29.5.3 Clocks
The SERCOM uses two generic clocks: GCLK_SERCOMx_CORE and GCLK_SERCOMx_SLOWGCLK_SERCOMx_SLOW. The core clock (GCLK_SERCOMx_CORE) is required to clock the SERCOM while working as a host. The slow clock (GCLK_SERCOMx_SLOW) is only required for certain functions. See specific mode chapters for details.
These clocks must be configured and enabled in the Clock and Reset Unit (CRU) registers before using the SERCOM.
The generic clocks are asynchronous to the bus clock (PBx_CLK). Therefore, writing to certain registers will require synchronization between the clock domains.