How to configure the softdevice clock and the rtc clock?

[Giannis Anastasopoulos]

Dear All,

I am trying to use the external crystal as the source clock of the softdevice, as well as of the rtc. I am not sure if all this is possible and because I am new to it, I would appreciate any detailed explanation. What I have at the moment is the following configuration:

// <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 1
#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

// </h> 

For the RTC, I have the following:

// <e> RTC_ENABLED - nrf_drv_rtc - RTC peripheral driver - legacy layer
//==========================================================
#ifndef RTC_ENABLED
#define RTC_ENABLED 1
#endif
// <o> RTC_DEFAULT_CONFIG_FREQUENCY - Frequency  <16-32768> 


#ifndef RTC_DEFAULT_CONFIG_FREQUENCY
#define RTC_DEFAULT_CONFIG_FREQUENCY 32768
#endif

// <q> RTC_DEFAULT_CONFIG_RELIABLE  - Ensures safe compare event triggering
 

#ifndef RTC_DEFAULT_CONFIG_RELIABLE
#define RTC_DEFAULT_CONFIG_RELIABLE 0
#endif

// <o> RTC_DEFAULT_CONFIG_IRQ_PRIORITY  - Interrupt priority
 

// <i> Priorities 0,2 (nRF51) and 0,1,4,5 (nRF52) are reserved for SoftDevice
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 
// <7=> 7 

#ifndef RTC_DEFAULT_CONFIG_IRQ_PRIORITY
#define RTC_DEFAULT_CONFIG_IRQ_PRIORITY 6
#endif

// <q> RTC0_ENABLED  - Enable RTC0 instance
 

#ifndef RTC0_ENABLED
#define RTC0_ENABLED 0
#endif

// <q> RTC1_ENABLED  - Enable RTC1 instance
 

#ifndef RTC1_ENABLED
#define RTC1_ENABLED 0
#endif

// <q> RTC2_ENABLED  - Enable RTC2 instance
 

#ifndef RTC2_ENABLED
#define RTC2_ENABLED 1
#endif

// <o> NRF_MAXIMUM_LATENCY_US - Maximum possible time[us] in highest priority interrupt 
#ifndef NRF_MAXIMUM_LATENCY_US
#define NRF_MAXIMUM_LATENCY_US 2000
#endif

// </e>

I am trying to call this function in order to initialize the softdevice:

err_code = nrf_sdh_enable_request();

This returns error code 7.

I am using an NRF52832 that has an external 32MHz crystal attached and I am using SDK 15.3.

The same code won't work on the NRF52DK. Finally, if I change the NRF_SDH_CLOCK_LF_SRC  to 0 (use the rtc), everything works normally.

The clock configuration is:

// <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

// <q> CLOCK_CONFIG_LF_CAL_ENABLED  - Calibration enable for LF Clock Source
 

#ifndef CLOCK_CONFIG_LF_CAL_ENABLED
#define CLOCK_CONFIG_LF_CAL_ENABLED 0
#endif

// <o> CLOCK_CONFIG_IRQ_PRIORITY  - Interrupt priority
 

// <i> Priorities 0,2 (nRF51) and 0,1,4,5 (nRF52) are reserved for SoftDevice
// <0=> 0 (highest) 
// <1=> 1 
// <2=> 2 
// <3=> 3 
// <4=> 4 
// <5=> 5 
// <6=> 6 
// <7=> 7 

#ifndef CLOCK_CONFIG_IRQ_PRIORITY
#define CLOCK_CONFIG_IRQ_PRIORITY 6
#endif

// </e>

The end goal of my application is to measure time spans accurately and transmit BLE packets also in an accurately timed manner. This is the reason why I want to make sure that I am using the external crystal.

[sewes]

Error code 7 means in this case NRF_ERROR_INVALID_PARAM.

Something is wrong with your configuration.

Please check if the values for NRF_SDH_CLOCK_LF_RC_CTIV and NRF_SDH_CLOCK_LF_RC_TEMP_CTIV are set correctly.

I would suggest you to set these values to 0 and test again.

[Vidar Berg]

Yes, NRF_SDH_CLOCK_LF_RC_CTIV and NRF_SDH_CLOCK_LF_RC_TEMP_CTIV must be set '0' when have selected the XTAL, they're not ignored as one might expect. You should also set NRF_SDH_CLOCK_LF_ACCURACY to a PPM value appropriate for your crystal in order to reduce power consumption (Softdevice use longer rx windows to account for clock drift).