#include <avr/io.h>
#include <avr/interrupt.h>
#include "timer_counter.h"

volatile uint16_t counter = 0;

void timer0_init(void)
{
    // Mode CTC: WGM01 = 1, WGM00 = 0
    TCCR0A = (1 << WGM01);

    // Prescaler 64: CS01 = 1, CS00 = 1 (CS02 = 0)
    // TCCR0B = (1 << CS01) | (1 << CS00);
    // Prescaler 8: CS01 = 1, (CS00 = 0, CS02 = 0)
    TCCR0B = (1 << CS01);

    // Setting OCR0A to 124 gives 1 ms with 8 MHz and prescaler of 64
    // OCR0A = 124;
    // Setting OCR0A to 99 gives 100 us with 8 MHz and prescaler of 8
    OCR0A = 99;

    // Enable Timer/Counter0 Output Compare Match A interrupt
    TIMSK0 = (1 << OCIE0A);
}

ISR(TIM0_COMPA_vect)
{
    counter++;
}

uint16_t ticks100us(void)
{
    uint16_t value1, value2;

    // Double-checked locking to ensure atomic read of counter
    do
    {
        value1 = counter;
        value2 = counter;
    } while (value1 != value2);

    return value1;
}