/* Name: main.c
 * Author: Toshi Nagata
 * Copyright: 2009-2018 (c) Toshi Nagata
 * License: Modified BSD License
 *
 * Clock: Internal 1.2MHz
 * Pin 5 (PB0): motor polarity (old: Pin 3)
 * Pin 6 (PB1): motor PWM control (old: Pin 5)
 * Pin 2, 3 (PB3, 4): IR receiver (old: Pin 6 and 7)
 * Pin 7 (PB2): LED
 */

#include <avr/io.h>
#include <avr/interrupt.h>
#include <util/delay.h>

#define NBITS 15
#define CL  6.67  /*  Timer clock in microseconds  */
#define T0  ((short)(1500 / CL))    /*  threshold for bit 0/1  */
#define T1  ((short)(20000 / CL))   /*  interval within one chunk  */
#define T2  ((short)(50000 / CL))   /*  interval between 2 separate chunks */
#define T3  ((short)(200000 / CL))  /*  minimum interval between 2 pushes  */

volatile unsigned short t, start;
volatile unsigned short tempData, oldData, data, lastData;
volatile char tempCount;
volatile char ready;
volatile unsigned char last_pin = 1;
char current;

/*  Masks for pin-change interrupt  */
#define MASK1 0b00001000
#define MASK2 0b00010000

#if 0
/*  For debug  */
void show_data(unsigned short data)
{
  char i;
  cli();
  for (i = 0; i < 16; i++) {
    if (data & 1) {
      PORTB |= 1;
    } else {
      PORTB |= 0b00000100;
    }
    _delay_ms(800);
    PORTB &= 0b11111010;
    _delay_ms(200);
    data >>= 1;
  }
  sei();
}
#endif

ISR(TIM0_OVF_vect)
{
  if (tempCount < 0)
    return;
  t++;
  if (t >= T2 / 256) {
    /*  Long interval is detected  */
    /*  Start waiting for the first interrupt  */
    /*  (The incomplete data is discarded if present)  */
    if (t >= T3 / 256) {
      /*  The button is released  */
      lastData = 0;
    }
    tempCount = -1;
    oldData = 0;
    start = t = 0;
  } else if (t >= T1 / 256) {
    /*  Short interval is detected  */
    if (tempCount >= 0 && tempCount < NBITS + 1) {
      /*  Not waiting for end of chunk  */
      tempCount = -1;  /*  Start waiting for new data (may be overridden later; see below)  */
      /*  Check the validity of the data  */
      /*  (Specific for old DENON remote controller)  */
      if ((tempData & 0x1f) == 0x10) {
        if (tempData & 0x4000)
          tempData ^= 0x7fe0;
        if (tempData == oldData) {
          data = tempData;
          ready = 1;  /*  Valid data  */
          tempCount = NBITS + 1;  /*  Skip until the end of chunk  */
        }
        oldData = tempData;
      }
      start = t = 0;
    }
  }
}

ISR(PCINT0_vect)
{
  unsigned char pin;
  if ((PINB & (MASK1 | MASK2)) == (MASK1 | MASK2)) {
    pin = 1;
  } else pin = 0;
  if (last_pin && pin == 0) {
    /*  Falling edge  */
    if (tempCount < 0) {
      /*  Start data collection  */
      tempData = 0;
      tempCount = 0;
    } else if (tempCount < NBITS) {
      /*  Read out one more bit  */
      unsigned short dt = t * 256 + (unsigned char)TCNT0 - start;
      if (dt >= T0)
        tempData |= (1 << tempCount);
      tempCount++;
    }
    t = 0;
    start = (unsigned char)TCNT0;
  }
  last_pin = pin;
}

void
setCurrent(void)
{
  if (current < 0) {
    if ((PORTB & 0b00000001) == 0) {
      PORTB |= 0b00000001;
      _delay_ms(50);
    }
    OCR0B = 255 + current * 2;
  } else {
    if ((PORTB & 0b00000001) != 0) {
      PORTB &= 0b11111110;
      _delay_ms(50);
    }
    OCR0B = 255 - current * 2;
  }
}

int main(void)
{
  cli();  /*  Disable interrupt globally  */

  DDRB   = 0b00000111; /* PB0/1/2 (pins 5/6/7) for output  */
  TCCR0A = 0b00110000  /* PWM: set OC0B on compare match and clear at TOP  */
         | 0b00000011; /* Fast PWM  */
  TCCR0B = 0b00000000  /* Fast PWM with TOP = MAX  */
         | 0b00000010; /* Clock prescale by 8 */
  current = 0;
  OCR0B = 255;         /* PWM duty ratio */
  TIMSK0 = 0b00000010; /* Timer0 overflow interrupt enabled  */
  GIMSK  = 0b00100000; /* PCINT enabled */
  PCMSK  = (MASK1 | MASK2); /* PCINT3/4 (pins 2/3) enabled  */

  tempCount = -1;
  t = start = 0;
  lastData = 0;

  sei();  /*  Enable interrupt globally  */

  for (;;) {
    char c1;
    if (!ready)
      continue;
    ready = 0;
    if (data == lastData)
      continue;
    /*  Data is available  */
    switch (data >> 5) {
    case 0b1000010:  /*  button 1 = forward  */
      c1 = 80;
      break;
    case 0b1000011: /* button 2 = backward */
      c1 = -80;
      break;
    case 0b1000100: /* button 3 = stop */
      c1 = 0;
      break;
    default:
      c1 = -127;    /* No valid button */
      break;
    }
    lastData = data;
    ready = 0;  /*  This data is processed  */
    if (c1 != -127) {
      PORTB |= 0b00000100;
      if (c1 != current) {
        do {
          if (c1 < current)
            current--;
          else
            current++;
          setCurrent();
          _delay_ms(10);
        } while (c1 != current);
      }
    } else {
      PORTB &= 0b11111011;
    }
  }
  return 0;  /*  Never reached  */
}