19.6.3.4 Configuration Lock

The peripheral clock configuration can be locked for further write accesses by setting the Write Lock bit in the Peripheral Channel Control register PCHCTRLm.WRTLOCK=1). All writing to the PCHCTRLm register will be ignored. It can only be unlocked by any reset.

The Generator source of a locked Peripheral Channel will be locked too. The corresponding GENCTRLn register is locked, and can be unlocked only by any reset.

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