7.3.2 Starting of Clocks

Once the power has stabilized and the internal Reset is released, the device will use a 4MHz clock by default. The clock source for this clock signal is OSC16M, which is enabled and configured at 4MHz after a reset by default. This is also the default time base for Generic Clock Generator 0. In turn, Generator 0 provides the main clock GCLK_MAIN which is used by the Power Manager (PM).

Some synchronous system clocks are active after Start-Up, allowing software execution. Refer to the “Clock Mask Register” section in the PM-Power Manager documentation for the list of clocks that are running by default. Synchronous system clocks that are running receive the 4MHz clock from Generic Clock Generator 0. Other generic clocks are disabled.