问使用atmega16和外部中断的七段项目

EN

    while(1){
        // at this point flag is 0, comparison failed
        if(flag==0) {
          ...
        }
// Interrupt happens here, changing flag to 0
// Then flag is immediately reset, thus flag change is missed in the loop
        flag=1; 
    }

    while (1) {
         cli(); // disabling interrupts ensuring no interrupt happens inside 
         if (flag==0) {
           ...
         }
         flag = 1;
         sei(); // re-enable interrupts
    }

    while (1) {
         if (flag==0) {
             flag = 1; // Reset flag only if it set, right after comparison
             ...
         }
    }

#include<avr/io.h>
#include<avr/interrupt.h>
char flag=1;
char num=0;

void INT2_Init(void){
    DDRB&=~(1<<2);
    SREG|=(1<<7);
    GICR|=(1<<INT2);
    MCUCSR|=(1<<ISC2);
}

// sets flag to 0 on external interrupt (button press)
ISR(INT2_vect){
    flag=0;
    GIFR|=(1<<INTF2);
}

int main(void){
    DDRC=0x0f;
    PORTC=0;
    DDRB&=~(1<<2);
    INT2_Init();

    while(1){
        // if flag was set to 0 in external interrupt -> increment (or overflow) number on segment display
        if(flag==0){
            if(num>8){
                num=0;
                PORTC=(PORTC&0xf0)|num;
            }
            else{
                num++;
                PORTC=(PORTC&0xf0)|num;
            }
        }
        // reset the flag to 1 to prevent num from being incremented continuously
        flag=1;
    }
}

    while(1) {
        // if flag was set to 0 in external interrupt -> increment (or overflow) number on segment display
        if(flag==0){
          // reset the flag to 1 to prevent num from being incremented continuously
          flag=1;

            if(num>8){
                num=0;
                PORTC=(PORTC&0xf0)|num;
            }
            else{
                num++;
                PORTC=(PORTC&0xf0)|num;
            }
        }
    }