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diff --git a/cores/arduino/HardwareSerial.cpp b/cores/arduino/HardwareSerial.cpp
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+/*
+  HardwareSerial.cpp - Hardware serial library for Wiring
+  Copyright (c) 2006 Nicholas Zambetti.  All right reserved.
+
+  This library is free software; you can redistribute it and/or
+  modify it under the terms of the GNU Lesser General Public
+  License as published by the Free Software Foundation; either
+  version 2.1 of the License, or (at your option) any later version.
+
+  This library is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+  Lesser General Public License for more details.
+
+  You should have received a copy of the GNU Lesser General Public
+  License along with this library; if not, write to the Free Software
+  Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301  USA
+  
+  Modified 23 November 2006 by David A. Mellis
+*/
+
+#include <stdio.h>
+#include <string.h>
+#include <inttypes.h>
+#include "wiring.h"
+#include "wiring_private.h"
+
+#include "HardwareSerial.h"
+
+// Define constants and variables for buffering incoming serial data.  We're
+// using a ring buffer (I think), in which rx_buffer_head is the index of the
+// location to which to write the next incoming character and rx_buffer_tail
+// is the index of the location from which to read.
+#define RX_BUFFER_SIZE 128
+
+struct ring_buffer {
+  unsigned char buffer[RX_BUFFER_SIZE];
+  int head;
+  int tail;
+};
+
+ring_buffer rx_buffer = { { 0 }, 0, 0 };
+
+#if defined(__AVR_ATmega1280__)
+ring_buffer rx_buffer1 = { { 0 }, 0, 0 };
+ring_buffer rx_buffer2 = { { 0 }, 0, 0 };
+ring_buffer rx_buffer3 = { { 0 }, 0, 0 };
+#endif
+
+inline void store_char(unsigned char c, ring_buffer *rx_buffer)
+{
+  int i = (rx_buffer->head + 1) % RX_BUFFER_SIZE;
+
+  // if we should be storing the received character into the location
+  // just before the tail (meaning that the head would advance to the
+  // current location of the tail), we're about to overflow the buffer
+  // and so we don't write the character or advance the head.
+  if (i != rx_buffer->tail) {
+    rx_buffer->buffer[rx_buffer->head] = c;
+    rx_buffer->head = i;
+  }
+}
+
+#if defined(__AVR_ATmega1280__)
+
+SIGNAL(SIG_USART0_RECV)
+{
+  unsigned char c = UDR0;
+  store_char(c, &rx_buffer);
+}
+
+SIGNAL(SIG_USART1_RECV)
+{
+  unsigned char c = UDR1;
+  store_char(c, &rx_buffer1);
+}
+
+SIGNAL(SIG_USART2_RECV)
+{
+  unsigned char c = UDR2;
+  store_char(c, &rx_buffer2);
+}
+
+SIGNAL(SIG_USART3_RECV)
+{
+  unsigned char c = UDR3;
+  store_char(c, &rx_buffer3);
+}
+
+#else
+
+#if defined(__AVR_ATmega8__)
+SIGNAL(SIG_UART_RECV)
+#else
+SIGNAL(USART_RX_vect)
+#endif
+{
+#if defined(__AVR_ATmega8__)
+  unsigned char c = UDR;
+#else
+  unsigned char c = UDR0;
+#endif
+  store_char(c, &rx_buffer);
+}
+
+#endif
+
+// Constructors ////////////////////////////////////////////////////////////////
+
+HardwareSerial::HardwareSerial(ring_buffer *rx_buffer,
+  volatile uint8_t *ubrrh, volatile uint8_t *ubrrl,
+  volatile uint8_t *ucsra, volatile uint8_t *ucsrb,
+  volatile uint8_t *udr,
+  uint8_t rxen, uint8_t txen, uint8_t rxcie, uint8_t udre, uint8_t u2x)
+{
+  _rx_buffer = rx_buffer;
+  _ubrrh = ubrrh;
+  _ubrrl = ubrrl;
+  _ucsra = ucsra;
+  _ucsrb = ucsrb;
+  _udr = udr;
+  _rxen = rxen;
+  _txen = txen;
+  _rxcie = rxcie;
+  _udre = udre;
+  _u2x = u2x;
+}
+
+// Public Methods //////////////////////////////////////////////////////////////
+
+void HardwareSerial::begin(long baud)
+{
+  uint16_t baud_setting;
+  bool use_u2x;
+
+  // U2X mode is needed for baud rates higher than (CPU Hz / 16)
+  if (baud > F_CPU / 16) {
+    use_u2x = true;
+  } else {
+    // figure out if U2X mode would allow for a better connection
+    
+    // calculate the percent difference between the baud-rate specified and
+    // the real baud rate for both U2X and non-U2X mode (0-255 error percent)
+    uint8_t nonu2x_baud_error = abs((int)(255-((F_CPU/(16*(((F_CPU/8/baud-1)/2)+1))*255)/baud)));
+    uint8_t u2x_baud_error = abs((int)(255-((F_CPU/(8*(((F_CPU/4/baud-1)/2)+1))*255)/baud)));
+    
+    // prefer non-U2X mode because it handles clock skew better
+    use_u2x = (nonu2x_baud_error > u2x_baud_error);
+  }
+  
+  if (use_u2x) {
+    *_ucsra = 1 << _u2x;
+    baud_setting = (F_CPU / 4 / baud - 1) / 2;
+  } else {
+    *_ucsra = 0;
+    baud_setting = (F_CPU / 8 / baud - 1) / 2;
+  }
+
+  // assign the baud_setting, a.k.a. ubbr (USART Baud Rate Register)
+  *_ubrrh = baud_setting >> 8;
+  *_ubrrl = baud_setting;
+
+  sbi(*_ucsrb, _rxen);
+  sbi(*_ucsrb, _txen);
+  sbi(*_ucsrb, _rxcie);
+}
+
+uint8_t HardwareSerial::available(void)
+{
+  return (RX_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail) % RX_BUFFER_SIZE;
+}
+
+int HardwareSerial::read(void)
+{
+  // if the head isn't ahead of the tail, we don't have any characters
+  if (_rx_buffer->head == _rx_buffer->tail) {
+    return -1;
+  } else {
+    unsigned char c = _rx_buffer->buffer[_rx_buffer->tail];
+    _rx_buffer->tail = (_rx_buffer->tail + 1) % RX_BUFFER_SIZE;
+    return c;
+  }
+}
+
+void HardwareSerial::flush()
+{
+  // don't reverse this or there may be problems if the RX interrupt
+  // occurs after reading the value of rx_buffer_head but before writing
+  // the value to rx_buffer_tail; the previous value of rx_buffer_head
+  // may be written to rx_buffer_tail, making it appear as if the buffer
+  // don't reverse this or there may be problems if the RX interrupt
+  // occurs after reading the value of rx_buffer_head but before writing
+  // the value to rx_buffer_tail; the previous value of rx_buffer_head
+  // may be written to rx_buffer_tail, making it appear as if the buffer
+  // were full, not empty.
+  _rx_buffer->head = _rx_buffer->tail;
+}
+
+void HardwareSerial::write(uint8_t c)
+{
+  while (!((*_ucsra) & (1 << _udre)))
+    ;
+
+  *_udr = c;
+}
+
+// Preinstantiate Objects //////////////////////////////////////////////////////
+
+#if defined(__AVR_ATmega8__)
+HardwareSerial Serial(&rx_buffer, &UBRRH, &UBRRL, &UCSRA, &UCSRB, &UDR, RXEN, TXEN, RXCIE, UDRE, U2X);
+#else
+HardwareSerial Serial(&rx_buffer, &UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UDR0, RXEN0, TXEN0, RXCIE0, UDRE0, U2X0);
+#endif
+
+#if defined(__AVR_ATmega1280__)
+HardwareSerial Serial1(&rx_buffer1, &UBRR1H, &UBRR1L, &UCSR1A, &UCSR1B, &UDR1, RXEN1, TXEN1, RXCIE1, UDRE1, U2X1);
+HardwareSerial Serial2(&rx_buffer2, &UBRR2H, &UBRR2L, &UCSR2A, &UCSR2B, &UDR2, RXEN2, TXEN2, RXCIE2, UDRE2, U2X2);
+HardwareSerial Serial3(&rx_buffer3, &UBRR3H, &UBRR3L, &UCSR3A, &UCSR3B, &UDR3, RXEN3, TXEN3, RXCIE3, UDRE3, U2X3);
+#endif