external XTAL and internal oscillator

[tscribne]

Is it possible to completely disable the internal oscillator and only use an external LF XTAL?

[haakonsh]

If you're talking about the LFRC, then yes. If you've configured the device to use an LF XTAL then the LF RC is automatically disabled. 

[tscribne]

Interesting.   I believe I have done that in this section of code, however, I never seem to get past the while statement, and if I comment out the while loop, the k_sleep never returns.  Is there something I'm missing here?

 // Make sure we are using the external 32.768 kHz crystal osciallator (LFXO)
	NRF_CLOCK->LFCLKSRC = (CLOCK_LFCLKSRC_SRC_Xtal << CLOCK_LFCLKSRC_SRC_Pos)|(CLOCK_LFCLKSRC_BYPASS_Enabled << CLOCK_LFCLKSRC_BYPASS_Pos ) |
		(CLOCK_LFCLKSRC_EXTERNAL_Enabled << CLOCK_LFCLKSRC_EXTERNAL_Pos);


	NRF_CLOCK->EVENTS_LFCLKSTARTED = 0;
	NRF_CLOCK->TASKS_LFCLKSTART = 1;

		while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {
			// Do Nothing
		}

    start_time = k_cycle_get_32();
    
    k_sleep(1000);
    

[haakonsh]

Are you using an external crystal or external oscillator?

[tscribne]

External Crystal.  Actually, I get past the LFCLKSTARTED while however, my k_sleep never returns.

[Turbo J]

Check LFCLKSTAT, the LF clock  might already be running on the crystal.

Also, BYPASS_Enable won't work with a crystal. That literally bypasses (=disables) the oscillator for the crystal - use that only with an external rail-to-rail oscillator.

[haakonsh]

What Jörg says!

You've bypassed the signal amplifier in the LF oscillator and the crystal will never resonate.