Tweak IO serial packet error handling slightly; on reception of a serial error send a line break back to FMU. This should cause FMU to stop sending immediately.

Flag these cases and discard the packet rather than processing it, rather than simply dropping the received packet and letting FMU time out.

1 files changed, 34 insertions, 10 deletions

diff --git a/src/modules/px4iofirmware/serial.c b/src/modules/px4iofirmware/serial.c
index 2f3184623..94d7407df 100644
--- a/src/modules/px4iofirmware/serial.c
+++ b/src/modules/px4iofirmware/serial.c
@@ -221,6 +221,10 @@ rx_handle_packet(void)
 static void
 rx_dma_callback(DMA_HANDLE handle, uint8_t status, void *arg)
 {
+	/*
+	 * We are here because DMA completed, or UART reception stopped and
+	 * we think we have a packet in the buffer.
+	 */
 	perf_begin(pc_txns);
 
 	/* disable UART DMA */
@@ -235,7 +239,7 @@ rx_dma_callback(DMA_HANDLE handle, uint8_t status, void *arg)
 	/* re-set DMA for reception first, so we are ready to receive before we start sending */
 	dma_reset();
 
-	/* send the reply to the previous request */
+	/* send the reply to the just-processed request */
 	dma_packet.crc = 0;
 	dma_packet.crc = crc_packet(&dma_packet);
 	stm32_dmasetup(
@@ -256,6 +260,8 @@ rx_dma_callback(DMA_HANDLE handle, uint8_t status, void *arg)
 static int
 serial_interrupt(int irq, void *context)
 {
+	static bool abort_on_idle = false;
+
 	uint32_t sr = rSR;	/* get UART status register */
 	(void)rDR;		/* required to clear any of the interrupt status that brought us here */
 
@@ -271,28 +277,46 @@ serial_interrupt(int irq, void *context)
 		if (sr & USART_SR_FE)
 			perf_count(pc_fe);
 
-		/* reset DMA state machine back to listening-for-packet */		
-		dma_reset();
+		/* send a line break - this will abort transmission/reception on the other end */
+		rCR1 |= USART_CR1_SBK;
 
-		/* don't attempt to handle IDLE if it's set - things went bad */
-		return 0;
+		/* when the line goes idle, abort rather than look at the packet */
+		abort_on_idle = true;
 	}
 
 	if (sr & USART_SR_IDLE) {
 
-		/* the packet might have been short - go check */
+		/* 
+		 * If we saw an error, don't bother looking at the packet - it should have
+		 * been aborted by the sender and will definitely be bad. Get the DMA reconfigured
+		 * ready for their retry.
+		 */
+		if (abort_on_idle) {
+
+			abort_on_idle = false;
+			dma_reset();
+			return 0;
+		}
+
+		/*
+		 * The sender has stopped sending - this is probably the end of a packet.
+		 * Check the received length against the length in the header to see if 
+		 * we have something that looks like a packet.
+		 */
 		unsigned length = sizeof(dma_packet) - stm32_dmaresidual(rx_dma);
 		if ((length < 1) || (length < PKT_SIZE(dma_packet))) {
+
+			/* it was too short - possibly truncated */
 			perf_count(pc_badidle);
 			return 0;
 		}
 
+		/*
+		 * Looks like we received a packet. Stop the DMA and go process the
+		 * packet.
+		 */
 		perf_count(pc_idle);
-
-		/* stop the receive DMA */
 		stm32_dmastop(rx_dma);
-
-		/* and treat this like DMA completion */
 		rx_dma_callback(rx_dma, DMA_STATUS_TCIF, NULL);
 	}