/* Name: main.c
 * Author: Toshi Nagata
 * Copyright: Copyright 2009 (c) Toshi Nagata
 * License: Modified BSD License
 * Pin 2 (in): IR receiver
 * Pin 3 (out): LED
 * Pin 5 (out): PWM (not in use yet)
 */

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

#define NBITS 16
#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 */

volatile unsigned short t, start;
volatile unsigned short tempData, oldData, data;
volatile char tempCount;
volatile char ready;

ISR(TIM0_OVF_vect)
{
  t += 256;
  if (t - start >= T2) {
    /*  Long interval is detected  */
    /*  Start waiting for the first interrupt  */
    /*  (The incomplete data is discarded if present)  */
    tempCount = -1;
    oldData = 0;
    start = t = 0;
  } else if (t - start >= T1) {
    /*  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) == 0x08) {
        tempData >>= 5;
        if (tempData & (1 << 9))
          tempData = (~tempData) & 0x03ff;
	if (tempData == oldData) {
	  data = tempData;
	  ready = 1;  /*  Valid data  */
	  tempCount = NBITS + 1;  /*  Skip until the end of chunk  */
	}
	oldData = tempData;
      }
      start = t = 0;
    }
  }
}

/*  INT0 should be more convenient, but PCINT3 is used instead,
    to avoid changing pin wiring between programming and testing modes.  */
ISR(PCINT0_vect)
{
  if (PINB & 0b00001000) {  /*  pin 2 (bit 3) is low -> falling edge  */
    if (tempCount < 0) {
      /*  Start data collection  */
      tempData = 0;
      tempCount = 0;
    } else if (tempCount < NBITS) {
      /*  Read out one more bit  */
      if (t + (unsigned char)TCNT0 - start >= T0)
	tempData |= (1 << tempCount);
      tempCount++;
    }
    t = 0;
    start = (unsigned char)TCNT0;
  }
}

void
blinkLED(void)
{
  PORTB ^= 0b00010000;
  _delay_ms(50);
  _delay_ms(50);
  PORTB ^= 0b00010000;
  _delay_ms(50);
  _delay_ms(50);
}

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

  DDRB   = 0b00010001; /* pin 3 (bit 4) and pin 5 (bit 0) for output  */
  TCCR0A = 0b11000000  /* PWM: set OC0A on compare match and clear at TOP  */
         | 0b00000011; /* Fast PWM  */
  TCCR0B = 0b00000000  /* Fast PWM with TOP = MAX  */
         | 0b00000010; /* Clock prescale by 8 */
  OCR0A = 255;         /* PWM duty ratio */
  TIMSK0 = 0b00000010; /* Timer0 overflow interrupt enabled  */
  /*  MCUCR  = 0b00000010; *//* INT0 interrupt on falling  */
  GIMSK  = 0b00100000; /* PCINT enabled */
  PCMSK  = 0b00001000; /* PCINT3 (pin 2) enabled  */

  tempCount = -1;
  t = start = 0;

  sei();  /*  Enable interrupt globally  */

  for (n = 0; n < 5; n++)
    blinkLED();

  for (;;) {
    if (ready) {
      /*  Data is available  */
      blinkLED();
      switch (data) {
      case 0b1000010:  /*  button 1  */
        OCR0A = 255;
	n = 1;
        break;
      case 0b1000011: /* button 2 */
	OCR0A = 80;
	n = 2;
	break;
      case 0b1000100: /* button 3 */
	OCR0A = 1;
	n = 3;
	break;
      case 0b1000101: /* button 4 */
	OCR0A = 80;
	n = 4;
	break;
      default:
	n = 0;
	break;
      }
      ready = 0;  /*  This data is processed  */
      while (n >= 0) {
	blinkLED();
	n--;
      }
    }
  }
  return 0;  /*  Never reached  */
}