diff --git a/build/shared/revisions.txt b/build/shared/revisions.txt
index 5944bfa18..512a88e85 100644
--- a/build/shared/revisions.txt
+++ b/build/shared/revisions.txt
@@ -6,6 +6,9 @@ The following changes are included also in the Arduino IDE 1.0.7:
 [ide]
 * Mitigated Serial Monitor resource exhaustion when the connected device sends a lot of data (Paul Stoffregen)
 
+[core]
+* sam: HardwareSerial now performs ISR based buffered transmission (Collin Kidder)
+
 ARDUINO 1.6.0rc1
 
 * IDE internals have been refactored and sorted out. (Claudio Indellicati)
diff --git a/hardware/arduino/sam/cores/arduino/RingBuffer.cpp b/hardware/arduino/sam/cores/arduino/RingBuffer.cpp
index f0b3ed1df..d9931c977 100644
--- a/hardware/arduino/sam/cores/arduino/RingBuffer.cpp
+++ b/hardware/arduino/sam/cores/arduino/RingBuffer.cpp
@@ -21,7 +21,7 @@
 
 RingBuffer::RingBuffer( void )
 {
-    memset( _aucBuffer, 0, SERIAL_BUFFER_SIZE ) ;
+    memset( (void *)_aucBuffer, 0, SERIAL_BUFFER_SIZE ) ;
     _iHead=0 ;
     _iTail=0 ;
 }
diff --git a/hardware/arduino/sam/cores/arduino/RingBuffer.h b/hardware/arduino/sam/cores/arduino/RingBuffer.h
index 28309df45..1a5861b0b 100644
--- a/hardware/arduino/sam/cores/arduino/RingBuffer.h
+++ b/hardware/arduino/sam/cores/arduino/RingBuffer.h
@@ -25,14 +25,14 @@
 // using a ring buffer (I think), in which head is the index of the location
 // to which to write the next incoming character and tail is the index of the
 // location from which to read.
-#define SERIAL_BUFFER_SIZE 64
+#define SERIAL_BUFFER_SIZE 128
 
 class RingBuffer
 {
   public:
-    uint8_t _aucBuffer[SERIAL_BUFFER_SIZE] ;
-    int _iHead ;
-    int _iTail ;
+    volatile uint8_t _aucBuffer[SERIAL_BUFFER_SIZE] ;
+    volatile int _iHead ;
+    volatile int _iTail ;
 
   public:
     RingBuffer( void ) ;
diff --git a/hardware/arduino/sam/cores/arduino/UARTClass.cpp b/hardware/arduino/sam/cores/arduino/UARTClass.cpp
index 16188b128..22ec20abb 100644
--- a/hardware/arduino/sam/cores/arduino/UARTClass.cpp
+++ b/hardware/arduino/sam/cores/arduino/UARTClass.cpp
@@ -23,33 +23,39 @@
 
 // Constructors ////////////////////////////////////////////////////////////////
 
-UARTClass::UARTClass( Uart* pUart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer )
+UARTClass::UARTClass( Uart *pUart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer *pRx_buffer, RingBuffer *pTx_buffer )
 {
-  _rx_buffer = pRx_buffer ;
+  _rx_buffer = pRx_buffer;
+  _tx_buffer = pTx_buffer;
 
-  _pUart=pUart ;
-  _dwIrq=dwIrq ;
-  _dwId=dwId ;
+  _pUart=pUart;
+  _dwIrq=dwIrq;
+  _dwId=dwId;
 }
 
 // Public Methods //////////////////////////////////////////////////////////////
 
 void UARTClass::begin( const uint32_t dwBaudRate )
+{
+  begin( dwBaudRate, UART_MR_PAR_NO | UART_MR_CHMODE_NORMAL );
+}
+
+void UARTClass::begin( const uint32_t dwBaudRate, const uint32_t config )
 {
   // Configure PMC
-  pmc_enable_periph_clk( _dwId ) ;
+  pmc_enable_periph_clk( _dwId );
 
   // Disable PDC channel
-  _pUart->UART_PTCR = UART_PTCR_RXTDIS | UART_PTCR_TXTDIS ;
+  _pUart->UART_PTCR = UART_PTCR_RXTDIS | UART_PTCR_TXTDIS;
 
   // Reset and disable receiver and transmitter
-  _pUart->UART_CR = UART_CR_RSTRX | UART_CR_RSTTX | UART_CR_RXDIS | UART_CR_TXDIS ;
+  _pUart->UART_CR = UART_CR_RSTRX | UART_CR_RSTTX | UART_CR_RXDIS | UART_CR_TXDIS;
 
   // Configure mode
-  _pUart->UART_MR = UART_MR_PAR_NO | UART_MR_CHMODE_NORMAL ;
+  _pUart->UART_MR = config;
 
   // Configure baudrate (asynchronous, no oversampling)
-  _pUart->UART_BRGR = (SystemCoreClock / dwBaudRate) >> 4 ;
+  _pUart->UART_BRGR = (SystemCoreClock / dwBaudRate) >> 4;
 
   // Configure interrupts
   _pUart->UART_IDR = 0xFFFFFFFF;
@@ -58,63 +64,99 @@ void UARTClass::begin( const uint32_t dwBaudRate )
   // 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
-  _pUart->UART_CR = UART_CR_RXEN | UART_CR_TXEN ;
+  _pUart->UART_CR = UART_CR_RXEN | UART_CR_TXEN;
 }
 
 void UARTClass::end( void )
 {
-  // clear any received data
-  _rx_buffer->_iHead = _rx_buffer->_iTail ;
-
-  // Disable UART interrupt in NVIC
-  NVIC_DisableIRQ( _dwIrq ) ;
+  // Clear any received data
+  _rx_buffer->_iHead = _rx_buffer->_iTail;
 
   // Wait for any outstanding data to be sent
   flush();
 
-  pmc_disable_periph_clk( _dwId ) ;
+  // Disable UART interrupt in NVIC
+  NVIC_DisableIRQ( _dwIrq );
+
+  pmc_disable_periph_clk( _dwId );
+}
+
+void UARTClass::setInterruptPriority(uint32_t priority)
+{
+  NVIC_SetPriority(_dwIrq, priority & 0x0F);
+}
+
+uint32_t UARTClass::getInterruptPriority()
+{
+  return NVIC_GetPriority(_dwIrq);
 }
 
 int UARTClass::available( void )
 {
-  return (uint32_t)(SERIAL_BUFFER_SIZE + _rx_buffer->_iHead - _rx_buffer->_iTail) % SERIAL_BUFFER_SIZE ;
+  return (uint32_t)(SERIAL_BUFFER_SIZE + _rx_buffer->_iHead - _rx_buffer->_iTail) % SERIAL_BUFFER_SIZE;
+}
+
+int UARTClass::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 UARTClass::peek( void )
 {
   if ( _rx_buffer->_iHead == _rx_buffer->_iTail )
-    return -1 ;
+    return -1;
 
-  return _rx_buffer->_aucBuffer[_rx_buffer->_iTail] ;
+  return _rx_buffer->_aucBuffer[_rx_buffer->_iTail];
 }
 
 int UARTClass::read( void )
 {
   // if the head isn't ahead of the tail, we don't have any characters
   if ( _rx_buffer->_iHead == _rx_buffer->_iTail )
-    return -1 ;
+    return -1;
 
-  uint8_t uc = _rx_buffer->_aucBuffer[_rx_buffer->_iTail] ;
-  _rx_buffer->_iTail = (unsigned int)(_rx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE ;
-  return uc ;
+  uint8_t uc = _rx_buffer->_aucBuffer[_rx_buffer->_iTail];
+  _rx_buffer->_iTail = (unsigned int)(_rx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE;
+  return uc;
 }
 
 void UARTClass::flush( void )
 {
+  while (_tx_buffer->_iHead != _tx_buffer->_iTail); //wait for transmit data to be sent
   // Wait for transmission to complete
   while ((_pUart->UART_SR & UART_SR_TXRDY) != UART_SR_TXRDY)
-    ;
+   ;
 }
 
 size_t UARTClass::write( const uint8_t uc_data )
 {
-  // Check if the transmitter is ready
-  while ((_pUart->UART_SR & UART_SR_TXRDY) != UART_SR_TXRDY)
-    ;
+  // Is the hardware currently busy?
+  if (((_pUart->UART_SR & UART_SR_TXRDY) != UART_SR_TXRDY) |
+      (_tx_buffer->_iTail != _tx_buffer->_iHead))
+  {
+    // 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
-  _pUart->UART_THR = uc_data;
+    _tx_buffer->_aucBuffer[_tx_buffer->_iHead] = uc_data;
+    _tx_buffer->_iHead = l;
+    // Make sure TX interrupt is enabled
+    _pUart->UART_IER = UART_IER_TXRDY;
+  }
+  else 
+  {
+     // Bypass buffering and send character directly
+     _pUart->UART_THR = uc_data;
+  }
   return 1;
 }
 
@@ -122,15 +164,28 @@ void UARTClass::IrqHandler( void )
 {
   uint32_t status = _pUart->UART_SR;
 
-  // Did we receive data ?
+  // Did we receive data?
   if ((status & UART_SR_RXRDY) == UART_SR_RXRDY)
     _rx_buffer->store_char(_pUart->UART_RHR);
 
-  // Acknowledge errors
-  if ((status & UART_SR_OVRE) == UART_SR_OVRE ||
-		  (status & UART_SR_FRAME) == UART_SR_FRAME)
+  // Do we need to keep sending data?
+  if ((status & UART_SR_TXRDY) == UART_SR_TXRDY) 
   {
-	// TODO: error reporting outside ISR
+    if (_tx_buffer->_iTail != _tx_buffer->_iHead) {
+      _pUart->UART_THR = _tx_buffer->_aucBuffer[_tx_buffer->_iTail];
+      _tx_buffer->_iTail = (unsigned int)(_tx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE;
+    }
+    else
+    {
+      // Mask off transmit interrupt so we don't get it anymore
+      _pUart->UART_IDR = UART_IDR_TXRDY;
+    }
+  }
+
+  // Acknowledge errors
+  if ((status & UART_SR_OVRE) == UART_SR_OVRE || (status & UART_SR_FRAME) == UART_SR_FRAME)
+  {
+    // TODO: error reporting outside ISR
     _pUart->UART_CR |= UART_CR_RSTSTA;
   }
 }
diff --git a/hardware/arduino/sam/cores/arduino/UARTClass.h b/hardware/arduino/sam/cores/arduino/UARTClass.h
index 5836f2e62..1bc223d80 100644
--- a/hardware/arduino/sam/cores/arduino/UARTClass.h
+++ b/hardware/arduino/sam/cores/arduino/UARTClass.h
@@ -28,32 +28,32 @@
 class UARTClass : public HardwareSerial
 {
   protected:
-    RingBuffer *_rx_buffer ;
+    RingBuffer *_rx_buffer;
+    RingBuffer *_tx_buffer;
 
   protected:
-    Uart* _pUart ;
-    IRQn_Type _dwIrq ;
-    uint32_t _dwId ;
+    Uart* _pUart;
+    IRQn_Type _dwIrq;
+    uint32_t _dwId;
 
   public:
-    UARTClass( Uart* pUart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer ) ;
+    UARTClass(Uart* pUart, IRQn_Type dwIrq, uint32_t dwId, RingBuffer* pRx_buffer, RingBuffer* pTx_buffer);
 
-    void begin( const uint32_t dwBaudRate ) ;
-    void end( void ) ;
-    int available( void ) ;
-    int peek( void ) ;
-    int read( void ) ;
-    void flush( void ) ;
-    size_t write( const uint8_t c ) ;
+    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);
+    size_t write(const uint8_t c);
+    using Print::write; // pull in write(str) and write(buf, size) from Print
 
-    void IrqHandler( void ) ;
+    void setInterruptPriority(uint32_t priority);
+    uint32_t getInterruptPriority();
 
-#if defined __GNUC__ /* GCC CS3 */
-    using Print::write ; // pull in write(str) and write(buf, size) from Print
-#elif defined __ICCARM__ /* IAR Ewarm 5.41+ */
-//    virtual void write( const char *str ) ;
-//    virtual void write( const uint8_t *buffer, size_t size ) ;
-#endif
+    void IrqHandler(void);
 
     operator bool() { return true; }; // UART always active
 };
diff --git a/hardware/arduino/sam/cores/arduino/USARTClass.cpp b/hardware/arduino/sam/cores/arduino/USARTClass.cpp
index d950c50c9..9fcfa30a6 100644
--- a/hardware/arduino/sam/cores/arduino/USARTClass.cpp
+++ b/hardware/arduino/sam/cores/arduino/USARTClass.cpp
@@ -23,121 +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, RingBuffer* pTx_buffer )
+  : UARTClass((Uart*)pUsart, dwIrq, dwId, pRx_buffer, pTx_buffer)
 {
-  _rx_buffer = pRx_buffer ;
-
-  _pUsart=pUsart ;
-  _dwIrq=dwIrq ;
-  _dwId=dwId ;
+  // In case anyone needs USART specific functionality in the future
+  _pUsart=pUsart;
 }
 
 // Public Methods //////////////////////////////////////////////////////////////
 
-void USARTClass::begin( const uint32_t dwBaudRate )
-{
-	begin( dwBaudRate, SERIAL_8N1 );
-}
-
 void USARTClass::begin( const uint32_t dwBaudRate, const uint32_t config )
 {
-  // Configure PMC
-  pmc_enable_periph_clk( _dwId ) ;
-
-  // Disable PDC channel
-  _pUsart->US_PTCR = US_PTCR_RXTDIS | US_PTCR_TXTDIS ;
-
-  // Reset and disable receiver and transmitter
-  _pUsart->US_CR = US_CR_RSTRX | US_CR_RSTTX | US_CR_RXDIS | US_CR_TXDIS ;
-
-  // Configure mode
-  _pUsart->US_MR = config;
-
-
-  // Configure baudrate, asynchronous no oversampling
-  _pUsart->US_BRGR = (SystemCoreClock / dwBaudRate) / 16 ;
-
-  // Configure interrupts
-  _pUsart->US_IDR = 0xFFFFFFFF;
-  _pUsart->US_IER = US_IER_RXRDY | US_IER_OVRE | US_IER_FRAME;
-
-  // Enable UART interrupt in NVIC
-  NVIC_EnableIRQ( _dwIrq ) ;
-
-  // Enable receiver and transmitter
-  _pUsart->US_CR = US_CR_RXEN | US_CR_TXEN ;
-}
-
-void USARTClass::end( void )
-{
-  // clear any received data
-  _rx_buffer->_iHead = _rx_buffer->_iTail ;
-
-  // Disable UART interrupt in NVIC
-  NVIC_DisableIRQ( _dwIrq ) ;
-
-  // Wait for any outstanding data to be sent
-  flush();
-
-  pmc_disable_periph_clk( _dwId ) ;
-}
-
-int USARTClass::available( void )
-{
-  return (uint32_t)(SERIAL_BUFFER_SIZE + _rx_buffer->_iHead - _rx_buffer->_iTail) % SERIAL_BUFFER_SIZE ;
-}
-
-int USARTClass::peek( void )
-{
-  if ( _rx_buffer->_iHead == _rx_buffer->_iTail )
-    return -1 ;
-
-  return _rx_buffer->_aucBuffer[_rx_buffer->_iTail] ;
-}
-
-int USARTClass::read( void )
-{
-  // if the head isn't ahead of the tail, we don't have any characters
-  if ( _rx_buffer->_iHead == _rx_buffer->_iTail )
-    return -1 ;
-
-  uint8_t uc = _rx_buffer->_aucBuffer[_rx_buffer->_iTail] ;
-  _rx_buffer->_iTail = (unsigned int)(_rx_buffer->_iTail + 1) % SERIAL_BUFFER_SIZE ;
-  return uc ;
-}
-
-void USARTClass::flush( void )
-{
-  // Wait for transmission to complete
-  while ((_pUsart->US_CSR & US_CSR_TXRDY) != US_CSR_TXRDY)
-	;
-}
-
-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)
-    ;
-
-  // Send character
-  _pUsart->US_THR = uc_data ;
-  return 1;
-}
-
-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 ) ;
-
-  // Acknowledge errors
-  if ((status & US_CSR_OVRE) == US_CSR_OVRE ||
-		  (status & US_CSR_FRAME) == US_CSR_FRAME)
-  {
-	// TODO: error reporting outside ISR
-    _pUsart->US_CR |= US_CR_RSTSTA;
-  }
+  UARTClass::begin(dwBaudRate, config);
 }
 
diff --git a/hardware/arduino/sam/cores/arduino/USARTClass.h b/hardware/arduino/sam/cores/arduino/USARTClass.h
index 9082cc6c2..235f54910 100644
--- a/hardware/arduino/sam/cores/arduino/USARTClass.h
+++ b/hardware/arduino/sam/cores/arduino/USARTClass.h
@@ -19,7 +19,7 @@
 #ifndef _USART_CLASS_
 #define _USART_CLASS_
 
-#include "HardwareSerial.h"
+#include "UARTClass.h"
 #include "RingBuffer.h"
 
 // Includes Atmel CMSIS
@@ -56,38 +56,16 @@
 #define SERIAL_7O2 (US_MR_USART_MODE_NORMAL | US_MR_USCLKS_MCK | US_MR_CHRL_7_BIT | US_MR_PAR_ODD | US_MR_NBSTOP_2_BIT | US_MR_CHMODE_NORMAL)
 #define SERIAL_8O2 (US_MR_USART_MODE_NORMAL | US_MR_USCLKS_MCK | US_MR_CHRL_8_BIT | US_MR_PAR_ODD | US_MR_NBSTOP_2_BIT | US_MR_CHMODE_NORMAL)
 
-class USARTClass : public HardwareSerial
+class USARTClass : public UARTClass
 {
   protected:
-    RingBuffer *_rx_buffer ;
-
-  protected:
-    Usart* _pUsart ;
-    IRQn_Type _dwIrq ;
-    uint32_t _dwId ;
+    Usart* _pUsart;
 
   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, 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 peek( void ) ;
-    int read( void ) ;
-    void flush( void ) ;
-    size_t write( const uint8_t c ) ;
-
-    void IrqHandler( void ) ;
-
-#if defined __GNUC__ /* GCC CS3 */
-    using Print::write ; // pull in write(str) and write(buf, size) from Print
-#elif defined __ICCARM__ /* IAR Ewarm 5.41+ */
-//    virtual void write( const char *str ) ;
-//    virtual void write( const uint8_t *buffer, size_t size ) ;
-#endif
-
-    operator bool() { return true; }; // USART always active
+    void begin( const uint32_t dwBaudRate , const uint32_t config );
+    using UARTClass::begin; // Needed only for polymorphic methods
 };
 
 #endif // _USART_CLASS_
diff --git a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
index ac066898d..4cbe0df80 100644
--- a/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
+++ b/hardware/arduino/sam/variants/arduino_due_x/variant.cpp
@@ -299,8 +299,9 @@ extern const PinDescription g_APinDescription[]=
  * UART objects
  */
 RingBuffer rx_buffer1;
+RingBuffer tx_buffer1;
 
-UARTClass Serial(UART, UART_IRQn, ID_UART, &rx_buffer1);
+UARTClass Serial(UART, UART_IRQn, ID_UART, &rx_buffer1, &tx_buffer1);
 void serialEvent() __attribute__((weak));
 void serialEvent() { }
 
@@ -317,14 +318,17 @@ void UART_Handler(void)
 RingBuffer rx_buffer2;
 RingBuffer rx_buffer3;
 RingBuffer rx_buffer4;
+RingBuffer tx_buffer2;
+RingBuffer tx_buffer3;
+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() { }