Milliseconds since startup?

Question

Hello everybody,

I've been digging through the forum and the documentation for hours now. But to be honest I don't understand the whole timer thing.

I need a simple way to count the milliseconds since the application/board startup.

My first attempt was to use the timer1 in CTC mode like so:

	NRF_TIMER1->MODE = TIMER_MODE_MODE_Timer; // Set the timer in Timer Mode
NRF_TIMER1->TASKS_CLEAR = 1; // clear the task first to be usable for later
NRF_TIMER1->PRESCALER = 7; //Set prescaler. Higher number gives slower timer. Prescaler = 0 gives 16MHz timer
NRF_TIMER1->BITMODE = TIMER_BITMODE_BITMODE_16Bit; //Set counter to 16 bit resolution
NRF_TIMER1->CC[0] = 125; //Set value for TIMER1 compare register 0 => 1ms interval

// Enable interrupt on Timer 1, both for CC[0] compare match events
NRF_TIMER1->INTENSET = (TIMER_INTENSET_COMPARE0_Enabled << TIMER_INTENSET_COMPARE0_Pos);
NVIC_EnableIRQ(TIMER1_IRQn);
NRF_TIMER1->TASKS_START = 1; // Start TIMER1

and the ISR:

void TIMER1_IRQHandler(void) {

if ((NRF_TIMER1->EVENTS_COMPARE[0] != 0) && ((NRF_TIMER1->INTENSET & TIMER_INTENSET_COMPARE0_Msk) != 0)) {
	NRF_TIMER1->EVENTS_COMPARE[0] = 0;

	runtime_ms++;
}

}

Which should increment the value of runtime_ms every millisecond, but somehow, this happens much slower.

What am I doing wrong? Or maybe there's a much simpler way I am missing here?

Greetings Matthias

Wojtek · Accepted Answer

Yes, there is simple way. 
 If you are using app_timer library, you can just use app_timer_cnt_get function to get RTC ticks since its startup. Just get ticks value from there, convert them to milis (according to your prescaler). Just remember that RTC overflows sometimes - app_timer_cnt_diff_compute is the best way to compute the difference, as it considers those overflows.

Milliseconds since startup?

Top Replies