TIMER2 ISR not working

Projects Programming
1

I cant have an ISR working on timer 2

int val=0;
ISR(TIMER2_OVF_vect)
{
    digitalWrite(13, val);
    val=1-val;
}

void setup()
{
    pinMode(13,OUTPUT);
    // initialize Timer1
    cli();             // disable global interrupts
    TCCR2A = 0;     // set entire TCCR1A register to 0
    TCCR2B = 0;     // same for TCCR1B
    
    // Set CS10 and CS12 bits for 1024 prescaler:
    //so we divide our clock source by 1024. This gives us a timer resolution of 1/(16*10^6 / 1024), or 6.4e-5 seconds.
    TCCR2B |= (1 << CS20);
    TCCR2B |= (1 << CS22);

    // (target time) = (timer resolution) * (# timer counts + 1)
    // set compare match register to desired timer count:
    OCR2A = 31; // -> 500 times per sec

    // turn on CTC mode: Clear Timer on Compare Match. Instead of counting until an overflow occurs, the timer compares its count to a value that was previously stored in a register.
    TCCR2A |= (1 << WGM21);

    // enable Timer2 overflow interrupt: Setting the TOIE1 bit tells the timer to trigger an interrupt when the timer overflows
    //TIMSK2 = (1 << TOIE1);
    // enable timer compare interrupt:
    TIMSK2 |= (1 << OCIE2A);
   
    //  actual 8 bits counter
    TCNT2 =0;
    // enable global interrupts:
    sei();

any help would be appreciated

thanks

2 
    // enable Timer2 overflow interrupt: Setting the TOIE1 bit tells the timer to trigger an interrupt when the timer overflows
    //TIMSK2 = (1 << TOIE1);
    // enable timer compare interrupt:
    TIMSK2 |= (1 << OCIE2A);

Your enabling the compare interrupt and not the overflow interrupt.
TOIE1 should also be TOIE2 in the commented out section.

I use the below and it works okay.

// defines for setting and clearing register bits
#ifndef cbi
  #define cbi(sfr, bit) (_SFR_BYTE(sfr) &= ~_BV(bit))
#endif
#ifndef sbi
  #define sbi(sfr, bit) (_SFR_BYTE(sfr) |= _BV(bit))
#endif

  //Timer2 Settings: Timer Prescaler /8
  TCCR2A = 0;                                               // Timer2 Settings: WGM mode 0
  cbi(TCCR2B,CS20);                                         // Turn off CS20 bit
  sbi(TCCR2B,CS21);                                         // Turn on CS21 bit
  cbi(TCCR2B,CS22);                                         // Turn off CS22 bit
  sbi(TIMSK2,TOIE2);                                        // Timer2 Overflow Interrupt Enable   
  TCNT2 = CLK_SPEED;                                        // Reset timer
3

I want a compare interrupt that triggers the ISR

either i have an ISR with a simple overflow
or I have a compare but the ISR is no triggered

I dont get it, I should be able to do both

4

hat to use TIMER2_COMPA_vect, not OVF

5

I don't think you actually know whether the interrupt is working. Global variables used in interrupt routines must be declared "volatile". Try volatile int val=0;

There are better ways of making sure the LED flashes, including some that don't involve global variables.
For example:

PINB |= (1<<PB5);

From the ATmegaxx8 data sheet

However, writing a logic one to a bit in the PINx Register, will result in a toggle in the corresponding bit in the Data Register.