- /* Read bytes from the USB OUT endpoint into the UART transmit buffer */
- if (CDC_Device_BytesReceived(&VirtualSerial_CDC_Interface))
- RingBuffer_Insert(&USBtoUART_Buffer, CDC_Device_ReceiveByte(&VirtualSerial_CDC_Interface));
-
- /* Read bytes from the UART receive buffer into the USB IN endpoint */
- if (UARTtoUSB_Buffer.Count)
- CDC_Device_SendByte(&VirtualSerial_CDC_Interface, RingBuffer_Remove(&UARTtoUSB_Buffer));
+ /* Only try to read in bytes from the CDC interface if the transmit buffer is not full */
+ if (!(RingBuffer_IsFull(&USBtoUART_Buffer)))
+ {
+ int16_t ReceivedByte = CDC_Device_ReceiveByte(&VirtualSerial_CDC_Interface);
+
+ /* Read bytes from the USB OUT endpoint into the UART transmit buffer */
+ if (!(ReceivedByte < 0))
+ RingBuffer_Insert(&USBtoUART_Buffer, ReceivedByte);
+ }
+
+ /* Check if the UART receive buffer flush timer has expired or buffer is nearly full */
+ uint16_t BufferCount = RingBuffer_GetCount(&UARTtoUSB_Buffer);
+ if ((TIFR0 & (1 << TOV0)) || (BufferCount > 200))
+ {
+ /* Clear flush timer expiry flag */
+ TIFR0 |= (1 << TOV0);
+
+ /* Read bytes from the USART receive buffer into the USB IN endpoint */
+ while (BufferCount--)
+ {
+ /* 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(&UARTtoUSB_Buffer)) != ENDPOINT_READYWAIT_NoError)
+ {
+ break;
+ }
+
+ /* Dequeue the already sent byte from the buffer now we have confirmed that no transmission error occurred */
+ RingBuffer_Remove(&UARTtoUSB_Buffer);
+ }
+ }