A 1KHz oscillator clock (CLK_WDT_OSC) is sourced from the internal ultra-low-power oscillator, OSCULP32K. Due to the ultra-low-power design, the oscillator is not very accurate, and so the exact time-out period may vary from device to device. This variation must be kept in mind when designing software that uses the WDT to ensure that the time-out periods used are valid for all devices.

The counter clock CLK_WDT_OSC is asynchronous to the system clock. Due to this asynchronicity, writing to WDT control register will require synchronization between the clock domains.