Merge pull request #213 from embassy-rs/nrf-flash-multiwrite

fix: support multiwrite for nrf flash

nrf-softdevice/src/flash.rs

@@ -4,7 +4,9 @@ use core::sync::atomic::{AtomicBool, Ordering};
 use embassy_sync::blocking_mutex::raw::CriticalSectionRawMutex;
 use embassy_sync::signal::Signal;
 use embedded_storage::nor_flash::{ErrorType, NorFlashError, NorFlashErrorKind, ReadNorFlash};
-use embedded_storage_async::nor_flash::{NorFlash as AsyncNorFlash, ReadNorFlash as AsyncReadNorFlash};
+use embedded_storage_async::nor_flash::{
+    MultiwriteNorFlash, NorFlash as AsyncNorFlash, ReadNorFlash as AsyncReadNorFlash,
+};
 
 use crate::util::DropBomb;
 use crate::{raw, RawError, Softdevice};
@@ -166,3 +168,11 @@ impl AsyncNorFlash for Flash {
         Ok(())
     }
 }
+
+/// According to Nordic, it is possible to perform multiple writes but only changing a bit from 1 -> 0, which
+/// is what MultiwriteNorFlash is for.
+///
+/// "The NVMC is only able to write 0 to bits in flash memory that are erased (set to 1). It cannot rewrite a bit back to 1.
+/// Only full 32-bit words can be written to flash memory using the NVMC interface. To write less than 32 bits, write the data
+/// as a full 32-bit word and set all the bits that should remain unchanged in the word to 1."
+impl MultiwriteNorFlash for Flash {}