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### Zephyr expects by default an external crystal clock By default, Zephyr assumes there's an external crystal and, at startup, it waits for that crystal to “settle” before continuing. OpenEarable EXG has by default no such crystal, and the NINA module doesn't contain one either. Its required to set in the project config `CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC`.

In addition, `CONFIG_CLOCK_CONTROL_NRF_K32SRC_RC_CALIBRATION` allows an internal calibration based on the fast high-frequency clock for the radio (BLE), based on heat changes, which might change the internal RC clock, it rechecks against the radio clock.