[20] RTC: Register values are invalid

This anomaly applies to IC Rev. Rev 2, build codes QFAA-E00, CIAA-E00, QFAB-E00.

It was inherited from the previous IC revision Rev 1.

Symptoms

RTC registers will not contain the correct/expected value if read.

Conditions

The RTC has been idle.

Consequences

RTC configuration cannot be determined by reading RTC registers.

Workaround

Execute the below code before you use RTC.
 
NRF_CLOCK->EVENTS_LFCLKSTARTED  = 0;
NRF_CLOCK->TASKS_LFCLKSTART     = 1;
while (NRF_CLOCK->EVENTS_LFCLKSTARTED == 0) {}
NRF_RTC0->TASKS_STOP = 0;