/*
  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
  Modified 28 September 2010 by Mark Sproul
*/

#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <inttypes.h>
#include "wiring.h"
#include "wiring_private.h"

// this next line disables the entire HardwareSerial.cpp, 
// this is so I can support Attiny series and any other chip without a uart
#if defined(UBRRH) || defined(UBRR0H) || defined(UBRR1H) || defined(UBRR2H) || defined(UBRR3H)

#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 };

inline void store_char(unsigned char c, ring_buffer *rx_buffer)
{
  int i = (unsigned int)(rx_buffer->head + 1) & (RX_BUFFER_SIZE -1);

  // 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;
  }
}

// fixed by Mark Sproul this is on the 644/644p
//SIGNAL(SIG_USART_RECV)
SIGNAL(USART0_RX_vect)
{
  unsigned char c  =  UDR0;
  store_char(c, &rx_buffer);
}


// 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 = true;

#if F_CPU == 16000000UL
  // hardcoded exception for compatibility with the bootloader shipped
  // with the Duemilanove and previous boards and the firmware on the 8U2
  // on the Uno and Mega 2560.
  if (baud == 57600) {
    use_u2x = false;
  }
#endif
  
  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);
}

void HardwareSerial::end()
{
  cbi(*_ucsrb, _rxen);
  cbi(*_ucsrb, _txen);
  cbi(*_ucsrb, _rxcie);  
}

int HardwareSerial::available(void)
{
  return (unsigned int)(RX_BUFFER_SIZE + _rx_buffer->head - _rx_buffer->tail) & (RX_BUFFER_SIZE-1);
}

int HardwareSerial::peek(void)
{
  if (_rx_buffer->head == _rx_buffer->tail) {
    return -1;
  } else {
    return _rx_buffer->buffer[_rx_buffer->tail];
  }
}

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 = (unsigned int)(_rx_buffer->tail + 1) & (RX_BUFFER_SIZE-1);
    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 //////////////////////////////////////////////////////
HardwareSerial Serial(&rx_buffer, &UBRR0H, &UBRR0L, &UCSR0A, &UCSR0B, &UDR0, RXEN0, TXEN0, RXCIE0, UDRE0, U2X0);

#endif // whole file

