Problem in understanding RTC

[adrianwong]

Hi, can anyone explain to me about this example in this link with details : github.com/.../main.c I'm a newbie in nordic and i found it difficult to understand this example. Kindly assist and reply asap. Thanks!

[Ole Bauck]

With prescaler 0, the RTC will run at 32.768 KHz which means 32768 counts per second. This means that the CC[0] needs to be initialized and incremented with 32768 instead of 1000. I suggest that you read the Reference Manual chapter about RTC to get a better understanding of how it works.

[adrianwong]

What you mean is by putting NRF_RTC0->CC[0] = 32768 when NRF_RTC0->PRESCALER = 0 then the IRQ handler will trigger every 1s right? Nope, this is not working.

[Ole Bauck]

And NRF_RTC0->CC[0] = NRF_RTC0->COUNTER + 32768; in the interrupt as the RTC is not reset unless it overflows.

[adrianwong]

Thanks Ole Bauck. What is the best way for me to set the timer to 100us accurately? By the way, If i wanted to change from RTC0 to RTC1 i just need to substitute all RTC0 to RTC1 only right?

[Ole Bauck]

You cannot get 100us accurately. Since the resolution of the RTC with prescaler 0 is 30.517us, the closest number would be 91.55us. To get 100us accurately, you have to use the TIMER peripheral that is able to run at 16MHz, however this will draw a lot more power (~250uA+ from crystal). To change to RTC1 susbstitute RTC0 by RTC1.