/* LED microcontroller dimmer for use with Soleil Sun Alarm
Written for Atmel ATMega8 and avr-gcc
Eric J. Wilhelm
Squid Labs, LLC

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*/

#include <inttypes.h>
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/signal.h>
#include <math.h>

#  define OC1 PB1
#  define DDROC DDRB
#  define OCR OCR1A

volatile uint16_t xtimer;
volatile uint16_t timer0;
volatile uint8_t status;

SIGNAL(SIG_OVERFLOW0)
{
  timer0++;
  TCNT0=96;          // preload the timer with 96 to make this interrupt occur every 20 us.
}

SIGNAL(SIG_OVERFLOW1)
{
  //The interrupts don't work properly without this definition.
}

// falling edge PWM signal (rising edge at clock; reversed due to optoisolator)
SIGNAL(SIG_INTERRUPT1) {
  // Zero timer0 to count the length of the positive pulse
  timer0=0;
  status=1;
}

//rising edge PWM signal (falling edge at clock; reversed due to optoisolator)
SIGNAL(SIG_INTERRUPT0) {
  //record the length of the positive pwm signal in xtimer
  // if timer0 is greater than approximately 263 (at 20 us per interrupt) than the pulse was missed
  if(timer0<270) xtimer=timer0;
  status=0;
}

void
ioinit (void)
{
    // Timer1 does ~16-bit PWM
    TCCR1A = _BV (COM1B1) | _BV (WGM11) | _BV (COM1A1);
    TCCR1B = _BV (WGM13) | _BV (WGM12) | _BV (CS10);

    ICR1 = 65535;

    //Timer0 counts
    TCCR0 =  _BV (CS00);
    TCNT0 = 96;
    timer0=0;

    // set PWM value to 0
    OCR = 0;

    //enable OC1 as output
    DDROC = _BV (OC1);

    //enable external interrupts
    GICR = _BV (INT1) | _BV (INT0);
    //INT0 is rising edge, INT1 is falling edge
    MCUCR = _BV (ISC01) | _BV (ISC00) | _BV(ISC11);

    xtimer=0;
    status=0;

    //enable timers
    timer_enable_int (_BV (TOIE1) | _BV (TOIE0) );

    // enable interrupts
    sei ();
}

int
main (void)
{
    #define B -0.00325
    #define C -11.09
    #define D 0.396503

    int i,on=0, oncounter=0;
    unsigned int x[100], y;
    long t[100], u;
    ioinit ();

    for (;;) {
      
      //average xtimer over samples because it jumps around alot
      for(i=99;i>0;i--) {
        x[i] = x[i-1];
      }
      x[0] = xtimer;
      y=0;
      for(i=0;i<100;i++) {
        y = y+x[i];
      }
      y=y/100;
      //divide by 5 because the clock has 120 us resolution on its PWM
      y=y/5;

      // average the output so it doesn't jump around
      for(i=99;i>0;i--) {
        t[i] = t[i-1];
      }

      //determine what to do
      if(timer0>270 && status == 1 && on == 1) {
        //Turn light on
        t[0] = 0;
        on=1;
        }
      else if(timer0>270 && status == 0) {
        //Turn light off
        t[0] = 65535;
        xtimer=0;
        on=0;
        oncounter=0;
        }
      else if(timer0<270){
        t[0] = 65535*(1-exp((B*y + D)*y + C));
        if(t[0]>65535) t[0] = 65535;
        if(t[0]<0) t[0] = 0;
      }
      //oncounter prevents the light from turning on suddenly from an off state if timer0>270, but there's a positive pulse on the PWM
      //this happens during the very start of a sunrise, when the clock's PWM hasn't quite turned on at the right frequency
      else if(timer0>270 && status == 1) {
        if(++oncounter==5) {
          on = 1;
          oncounter=0;
        }
      }

      // average the output so it doesn't jump around
      u=0;
      for(i=0;i<100;i++) {
        u=u+t[i];
      }

      //Change the output PWM
      OCR = u/100;

    }
    return (0);
}