/*
 * Use the timers pwm to dim a light on demand.
 */
#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>

#define PWM_LOW 24
#define PWM_HIGH 192

int state = 0;

// code for INT0
ISR(INT0_vect) {
  OCR0A = PWM_HIGH;              // max value for timer
  PORTB |= (1<<PORTB5);
}

// code for INT1
ISR(INT1_vect) {
  OCR0A = PWM_LOW;              // max value for timer
  PORTB &= ~(1<<PORTB5);
}

int main(void) {

  // read from D2 and D3, write to D6
  DDRD |= (1 << PORTD6);
  DDRB = 0xff; // used for internal led only

  PORTD |= (1 << PORTD2) | (1 << PORTD3); // pull up D2 and D3

  // enable external interruprs
  EIMSK |= (1 << INT0);
  EIMSK |= (1 << INT1);

  // trigger when anything changes
  EICRA |= (1 << ISC00); // for INT0
  EICRA |= (1 << ISC10); // for INT1

  // Timer 0
  // Mode: Fast PWM
  // Prescaler: /8
  // max: dynamic depending on pushed button
  TCCR0A |= (1 << WGM01) | (1 << WGM00);  // Fast PWM Mode
  OCR0A = PWM_HIGH;   // max value for timer
  TCCR0A |= (1 << COM0A1); // set non inverting mode, start initialized

  TCCR0B |= (1 << CS01); // enable with prescaler 8

  sei(); // magic interrupt macro
  while (1) {
    // do nothing
  }
}