ISR for Timer Compare Match not running

Question

so basically I'm trying set up a ISR(Interrupt subroutine) to simply turn a light on, but the ISR doesn't seem to run. I've looked through the microcontroller datasheet a lot to see if I'm doing something wrong but I couldn't find anything.

Heres my code.

#include <asf.h>

int main (void) {
    DDRD = 0b10000000;

    cli();                              // turn off global interrupts
    //Timer
    TCCR2A |=_BV(WGM21);                //CTC mode
    TCCR2B |=_BV(CS22)|_BV(CS21);       //clk pre-scale 1/256
    OCR2A = 0x7d;                       //125clk cycles = 2ms
    TIMSK2 |=_BV(OCIE2A);               //enable interrupt on compare matchA
    TIFR2 |= _BV(OCF2A);                //clear flag
    TCNT2 = 0x00;                       // reset counter
    sei();                              // enable global interrupts
}

ISR(TIMER2_COMPA_vect) {
    PORTD = 0b10000000;
}

Answer 1

你应该在main（）函数的末尾有一个无限循环：

#include <asf.h>

int main (void) {
    DDRD = 0b10000000;

    cli();                              // turn off global interrupts
    //Timer
    TCCR2A |=_BV(WGM21);                //CTC mode
    TCCR2B |=_BV(CS22)|_BV(CS21);       //clk pre-scale 1/256
    OCR2A = 0x7d;                       //125clk cycles = 2ms
    TIMSK2 |=_BV(OCIE2A);               //enable interrupt on compare matchA
    TIFR2 |= _BV(OCF2A);                //clear flag
    TCNT2 = 0x00;                       // reset counter
    sei();                              // enable global interrupts
    while(1);
}

ISR(TIMER2_COMPA_vect) {
    PORTD = 0b10000000;
}

如果没有无限循环，AVR会达到未定义的状态！