6.3.1 Starting of Clocks

After power-up, the device is set to its Initial state and kept in Reset until the power has stabilized throughout the device. Once the power has stabilized, the device will use a 1 MHz clock. This clock is derived from the 8 MHz Internal Oscillator (OSC8M), which is divided by eight and used as a clock source for generic clock generator 0. Generic clock generator 0 is the main clock for the Power Manager (PM).

Some synchronous system clocks are active, allowing software execution.

Refer to the Clock Mask Register section in the PM – Power Manager chapter for the list of default peripheral clocks running. Synchronous system clocks that are running are by default not divided and receive a 1 MHz clock through generic clock generator 0. Other generic clocks are disabled except GCLK_WDT, which is used by the Watchdog Timer (WDT).