uart: enable auto-retriggering for ping-pong DMA

- remove redundant error checking in `read_buffered()`

Author: jerrysxie

src/dma/channel.rs

@@ -202,8 +202,8 @@ impl<'d> Channel<'d> {
         // SAFETY: unsafe due to .bits usage
         self.info.regs.channel(channel).xfercfg().write(|w| unsafe {
             w.cfgvalid().set_bit();
-            // Descriptor is exhausted and we need to manually hit SWTRIG to trigger the next one.
-            w.clrtrig().set_bit();
+            // Auto-retrigger on completion for ping-pong operation
+            w.clrtrig().clear_bit();
             // Set reload to enable continuous ping-pong operation
             w.reload().set_bit();
             w.setinta().set_bit();

src/dma/mod.rs

@@ -170,10 +170,6 @@ fn dma0_irq_handler<const N: usize>(wakers: &[AtomicWaker; N]) {
                         if ping_pong_status.buffer_b_status == BufferStatus::Granted {
                             ping_pong_status.overrun_error = true;
                             error!("DMA Ping-Pong buffer overrun on channel {}!", channel);
-                        } else {
-                            reg.channel(channel as usize)
-                                .xfercfg()
-                                .modify(|_, w| w.swtrig().set_bit());
                         }
                     } else {
                         // Just finished Buffer B, switching to Buffer A
@@ -183,10 +179,6 @@ fn dma0_irq_handler<const N: usize>(wakers: &[AtomicWaker; N]) {
                         if ping_pong_status.buffer_a_status == BufferStatus::Granted {
                             ping_pong_status.overrun_error = true;
                             error!("DMA Ping-Pong buffer overrun on channel {}!", channel);
-                        } else {
-                            reg.channel(channel as usize)
-                                .xfercfg()
-                                .modify(|_, w| w.swtrig().set_bit());
                         }
                     }
                 }

src/uart.rs

@@ -814,10 +814,6 @@ impl<'a> UartRx<'a, Async> {
     async fn read_buffered(&mut self, buf: &mut [u8]) -> Result<usize> {
         let rx_dma = self._rx_dma.as_ref().ok_or(Error::Fail)?;
         let buffer_config = self._buffer_config.as_mut().ok_or(Error::Fail)?;
-        // Check for ping-pong buffer overrun error from DMA
-        if rx_dma.check_and_clear_overrun_error() {
-            return Err(Error::Overrun);
-        }
 
         let half_size = buffer_config.buffer_a.len();