/*
 * Use the timer to produce a sound in a speaker.
 *
 * Formular for the frequency:
 * (F_CPU/wanted_frequency*2*Prescaler)+1
 *
 * Cut off the decimal part and see which is
 * closer to the wanted frequency.
 *
 * Task: Sum at start with 440 Hz, when a button is pushed, sum at 264 Hz. The
 * other button reverses.
 */
#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#include <avr/interrupt.h>
#include <avr/io.h>
#include <util/delay.h>

#define SOUND_A 17
#define SOUND_C 30

#define MINUTE 60 * 1000
const int TIME = 45 * MINUTE;

int state = 0;

// Timer0 interrupt
ISR(TIMER0_COMPA_vect) {
  PORTB ^= (1 << PORTB5); // toggle the speaker
}

// code for INT0
ISR(INT0_vect) {
  OCR0A = SOUND_A;              // max value for timer
}

// code for INT1
ISR(INT1_vect) {
  OCR0A = SOUND_C;              // max value for timer
}

int main(void) {

  DDRB = 0xff; // write to B
  DDRD = 0;    // read from D

  PORTD |= (1 << PORTD2) | (1 << PORTD3); // pull up D2 and D3
  PORTB = 0;  // pull down PORT B

  // 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: Overflow, Interrupt
  // Prescaler: /1024
  // max: dynamic depending on pushed button
  TCCR0A |= (1 << WGM01);  // CTC Mode
  OCR0A = SOUND_C;         // max value for timer
  TIMSK0 |= (1 << OCIE0A); // enable interrupt ISR_COMPA_vect

  sei(); // magic interrupt macro

  TCCR0B |= (1 << CS02) | (1 << CS00); // enable with prescaler 1024
  while (1) {
    // do nothing
  }
}