Merge #373

373: Implement MultiwriteNorFlash for nRF52 boards that support it r=jonas-schievink a=ia0

This PR implements `MultiwriteNorFlash` as suggested [here](#336 (comment)).

I only listed nRF52 boards that support writing twice to the same word, because I'm not familiar with the other boards or crate features.

Co-authored-by: ia0 <[email protected]>

Author: bors[bot]

nrf-hal-common/src/nvmc.rs

@@ -183,6 +183,21 @@ where
     }
 }
 
+// Only nRF52 boards have been checked. There are 2 things to note:
+//
+// 1. The nRF52832 doesn't support 2 writes per word. Instead it supports 181 writes per block,
+// where a block is 128 words. So on average it's a bit less than 2 writes per word, and thus we
+// can't implement MultiwriteNorFlash.
+//
+// 2. The nRF52820 supports 2 writes per word but doesn't have an associated feature.
+#[cfg(any(
+    feature = "52810",
+    feature = "52811",
+    feature = "52833",
+    feature = "52840",
+))]
+impl<T: Instance> embedded_storage::nor_flash::MultiwriteNorFlash for Nvmc<T> {}
+
 pub trait Instance: Deref<Target = nvmc::RegisterBlock> + sealed::Sealed {}
 
 impl Instance for NVMC {}