sysprog-basic/beep/main.c

/*
 * Control PB5 with the two buttons. One button disables, the other enables.
 * The board uses interrupts for this. PB5 will quickly oscilate between on and
 * off to make cool sounds with a summer.
 */
#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#include <util/delay.h>
#include <avr/interrupt.h>
#include <avr/io.h>

int beep = 0;
int sound = 0;

// code for INT0
ISR(INT0_vect) { beep = 1; }

// code for INT1
ISR(INT1_vect) { beep = 0; PORTB &= ~(1 << PORTB5); sound = 0;}

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;

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

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

  sei(); // interrupt magic macro
  while (1) {
    if (beep) {
      PORTB |= (1 << PORTB5);
      _delay_us(sound);
      PORTB &= ~(1 << PORTB5);
      _delay_us(sound);
      sound++;
      if (sound > 1000) {
        sound = 0;
      }
    }
  }
}