在avrstudio4.09里面进行调试：





这个是溢出中断程序





void timer0_ovf_isr(void)      经仔细检查，进入此行时cycle=2089

{  

TCNT0 = 236;                  此时cycle=2140

a++;                          此时cycle=2142

if(a<4)

PORTA=a;

else

{delay(2);

PORTA=a;

a=0;}

}



51个时钟周期啊，cpu干什么去了？？这样搞得时间很不准啊!!如果用来编写显示时间的程序，要出大问题了！要不就把那段时间也算进去，那位高手能说一下吗？？





整个程序在这里

// Target : M16

// Crystal: 8.0000Mhz



#include <iom16v.h>

#include <macros.h>



void port_init(void);

void timer0_init(void);

void timer0_ovf_isr(void);

void init_devices(void);

void delay (unsigned int dt);

unsigned char a;





void port_init(void)

{

PORTA = 0x00;

DDRA  = 0x03;

PORTB = 0x00;

DDRB  = 0x00;

PORTC = 0x00; //m103 output only

DDRC  = 0x00;

PORTD = 0x00;

DDRD  = 0x00;

}



//TIMER0 initialize - prescale:8

// WGM: Normal

// desired value: 1Hz

// actual value: Out of range

void timer0_init(void)

{

TCCR0 = 0x00; //stop

TCNT0 = 251; /*INVALID SETTING*/; //set count

OCR0  = 0x00 /*INVALID SETTING*/;  //set compare

TCCR0 = 0x02; //start timer

}



#pragma interrupt_handler timer0_ovf_isr:10

void timer0_ovf_isr(void)

{

TCNT0 = 236; /*INVALID SETTING*/; //reload counter value



a++;

if(a<4)

PORTA=a;

else

{delay(2);

PORTA=a;

a=0;}

}



//call this routine to initialize all peripherals

void init_devices(void)

{

//stop errant interrupts until set up

CLI(); //disable all interrupts

port_init();

timer0_init();



MCUCR = 0x00;

GICR  = 0x00;

TIMSK = 0x01; //timer interrupt sources

SEI(); //re-enable interrupts

//all peripherals are now initialized

}

//精确延时程序（us）  延时(dt+2)/2 us

#pragma ctask delay

void delay (unsigned int dt)

         {

         while(dt)

                 dt--;

        asm("nop");

        }





void main(void)

{

init_devices();

timer0_init();

while(1)

  {asm("nop");

    }

}