Can not use XTAL LF CLK source without softdevice on SDK15.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

masataka hasegawa — Fri, 10 Aug 2018 13:24:52 GMT

thank you

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

RK — Fri, 10 Aug 2018 04:17:45 GMT

Yes - one or the other. Whichever suits your code best then pick.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

masataka hasegawa — Fri, 10 Aug 2018 03:28:38 GMT

Hi,

I checked your advice points (added handler and receive event).
I understood it (firstly RC clock starts, and takes a long time to change XTAL).

So, If I want to wait the XTAL clock starting correctly,
I should check LFCLKSTAT = 0x00010001, or should add the event handler.

Is this correct?

Thanks,

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

Einar Thorsrud — Thu, 09 Aug 2018 10:49:21 GMT

Hi,

As RK said, this is expected behaviour. Using the driver you can provide a event handler to the call to nrf_drv_clock_lfclk_request(), which so that you get a callback when the clock has started. This is not done in the flash_fds example, where a NULL pointer is passed instead of a function pointer to the event handler.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

RK — Thu, 09 Aug 2018 10:46:00 GMT

yes the 32.768kHz crystal has a long startup time, the documentation says 250ms is normal.

If you read the description in the manual

If the LFXO is selected as the clock source, the LFCLK will initially start running from the 32.768 kHz LFRC while the LFXO is starting up and automatically switch to using the LFXO once this oscillator is running.

So nrf_clock_lf_is_running() correctly returns as there *is* an LF clock running. However until the crystal has started, it's not yet the LFXO. If you actually need that clock source to be active, you need to wait for it. I assume the softdevice actually waits for the LFXO source to be active (which is why people with no crystal who forget to change the source complain the softdevice hangs).

So there is a slight difference between the softdevice and non-softdevice versions of the code in that one waits for the actual crystal source to run, the other just waits until there's some LF clock source started even if it's not yet the crystal.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

masataka hasegawa — Thu, 09 Aug 2018 10:21:07 GMT

I checked it with debugger, and I got 0x00010001 value,
but, printf debug value is 0x00010000.

I found new phenomenon.
I add printf debug into main loop of main.c

and execute it,
register value is changed on the way.

<info> app: LFCLKSTAT = 00010000
:
about 50 times
:
<info> app: LFCLKSTAT = 00010000
<info> app: LFCLKSTAT = 00010001

Why?

Bit 16 of LFCLKSTAT is RUN state,
and I think that bit 1-0 of LFCLKSTAT is validate at bit 16 rise timing.

does it take long time to change RC to XTAL?

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

Einar Thorsrud — Thu, 09 Aug 2018 09:03:59 GMT

Indeed! I only glanced at the example earlier, but I see that you are correct. In that case, the clock source depend on the driver configuration, and the example is configured to use the xtal by default, as CLOCK_CONFIG_LF_SRC in sdk_config.h is set to 1. I tested the unmodified example now, and it seems to work as expected. LFCLKSTAT is 0x001001 when I check with a debugger. Can you check to verify that you have not accidentally changed that in your sdk_config.h?

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

masataka hasegawa — Thu, 09 Aug 2018 08:49:46 GMT

"flash_fds example without softdevice" calls clock_init().
and, clock_init() calls nrf_drv_clock_lfclk_request() and waits clock start by nrf_clock_lf_is_running().
So, I think that your review point is already executed.
"LFCLKSTAT = 0x00010000" indicated to already run LF clock also.
But, RC source instead of XTAL.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

Einar Thorsrud — Thu, 09 Aug 2018 08:31:12 GMT

The Flash Data Storage Example example can be used both with and without the SoftDevice. The SoftDevice will always start the LF clock, but the application need to start the LF clock (if needed) in case you run the example without the SoftDevice, as RK suggested. You can do that using the clock driver, or by writing to the clock CLOCK registers directly:

NRF_CLOCK->LFCLKSRC = 1;                    // Select xtal
NRF_CLOCK->TASKS_LFCLKSTART = 1;            // Start LFCLK
while(NRF_CLOCK->EVENTS_LFCLKSTARTED == 0); // Wait for clock to start

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

masataka hasegawa — Thu, 09 Aug 2018 05:01:47 GMT

I use flash_fds sample in SDK as it is.

RE: Can not use XTAL LF CLK source without softdevice on SDK15.

RK — Thu, 09 Aug 2018 04:12:46 GMT

Are you actually starting the LF clock in the code? Just setting the defines won't do anything.