X-Git-Url: http://git.linex4red.de/pub/USBasp.git/blobdiff_plain/3e1f3869c1678fa89c40e9afef06efa2d7f24326..e186907e393939f1b417f0f7ba7406b46c76bece:/Projects/USBtoSerial/USBtoSerial.c

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);
+				}
 			}
 		}