Fixed lengthy timeouts in the USBtoSerial project if no application on the host is...

[pub/USBasp.git] / Projects / USBtoSerial / USBtoSerial.c

diff --git a/Projects/USBtoSerial/USBtoSerial.c b/Projects/USBtoSerial/USBtoSerial.c
index 7fe67da..a0b8de4 100644 (file)
--- 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);
+                               }
                        }
                }