sysprog-basic/buttons/main.c

/*
 * Control PB5 with the two buttons. One button disables, the other enables.
 * The board uses interrupts for this.
 */
#define F_CPU 16000000UL
#define __AVR_ATmega328P__
#include <avr/interrupt.h>
#include <avr/io.h>

// code for INT0
ISR(INT0_vect) { PORTB |= (1 << PORTB5); }

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

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) {
    // do nothing
  }
}