Using external clk for lfclk

[Shimon_nohayo]

Hi

I'm using SDK 15.2.0 SD 6.1.0

I'm using external RTC device and I am connected the external RTC 32.7k Hz output square Wave to XL1 and XL2 is connected to ground.

I would like to ask for your advice how to configure the soft device and the clk to operate from the external clock and not from a crystal.

Shimon

[Simon]

Have you seen this post, I think it answers your question.

Best regards,

Simon

[Shimon_nohayo]

Hi,

I've read this post, though I'm using SDK 15 and the set of the LFCLK done in the SDK_Config.h file.

In the SDK_Config.h there are three places to set LFCLK:

/**************** First CLOCK peripheral driver ***************************/

// <e> NRFX_CLOCK_ENABLED - nrfx_clock - CLOCK peripheral driver
//==========================================================
#ifndef NRFX_CLOCK_ENABLED
#define NRFX_CLOCK_ENABLED 1
#endif
// <o> NRFX_CLOCK_CONFIG_LF_SRC - LF Clock Source

// <0=> RC
// <1=> XTAL
// <2=> Synth
// <131073=> External Low Swing
// <196609=> External Full Swing

#ifndef NRFX_CLOCK_CONFIG_LF_SRC
#define NRFX_CLOCK_CONFIG_LF_SRC 1

/****************** Second CLOCK peripheral driver - legacy layer ***********************/

// <e> NRF_CLOCK_ENABLED - nrf_drv_clock - CLOCK peripheral driver - legacy layer
//==========================================================
#ifndef NRF_CLOCK_ENABLED
#define NRF_CLOCK_ENABLED 1
#endif
// <o> CLOCK_CONFIG_LF_SRC - LF Clock Source

// <0=> RC
// <1=> XTAL
// <2=> Synth
// <131073=> External Low Swing
// <196609=> External Full Swing

#ifndef CLOCK_CONFIG_LF_SRC
#define CLOCK_CONFIG_LF_SRC 1
#endif

/****************** Third oftDevice clock configuration ***********************/

// </h>
//==========================================================

// <h> Clock - SoftDevice clock 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 //0
#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 //0
#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 //7
#endif

Please advise how can I define the order of LFCLK setup, as you can see the SoftDevice clock configuration do not contain // <131073=> External Low Swing  // <196609=> External Full Swing options

Shimon

[Simon]

Take a look at the configurations in this case, which my colleague ketiljo confirms as correct settings.

Best regards,

Simon

[Shimon_nohayo]

Thanks - very helpful, now it works.