Timer Calls - overruns?

Using Arduino Project Guidance
1

Guys, I'm using a timer on my project and I want to know what happens if my timer call takes too long. Does the next timer call stops the previous one, or a total mess happens? What will exactly happen? I tried to make it take forever and added a boolean variable check but couldn't make it overrun, not sure what I did wrong. I need to figure out a way to check when overruns happens on my timer call, any ideas?

ISR(TIMER2_COMPA_vect) 
{
// CODE HERE 
}

void timerStart()
{
    float frequency = ((float(midiClockBPM)*float(PPQ))/60.0f);
    
    TCCR2A = 0;
    TCCR2B = 0;
    bitWrite(TCCR2A, WGM21, 1);
    bitWrite(TCCR2B, CS20, 1);

	uint32_t ocr = F_CPU / frequency - 1;
	uint8_t prescalarbits = 0b001;

	if (ocr > 255)
	{
		ocr = F_CPU / frequency / 8 - 1;
		prescalarbits = 0b010;

		if (ocr > 255)
		{
			ocr = F_CPU / frequency / 32 - 1;
			prescalarbits = 0b011;
		}

		if (ocr > 255)
		{
			ocr = F_CPU / frequency / 64 - 1;
			prescalarbits = 0b100;

			if (ocr > 255)
			{
				ocr = F_CPU / frequency / 128 - 1;
				prescalarbits = 0b101;
			}

			if (ocr > 255)
			{
				ocr = F_CPU / frequency / 256 - 1;
				prescalarbits = 0b110;
				
				if (ocr > 255)
				{
					ocr = F_CPU / frequency / 1024 - 1;
					prescalarbits = 0b111;

					if (ocr > 255)
					{
						timerStop();
						return;
					}
				}
			}
		}
	}

	TCCR2B = prescalarbits;
	OCR2A = ocr;
	bitWrite(TIMSK2, OCIE2A, 1);
}

void timerStop(void)
{
	bitWrite(TIMSK2, OCIE2A, 0);
	TCCR2A = (1 << WGM20);
	TCCR2B = (TCCR2B & 0b11111000) | (1 << CS22);
	OCR2A = 0;
}

Best Regards, WilliamK

2

Does the next timer call stops the previous one

No. Unless you re-enable interrupts (which is a very bad idea), your interrupt service routine runs to completion.

What will exactly happen?

Your interrupt service routine completes. A single machine instruction is executed on the loop side. Your interrupt service routine is called again. Essentially, loop gets starved.

I need to figure out a way to check when overruns happens on my timer call, any ideas?

Time loop...

unsigned long PreviousLoop;

void loop( void )
{
  unsigned long CurrentLoop;
  unsigned long DeltaLoop;

  CurrentLoop = micros();  // or millis()
  DeltaLoop = CurrentLoop - PreviousLoop;
  PreviousLoop = CurrentLoop;

  // DeltaLoop continues to increase as loop becomes starved.  At a certain point, for all practical purposes, loop stops running.
}