T0定时器溢出标志问题？

只看该作者 · 2010-1-6 11:55

刚学AVR，关于T0定时器做延时用，注意红色标记的地方。
//ICC-AVR application builder : 2010-1-4 10:37:07
// Target : M16
// Crystal: 8.0000Mhz
#include <iom16v.h>
#include <macros.h>
void port_init(void)
{
PORTA = 0x00;
DDRA  = 0x01;
PORTB = 0x00;
DDRB  = 0x00;
PORTC = 0x00; //m103 output only
DDRC  = 0x00;
PORTD = 0x00;
DDRD  = 0x00;
}
//TIMER0 initialize - prescale:64
// WGM: Normal
// desired value: 1mSec
// actual value:  1.000mSec (0.0%)
void Delay_ms(void)
{
TCCR0 = 0x00; //stop
TCNT0 = 0x83; //set count
OCR0  = 0x7D;  //set compare
TCCR0 = 0x03; //start timer
while ((TIFR & 0x01) == 0); // 为什么TIFR的D0位不会溢出？？？？
  TIFR &= ~ (1<<TOV0);
  TCCR0 = 0x00; //stop
}
void Delay_Xms(unsigned int i)
{
unsigned int x;
  for (x=0; x<i; x++)
  {
   Delay_ms();
  }
}
//call this routine to initialize all peripherals
void init_devices(void)
{
//stop errant interrupts until set up
CLI(); //disable all interrupts
port_init();
MCUCR = 0x00;
GICR  = 0x00;
TIMSK = 0x00; //timer interrupt sources
SEI(); //re-enable interrupts
//all peripherals are now initialized
}
//
void main(void)
{
init_devices();
  while (1)
  {
   PORTA &= ~(1<<0);
   Delay_Xms(1000);
   PORTA |= (1<<0);
  }
}