15.6.3.4 Configuration Lock

The generic clock configuration can be locked for further write accesses by setting the Write Lock bit in the CLKCTRL register (CLKCTRL.WRTLOCK). All writes to the CLKCTRL register will be ignored. It can only be unlocked by a Power Reset.

The Generator source of a locked generic clock are also locked, too: The corresponding GENCTRL and GENDIV are locked, and can be unlocked only by a Power Reset.

There is one exception concerning the GCLKGEN[0]. As it is used as GCLK_MAIN, it can not be locked. It is reset by any Reset and will start up in a known configuration. The software reset (CTRL.SWRST) can not unlock the registers.