[192] CLOCK: LFRC frequency offset after calibration

This anomaly applies to IC Rev. Engineering C, build codes QIAA-CA0, CKAA-CA0.

It was inherited from the previous IC revision Engineering B nRF52840.

Symptoms

LFRC oscillator frequency is wrong after calibration, exceeding 500 ppm.

Conditions

On some devices, when entering System ON Idle while calibration is ongoing.

Consequences

After calibration, LFRC has a frequency offset that is outside specification.

Workaround

Apply the following code before starting the RCOSC32K calibration:

*(volatile uint32_t *)0x40000C34 = 0x00000002; 
Apply the following code after the RCOSC32K calibration is finished:

*(volatile uint32_t *)0x40000C34 = 0x00000000;
This workaround is included in SDK v15.0.0 and SoftDevices S140, S132, and S112 v6.0.0.