timer.c

来自「ATmega8实现USB接口（采用USB的CDC类」· C语言 代码 · 共 54 行

#include "hardware.h"
#include <avr/io.h>
#include <avr/interrupt.h>
#include <avr/wdt.h>
#include <util/delay.h>
#include "timer.h"

volatile uchar  timerTimeoutCnt;
volatile uchar  timerLongTimeoutCnt;

/* ------------------------------------------------------------------------- */

void timerMsDelay(uchar ms)
{
    timerSetupTimeout(ms);
    while(!timerTimeoutOccurred());
}

/* ------------------------------------------------------------------------- */

/* main configures Timer 0 with 1/64 prescaler
 * -> 12MHz/64 = 187.5kHz --> 5.333us
 * overflow every 256 counts = 732.422Hz --> 1.365ms
 */
UTIL_INTERRUPT(SIG_OVERFLOW0)   /* run with global interrupt enable */
{
static uchar    prescaler = 1;

    cli();
    if(timerTimeoutCnt != 0)
        timerTimeoutCnt--;
    sei();  /* allow interrupts here */
    cli();
    if(--prescaler == 0){   /* scale down to 10 Hz */
        prescaler = 73;
        if(timerLongTimeoutCnt != 0)
            timerLongTimeoutCnt--;
    }
    sei();
}

/* ------------------------------------------------------------------------- */

void    timerSetupTimeout(uchar msDuration)
{
    msDuration -= msDuration >> 2;  /* approximate milliseconds with our timebase */
    /* 1 - 1/4 = 0.75; 1.365 ms * 0.75 = 1.024 ms --> 2.4% deviation */
    timerTimeoutCnt = msDuration;
}

/* ------------------------------------------------------------------------- */