SoftwareSerial.cpp

/*
 * SoftwareSerial.cpp (formerly NewSoftSerial.cpp)
 *
 * Multi-instance software serial library for Arduino/Wiring
 * -- Interrupt-driven receive and other improvements by ladyada
 *    (http://ladyada.net)
 * -- Tuning, circular buffer, derivation from class Print/Stream,
 *    multi-instance support, porting to 8MHz processors,
 *    various optimizations, PROGMEM delay tables, inverse logic and
 *    direct port writing by Mikal Hart (http://www.arduiniana.org)
 * -- Pin change interrupt macros by Paul Stoffregen (http://www.pjrc.com)
 * -- 20MHz processor support by Garrett Mace (http://www.macetech.com)
 * -- ATmega1280/2560 support by Brett Hagman (http://www.roguerobotics.com/)
 *
 * 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
 *
 * The latest version of this library can always be found at
 * http://arduiniana.org.
 */

//
// Includes
//
#include <stdint.h>
#include <stdarg.h>
#include <Arduino.h>
#include "SoftwareSerial.h"
#include "HAL_softserial.h"

//#define FORCE_BAUD_RATE 19200

//
// Statics
//
bool SoftwareSerial::initialised = false;
SoftwareSerial * SoftwareSerial::active_listener = NULL;
SoftwareSerial * volatile SoftwareSerial::active_out = NULL;
SoftwareSerial * volatile SoftwareSerial:: active_in = NULL;
int32_t SoftwareSerial::tx_tick_cnt = 0;
int32_t SoftwareSerial::rx_tick_cnt = 0;
uint32_t SoftwareSerial::tx_buffer = 0;
int32_t SoftwareSerial::tx_bit_cnt = 0;
uint32_t SoftwareSerial::rx_buffer = 0;
int32_t SoftwareSerial::rx_bit_cnt = -1;
uint32_t SoftwareSerial::cur_speed = 0;

//
// Private methods
//

void SoftwareSerial::setSpeed(uint32_t speed)
{
  if (speed != cur_speed) {
    HAL_softserial_setSpeed(speed);
    cur_speed = speed;
  }
}

// This function sets the current object as the "listening"
// one and returns true if it replaces another
bool SoftwareSerial::listen() {
  if (_receivePin < 0) return false;

  // wait for any transmit to complete as we may change speed
  while(active_out) ;
  if (active_listener) {
    active_listener->stopListening();
  }
  rx_tick_cnt = 1;
  rx_bit_cnt = -1;
  setSpeed(_speed);
  active_listener = this;
  if (!_half_duplex)
    active_in = this;
  return true;
}

// Stop listening. Returns true if we were actually listening.
bool SoftwareSerial::stopListening() {
  if (active_listener != this) return false;

  // wait for any output to complete
  while (active_out) ;
  if (_half_duplex)
    setRXTX(false);
  active_listener = NULL;
  active_in = NULL;
  // turn off interrupts
  setSpeed(0);
  return true;
}

inline void SoftwareSerial::setTX() {
  // First write, then set output. If we do this the other way around,
  // the pin would be output low for a short while before switching to
  // output hihg. Now, it is input with pullup for a short while, which
  // is fine. With inverse logic, either order is fine.

  gpio_set(_transmitPin, _inverse_logic ? LOW : HIGH);
  pinMode(_transmitPin, OUTPUT);
}

inline void SoftwareSerial::setRX() {
  if (_receivePin >= 0) {
    pinMode(_receivePin, _inverse_logic ? INPUT_PULLDOWN : INPUT_PULLUP); // pullup for normal logic!
  }
}

inline void SoftwareSerial::setRXTX(bool input) {
  if (_half_duplex) {
    if (input) {
      if (active_in != this) {
        setRX();
        rx_bit_cnt = -1;
        rx_tick_cnt = 2;
        active_in = this;
      }
    }
    else {
      if (active_in == this) {
        setTX();
        active_in = NULL;
      }
    }
  }
}

inline void SoftwareSerial::send() {
  if (--tx_tick_cnt > 0) return;

  if (tx_bit_cnt++ < 10 ) {
    // send data (including start and stop bits)
    gpio_set(_transmitPin, tx_buffer & 1);
    tx_buffer >>= 1;
    tx_tick_cnt = OVERSAMPLE;
  }
  else {
    tx_tick_cnt = 1;
    if (_output_pending)
      active_out = NULL;
    else if (tx_bit_cnt > 10 + OVERSAMPLE*5) {
      if (_half_duplex && active_listener == this) {
        pinMode(_receivePin, _inverse_logic ? INPUT_PULLDOWN : INPUT_PULLUP); // pullup for normal logic!
        rx_bit_cnt = -1;
        rx_tick_cnt = 2;
        active_in = this;
      }
      active_out = NULL;
    }
  }
}

//
// The receive routine called by the interrupt handler
//
inline void SoftwareSerial::recv() {
  if (--rx_tick_cnt > 0) return;

  uint8_t inbit = gpio_get(_receivePin);
  if (rx_bit_cnt == -1) {
    // waiting for start bit
    if (inbit)
      rx_tick_cnt = 1;
    else {
      // got start bit
      rx_bit_cnt = 0;
      rx_tick_cnt = OVERSAMPLE + 1;
      rx_buffer = 0;
    }
  }
  else if (rx_bit_cnt < 8) {
    // data bits
    rx_buffer >>= 1;
    if (inbit)
      rx_buffer |= 0x80;
    rx_bit_cnt++;
    rx_tick_cnt = OVERSAMPLE;
  }
  else {
    if (inbit) {
      // stop bit read complete add to buffer
      uint8_t next = (_receive_buffer_tail + 1) % _SS_MAX_RX_BUFF;
      if (next != _receive_buffer_head) {
        // save new data in buffer: tail points to where byte goes
        _receive_buffer[_receive_buffer_tail] = rx_buffer; // save new byte
        _receive_buffer_tail = next;
      }
      else
        _buffer_overflow = true;
    }
    rx_tick_cnt = 1;
    rx_bit_cnt = -1;
  }
}

//
// Interrupt handling
//

/* static */
inline void SoftwareSerial::handle_interrupt() {
  if (active_in) active_in->recv();
  if (active_out) active_out->send();
}

HAL_SOFTSERIAL_TIMER_ISR() {
  HAL_softserial_timer_isr_prologue();

  SoftwareSerial::handle_interrupt();

  HAL_softserial_timer_isr_epilogue();
}

//
// Constructor
//
SoftwareSerial::SoftwareSerial(int16_t receivePin, int16_t transmitPin, bool inverse_logic /* = false */) :
  _receivePin(receivePin),
  _transmitPin(transmitPin),
  _speed(0),
  _buffer_overflow(false),
  _inverse_logic(inverse_logic),
  _half_duplex(receivePin == transmitPin),
  _output_pending(0),
  _receive_buffer_tail(0),
  _receive_buffer_head(0) {
}

//
// Destructor
//
SoftwareSerial::~SoftwareSerial() {
  end();
}


//
// Public methods
//

void SoftwareSerial::begin(long speed) {
  #ifdef FORCE_BAUD_RATE
    speed = FORCE_BAUD_RATE;
  #endif
  _speed = speed;
  if (!initialised) {
    HAL_softSerial_init();
    initialised = true;
  }

  // Set output pin as input, to ensure GPIO clock is started before calling setTX().
  pinMode(_transmitPin, _inverse_logic ? INPUT_PULLDOWN : INPUT_PULLUP);

  setTX();
  if (!_half_duplex) {
    setRX();
    listen();
  }
}

void SoftwareSerial::end() {
  stopListening();
}

// Read data from buffer
int SoftwareSerial::read() {
  // Empty buffer?
  if (_receive_buffer_head == _receive_buffer_tail) return -1;

  // Read from "head"
  uint8_t d = _receive_buffer[_receive_buffer_head]; // grab next byte
  _receive_buffer_head = (_receive_buffer_head + 1) % _SS_MAX_RX_BUFF;
  return d;
}

int SoftwareSerial::available() {
  return (_receive_buffer_tail + _SS_MAX_RX_BUFF - _receive_buffer_head) % _SS_MAX_RX_BUFF;
}

size_t SoftwareSerial::write(uint8_t b) {
  // wait for previous transmit to complete
  _output_pending = 1;
  while(active_out) ;
  // add start and stop bits.
  tx_buffer = b << 1 | 0x200;
  tx_bit_cnt = 0;
  tx_tick_cnt = OVERSAMPLE;
  setSpeed(_speed);
  if (_half_duplex)
    setRXTX(false);
  _output_pending = 0;
  // make us active
  active_out = this;
  return 1;
}

void SoftwareSerial::flush() {
  cli();
  _receive_buffer_head = _receive_buffer_tail = 0;
  sei();
}

int SoftwareSerial::peek() {
  // Empty buffer?
  if (_receive_buffer_head == _receive_buffer_tail)
    return -1;

  // Read from "head"
  return _receive_buffer[_receive_buffer_head];
}