Timer value not accurate using app_timer.c in nRF51822?

RE: Timer value not accurate using app_timer.c in nRF51822?

Mo A — Thu, 15 May 2014 11:03:23 GMT

Great , Its working, Thank you

RE: Timer value not accurate using app_timer.c in nRF51822?

FormerMember — Wed, 14 May 2014 18:39:49 GMT

If you are using a development board of sorts, it will most likely have crystals for both LF and HF clock. Then adding a line specifying the clock source for LFCLK will make it use the crystal oscillator. The code snippet would be (edited, source must be specified before starting):

NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos); NRF_CLOCK->TASKS_LFCLKSTART = 1; while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0);

RE: Timer value not accurate using app_timer.c in nRF51822?

Mo A — Wed, 14 May 2014 14:18:33 GMT

How can I know that?, or should I explicitly enable the crystal in my code. ?(Sorry Prithvi, as I am new to this)

RE: Timer value not accurate using app_timer.c in nRF51822?

FormerMember — Wed, 14 May 2014 14:02:43 GMT

Are (can) you using a crystal for either of the clocks?

RE: Timer value not accurate using app_timer.c in nRF51822?

Mo A — Wed, 14 May 2014 13:59:47 GMT

Hi,

I am measuring this using CRO, (as in the code the pin 4 is used as gpio o/p).

And yes, 920ms is too low, I hope my code is not wrong (not using softdevice)

Any way?

RE: Timer value not accurate using app_timer.c in nRF51822?

FormerMember — Wed, 14 May 2014 13:32:53 GMT

I guess you are using the RC oscillator for the LF clock, this will result in inaccuracy. Could you use a crystal? Either a 32.768 kHz one for LFCLK or 16MHz one for HFCLK so that you can synthesize the LFCLK. If you have a 16 MHz crystal, you could also calibrate the RC oscillator of LFCLK. Even if you are using RC oscillator for LF CLK, 920 ms is way off. How are you measuring this?

RE: Timer value not accurate using app_timer.c in nRF51822?

Mo A — Wed, 14 May 2014 13:13:50 GMT

Hi Prithvi,

Still It is 920 ms. Why is this so? Any hardware issues?

Mo,

RE: Timer value not accurate using app_timer.c in nRF51822?

FormerMember — Wed, 14 May 2014 12:30:16 GMT

The basis of using a 32.768kHz frequency for RTC is that it is a power of 2. So, having a PRESCALAR of 255 and waiting for 128 ticks would result in accurate 1s interval.