/* Name: main.c
 * Author: Toshi Nagata
 * Copyright: 2009-2018 (c) Toshi Nagata
 * License: Modified BSD License
 *
 * Clock: Internal 1.2MHz
 * Pin 7 (PB2): motor polarity (old: Pin 3)
 * Pin 5/6 (PB0/1): motor1/2 PWM control
 * Pin 3/7 (PB4/2): motor1/2 Phase control
 * Pin 2 (PB3): IR receiver (old: Pin 6 and 7)
 */

#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;
signed char current1, current2;

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

#if 0
/*  For debug  */
void show_data(unsigned short data)
{
  char i;
  cli();
  for (i = 0; i < 16; i++) {
    if (data & 1) {
      PORTB |= 0b00000100;
    } else {
      PORTB |= 0b00010000;
    }
    _delay_ms(800);
    PORTB &= 0b11101011;
    _delay_ms(200);
    data >>= 1;
  }
  sei();
}
#endif

ISR(TIM0_OVF_vect)
{
  if (tempCount < 0)
    return;  /*  Wait until the first trigger is detected  */
  t++;
  if (t >= T2 / 256) {
    /*  No input for certain period (longer than GAP) */
    data = 0;  /*  Indicate the button is released  */
    ready = 1;
    tempCount = -1;  /*  Start over  */
    oldData = 0;
  } else if (t >= T1 / 256) {
    /*  Short interval is detected  */
    tempCount = NBITS;  /*  Start over (the key may be still pressed)  */
  }
}

ISR(PCINT0_vect)
{
  unsigned char pin;
  pin = PINB & MASK1;
  if (last_pin && pin == 0) {
    /*  Falling edge  */
    if (tempCount < 0 || tempCount >= NBITS) {
      /*  Start data collection  */
      tempData = 0;
      tempCount = 0;
    } else {
      /*  Read out one more bit  */
      unsigned short dt = t * 256 + (unsigned char)TCNT0 - start;
      if (dt >= T0)
        tempData |= (1 << tempCount);
      tempCount++;
      /*  Are all bits received?  */
      if (tempCount == NBITS) {
        if ((tempData & 0x1f) == 0x10) {
          if (tempData & 0x4000)
            tempData ^= 0x7fe0;
          if (tempData == oldData) {
            data = tempData;
            ready = 1;  /*  Valid data  */
          } else oldData = tempData;
        }
        tempCount = NBITS;  /* One data complete; acquisition will continue after the GAP */
      }
    }
    t = 0;
    start = (unsigned char)TCNT0;
  }
  last_pin = pin;
}

void
setCurrent(void)
{
  unsigned char c;
  if (current1 < 0) {
    PORTB |= 0b00010000;
    c = 255 + current1 + current1;
  } else {
    PORTB &= 0b11101111;
    c = 255 - current1 - current1;
  }
  OCR0A = c;
  if (current2 < 0) {
    PORTB |= 0b00000100;
    c = 255 + current2 + current2;
  } else {
    PORTB &= 0b11111011;
    c = 255 - current2 - current2;
  }
  OCR0B = c;
}

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

  DDRB   = 0b00010111; /* PB0/1/2/4 (pins 5/6/7/3) for output  */
  TCCR0A = 0b11110000  /* PWM: set OC0A/OC0B on compare match and clear at TOP  */
         | 0b00000011; /* Fast PWM  */
  TCCR0B = 0b00000000  /* Fast PWM with TOP = MAX  */
         | 0b00000010; /* Clock prescale by 8 */
  current1 = current2 = 0;
  OCR0B = 255;         /* PWM duty ratio */
  OCR0A = 255;
  TIMSK0 = 0b00000010; /* Timer0 overflow interrupt enabled  */
  GIMSK  = 0b00100000; /* PCINT enabled */
  PCMSK  = MASK1;      /* PCINT3 (pin 2) enabled  */

  tempCount = -1;
  t = start = 0;
  lastData = 0;
  last_pin = MASK1;

  sei();  /*  Enable interrupt globally  */

  for (;;) {
    unsigned short d;
    signed char m1, c1, c2, dc1, dc2;
    if (!ready)
      continue;
    if (data == 0 && current1 == 0 && current2 == 0)
      continue;
    ready = 0;
    /*  Data is available  */
    d = data >> 5;
    if (d & 1) {
      /*  Forward  */
      if (d & 8) {
        /*  Forward + Backward = no move  */
        m1 = 0;
      } else m1 = 1;
    } else if (d & 8) {
      m1 = -1;
    } else m1 = 0;
    switch (d & 0b0110) {
      case 0b0010: /* left  */
        c1 = m1 * 64;
        c2 = m1 * 120;
        break;
      case 0b0100: /*  right  */
        c1 = m1 * 120;
        c2 = m1 * 64;
        break;
      default:     /*  straight  */
        c1 = c2 = m1 * 120;
        break;
    }

    if (c1 > current1)
      dc1 = 8;
    else if (c1 < current1)
      dc1 = -8;
    else dc1 = 0;
    if (c2 > current2)
      dc2 = 8;
    else if (c2 < current2)
      dc2 = -8;
    else dc2 = 0;
    while (c1 != current1 || c2 != current2) {
      if (c1 != current1)
        current1 += dc1;
      if (c2 != current2)
        current2 += dc2;
      setCurrent();
      _delay_ms(10);
    }
  }
  return 0;  /*  Never reached  */
}