23.4.3 Clocks

The WDT bus clock (CLK_WDT_APB) can be enabled and disabled (masked) in the Main Clock module (MCLK).

A 1024 Hz oscillator clock (CLK_WDT_OSC) is required to clock the WDT internal counter.

The CLK_WDT_OSC clock is sourced from the clock of the internal Ultra Low-Power Oscillator (OSCULP32K).

CAUTION: Watchdog time-out period variations must be considered when implementing software that uses the WDT to ensure that the time-out periods used are valid for all devices. Refer to the OSCULP32K Electrical Specifications section of the Electrical Characteristics chapter.

The counter clock CLK_WDT_OSC is asynchronous to the bus clock (CLK_WDT_APB). Due to this asynchronicity, writing to certain registers will require synchronization between the clock domains. Refer to Synchronization section for further details.

Note: The FREQM module can be used to calibrate the output of the OSCULP32K clock against a refererence clock, thereby reducing the uncertainty in setting WDT windows.