AVR external interrupt0

// External Interrupt 0 service routine
interrupt [EXT_INT0] void ext_int0_isr(void)
    {
    // Place your code here
    delay_ms(1000);
    PORTB.0=0;
    delay_ms(1000);
    PORTB.0=1;
    }


#define ADC_VREF_TYPE 0x40

// Read the AD conversion result
unsigned int read_adc(unsigned char adc_input)
    {
    ADMUX=adc_input | (ADC_VREF_TYPE & 0xff);
    // Delay needed for the stabilization of the ADC input voltage
    delay_us(10);
    // Start the AD conversion
    ADCSRA|=0x40;
    // Wait for the AD conversion to complete
    while ((ADCSRA & 0x10)==0);
    ADCSRA|=0x10;
    return ADCW;
    }


// Declare your global variables here
void main(void)
    {
    // Declare your local variables here

    PORTB=0x07;
    DDRB=0xFF;

    // External Interrupt(s) initialization
    GICR|=0x40;
    MCUCR=0x02;
    MCUCSR=0x00;
    GIFR=0x40;
          
    // Global enable interrupts
    #asm("sei")

    while (1)
        {

        }

    }

unsigned char counter=0;

	while(1)
	{	if (counnt_enable==1)
		{
			delay_ms(1000);
			counter++;

			if (counter==1) --blink led1-- ;
			if (counter==2) --blink led2-- ;
			if (counter==3) 
			{
				--blink led3-- ;
				counter=0;  // clear counter
			}
		}
	}

volatile counnt_enable=0;