See the top level README for information on where to find the schematic and programmers reference manual for the ARM processor on the raspberry pi. Also find information on how to load and run these programs. There is a free-running 64 bit timer, super easy to use, just read it. Based on a couple of experiments, without messing with anything else it appears that the timer is runing at about a megahertz, 1 million ticks per second. Hmm, there are comments in the manual about the system clock coming up at 250MHz. I wonder if this system timer is 250MHz/256 = 0.976MHz.