From 8e79b096c1044abd40e59cc85f2388f92330baa0 Mon Sep 17 00:00:00 2001
From: chemicstry <chemicstry@gmail.com>
Date: Tue, 7 Feb 2023 17:41:29 +0200
Subject: [PATCH] Use byte slices for sdmmc

---
 embassy-stm32/src/sdmmc/mod.rs | 33 ++++++++++++++++++++++-----------
 1 file changed, 22 insertions(+), 11 deletions(-)

diff --git a/embassy-stm32/src/sdmmc/mod.rs b/embassy-stm32/src/sdmmc/mod.rs
index a52c65b9..e02c97c3 100644
--- a/embassy-stm32/src/sdmmc/mod.rs
+++ b/embassy-stm32/src/sdmmc/mod.rs
@@ -39,9 +39,6 @@ impl Default for Signalling {
     }
 }
 
-#[repr(align(4))]
-pub struct DataBlock([u8; 512]);
-
 /// Errors
 #[non_exhaustive]
 #[derive(Debug, Copy, Clone)]
@@ -58,6 +55,10 @@ pub enum Error {
     BadClock,
     SignalingSwitchFailed,
     PeripheralBusy,
+    /// Buffers must be aligned to 4 bytes
+    UnalignedBuffer,
+    /// Buffer capacity did not match block size
+    UnsupportedBufferSize,
 }
 
 /// A SD command
@@ -471,17 +472,22 @@ impl<'d, T: Instance, Dma: SdmmcDma<T>> Sdmmc<'d, T, Dma> {
     }
 
     #[inline(always)]
-    pub async fn read_block(&mut self, block_idx: u32, buffer: &mut DataBlock) -> Result<(), Error> {
+    pub async fn read_block(&mut self, block_idx: u32, buffer: &mut [u8]) -> Result<(), Error> {
         let card_capacity = self.card()?.card_type;
         let inner = T::inner();
         let state = T::state();
 
-        // NOTE(unsafe) DataBlock uses align 4
-        let buf = unsafe { &mut *((&mut buffer.0) as *mut [u8; 512] as *mut [u32; 128]) };
+        let (prefix, aligned, suffix) = unsafe { buffer.align_to_mut::<u32>() };
+        if !prefix.is_empty() || !suffix.is_empty() {
+            return Err(Error::UnalignedBuffer);
+        }
+
+        let block: &mut [u32; 128] = aligned.try_into().map_err(|_| Error::UnsupportedBufferSize)?;
+
         inner
             .read_block(
                 block_idx,
-                buf,
+                block,
                 card_capacity,
                 state,
                 self.config.data_transfer_timeout,
@@ -490,17 +496,22 @@ impl<'d, T: Instance, Dma: SdmmcDma<T>> Sdmmc<'d, T, Dma> {
             .await
     }
 
-    pub async fn write_block(&mut self, block_idx: u32, buffer: &DataBlock) -> Result<(), Error> {
+    pub async fn write_block(&mut self, block_idx: u32, buffer: &[u8]) -> Result<(), Error> {
         let card = self.card.as_mut().ok_or(Error::NoCard)?;
         let inner = T::inner();
         let state = T::state();
 
-        // NOTE(unsafe) DataBlock uses align 4
-        let buf = unsafe { &*((&buffer.0) as *const [u8; 512] as *const [u32; 128]) };
+        let (prefix, aligned, suffix) = unsafe { buffer.align_to::<u32>() };
+        if !prefix.is_empty() || !suffix.is_empty() {
+            return Err(Error::UnalignedBuffer);
+        }
+
+        let block: &[u32; 128] = aligned.try_into().map_err(|_| Error::UnsupportedBufferSize)?;
+
         inner
             .write_block(
                 block_idx,
-                buf,
+                block,
                 card,
                 state,
                 self.config.data_transfer_timeout,