nRF52840 examples with LFRC and calibration?

[samsam]

I am designing a custom board with a nRF52840 module that has no 32.768 kHz crystal embedded in it and as a first step want to test it with some examples that use only RC LFCLK.

The Blinky example doesn’t have any clock configured in the sdk_config.h (even the section for such configuration is missing), so can I assume that this example uses LFRC as it declared as default source  in the documentation?

Which other examples use LFRC and is there any example with a calibration?

Thanks

[Vidar Berg]

Hi,

All project configurations for the 52840 DK (pca10056) use the LFXTAL by default, but you can easily change this in the project's sdk_config header.

Softdevice LFRC configuration

//==========================================================
// <o> NRF_SDH_CLOCK_LF_SRC  - SoftDevice clock source.
 
// <0=> NRF_CLOCK_LF_SRC_RC 
// <1=> NRF_CLOCK_LF_SRC_XTAL 
// <2=> NRF_CLOCK_LF_SRC_SYNTH 

#ifndef NRF_SDH_CLOCK_LF_SRC
#define NRF_SDH_CLOCK_LF_SRC 0
#endif

// <o> NRF_SDH_CLOCK_LF_RC_CTIV - SoftDevice calibration timer interval. 
#ifndef NRF_SDH_CLOCK_LF_RC_CTIV
#define NRF_SDH_CLOCK_LF_RC_CTIV 16
#endif

// <o> NRF_SDH_CLOCK_LF_RC_TEMP_CTIV - SoftDevice calibration timer interval under constant temperature. 
// <i> How often (in number of calibration intervals) the RC oscillator shall be calibrated
// <i>  if the temperature has not changed.

#ifndef NRF_SDH_CLOCK_LF_RC_TEMP_CTIV
#define NRF_SDH_CLOCK_LF_RC_TEMP_CTIV 2
#endif

// <o> NRF_SDH_CLOCK_LF_ACCURACY  - External clock accuracy used in the LL to compute timing.
 
// <0=> NRF_CLOCK_LF_ACCURACY_250_PPM 
// <1=> NRF_CLOCK_LF_ACCURACY_500_PPM 
// <2=> NRF_CLOCK_LF_ACCURACY_150_PPM 
// <3=> NRF_CLOCK_LF_ACCURACY_100_PPM 
// <4=> NRF_CLOCK_LF_ACCURACY_75_PPM 
// <5=> NRF_CLOCK_LF_ACCURACY_50_PPM 
// <6=> NRF_CLOCK_LF_ACCURACY_30_PPM 
// <7=> NRF_CLOCK_LF_ACCURACY_20_PPM 
// <8=> NRF_CLOCK_LF_ACCURACY_10_PPM 
// <9=> NRF_CLOCK_LF_ACCURACY_5_PPM 
// <10=> NRF_CLOCK_LF_ACCURACY_2_PPM 
// <11=> NRF_CLOCK_LF_ACCURACY_1_PPM 

#ifndef NRF_SDH_CLOCK_LF_ACCURACY
#define NRF_SDH_CLOCK_LF_ACCURACY 1
#endif

[samsam]

I was referring  to this example, which doesn’t have any clock initialization in the the sdk_config.h (even the section for such configuration or any NRF_SDH_CLOCK* is missing):

…\SDK17\examples\peripheral\blinky\pca10056\blank\ses\blinky_pca10056.emProject

So the initial question is still on the table 

Thanks

[Vidar Berg]

Sorry, I just assumed you were using the Bluetooth blinky example. The blinky example you're referring to does not use the 32K clock source, only the HFINT.

[samsam]

Ok, thanks, but could you point me to some example in SDK that shows 

Calibrating the 32.768 kHz RC oscillator

Not necessary to be for PCA10056 - I anyway have only PCA10040 so far ...

Thanks

[Vidar Berg]

None of the SDK peripheral examples includes clock calibration as far as I can tell, but the clock driver documentation does explain how you can enable it (link). I would recommend you to start with the Real Time Counter Example as it already includes the clock driver. I can also try to set up a simple example if needed, just let me know.  

[Vidar Berg]

Maybe you have implemented it already, but I've modified the RTC example as I suggested now, see attached below.

0878.SDK17.0.2_peripheral_rtc_w_rcosc.zip