Disabling the clock hangs when using LFCLK with an active watchdog

[dmitry.gorohov]

Using LFCLK, enabling and running the WDT causes the nRF52840 to hang until the watchdog reset when calling nrf_drv_clock_lfclk_release. This is with SDK v15.2.0
Steps to recreate 

1) start the lfclk by 
ret_code_t err_code = nrf_drv_clock_init();
APP_ERROR_CHECK(err_code);
nrf_drv_clock_lfclk_request(NULL);

2) stop the clock 

nrf_drv_clock_lfclk_release();
NRF_LOG_INFO("clock release.");
nrf_drv_clock_uninit();


3) init the BLE Device as mentioned in the BLE Example 
void iot_ble_initialize(void)
{
    ble_stack_init();
    gap_params_init();
    gatt_init();
    advertising_init();
    services_init();
    conn_params_init();
}

4) reset  after 3 mins and go back to step1If the resets continuously happen
then randomly I see that the nrf_drv_clock_lfclk_release is getting stuck 

I was able to trace the call to following:
a. nrf_drv_clock_lfclk_release
b. lfclk_stop
c. nrfx_clock_lfclk_stop
d. while(nrf_clock_lf_is_running()). <--- Hangs here Is there a reason as to why the nrf_drv_clock_lfclk_release is getting stuck

Thanks in advance.

[Vidar Berg]

Hi,

The reason the program gets stuck in this while loop is that it's not possible the release the LF clock while the WD timer is running.  Excerpt from the PS:

When started, the watchdog will automatically force the 32.768 kHz RC oscillator on as long as no other 32.768 kHz clock source is running and generating the 32.768 kHz system clock, see chapter CLOCK — Clock control.

But is it necessary to disable the LF clock source in your case?