12.3.7.2 Condition Clearing
The CFD condition is cleared after a Reset, the monitored source starts toggling again, or the
                        CFD flag in the Main Clock Interrupt Flags (CLKCTRL.MCLKINTFLAGS) register
                        is set. As long as the failure condition is met, the interrupt will trigger
                        every ten OSC32K cycles. If these repeated interrupts are not wanted, write
                        a ‘0’ to the Clock Failure Detection (CFD) interrupt enable
                        bit in the Main Clock Interrupt Control (CLKCTRL.MCLKCTRL) register. If it
                        is the main clock that is being monitored, changing back to the default
                        start-up clock will make the main clock start toggling again, clearing the
                        condition. 
