RE: how can i change RTC Interrupt calling time?

jignesh — Mon, 24 Oct 2016 18:56:44 GMT

can i get accurate 1 second interrupt by timer... same as rtc....

RE: how can i change RTC Interrupt calling time?

Sigurd — Mon, 24 Oct 2016 09:39:10 GMT

The COUNTER_PRESCALER is used to set the NRF_RTC0->PRESCALER register. The prescaler register of the RTC is a 12 bit wide register, which means that the maximum value the prescaler is capable of holding is 2^12 - 1 = 4095.

The RTC uses the 32KHz (actually 32768Hz) clock, so the formula for calculating the prescaler value is:

Prescaler value = 32768 / Frequency - 1

So if we want a frequency of 1, we get an prescaler value of 32768 / 1 - 1 = 32767. This number is too big to fit inside the prescale register (16 bits is required to represent 32767), so we get an overflow.

We can change the formula to calculate frequency instead:

Frequency = 32768 / (Precsaler value + 1)

Setting the prescaler value to the maximum value gives: 32768 / (4095 + 1) = 8 Hz. This is the lowest frequency possible in the RTC. (interrupt every 0.125sec)

So to get an interrupt every 1 second, I would recommend to use either the timer or application timer.

Take a look at e.g. the Timer example. Here you can set uint32_t time_ms in main.c to 1000 to get the interrupt timer_led_event_handler to trigger every 1 second.

RE: how can i change RTC Interrupt calling time?

jignesh — Mon, 24 Oct 2016 03:16:25 GMT

please give me solution