Alter the ring buffer library headers to have both atomic and non-atomic insertion/removal routines. Modify the existing projects so that buffer operations performed in an ISR use the shorted non-atomic versions, as they are already performed in a blocking ISR.

Alter USBtoSerial demo so that it does not enter a blocking loop to send data from the USB to the USART, as this can cause dropped bytes in the reception code if large amounts of data are sent in both directions at the same time. Added a flush timer to the USBtoSerial code for the USART to USB interface, so that multiple bytes can be sent in the same USB packet.

2 files changed, 53 insertions, 11 deletions

diff --git a/Projects/USBtoSerial/Lib/LightweightRingBuff.h b/Projects/USBtoSerial/Lib/LightweightRingBuff.h
index 1dc05935c..9c25707b4 100644
--- a/Projects/USBtoSerial/Lib/LightweightRingBuff.h
+++ b/Projects/USBtoSerial/Lib/LightweightRingBuff.h
@@ -75,12 +75,12 @@
 			Buffer->Count = 0;
 		}
 		
-		/** Inserts an element into the ring buffer.
+		/** Atomically inserts an element into the ring buffer.
 		 *
 		 *  \param[in,out] Buffer  Pointer to a ring buffer structure to insert into
 		 *  \param[in]     Data    Data element to insert into the buffer
 		 */
-		static inline void RingBuffer_Insert(RingBuff_t* const Buffer, RingBuff_Data_t Data)
+		static inline void RingBuffer_AtomicInsert(RingBuff_t* const Buffer, RingBuff_Data_t Data)
 		{
 			ATOMIC_BLOCK(ATOMIC_RESTORESTATE)
 			{
@@ -93,13 +93,13 @@
 			}
 		}
 
-		/** Retrieves an element from the ring buffer.
+		/** Atomically retrieves an element from the ring buffer.
 		 *
 		 *  \param[in,out] Buffer  Pointer to a ring buffer structure to retrieve from
 		 *
 		 *  \return Next data element stored in the buffer
 		 */
-		static inline RingBuff_Data_t RingBuffer_Remove(RingBuff_t* const Buffer)
+		static inline RingBuff_Data_t RingBuffer_AtomicRemove(RingBuff_t* const Buffer)
 		{
 			RingBuff_Data_t Data;
 			
@@ -116,5 +116,38 @@
 			return Data;
 		}
 
+		/** Inserts an element into the ring buffer.
+		 *
+		 *  \param[in,out] Buffer  Pointer to a ring buffer structure to insert into
+		 *  \param[in]     Data    Data element to insert into the buffer
+		 */
+		static inline void RingBuffer_Insert(RingBuff_t* const Buffer, RingBuff_Data_t Data)
+		{
+			*Buffer->In = Data;
+			
+			if (++Buffer->In == &Buffer->Buffer[BUFFER_SIZE])
+			  Buffer->In = Buffer->Buffer;
+				  
+			Buffer->Count++;
+		}
+
+		/** Retrieves an element from the ring buffer.
+		 *
+		 *  \param[in,out] Buffer  Pointer to a ring buffer structure to retrieve from
+		 *
+		 *  \return Next data element stored in the buffer
+		 */
+		static inline RingBuff_Data_t RingBuffer_Remove(RingBuff_t* const Buffer)
+		{
+			RingBuff_Data_t Data = *Buffer->Out;
+			
+			if (++Buffer->Out == &Buffer->Buffer[BUFFER_SIZE])
+			  Buffer->Out = Buffer->Buffer;
+				  
+			Buffer->Count--;
+
+			return Data;
+		}
+
 #endif
  
\ No newline at end of file
diff --git a/Projects/USBtoSerial/USBtoSerial.c b/Projects/USBtoSerial/USBtoSerial.c
index 7a0f6866a..918986883 100644
--- a/Projects/USBtoSerial/USBtoSerial.c
+++ b/Projects/USBtoSerial/USBtoSerial.c
@@ -87,16 +87,22 @@ int main(void)
 			if (!(BUFFER_SIZE - USBtoUSART_Buffer.Count))
 			  break;
 			  
-			RingBuffer_Insert(&USBtoUSART_Buffer, CDC_Device_ReceiveByte(&VirtualSerial_CDC_Interface));
+			RingBuffer_AtomicInsert(&USBtoUSART_Buffer, CDC_Device_ReceiveByte(&VirtualSerial_CDC_Interface));
 		}
 		
-		/* Read bytes from the USART receive buffer into the USB IN endpoint */
-		while (USARTtoUSB_Buffer.Count)
-		  CDC_Device_SendByte(&VirtualSerial_CDC_Interface, RingBuffer_Remove(&USARTtoUSB_Buffer));
+		/* Check if the software USART flush timer has expired */
+		if (TIFR0 & (1 << TOV0))
+		{
+			TIFR0 |= (1 << TOV0);
+
+			/* Read bytes from the USART receive buffer into the USB IN endpoint */
+			while (USARTtoUSB_Buffer.Count)
+			  CDC_Device_SendByte(&VirtualSerial_CDC_Interface, RingBuffer_AtomicRemove(&USARTtoUSB_Buffer));
+		}
 		
-		/* Load bytes from the USART transmit buffer into the USART */
-		while (USBtoUSART_Buffer.Count)
-		  Serial_TxByte(RingBuffer_Remove(&USBtoUSART_Buffer));
+		/* Load the next byte from the USART transmit buffer into the USART */
+		if (USBtoUSART_Buffer.Count)
+		  Serial_TxByte(RingBuffer_AtomicRemove(&USBtoUSART_Buffer));
 		
 		CDC_Device_USBTask(&VirtualSerial_CDC_Interface);
 		USB_USBTask();
@@ -117,6 +123,9 @@ void SetupHardware(void)
 	Serial_Init(9600, false);
 	LEDs_Init();
 	USB_Init();
+
+	/* Configure the UART flush timer - run at Fcpu/1024 for maximum interval before overflow */
+	TCCR0B = ((1 << CS02) | (1 << CS00));
 }
 
 /** Event handler for the library USB Connection event. */