The SoftDevice can use one of three available LFCLK sources: the internal RC oscillator, external crystal oscillator, or synthesized low-frequency clock. The synthesized low-frequency clock is not tested or intended for use with the Bluetooth® Low Energy protocol stack.
The application must provide the selected clock source and some clock source characteristics, such as accuracy, when it enables the SoftDevice. The SoftDevice Manager (SDM) is responsible for configuring the LFCLK 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, periodic clock
calibration is required to adjust the RC oscillator frequency. Additional calibration is
required for temperature changes of more than 0.5°C. See the relevant product specification
(Additional 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. The application must
consider 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 (.rc_ctiv=16,
.rc_temp_ctiv=2).