thanks for reading in advance. Please have a look at the code below and note that TCCR0's interrupt is being triggered every now and then, which means what's inside ISR(TIMER0_OVF_vect) is run. However, I have set up TCCR2 the same way, but ISR(TIMER2_OVF_vect) will not be called. Also, what's inside ISRs are just temporary codes for testing purposes.

void init_timer0(void)
{
    TCCR0 = 0x07;// 32 prescaler 
    // 0000 0111b
    // clkI/O/1024 (From prescaler)
    TCNT0 = 10;

    TCCR2 = 0x07;
    //TCCR2 = 0x0E;
    TCNT2 = 20;
    
    TIMSK |= 0x01;
    TIMSK |= 0x40;
}



volatile int i = 0;

ISR(TIMER2_OVF_vect)
{
    TCNT2 = 20;
    
    i = 1;
    i = 2;
    
}


ISR(TIMER0_OVF_vect)
{
    TCNT0 = 10;
}

CodePudding user response：

Table 68 of the data sheet says for TCCR2 (excerpt):

You tell the AVR to use an external clock (TCCR2 = 0x07;) but you want to use the system clock.

Use TCCR2 = 0x05; instead.