/*
 *  spreadspace avr utils
 *
 *
 *  Copyright (C) 2013-2015 Christian Pointner <equinox@spreadspace.org>
 *
 *  This file is part of spreadspace avr utils.
 *
 *  spreadspace avr utils is free software: you can redistribute it and/or modify
 *  it under the terms of the GNU General Public License as published by
 *  the Free Software Foundation, either version 3 of the License, or
 *  any later version.
 *
 *  spreadspace avr utils 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 General Public License for more details.
 *
 *  You should have received a copy of the GNU General Public License
 *  along with spreadspace avr utils. If not, see <http://www.gnu.org/licenses/>.
 */

#include "Arduino.h"


extern "C" {

#ifndef cbi
#define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
#define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

/*
  wiring.c - Partial implementation of the Wiring API for the ATmega8.
  Part of Arduino - http://www.arduino.cc/

  Copyright (c) 2005-2006 David A. Mellis

  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., 59 Temple Place, Suite 330,
  Boston, MA  02111-1307  USA

  $Id$
*/

//#include "wiring_private.h"

// the prescaler is set so that timer0 ticks every 64 clock cycles, and the
// the overflow handler is called every 256 ticks.
#define MICROSECONDS_PER_TIMER0_OVERFLOW (clockCyclesToMicroseconds(64 * 256))

// the whole number of milliseconds per timer0 overflow
#define MILLIS_INC (MICROSECONDS_PER_TIMER0_OVERFLOW / 1000)

// the fractional number of milliseconds per timer0 overflow. we shift right
// by three to fit these numbers into a byte. (for the clock speeds we care
// about - 8 and 16 MHz - this doesn't lose precision.)
#define FRACT_INC ((MICROSECONDS_PER_TIMER0_OVERFLOW % 1000) >> 3)
#define FRACT_MAX (1000 >> 3)

volatile unsigned long timer0_overflow_count = 0;
#  if defined(CORE_TEENSY) || defined(TEENSYDUINO)
volatile unsigned long timer0_millis_count;
#    define MS_COUNTER timer0_millis_count
#  else
volatile unsigned long timer0_millis;
#    define MS_COUNTER timer0_millis
#  endif
static unsigned char timer0_fract = 0;

#if defined(__AVR_ATtiny24__) || defined(__AVR_ATtiny44__) || defined(__AVR_ATtiny84__)
ISR(TIM0_OVF_vect)
#else
ISR(TIMER0_OVF_vect)
#endif
{
  // copy these to local variables so they can be stored in registers
  // (volatile variables must be read from memory on every access)
  unsigned long m = MS_COUNTER;
  unsigned char f = timer0_fract;

  m += MILLIS_INC;
  f += FRACT_INC;
  if (f >= FRACT_MAX) {
    f -= FRACT_MAX;
    m += 1;
  }

  timer0_fract = f;
  MS_COUNTER = m;
  timer0_overflow_count++;
}

unsigned long millis()
{
  unsigned long m;
  uint8_t oldSREG = SREG;

  // disable interrupts while we read MS_COUNTER or we might get an
  // inconsistent value (e.g. in the middle of a write to MS_COUNTER)
  cli();
  m = MS_COUNTER;
  SREG = oldSREG;

  return m;
}

unsigned long micros() {
  unsigned long m;
  uint8_t oldSREG = SREG, t;

  cli();
  m = timer0_overflow_count;
#if defined(TCNT0)
  t = TCNT0;
#elif defined(TCNT0L)
  t = TCNT0L;
#else
  #error TIMER 0 not defined
#endif


#ifdef TIFR0
  if ((TIFR0 & _BV(TOV0)) && (t < 255))
    m++;
#else
  if ((TIFR & _BV(TOV0)) && (t < 255))
    m++;
#endif

  SREG = oldSREG;

  return ((m << 8) + t) * (64 / clockCyclesPerMicrosecond());
}

void delay(unsigned long ms)
{
  uint16_t start = (uint16_t)micros();

  while (ms > 0) {
    if (((uint16_t)micros() - start) >= 1000) {
      ms--;
      start += 1000;
    }
  }
}

/* Delay for the given number of microseconds.  Assumes a 8 or 16 MHz clock. */
void delayMicroseconds(unsigned int us)
{
  // calling avrlib's delay_us() function with low values (e.g. 1 or
  // 2 microseconds) gives delays longer than desired.
  //delay_us(us);
#if F_CPU >= 20000000L
  // for the 20 MHz clock on rare Arduino boards

  // for a one-microsecond delay, simply wait 2 cycle and return. The overhead
  // of the function call yields a delay of exactly a one microsecond.
  __asm__ __volatile__ (
    "nop" "\n\t"
    "nop"); //just waiting 2 cycle
  if (--us == 0)
    return;

  // the following loop takes a 1/5 of a microsecond (4 cycles)
  // per iteration, so execute it five times for each microsecond of
  // delay requested.
  us = (us<<2) + us; // x5 us

  // account for the time taken in the preceeding commands.
  us -= 2;

#elif F_CPU >= 16000000L
  // for the 16 MHz clock on most Arduino boards

  // for a one-microsecond delay, simply return.  the overhead
  // of the function call yields a delay of approximately 1 1/8 us.
  if (--us == 0)
    return;

  // the following loop takes a quarter of a microsecond (4 cycles)
  // per iteration, so execute it four times for each microsecond of
  // delay requested.
  us <<= 2;

  // account for the time taken in the preceeding commands.
  us -= 2;
#else
  // for the 8 MHz internal clock on the ATmega168

  // for a one- or two-microsecond delay, simply return.  the overhead of
  // the function calls takes more than two microseconds.  can't just
  // subtract two, since us is unsigned; we'd overflow.
  if (--us == 0)
    return;
  if (--us == 0)
    return;

  // the following loop takes half of a microsecond (4 cycles)
  // per iteration, so execute it twice for each microsecond of
  // delay requested.
  us <<= 1;

  // partially compensate for the time taken by the preceeding commands.
  // we can't subtract any more than this or we'd overflow w/ small delays.
  us--;
#endif

  // busy wait
  __asm__ __volatile__ (
    "1: sbiw %0,1" "\n\t" // 2 cycles
    "brne 1b" : "=w" (us) : "0" (us) // 2 cycles
  );
}

void init()
{
  // on the ATmega168, timer 0 is also used for fast hardware pwm
  // (using phase-correct PWM would mean that timer 0 overflowed half as often
  // resulting in different millis() behavior on the ATmega8 and ATmega168)
#if defined(TCCR0A) && defined(WGM01)
  sbi(TCCR0A, WGM01);
  sbi(TCCR0A, WGM00);
#endif

  // set timer 0 prescale factor to 64
#if defined(__AVR_ATmega128__)
  // CPU specific: different values for the ATmega128
  sbi(TCCR0, CS02);
#elif defined(TCCR0) && defined(CS01) && defined(CS00)
  // this combination is for the standard atmega8
  sbi(TCCR0, CS01);
  sbi(TCCR0, CS00);
#elif defined(TCCR0B) && defined(CS01) && defined(CS00)
  // this combination is for the standard 168/328/1280/2560
  sbi(TCCR0B, CS01);
  sbi(TCCR0B, CS00);
#elif defined(TCCR0A) && defined(CS01) && defined(CS00)
  // this combination is for the __AVR_ATmega645__ series
  sbi(TCCR0A, CS01);
  sbi(TCCR0A, CS00);
#else
  #error Timer 0 prescale factor 64 not set correctly
#endif

  // enable timer 0 overflow interrupt
#if defined(TIMSK) && defined(TOIE0)
  sbi(TIMSK, TOIE0);
#elif defined(TIMSK0) && defined(TOIE0)
  sbi(TIMSK0, TOIE0);
#else
  #error	Timer 0 overflow interrupt not set correctly
#endif

}

} // extern "C"

void arduino_init(void)
{
  init();
}