Add a NOR trait to encode that word clearing is supported

This is to encode MCU flashes that have ECC, where
it is common that only a complete clear of the
word is allowed. This is a more restrictive
version of `MultiwriteNorFlash` as it cannot
encode flashes with ECC support.

CHANGELOG.md

@@ -7,6 +7,7 @@ and this project adheres to [Semantic Versioning](http://semver.org/spec/v2.0.0.
 
 ## Unreleased
 
+- Add `WordclearNorFlash` to encode relaxed `write` requirements similar to `MultiwriteNorFlash` but that allows for flashes with ECC.
 - Add `start()` and `end()` method to the `Region` trait.
 - Much faster `OverlapIterator`.
 

src/nor_flash.rs

@@ -178,6 +178,15 @@ impl<T: NorFlash> NorFlash for &mut T {
 	}
 }
 
+/// Marker trait for NorFlash relaxing the restrictions on `write`.
+///
+/// Writes to the same word twice are now allowed as long as the second write is all 0s.
+/// This is common for flashes that have ECC, where after the first write only a complete clear of
+/// the word is allowed after initial write.
+pub trait WordclearNorFlash: NorFlash {}
+
+impl<T> WordclearNorFlash for T where T: MultiwriteNorFlash {}
+
 /// Marker trait for NorFlash relaxing the restrictions on `write`.
 ///
 /// Writes to the same word twice are now allowed. The result is the logical AND of the