Altered the CDC Deivice and Host Class drivers' receive byte routines, so that no data is indicated by a negative return value.

Added auto flushing of OUT data to the CDC Host Class driver's USBTask function to automatically flush the send pipe buffer.

2 files changed, 27 insertions, 19 deletions

diff --git a/LUFA/Drivers/USB/Class/Device/CDC.c b/LUFA/Drivers/USB/Class/Device/CDC.c
index 453d21d84..026ac269a 100644
--- a/LUFA/Drivers/USB/Class/Device/CDC.c
+++ b/LUFA/Drivers/USB/Class/Device/CDC.c
@@ -128,11 +128,6 @@ void CDC_Device_USBTask(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo)
 {
 	if ((USB_DeviceState != DEVICE_STATE_Configured) || !(CDCInterfaceInfo->State.LineEncoding.BaudRateBPS))
 	  return;
-
-	Endpoint_SelectEndpoint(CDCInterfaceInfo->Config.DataOUTEndpointNumber);
-
-	if (Endpoint_IsOUTReceived() && !(Endpoint_BytesInEndpoint()))
-	  Endpoint_ClearOUT();
 	  
 	CDC_Device_Flush(CDCInterfaceInfo);
 }
@@ -222,19 +217,24 @@ uint16_t CDC_Device_BytesReceived(USB_ClassInfo_CDC_Device_t* const CDCInterface
 	}
 }
 
-uint8_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo)
+int16_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo)
 {
+	uint8_t ReceivedByte = -1;
+
 	if ((USB_DeviceState != DEVICE_STATE_Configured) || !(CDCInterfaceInfo->State.LineEncoding.BaudRateBPS))
 	  return 0;
 
 	Endpoint_SelectEndpoint(CDCInterfaceInfo->Config.DataOUTEndpointNumber);
 	
-	uint8_t DataByte = Endpoint_Read_Byte();
+	if (!(Endpoint_IsOUTReceived()))
+	  return -1;
+	else if (Endpoint_BytesInEndpoint())
+	  ReceivedByte = Endpoint_Read_Byte();
 	
 	if (!(Endpoint_BytesInEndpoint()))
 	  Endpoint_ClearOUT();
-	  
-	return DataByte;
+	
+	return ReceivedByte;
 }
 
 void CDC_Device_SendControlLineStateChange(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo)
@@ -282,24 +282,28 @@ static int CDC_Device_putchar(char c,
 
 static int CDC_Device_getchar(FILE* Stream)
 {
-	if (!(CDC_Device_BytesReceived((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream))))
+	int16_t ReceivedByte = CDC_Device_ReceiveByte((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream));
+
+	if (ReceivedByte < 0)
 	  return _FDEV_EOF;
 
-	return CDC_Device_ReceiveByte((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream));
+	return ReceivedByte;
 }
 
 static int CDC_Device_getchar_Blocking(FILE* Stream)
 {
-	while (!(CDC_Device_BytesReceived((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream))))
+	int16_t ReceivedByte;
+	
+	while ((ReceivedByte = CDC_Device_ReceiveByte((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream))) < 0)
 	{
 		if (USB_DeviceState == DEVICE_STATE_Unattached)
 		  return _FDEV_EOF;
 	
 		CDC_Device_USBTask((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream));
-		USB_USBTask();
+		USB_USBTask();	
 	}
 
-	return CDC_Device_ReceiveByte((USB_ClassInfo_CDC_Device_t*)fdev_get_udata(Stream));
+	return ReceivedByte;
 }
 
 #endif
diff --git a/LUFA/Drivers/USB/Class/Device/CDC.h b/LUFA/Drivers/USB/Class/Device/CDC.h
index 9e92d5f6c..3ada8f7af 100644
--- a/LUFA/Drivers/USB/Class/Device/CDC.h
+++ b/LUFA/Drivers/USB/Class/Device/CDC.h
@@ -233,7 +233,10 @@
 			uint8_t CDC_Device_SendByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo,
 			                            const uint8_t Data) ATTR_NON_NULL_PTR_ARG(1);
 			
-			/** Determines the number of bytes received by the CDC interface from the host, waiting to be read.
+			/** Determines the number of bytes received by the CDC interface from the host, waiting to be read. This indicates the number
+			 *  of bytes in the OUT endpoint bank only, and thus the number of calls to \ref CDC_Device_ReceiveByte() which are guaranteed to
+			 *  succeed immediately. If multiple bytes are to be received, they should be buffered by the user application, as the endpoint
+			 *  bank will not be released back to the USB controller until all bytes are read.
 			 *
 			 *  \pre This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or
 			 *       the call will fail.
@@ -245,17 +248,18 @@
 			uint16_t CDC_Device_BytesReceived(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1);
 			
 			/** Reads a byte of data from the host. If no data is waiting to be read of if a USB host is not connected, the function
-			 *  returns 0. The \ref CDC_Device_BytesReceived() function should be queried before data is received to ensure that no data
-			 *  underflow occurs.
+			 *  returns a negative value. The \ref CDC_Device_BytesReceived() function may be queried in advance to determine how many
+			 *  bytes are currently buffered in the CDC interface's data receive endpoint bank, and thus how many repeated calls to this
+			 *  function which are guaranteed to succeed.
 			 *
 			 *  \pre This function must only be called when the Device state machine is in the DEVICE_STATE_Configured state or
 			 *       the call will fail.
 			 *
 			 *  \param[in,out] CDCInterfaceInfo  Pointer to a structure containing a CDC Class configuration and state.
 			 *
-			 *  \return Next received byte from the host, or 0 if no data received.
+			 *  \return Next received byte from the host, or a negative value if no data received.
 			 */
-			uint8_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1);
+			int16_t CDC_Device_ReceiveByte(USB_ClassInfo_CDC_Device_t* const CDCInterfaceInfo) ATTR_NON_NULL_PTR_ARG(1);
 			
 			/** Flushes any data waiting to be sent, ensuring that the send buffer is cleared.
 			 *