20.5.2.3 Generic Clock Generator
Each Generator (GCLK_GEN) can be set to run from one of 11 different clock sources, GENCTRLn.SRC, except GCLK_GEN[1], which can be set to run from one of seven sources. GCLK_GEN1 is the only Generator that can be selected as source to others Generators.
Each Generator GCLK_GEN[x] can be connected to only one specific pin GCLK_IO[x] in a one-to-one GCLK_GENx to GCLK_IOx relationship. A pin GCLK_IO[x] can be set either to act as source to GCLK_GEN[x] or to output the clock signal generated by GCLK_GEN[x].
The selected source can be divided. Each Generator can be enabled or disabled independently.
Each GCLK_GEN clock signal can then be used as the clock source for Peripheral Channels. Each Generator output is allocated to one or several Peripherals.
GCLK_GEN[0] is used as GCLK_MAIN for the synchronous clock controller inside the Main Clock Controller. Refer to the Main Clock Controller section for details on synchronous clock generation.