AVR-Template/main.c

#include <avr/interrupt.h>
#include <avr/io.h>
#include <avr/sleep.h>
#include <avr/wdt.h>
#include <util/delay.h>

#define LED_PIN PB5  // Define the pin connected to the LED

// Flipping the led every 0.5s using the overflow interrupt
ISR(TIMER1_OVF_vect) {
    PORTB ^= _BV(LED_PIN);                             // Toggle the LED
    TCNT1 = (uint16_t)(65535 - (F_CPU / 1024) * 0.5);  // Reset the counter
    TIFR1 |= (1 << TOV1);  // Clear the interrupt flag
}

// 'Pulse' the LED
ISR(TIMER1_COMPA_vect) {
    // Static variable to keep track of the number of interrupts
    static uint16_t counter = 0;

    PORTB ^= _BV(LED_PIN);  // Toggle the LED

    // Modulo magic, see below for explanation
    if (++counter % 2 == 0) {
        OCR1A = 15624 / 2;
        counter = 0;
    } else {
        OCR1A = 15624 / 16;
    }

    // Clear the interrupt flag
    TIFR1 |= (1 << TOV1);
}

// External interrupt
ISR(INT0_vect) {
    PORTB ^= _BV(LED_PIN);  // Toggle the LED
    _delay_ms(200);         // Debounce
}

// We will use Timer1 for the interrupt
void configure_interrupt() {
    TCCR1A = 0;                           // Set the timer to normal mode
    TCCR1B = 0;                           // Set the timer to normal mode
    TCCR1B |= (1 << WGM12);               // Set the timer to CTC mode
    TCCR1B |= (1 << CS02) | (1 << CS00);  // Set the prescaler to 1024
    TIMSK1 |= (1 << OCIE1A);              // Enable overflow interrupt
    sei();      // Enable global interrupts (cli() to disable)
    OCR1A = 0;  // 31250 for a 2s delay, 15624 for a 1s delay
    TCNT1 = (uint16_t)(65535 - (F_CPU / 1024) * 0.5);  // Reset the counter
}

void configure_external_interrupt() {
    // Set the external interrupt to trigger on the falling edge
    EICRA |= (1 << ISC01);
    EICRA &= ~(1 << ISC00);

    // Enable the external interrupt
    EIMSK |= (1 << INT0);  // Pin D2 is INT0

    DDRD &= ~_BV(PD2);  // Set the pin as an input
    PORTD |= _BV(PD2);  // Enable the pull-up resistor

    // Enable global interrupts
    sei();
}

void configure_ovf_interrupt() {
    // Set the timer to normal mode
    TCCR1A = 0;
    TCCR1B = 0;

    // Initialize the counter to 0xFFFF
    TCNT1 = 0xFFFF;

    // Set the prescaler to 1024
    TCCR1B |= _BV(CS12) | _BV(CS10);

    // Enable overflow interrupt
    TIMSK1 |= (1 << TOIE1);

    // Enable global interrupts
    sei();
}

int main(void) {
    // Configure the LED pin as an output
    DDRB |= _BV(LED_PIN);

    // Choose one (or both)
    // configure_interrupt();
    // configure_ovf_interrupt();
    configure_external_interrupt();

    // Set the watchdog timer to 8 seconds
    // wdt_enable(WDTO_8S);
    // wdt_disable();
    // wdt_reset(); // Reset the watchdog timer

    // Set the sleep mode to idle
    set_sleep_mode(SLEEP_MODE_IDLE);

    // Pat the dog and sleep until the next interrupt
    while (1) {
        sleep_mode();  // Doesent sleep through interrupts
    }

    return 0;
}