编程点滴：8位AVR定时器溢出中断测试程序

/* *****************************************
 * File name: timer_8bit_test1.c
 * Function:  8位定时器溢出中断方式测试程序
 * Description: 定时器控制LED以500ms间隔闪烁
 * Author & Date: Joshua Chan, 2012/03/24
 * *****************************************/
#include 
#include 
#include 
#include 
#include 
#include "timer_8bit_test1.h"

/* 配置8位定时器timer0溢出中断使能 */
void timer0_ovf_init(void)
{
    TCCR0 |= 0x07;              /* 预分频 1024 */
    TIMSK |= 0x01;              /* 溢出中断使能 */
    TCNT0 = 0x64; /* 中断发生间隔 ((0xFF-0x64)+1)*1024*(1/16.0MHz)*1000 = 10ms */
}

/* 配置LED管脚为输出 */
void set_pb0_output(void)
{
    DDRB |= 0x01;
}

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

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

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

/* 定义timer0溢出中断处理函数 */
#pragma vector = TIMER0_OVF_vect
__interrupt void timer0_isr(void)
{
    static volatile unsigned char count = 50;

    TCNT0 = 0x64;  /* 溢出中断处理函数中需对TCNT0值从新设置 */
    if (!(--count)) {
        count = 50;
        if (pb0_is_high())
            set_pb0_low();
        else
            set_pb0_high();
    }
}