: Read<Word>, Word: Copy> Read<Word> for &mut T {
     fn read(&mut self, words: &mut [Word]) -> Result<(), Self::Error> {
         T::read(self, words)
@@ -56,6 +59,7 @@ pub trait Write<Word: Copy = u8>: ErrorType {
     fn write(&mut self, words: &[Word]) -> Result<(), Self::Error>;
 }
 
+#[cfg(conflicting)]
 impl<T: Write<Word>, Word: Copy> Write<Word> for &mut T {
     fn write(&mut self, words: &[Word]) -> Result<(), Self::Error> {
         T::write(self, words)
@@ -101,8 +105,221 @@ pub trait Transactional<Word: 'static + Copy = u8>: ErrorType {
     fn exec<'a>(&mut self, operations: &mut [Operation<'a, Word>]) -> Result<(), Self::Error>;
 }
 
+#[cfg(conflicting)]
 impl<T: Transactional<Word>, Word: 'static + Copy> Transactional<Word> for &mut T {
     fn exec<'a>(&mut self, operations: &mut [Operation<'a, Word>]) -> Result<(), Self::Error> {
         T::exec(self, operations)
     }
 }
+
+/// SPI Managed CS trait
+///
+/// This uses a bunch of magic to manage CS for all SPI methods, and conflicts with the `&mut T` impls for each trait.
+///
+/// ```
+/// use embedded_hal::spi::blocking::{ManagedCs, Write};
+///
+/// // Automatic CS assertion
+/// fn spi_write_auto_cs<SPI: ManagedCs + Write>(spi: &mut SPI) {
+///   let _ = spi.write(&[0xaa, 0xbb, 0xcc]);
+/// }
+/// // Manual CS assertion
+/// fn spi_write_manual_cs<SPI: ManagedCs<Inner=P>, P: Write>(spi: &mut SPI) {
+///   let _ = spi.with_cs(|d|{
+///     let _ = d.write(&[0xaa, 0xbb, 0xcc]);
+///     Ok(())
+///   });
+/// }
+/// ```
+pub trait ManagedCs: ErrorType {
+    /// Inner SPI type
+    type Inner: ErrorType;
+
+    /// Execute the provided closure within a CS assertion
+    fn with_cs<F: FnMut(&mut Self::Inner) -> Result<(), Self::Error>>(
+        &mut self,
+        f: F,
+    ) -> Result<(), Self::Error>;
+
+    /// Reference the inner SPI object without manipulating CS
+    fn inner(&mut self) -> &mut Self::Inner;
+}
+
+/// Alternate managed CS trait
+///
+/// This one doesn't require any defaults / provide any magic, if you want
+/// to do things within a CS assertion you call `with_cs`.
+///
+/// ```
+/// use embedded_hal::spi::blocking::{ManagedCsAlt, Write};
+///
+/// // Manual CS assertion
+/// fn spi_write_manual_cs<SPI: ManagedCsAlt + Write>(spi: &mut SPI) {
+///   let _ = spi.with_cs(|d|{
+///     let _ = d.write(&[0xaa, 0xbb, 0xcc]);
+///     Ok(())
+///   });
+/// }
+/// ```
+pub trait ManagedCsAlt: ErrorType {
+    /// Execute the provided closure within a CS assertion
+    fn with_cs<F: FnMut(&mut Self) -> Result<(), Self::Error>>(
+        &mut self,
+        f: F,
+    ) -> Result<(), Self::Error>;
+}
+
+/// These default conflict with the &mut impls, we could just not have them / require folks to always call [`ManagedCs::with_cs`]?
+mod defaults {
+    use super::*;
+
+    /// Default blocking [`Transfer`] with CS management
+    impl<T, I, E, Word> Transfer<Word> for T
+    where
+        T: ManagedCs<Inner = I> + ErrorType<Error = E>,
+        I: Transfer<Word> + ErrorType<Error = E>,
+        Word: Copy + 'static,
+    {
+        fn transfer<'a>(&mut self, read: &mut [Word], write: &[Word]) -> Result<(), Self::Error> {
+            self.with_cs(|i: &mut I| i.transfer(read, write))
+        }
+    }
+
+    /// Default blocking [`TransferInplace`] with CS management
+    impl<T, I, E, Word> TransferInplace<Word> for T
+    where
+        T: ManagedCs<Inner = I> + ErrorType<Error = E>,
+        I: TransferInplace<Word> + ErrorType<Error = E>,
+        Word: Copy + 'static,
+    {
+        fn transfer_inplace<'a>(&mut self, words: &mut [Word]) -> Result<(), Self::Error> {
+            self.with_cs(|i: &mut I| i.transfer_inplace(words))
+        }
+    }
+
+    /// Default blocking [`Read`] with CS management
+    impl<T, I, E, Word> Read<Word> for T
+    where
+        T: ManagedCs<Inner = I> + ErrorType<Error = E>,
+        I: Read<Word> + ErrorType<Error = E>,
+        Word: Copy + 'static,
+    {
+        fn read<'a>(&mut self, words: &mut [Word]) -> Result<(), Self::Error> {
+            self.with_cs(|i: &mut I| i.read(words))
+        }
+    }
+
+    /// Default blocking [`Write`] with CS management
+    impl<T, I, E, Word> Write<Word> for T
+    where
+        T: ManagedCs<Inner = I> + ErrorType<Error = E>,
+        I: Write<Word> + ErrorType<Error = E>,
+        Word: Copy + 'static,
+    {
+        fn write<'a>(&mut self, words: &[Word]) -> Result<(), Self::Error> {
+            self.with_cs(|i: &mut I| i.write(words))
+        }
+    }
+
+    /// Default blocking [`Transactional`] with CS management
+    impl<T, I, E, Word> Transactional<Word> for T
+    where
+        T: ManagedCs<Inner = I> + ErrorType<Error = E>,
+        I: Transactional<Word> + ErrorType<Error = E>,
+        Word: Copy + 'static,
+    {
+        fn exec<'a>(&mut self, operations: &mut [Operation<'a, Word>]) -> Result<(), Self::Error> {
+            self.with_cs(|i: &mut I| i.exec(operations))
+        }
+    }
+}
+
+/// [`SpiWithCs`] wraps an SPI implementation with Chip Select (CS)
+/// pin management for exclusive (non-shared) use.
+/// For sharing SPI between peripherals, see [shared-bus](https://crates.io/crates/shared-bus)
+pub struct SpiWithCs<Spi, Pin> {
+    spi: Spi,
+    cs: Pin,
+}
+
+/// Wrapper for errors returned by [`SpiWithCs`]
+#[derive(Clone, Debug, PartialEq)]
+pub enum SpiWithCsError<SpiError, PinError> {
+    /// Underlying SPI communication error
+    Spi(SpiError),
+    /// Underlying chip-select pin state setting error
+    Pin(PinError),
+}
+
+/// [`ErrorType`] implementation for [`SpiWithCs`] wrapper
+impl<Spi, Pin> ErrorType for SpiWithCs<Spi, Pin>
+where
+    Spi: ErrorType,
+    Pin: crate::digital::blocking::OutputPin + crate::digital::ErrorType,
+{
+    type Error =
+        SpiWithCsError<<Spi as ErrorType>::Error, <Pin as crate::digital::ErrorType>::Error>;
+}
+
+/// [`ManagedCs`] implementation for [`SpiWithCs`] wrapper.
+/// Provides `with_cs` function that asserts and deasserts CS
+impl<Spi, Pin> ManagedCs for SpiWithCs<Spi, Pin>
+where
+    Spi: ErrorType,
+    Pin: crate::digital::blocking::OutputPin + crate::digital::ErrorType,
+{
+    type Inner = Spi;
+
+    /// Executes the provided closure within a CS assertion
+    fn with_cs<F: FnMut(&mut Self::Inner) -> Result<(), Self::Error>>(
+        &mut self,
+        mut f: F,
+    ) -> Result<(), Self::Error> {
+        self.cs.set_low().map_err(SpiWithCsError::Pin)?;
+
+        let r = f(&mut self.spi);
+
+        self.cs.set_high().map_err(SpiWithCsError::Pin)?;
+
+        r
+    }
+
+    /// Reference the inner SPI object without manipulating CS
+    fn inner(&mut self) -> &mut Self::Inner {
+        &mut self.spi
+    }
+}
+
+/// [`ManagedCs`] implementation for [`SpiWithCs`] wrapper.
+/// Provides `with_cs` function that asserts and deasserts CS
+impl<Spi, Pin> ManagedCsAlt for SpiWithCs<Spi, Pin>
+where
+    Spi: ErrorType,
+    Pin: crate::digital::blocking::OutputPin + crate::digital::ErrorType,
+{
+    /// Executes the provided closure within a CS assertion
+    fn with_cs<F: FnMut(&mut Self) -> Result<(), Self::Error>>(
+        &mut self,
+        mut f: F,
+    ) -> Result<(), Self::Error> {
+        self.cs.set_low().map_err(SpiWithCsError::Pin)?;
+
+        let r = f(self);
+
+        self.cs.set_high().map_err(SpiWithCsError::Pin)?;
+
+        r
+    }
+}
+
+/// [`super::Error`] implementation for [`SpiWithCsError`]
+impl<SpiError: super::Error + core::fmt::Debug, PinError: core::fmt::Debug> super::Error
+    for SpiWithCsError<SpiError, PinError>
+{
+    fn kind(&self) -> super::ErrorKind {
+        match self {
+            SpiWithCsError::Spi(spi) => spi.kind(),
+            SpiWithCsError::Pin(_pin) => super::ErrorKind::Other,
+        }
+    }
+}