diff --git a/hardware/arduino/sam/cores/arduino/USARTClass.cpp b/hardware/arduino/sam/cores/arduino/USARTClass.cpp
index 44f92be5a..ce2c28a5c 100644
--- a/hardware/arduino/sam/cores/arduino/USARTClass.cpp
+++ b/hardware/arduino/sam/cores/arduino/USARTClass.cpp
@@ -23,7 +23,7 @@
 
 // Constructors ////////////////////////////////////////////////////////////////
 
-USARTClass::USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, volatile RingBuffer* pTx_buffer )
+USARTClass::USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, RingBuffer* pTx_buffer )
 {
   _rx_buffer = pRx_buffer;
   _tx_buffer = pTx_buffer;
@@ -33,7 +33,6 @@ USARTClass::USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffe
   _dwId=dwId ;
 }
 
-
 // Public Methods //////////////////////////////////////////////////////////////
 
 void USARTClass::begin( const uint32_t dwBaudRate )
@@ -66,6 +65,10 @@ void USARTClass::begin( const uint32_t dwBaudRate, const uint32_t config )
   // Enable UART interrupt in NVIC
   NVIC_EnableIRQ( _dwIrq ) ;
 
+  //make sure both ring buffers are initialized back to empty.
+  _rx_buffer->_iHead = _rx_buffer->_iTail = 0;
+  _tx_buffer->_iHead = _tx_buffer->_iTail = 0;
+
   // Enable receiver and transmitter
   _pUsart->US_CR = US_CR_RXEN | US_CR_TXEN ;
 }
@@ -91,6 +94,14 @@ int USARTClass::available( void )
   return (uint32_t)(SERIAL_BUFFER_SIZE + _rx_buffer->_iHead - _rx_buffer->_iTail) % SERIAL_BUFFER_SIZE ;
 }
 
+int USARTClass::availableForWrite(void)
+{
+  int head = _tx_buffer->_iHead;
+  int tail = _tx_buffer->_iTail;
+  if (head >= tail) return SERIAL_BUFFER_SIZE - 1 - head + tail;
+  return tail - head - 1;
+}
+
 int USARTClass::peek( void )
 {
   if ( _rx_buffer->_iHead == _rx_buffer->_iTail )
@@ -142,17 +153,20 @@ void USARTClass::IrqHandler( void )
   uint32_t status = _pUsart->US_CSR;
 
   // Did we receive data ?
-  if ((status & US_CSR_RXRDY) == US_CSR_RXRDY)
-    _rx_buffer->store_char( _pUsart->US_RHR ) ;
-
+  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
+	  if (_tx_buffer->_iTail != _tx_buffer->_iHead) { //just in case
+		_pUsart->US_THR = _tx_buffer->_aucBuffer[_tx_buffer->_iTail];
+		_tx_buffer->_iTail = (unsigned int)(_tx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE;
+	  }
+	  else
 	  {
-		  _pUsart->US_IDR = US_IDR_TXRDY; //mask off transmit interrupt so we don't get it anymore
+		_pUsart->US_IDR = US_IDR_TXRDY; //mask off transmit interrupt so we don't get it anymore
 	  }
   }
 
diff --git a/hardware/arduino/sam/cores/arduino/USARTClass.h b/hardware/arduino/sam/cores/arduino/USARTClass.h
index 9d820c982..fcce9fd12 100644
--- a/hardware/arduino/sam/cores/arduino/USARTClass.h
+++ b/hardware/arduino/sam/cores/arduino/USARTClass.h
@@ -59,8 +59,8 @@
 class USARTClass : public HardwareSerial
 {
   protected:
-    RingBuffer *_rx_buffer ;
-	volatile RingBuffer *_tx_buffer;
+    RingBuffer *_rx_buffer;
+	RingBuffer *_tx_buffer;
 
   protected:
     Usart* _pUsart ;
@@ -68,12 +68,13 @@ class USARTClass : public HardwareSerial
     uint32_t _dwId ;
 
   public:
-    USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, volatile RingBuffer* pTx_buffer ) ;
+    USARTClass( Usart* pUsart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, RingBuffer* pTx_buffer ) ;
 
     void begin( const uint32_t dwBaudRate ) ;
     void begin( const uint32_t dwBaudRate , const uint32_t config ) ;
     void end( void ) ;
     int available( void ) ;
+	int availableForWrite(void);
     int peek( void ) ;
     int read( void ) ;
     void flush( void ) ;
diff --git a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
index f4ccc0c12..f746fdf44 100644
--- a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
+++ b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
@@ -317,9 +317,9 @@ 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;
+RingBuffer tx_buffer2;
+RingBuffer tx_buffer3;
+RingBuffer tx_buffer4;
 
 USARTClass Serial1(USART0, USART0_IRQn, ID_USART0, &rx_buffer2, &tx_buffer2);
 void serialEvent1() __attribute__((weak));