Waiting for the Low Frequency Clock to be started

[JeanMBoones]

nRF52840

SDK15.3

My question is regarding the low frequency clock.I am initializing the low frequency clock as follows:

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

while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0)
{
}

When TASKS_LFCLKSTART is initiated in line 3, it will generate the EVENTS_LFCLKSTARTED event.

1) My question is do I need to explicitly wait for the EVENTS_LFCLKSTARTED event to be generated before I proceed or can I remove the while loop. I do not want to have a while loop which could potentially turn into an infinite while loop if the EVENTS_LFCLKSTARTED event is never triggered. Currently, I have removed the while loop.

2) How much time does it take from when the LFCLKSTART task is triggered to when the LFCLKSTARTED event is generated? Does this time vary or is it consistent? Is this event generated in the next instruction or can it take even longer?

3) What other ways can I make sure the clock is started, but not have that potentially infinite loop?

Thanks.

[run_ar]

1. Depends on you application. If you plan on using the LFCLK, which is probably why you are waiting for this to initialize, I would wait for the event before continuing assuming the application would not be able to do anything anyway in case the lfclk fails to initialize.

2. It depends on what crystal you are using, but the typical startup time is 0.25s according to product spec.

3. You could wait for the event, if you enable an interrupt for LFCLKSTARTED

[JeanMBoones]

Thanks. I had another question. Does there need to be a wait time between setting the LFCLKSRC and triggering the TASKS_LFCLKSTART? Can setting the source be right before starting the clock?

[run_ar]

yes, that should be fine.