Issue regarding the delay generated

Projects General Guidance
1

I have written 3 codes for led toggling and checked the delay on osciloscope to find that the delay of these three codes was not same .

#include <Arduino.h>

void setup() {
 

  cli();
  DDRB = (1 << DDB5);
  
  //TCNT2=5;
  
  
  TIMSK2 |= (1 << TOIE2);
  TCCR2B = (1<<CS22);

  sei();
}

ISR(TIMER2_OVF_vect) {
  static short short_cnt= 0;
  //TCNT2=5;
  short_cnt++;
  //if(short_cnt==500)
  {
  PORTB ^= (1 << PORTB5);
  short_cnt=0; 
  }
  
 
}

void loop() {
 
}

in this code the led is toggled every 2ms rather than the expected 1 ms.
Similar behavior is seen in the following code :-












void setup() {
 TCNT2=5;
 TCCR2B = (1<<CS22);
 
 DDRB=B00100000;
}

void loop() {
  // put your main code here, to run repeatedly:
long counter = 0; 
//while(counter<1000){
while((TIFR2&(1<<TOV2))==0);
counter++;
TCNT2=5;
TIFR2|=(1<<TOV2);
//}

PORTB ^= (1<<5);

}

but in the following code the delay is found to be 1ms as expected : -

#include <Arduino.h>

void setup() {
 cli();
  DDRB = (1 << DDB5);
  
  TCCR2A=(1<<WGM21);
  
  TIMSK2 |= (1 << OCIE2A);
  OCR2A = 250;
  TCCR2B = (1<<CS22);

  sei();
}

ISR(TIMER2_COMPA_vect) {
  
 
  
  PORTB ^= (1 << PORTB5);
  
  
 
}

void loop() {
 
}
2

What is your question?

3

Careful analysis of the code will reveal that in each case the computer is doing exactly what it is instructed to do.

4

So where is the rest of the timer initialization? The Arduino core will have initialized timer2 for its purposes (PWM), and you haven't undone that. This explains why the code where you do set TCCR2A works as you expect...