Switching between RC and XTAL for HF clock

[cmag]

I need to measure periods with high precision, so I need to make sure that the HF clock is using the external XTAL; when the softdevice is not started (for testing mode) I can use the nrfx_clock_hfclk_start() function or nrf_clock_task_trigger(NRF_CLOCK_TASK_HFCLKSTART) and the corresponding calls to return to the low power internal RC; when he softdevice is running, using these functions causes the program to crash.
I can start the XTAL before starting the softdevice and it will stay on, but I would like to return to the RC for lower power consumption. Is it possible to switch between the RC and the XTAL when the softdevice is running?

[isdv]

Perhaps this will help:

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

[cmag]

It still crashed; my feeling is that, when the Softdevice is running, trying to operate on the clock is forbidden.

I am using s140_nrf52_7.2.0_softdevice.

[isdv]

ble_stack_init();

nrf_sdh_disable_request();
NRF_CLOCK->TASKS_HFCLKSTART = 0;
//// ...
NRF_CLOCK->TASKS_HFCLKSTART = 1;
while (NRF_CLOCK->EVENTS_HFCLKSTARTED == 0) {
    //
};
ble_stack_init();

>Is it possible to switch between the RC and the XTAL when the softdevice >is running?

It seems as long as softdevice works it will not be possible to do it.

it would be better to wait for support engineers to respond.

[Vidar Berg]

Hello,

You can use sd_clock_hfclk_request() and sd_clock_hfclk_release() to request/release the HFXO after the Softdevice is enabled.

As you have already experienced, writing directly to the CLOCK registers after enabling the Softdevice doesn't work. The reason is that CLOCK is one of the peripheral which the softdevice reserves access to (Hardware peripherals) and writing to its registers will trigger the Memory isolation and runtime protection mechanism.

[cmag]

I have seen in the documentation that the program should wait for sd_clock_hfclk_is_running() to return true to be sure the clock switched to xtal. What is expected duration of the switch? Just to know if it is appropriate to wait in a loop or it is preferable to switch to low power while waiting.

[Vidar Berg]

The start up time is less than 1 ms, an usually closer to around 0.3 ms (depends on crystal and load capacitance).