Clock source

The SoftDevice can use one of two available low frequency clock sources: the internal RC Oscillator, or external Crystal Oscillator.

The application must provide the selected clock source and some clock source characteristics, such as accuracy, when it enables the SoftDevice. The SoftDevice Manager is responsible for configuring the low frequency clock source and for keeping it calibrated when the RC oscillator is the selected clock source.

If the SoftDevice is configured with the internal RC oscillator clock option, clock calibration is required periodically, and when a temperature change of more than 0.5 degrees has occurred to adjust the RC oscillator frequency. See the relevant product specification (S132 SoftDevice core documentation) for more information. The SoftDevice will perform this function automatically. The application may choose how often the SoftDevice will make a measurement to detect temperature change depending on how frequently significant temperature changes are expected to occur in the intended environment of the end product. It is recommended to use a temperature polling interval of 4 seconds, and to force clock calibration every second interval (.ctiv=16, .temp_ctiv=2).