Implement transmit buffering with interrupts for USART devices

Author: collin80

hardware/arduino/sam/cores/arduino/USARTClass.cpp

@@ -23,15 +23,17 @@
 
 // Constructors ////////////////////////////////////////////////////////////////
 
-USARTClass::USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer )
+USARTClass::USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, volatile RingBuffer* pTx_buffer )
 {
-  _rx_buffer = pRx_buffer ;
+  _rx_buffer = pRx_buffer;
+  _tx_buffer = pTx_buffer;
 
   _pUsart=pUsart ;
   _dwIrq=dwIrq ;
   _dwId=dwId ;
 }
 
+
 // Public Methods //////////////////////////////////////////////////////////////
 
 void USARTClass::begin( const uint32_t dwBaudRate )
@@ -73,6 +75,8 @@ void USARTClass::end( void )
   // clear any received data
   _rx_buffer->_iHead = _rx_buffer->_iTail ;
 
+  while (_tx_buffer->_iHead != _tx_buffer->_iTail); //wait for transmit data to be sent
+
   // Disable UART interrupt in NVIC
   NVIC_DisableIRQ( _dwIrq ) ;
 
@@ -115,12 +119,21 @@ void USARTClass::flush( void )
 
 size_t USARTClass::write( const uint8_t uc_data )
 {
-  // Check if the transmitter is ready
-  while ((_pUsart->US_CSR & US_CSR_TXRDY) != US_CSR_TXRDY)
-    ;
+  if ((_pUsart->US_CSR & US_CSR_TXRDY) != US_CSR_TXRDY) //is the hardware currently busy?
+  {
+	  //if busy we buffer
+	  unsigned int l = (_tx_buffer->_iHead + 1) % SERIAL_BUFFER_SIZE;
+	  while (_tx_buffer->_iTail == l); //spin locks if we're about to overwrite the buffer. This continues once the data is sent
 
-  // Send character
-  _pUsart->US_THR = uc_data ;
+	  _tx_buffer->_aucBuffer[_tx_buffer->_iHead] = uc_data;
+	  _tx_buffer->_iHead = l;
+	  _pUsart->US_IER = US_IER_TXRDY; //make sure TX interrupt is enabled
+  }
+  else 
+  {
+     // Send character
+     _pUsart->US_THR = uc_data ;
+  }
   return 1;
 }
 
@@ -132,6 +145,17 @@ void USARTClass::IrqHandler( void )
   if ((status & US_CSR_RXRDY) == US_CSR_RXRDY)
     _rx_buffer->store_char( _pUsart->US_RHR ) ;
 
+  //Do we need to keep sending data?
+  if ((status & US_CSR_TXRDY) == US_CSR_TXRDY) 
+  {
+	  _pUsart->US_THR = _tx_buffer->_aucBuffer[_tx_buffer->_iTail];
+	  _tx_buffer->_iTail = (unsigned int)(_tx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE;
+	  if (_tx_buffer->_iTail == _tx_buffer->_iHead) //if this is true we have no more data to transmit
+	  {
+		  _pUsart->US_IDR = US_IDR_TXRDY; //mask off transmit interrupt so we don't get it anymore
+	  }
+  }
+
   // Acknowledge errors
   if ((status & US_CSR_OVRE) == US_CSR_OVRE ||
 		  (status & US_CSR_FRAME) == US_CSR_FRAME)

hardware/arduino/sam/cores/arduino/USARTClass.h

@@ -60,14 +60,15 @@ class USARTClass : public HardwareSerial
 {
   protected:
     RingBuffer *_rx_buffer ;
+	volatile RingBuffer *_tx_buffer;
 
   protected:
     Usart* _pUsart ;
     IRQn_Type _dwIrq ;
     uint32_t _dwId ;
 
   public:
-    USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer ) ;
+    USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, volatile RingBuffer* pTx_buffer ) ;
 
     void begin( const uint32_t dwBaudRate ) ;
     void begin( const uint32_t dwBaudRate , const uint32_t config ) ;

hardware/arduino/sam/variants/arduino_due_x/variant.cpp

@@ -317,14 +317,17 @@ void UART_Handler(void)
 RingBuffer rx_buffer2;
 RingBuffer rx_buffer3;
 RingBuffer rx_buffer4;
+volatile RingBuffer tx_buffer2;
+volatile RingBuffer tx_buffer3;
+volatile RingBuffer tx_buffer4;
 
-USARTClass Serial1(USART0, USART0_IRQn, ID_USART0, &rx_buffer2);
+USARTClass Serial1(USART0, USART0_IRQn, ID_USART0, &rx_buffer2, &tx_buffer2);
 void serialEvent1() __attribute__((weak));
 void serialEvent1() { }
-USARTClass Serial2(USART1, USART1_IRQn, ID_USART1, &rx_buffer3);
+USARTClass Serial2(USART1, USART1_IRQn, ID_USART1, &rx_buffer3, &tx_buffer3);
 void serialEvent2() __attribute__((weak));
 void serialEvent2() { }
-USARTClass Serial3(USART3, USART3_IRQn, ID_USART3, &rx_buffer4);
+USARTClass Serial3(USART3, USART3_IRQn, ID_USART3, &rx_buffer4, &tx_buffer4);
 void serialEvent3() __attribute__((weak));
 void serialEvent3() { }