Fixed lengthy timeouts in the USBtoSerial project if no application on the host is consuming data (thanks to Nicolas Saugnier).

Fixed lengthy automatic data flushing in the CDC and MIDI device class drivers.

1 files changed, 23 insertions, 12 deletions

diff --git a/Projects/USBtoSerial/USBtoSerial.c b/Projects/USBtoSerial/USBtoSerial.c
index 7fe67da44..a0b8de4c4 100644
--- a/Projects/USBtoSerial/USBtoSerial.c
+++ b/Projects/USBtoSerial/USBtoSerial.c
@@ -108,21 +108,32 @@ int main(void)
 		uint16_t BufferCount = RingBuffer_GetCount(&USARTtoUSB_Buffer);
 		if ((TIFR0 & (1 << TOV0)) || (BufferCount > (uint8_t)(sizeof(USARTtoUSB_Buffer_Data) * .75)))
 		{
-			/* Clear flush timer expiry flag */
-			TIFR0 |= (1 << TOV0);
-
-			/* Read bytes from the USART receive buffer into the USB IN endpoint */
-			while (BufferCount--)
+			Endpoint_SelectEndpoint(VirtualSerial_CDC_Interface.Config.DataINEndpoint.Address);
+			
+			/* Check if a packet is already enqueued to the host - if so, we shouldn't try to send more data
+			 * until it completes as there is a chance nothing is listening and a lengthy timeout could occur */
+			if (Endpoint_IsINReady())
 			{
-				/* Try to send the next byte of data to the host, abort if there is an error without dequeuing */
-				if (CDC_Device_SendByte(&VirtualSerial_CDC_Interface,
-				                        RingBuffer_Peek(&USARTtoUSB_Buffer)) != ENDPOINT_READYWAIT_NoError)
+				/* Clear flush timer expiry flag */
+				TIFR0 |= (1 << TOV0);
+			
+				/* Never send more than one bank size less one byte to the host at a time, so that we don't block
+				 * while a Zero Length Packet (ZLP) to terminate the transfer is sent if the host isn't listening */
+				uint8_t BytesToSend = MIN(BufferCount, (CDC_TXRX_EPSIZE - 1));
+
+				/* Read bytes from the USART receive buffer into the USB IN endpoint */
+				while (BytesToSend--)
 				{
-					break;
-				}
+					/* Try to send the next byte of data to the host, abort if there is an error without dequeuing */
+					if (CDC_Device_SendByte(&VirtualSerial_CDC_Interface,
+											RingBuffer_Peek(&USARTtoUSB_Buffer)) != ENDPOINT_READYWAIT_NoError)
+					{
+						break;
+					}
 
-				/* Dequeue the already sent byte from the buffer now we have confirmed that no transmission error occurred */
-				RingBuffer_Remove(&USARTtoUSB_Buffer);
+					/* Dequeue the already sent byte from the buffer now we have confirmed that no transmission error occurred */
+					RingBuffer_Remove(&USARTtoUSB_Buffer);
+				}
 			}
 		}