Configuration of the MCLK for the Arduino Due

Hello everybody,

I have concerning the time and clock management of the Arduino Due (uC Atmel ATSAM3X8E). There are many different clocks and I do not really understand how to configure the PMC (Power Management Controller) to work at a specified frequency, what makes it difficult then to control time for the ADC and DAC for example.

Thank you in advance for your help ;-)!