Programming Tips: 8-bit AVR timer overflow interrupt test program

/* *****************************************
 * File name: timer_8bit_test1.c
 * Function: 8-bit timer overflow interrupt mode test program
 * Description: The timer controls the LED to flash at 500ms intervals
 * Author & Date: Joshua Chan, 2012/03/24
 * *****************************************/
#include 
#include 
#include 
#include 
#include 
#include "timer_8bit_test1.h"

/* Configure 8-bit timer timer0 overflow interrupt enable */
void timer0_ovf_init(void)
{
    TCCR0 |= 0x07; /* Prescaler 1024 */
    TIMSK |= 0x01; /* Overflow interrupt enable*/
    TCNT0 = 0x64; /* Interrupt interval ((0xFF-0x64)+1)*1024*(1/16.0MHz)*1000 = 10ms */
}

/* Configure LED pin as output */
void set_pb0_output(void)
{
    DDRB |= 0x01;
}

/* LED turns on */
void set_pb0_low(void)
{
    PORTB &= ~(0x01);
}

/* LED off*/
void set_pb0_high(void)
{
    PORTB |= 0x01;
}

/* Check LED status */
unsigned char pb0_is_high(void)
{
    return (PORTB & 0x01);
}

/* Define timer0 overflow interrupt processing function*/
#pragma vector = TIMER0_OVF_vect
__interrupt void timer0_isr(void)
{
    static volatile unsigned char count = 50;

    TCNT0 = 0x64; /* The TCNT0 value needs to be reset in the overflow interrupt processing function*/
    if (!(--count)) {
        count = 50;
        if (pb0_is_high())
            set_pb0_low();
        else
            set_pb0_high();
    }
}