15.6.2.6 Selecting a Clock Source for the Generic Clock Generator

Each Generator can individually select a clock source by setting the Source Select bit group in GENCTRL (GENCTRL.SRC).

Changing from one clock source, for example A, to another clock source, B, can be done on the fly: If clock source B is not ready, the Generator will continue running with clock source A. As soon as clock source B is ready, however, the generic clock generator will switch to it. During the switching operation, the Generator holds clock requests to clock sources A and B and then releases the clock source A request when the switch is done.

The available clock sources are device dependent (usually the crystal oscillators, RC oscillators, PLL and DFLL). Only GCLKGEN[1] can be used as a common source for all other generators except Generator 1.

Note: Before switching the Generic Clock Generator 0 (GCLKGEN0) from a clock source A to another clock source B, enable the "ONDEMAND" feature of the clock source A to ensure a proper transition from clock source A to clock source B.