Timer 2 CTC mode without interruption

Using Arduino Programming Questions
#1

Hello. I would like to use timer2 to count an amount of time and set a flag after this time has elapsed. But no interruptions.

I find that CTC mode is what I want so I configure it like that:

void configureTimer2(void) {
  // initialize timer2
  noInterrupts();           // disable all interrupts
  TCCR2A = 0;
  TCCR2B = 0;
  TCNT2  = 0;
  
  TCCR2A |= (1 << WGM21); // Configure timer 2 for CTC mode
  TCCR2B |= (1 << CS22);  // 1024 prescaler
  TCCR2B |= (1 << CS20);  // 1024 prescaler
  TIMSK2 &= ~(1<

The timer is supposed to set to 1 some flag bit in the TIFR2 register.

Now what I do not know is which one of the bits is supposed to be on. OCF2B, OCF2A or TOV2

My guess is that it is OCF2A but I had unexpected behaviours using that approach.

Something else sounds wierd to me: "OCF2A can also be cleared by writing a logic one to the flag." -To clear it, a 1 has to be written into, sound a bit extrange for me.

To check for this flag, what I do is: Polling for the bit **OCF2A* until it is 1. Clear the flag by writting again 1 into it. *Do the stuff.... *Again Polling for the bit **OCF2A* until it is 1... This way the "stuff" is done at a frequency of timer2 but with no Timer2 interruption.

Is it sensible, for some reasson it is not working and I will try to dig into it a little bit more tomorrow, I just wanted to share it to have a 2nd oppinion.

Ill post back if I find a solution.

#2

Now what I do not know is which one of the bits is supposed to be on. OCF2B, OCF2A or TOV2

According to the datasheet, OCF2A.

OCF2A can also be cleared by writing a logic one to the flag.

Correct. To clear that flag, use the instruction

TIFR2 = (1<

It would probably be a good idea to clear the TIMSK2 register, unless you are planning on overflow or OCF2B interrupts.

TIMSK2 = 0; //no interrupts from this timer
#3

Thanks.

Just another question.

I have no plans to overflow the timer, if I am not wrong, in CTC mode, the TCNT2 is reloaded to 0 after a success match with OCR2A.

#4

After applying the sugested changes:

void configureTimer2(void) {
  // initialize timer2
  noInterrupts();           // disable all interrupts
  TCCR2A = 0;
  TCCR2B = 0;
  TCNT2  = 0;
  
  //TCCR2B |= (1 << WGM12);   // CTC mode---- WRONG
  TCCR2A |= (1 << WGM21); // Configure timer 2 for CTC mode
  
  //TCCR2B |= (1 << CS12);    // 1024 prescaler
  //TCCR2B |= (1 << CS10);    // 1024 prescaler
  TCCR2B |= (1 << CS22);  // 1024 prescaler
  TCCR2B |= (1 << CS20);  // 1024 prescaler
  
  //TIMSK2 |= (1 << OCIE2A);  // enable timer compare interrupt
  TIMSK2 =0;   //Disable timer compare interrupt. and everything unles overflow or OCF2B interrupts are used
  OCR2A = 163;     //163       // compare match to achieve 96Hz.
  interrupts();
}

and

In the loop I check the flag this way:

void countAndCheckInput(void) {
  if ((TIFR2 & (1 << OCF2A)) == 0) {
    return;  //The flag is not set, so return
  } else {  //The flag is set.
    //digitalWrite(TRIGGERPIN, digitalRead(TRIGGERPIN) ^ 1);  //Measuring here with the oscope T=1.3ms
    countForNewFrame++;
    TIFR2 = (1 << OCF2A); // This is to clear the bit.
      ...
      ...
      ...

The tick time is 1.3ms !! But based on calculations I expect a tick time arround 10.4ms

16.000.000Hz /(1024*163)=96Hz --> Period = 10.4ms

How is possible the big difference? I would understand if the result was bigger than expected, but this much smaller I am totally lost here.

#5

These two lines select 128 as the clock prescaler, not 1024:

  TCCR2B |= (1 << CS22);  // 1024 prescaler
  TCCR2B |= (1 << CS20);  // 1024 prescaler
#6

OMG, rookie mistake, I checked a table from the Atmega168 datasheet instead of the 328p.

Aniway 10.4ms/1.3ms = 8 should have given me some information about what was happening.

 TCCR2B |= (1 << CS22) | (1 << CS21) | (1 << CS20);  // 1024 prescaler

Solved. Thanks for your help.