Split up the SPI trait into several with shared Error associated type.

embassy-traits/src/spi.rs

@@ -18,25 +18,39 @@ use core::future::Future;
 ///
 /// - Some SPIs can work with 8-bit *and* 16-bit words. You can overload this trait with different
 /// `Word` types to allow operation in both modes.
-pub trait FullDuplex<Word> {
+
+pub trait Spi<Word> {
     /// An enumeration of SPI errors
     type Error;
+}
+
+pub trait FullDuplex<Word> : Spi<Word> + Write<Word> + Read<Word> {
 
-    type WriteFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
-    where
-        Self: 'a;
-    type ReadFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
-    where
-        Self: 'a;
     type WriteReadFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
     where
         Self: 'a;
 
-    fn read<'a>(&'a mut self, data: &'a mut [Word]) -> Self::ReadFuture<'a>;
-    fn write<'a>(&'a mut self, data: &'a [Word]) -> Self::WriteFuture<'a>;
     fn read_write<'a>(
         &'a mut self,
         read: &'a mut [Word],
         write: &'a [Word],
     ) -> Self::WriteReadFuture<'a>;
 }
+
+pub trait Write<Word> : Spi<Word>{
+
+    type WriteFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+    Self: 'a;
+
+    fn write<'a>(&'a mut self, data: &'a [Word]) -> Self::WriteFuture<'a>;
+}
+
+pub trait Read<Word> : Spi<Word>{
+
+    type ReadFuture<'a>: Future<Output = Result<(), Self::Error>> + 'a
+    where
+    Self: 'a;
+
+    fn read<'a>(&'a mut self, data: &'a mut [Word]) -> Self::ReadFuture<'a>;
+}