Fast internal timer/interrupt for Due

Hi,

I'm at the very beginning and just try to get a feeling for the Arduino Due - with a focus to what I plan to do with it. So to find a starting point I'm asking this possibly stupid question:

I need a timer/cyclic internal interrupt that executes a function repeatedly with a clock of 4 MHz (should be possible on a Due with 84 MHz). My question: how can I do that? Are there any useful code examples out there?

Thanks!