Merge pull request #3545 from elagil/feat_wait_for_sai_ringbuf_write_error

Add a function that waits for any SAI/ringbuffer write error

embassy-stm32/src/dma/dma_bdma.rs

@@ -1006,6 +1006,13 @@ impl<'a, W: Word> WritableRingBuffer<'a, W> {
             .await
     }
 
+    /// Wait for any ring buffer write error.
+    pub async fn wait_write_error(&mut self) -> Result<usize, Error> {
+        self.ringbuf
+            .wait_write_error(&mut DmaCtrlImpl(self.channel.reborrow()))
+            .await
+    }
+
     /// The current length of the ringbuffer
     pub fn len(&mut self) -> Result<usize, Error> {
         Ok(self.ringbuf.len(&mut DmaCtrlImpl(self.channel.reborrow()))?)

embassy-stm32/src/dma/ringbuffer/mod.rs

@@ -260,6 +260,19 @@ impl<'a, W: Word> WritableDmaRingBuffer<'a, W> {
         Ok((written, self.cap() - written))
     }
 
+    /// Wait for any ring buffer write error.
+    pub async fn wait_write_error(&mut self, dma: &mut impl DmaCtrl) -> Result<usize, Error> {
+        poll_fn(|cx| {
+            dma.set_waker(cx.waker());
+
+            match self.len(dma) {
+                Ok(_) => Poll::Pending,
+                Err(e) => Poll::Ready(Err(e)),
+            }
+        })
+        .await
+    }
+
     /// Write an exact number of elements to the ringbuffer.
     pub async fn write_exact(&mut self, dma: &mut impl DmaCtrl, buffer: &[W]) -> Result<usize, Error> {
         let mut written_data = 0;

embassy-stm32/src/sai/mod.rs

@@ -1003,6 +1003,22 @@ impl<'d, T: Instance, W: word::Word> Sai<'d, T, W> {
         }
     }
 
+    /// Wait until any SAI write error occurs.
+    ///
+    /// One useful application for this is stopping playback as soon as the SAI
+    /// experiences an overrun of the ring buffer. Then, instead of letting
+    /// the SAI peripheral play the last written buffer over and over again, SAI
+    /// can be muted or dropped instead.
+    pub async fn wait_write_error(&mut self) -> Result<(), Error> {
+        match &mut self.ring_buffer {
+            RingBuffer::Writable(buffer) => {
+                buffer.wait_write_error().await?;
+                Ok(())
+            }
+            _ => return Err(Error::NotATransmitter),
+        }
+    }
+
     /// Write data to the SAI ringbuffer.
     ///
     /// The first write starts the DMA after filling the ring buffer with the provided data.