Would calculation affect timer

[mich_x]

I am using a power profiler to measure the timing of my program and I found something wrong. So I tested with a simple pure timer.

So first I set the timer during to 300ms

#define half_epoch_during		APP_TIMER_TICKS(300)
err_code = app_timer_create(&half_epoch_timer, APP_TIMER_MODE_SINGLE_SHOT, half_epoch_timer_handler);
err_code=app_timer_start(half_epoch_timer,half_epoch_during,NULL);

And I did nothing in the callback function

static void half_epoch_timer_handler (void * p_context)
{}

The timing is all right. I measure a periodic change in current every 300ms. Then I add a for loop to simulate calculations in the callback function.

static void half_epoch_timer_handler (void * p_context)
{
	int d;
	for (int i =0; i<3000000; i++)
	{	
		d = i;
	}
}

And now, the timing is wrong. I can measure a current change every 240ms. So my question is why would calculation make the timer shorter?

ps: My board is nRF52840 PDK.

[AmbystomaLabs]

You are correct. You are defining the tick rate.

On the for loop, I think it is minimum 6million opcodes since you force it to write i to d. Or about 93 msec to execute.

It is an interesting problem. Still I would probably choose to let it keep track of time and see if it does that correctly while running the for loop.