Custom NRF52840 Board Softdevice Clock Configuration

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Mon, 18 May 2020 06:47:56 GMT

You need to specify a calibration interval and also adjust the accuracy when selecting the internal RC oscillator.

Configuration settings for RC source:

//==========================================================

// <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

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Fri, 15 May 2020 20:35:37 GMT

I agree. I have tested on multiple boards and they call give the same results.

I am also not able to use the internal RC as the softdevice clock source. I try to select NRF_SDH_CLOCK_LF_SRC as 0, but My program also hangs.

Is there any other clock setting I am missing in order to use this?

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Thu, 07 May 2020 13:50:18 GMT

Could it be a problem with soldering or mounting of the crystal then? Also, did you have multiple boards to test this on, or have you only tested this on one board? I think you should be able to start the crystal even if the layout is not optimal.

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Wed, 06 May 2020 10:35:05 GMT

I have been using this as my reference design and it has been working. The other little thing to note is the LFCLK is physically close to the HFCLK because this is a very small form factor board. Could this be an issue?

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Wed, 06 May 2020 09:41:57 GMT

C12 and C15 should be closer to 8pF (see 32.768 kHz crystal oscillator (LFXO) chapter for calculation) if the load capacitance of your crystal is CL=6pF. Wrong loading of the crystal will offset the frequency, but I would still have expected the crystal to ramp up. Have you seen this on more than one board?

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Tue, 05 May 2020 12:52:02 GMT

This is the clock circuit I am using.

https://lcsc.com/product-detail/SMD-Crystal-Resonators_Seiko-Epson_X1A000141000600_Seiko-Epson-X1A000141000600_C94673.html

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Tue, 05 May 2020 12:45:52 GMT

You have to explicitly select the crystal to use it. Otherwise, you will be starting the internal RC oscillator.

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Tue, 05 May 2020 12:39:51 GMT

This is a different board. It seems a bit odd that the crystal will start if it's not explicitly selected. Can you offer a reasoning behind this?

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Tue, 05 May 2020 06:30:18 GMT

So the crystal never starts indicating that this a HW problem. Is it the same board that was discussed in your previous ticket? Maybe you can get Kaja to review your clock circuit.

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Mon, 04 May 2020 12:57:50 GMT

So now the code hangs here:

while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0);

Is seems like that lfclk doesnt start when it is selected. But with our this NRF_CLOCK->LFCLKSRC = 1;

passes the while loop.

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Mon, 04 May 2020 12:46:52 GMT

The sdk_config setting will not be applied when you don't use the clock driver. Try this instead:

NRF_CLOCK->LFCLKSRC = 1; /* Select xtal source */
NRF_CLOCK->TASKS_LFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0);

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Mon, 04 May 2020 12:34:43 GMT

Should this be selected in the sdk_config file or it should be called as a function?

My config file already selects this.

#define NRFX_CLOCK_CONFIG_LF_SRC 1

RE: Custom NRF52840 Board Softdevice Clock Configuration

Vidar Berg — Mon, 04 May 2020 12:13:58 GMT

Hello,

You need to select xtal as the clock source in LFCLKSRC before running the LF clock start task. RC is the default clock source after reset.

RE: Custom NRF52840 Board Softdevice Clock Configuration

David — Fri, 01 May 2020 15:13:21 GMT

Hello, I changed this to LFCLKSTARTED and I still get the same result. The code passes the test and LFCLK is started. But still hangs at ble_stack_init

RE: Custom NRF52840 Board Softdevice Clock Configuration

Turbo J — Fri, 01 May 2020 07:50:53 GMT

Clean your glasses and look closely at the posted source code:

In the second step you start the LF clock with LFCLKSTART but then use the already set HFCLKSTARTED when trying to wait. You wanted to use the LFCLKSTARTED event instead.