Using nRF52832 with SDK v11.0.0 and SD132 - How to Determine if External Crystal is Selected

[Sami]

Hello,

We are currently using RTC1 and RTC2 to keep track of various times. RTC2 is our dedicated clock to keep track of time. I want to ensure that indeed, our application is using our external 32,768 Hz oscillator (referred to as 'LFXO' in the manual). Additionally, our application is using the soft device for BLE communications.

To summarize, the LFCLK controller input can choose 1 of 3 sources, RC oscillator (LFRC), external crystal oscillator (LFXO), and lastly, a synthesized clock from HFCLK (LFSYNT). I want to ensure and confirm that our application is using the external crystal oscillator (LFXO). 

Thanks! 

[MartinBL]

Hi,

You can use the register NRF_CLOCK->LFCLKSTAT for this. It gives you the clock source and whether or not it is running.

[Sami]

Thank you MartinBL. Yes, and:

// does this select the external crystal? 

NRF_CLOCK->LFCLKSRC            = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos);

// I'm assuming this starts the external crystal:

NRF_CLOCK->TASKS_LFCLKSTART    = 1;

[MartinBL]

Yes and yes.