If don't use 32.768k low frequency crystal, what will happen?

[liujirong888]

Dear ,

          I use nRF52833 to transfer audio,but I found that this audio will delay 130ms.

I didn't use 32.768K low frequency crystal, do you think this will affect delay time?

I modified below definition from 1 to 2 in sdk_config.h

#define NRFX_CLOCK_CONFIG_LF_SRC   2

#define CLOCK_CONFIG_LF_SRC   2

[Vidar Berg]

Hello,

The LF clock does not affect the latency. Probably what you should look at is the connection interval. You can use the Connection Parameters Negotiation module for requesting a shorter interval in your application.

Best regards,

Vidar

[liujirong888]

Dear Vidar,

          May I know how to set sdk_config.h if I don't want to use 32.768K crystal?

Does my current setting OK for not using 32.768K ?

#define NRFX_CLOCK_CONFIG_LF_SRC   2

#define CLOCK_CONFIG_LF_SRC   2

[Vidar Berg]

Hello,

The Softdevice clock source is configured through the NRF_SDH_CLOCK_* symbols, and these are the recommended settings if you don't have a crystal:

// </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
#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

The NRF_CLOCK_LF_SRC_SYNTH source is not low power, and is generally not recommended.