Fix Uart::flush_async

esp-hal/CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 ### Fixed
 
 - Full-duplex SPI works when mixed with half-duplex SPI (#3176)
+- `Uart::flush_async` should no longer return prematurely (#3186)
 
 ### Removed
 

esp-hal/src/uart.rs

@@ -1935,7 +1935,7 @@ impl UartTx<'_, Async> {
     ///
     /// This function is cancellation safe.
     pub async fn flush_async(&mut self) -> Result<(), TxError> {
-        if self.tx_fifo_count() > 0 {
+        while self.tx_fifo_count() > 0 {
             UartTxFuture::new(self.uart.reborrow(), TxEvent::Done).await;
         }
 

hil-test/tests/uart_tx_rx_async.rs

@@ -75,6 +75,25 @@ mod tests {
         }
     }
 
+    #[test]
+    async fn flush_async_does_not_return_prematurely(mut ctx: Context) {
+        // Force TX_DONE to be set
+        ctx.tx.write_async(&[0u8; 10]).await.unwrap();
+
+        let mut read = [0u8; 10];
+        ctx.rx.read_exact_async(&mut read).await.unwrap();
+
+        // The flush should not return until the data is actually sent, regardless of
+        // previous TX_DONE status.
+        ctx.tx.write_async(&[1u8; 10]).await.unwrap();
+        ctx.tx.flush_async().await.unwrap();
+
+        let read_count = ctx.rx.read_buffered(&mut read).unwrap();
+
+        assert_eq!(read_count, 10);
+        assert_eq!(&read, &[1u8; 10]);
+    }
+
     #[test]
     async fn rx_overflow_is_detected(mut ctx: Context) {
         let mut to_send: &[u8] = &[0; 250];