nrf52810: HFXO is not turned on as expected

[SeanKao]

Hi,
I have a Nordic 52810/PCA10040 DEV board with the latest zephyr.

In Zephyr configuration I using hardware clock option -> 32KHz clock source (RC oscillator)

I expect zephyr using the external 32MHz oscillator (HFXO) as source of the HFCLK

According to the Nordic spec, we check two registers below.

Seems the value isn't as expected.
Please correct me if I'm wrong.

＊nrfjprog --memrd 0x40000408
[Expected value]
0x00000001
[Actual value]
0x00000000

＊nrfjprog --memrd 0x4000040C
[Expected value]
0x00010001
[Actual value]
0x00010000

[SeanKao]

I use this example

west build -p auto -b nrf52810_pca10040 samples/bluetooth/peripheral_hr

After west flash I power off and on the board then check the register value, even I wait a few minutes and check the register value again, the value is still the same.

[Håkon Alseth]

Hi,

 

The menuconfig picture is related to the LFCLK (the 32kHz clock source), while the register you're checking is the high frequency clock (HFCLK). The HFCLK will run only when needed, to save power. The system runs on the more inaccurate HFINT (64M RC oscillator) for generic processing.

 

SoftDevice also behaves like this, to ensure low power consumption.

 

Kind regards,

Håkon

[SeanKao]

Håkon,

thanks, is there anything I can do to force the HFCLK to work with external 32M crystal? So that I can verify the external 32M crystal is working as expected.

Regard.

[Håkon Alseth]

Hi,

 

SeanKao said:

thanks, is there anything I can do to force the HFCLK to work with external 32M crystal? So that I can verify the external 32M crystal is working as expected.

You can run this sequence, and if you hang in the while-loop, the hardware has issues with starting up the external HFCLK:

NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0);
NRF_CLOCK->EVENTS_HFCLKSTARTED = 0;

 

Note that this might be overridden by other modules if they also control the HFCLK directly.

 

Kind regards,

Håkon