[SOLVED] Interrupt problem using ATmega32A

[sgreen]

I used ATmega32A to scan a keypad every 30ms. I want to create interrupt in Clear Timer on Compare Match (CTC) Mode. But interrupt is not working. What is the problem in my code? Code is included here.

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#include <avr/io.h>
//#include <util/delay.h>
#include <avr/interrupt.h>
// Port Mapping
#define KEYPAD_UPPER_PORT_DIR       DDRA
#define KEYPAD_UPPER_PORT_DATA  PORTA
#define KEYPAD_UPPER_PORT_IN        PINA
#define KEYPAD_LOWER_PORT_DIR       DDRB
#define KEYPAD_LOWER_PORT_DATA  PORTB
#define KEYPAD_LOWER_PORT_IN        PINB
#define TASK_PERIOD_DEBOUNCE_MS     30  
volatile uint32_t task_time_debounce = TASK_PERIOD_DEBOUNCE_MS;
unsigned char key;
void timer0_init(void);
 
 
int main(void)
{
    timer0_init();                          
    
    while(1)
    {
        if(task_time_debounce==0)
        {
        
    KEYPAD_UPPER_PORT_DIR &= 0x0f;
    KEYPAD_UPPER_PORT_DATA |= 0xf0;
    KEYPAD_LOWER_PORT_DIR |= 0x0f;
    KEYPAD_LOWER_PORT_DATA &= 0xf0;
    //_delay_us(5);
    key = (KEYPAD_UPPER_PORT_IN & 0xf0);
 
    // Get lower nibble
    KEYPAD_LOWER_PORT_DIR &= 0xf0;
    KEYPAD_LOWER_PORT_DATA |= 0x0f;
    KEYPAD_UPPER_PORT_DIR |= 0xf0;
    KEYPAD_UPPER_PORT_DATA &= 0x0f;
    //_delay_us(5);
    key = key | (KEYPAD_LOWER_PORT_IN & 0x0f);
      task_time_debounce=TASK_PERIOD_DEBOUNCE_MS;
        }     
    }     
}
void timer0_init(void){
 
   TIMSK |= (1<<OCIE0);
   TCCR0 = (1<<WGM01);              //Timer in CTC mode
   TCCR0 = ((1<<CS01)|(1<<CS00));   //1:64 prescaler
   OCR0=249;                        //Value to have an compare at every 1ms
                //Enable timer interrupts
   sei();                           //Enable global interrupts
}
ISR (TIMER0_COMP0_Vect) {
    // update system time
    //systime++;
 
    // decrement debouncing task time
    if (task_time_debounce > 0) {
        task_time_debounce--;
    }
}

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