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

[samsam]

Thanks, will try it soon - still haven't received all the electronic components, but hope this week to start assemble the PCB (step by step with test) and the first step will be only BT module, switch and LED. Then if Ok wil go further incl. 32768 crystal ...

Regards

[Vidar Berg]

No problem. Good luch with the board bring up.