In userland you run library functions that call system functions or call those functions directly. The kernel carries out these actions for you.
In kernel programming, you are on the other side of the fence. You aren't using the same C runtime library and the same standard libraries. Functions like printf do not exist. There are books on Linux Kernel development. You will also need to resort to reading kernel source code, as the code changes rapidly.
For low-resolution time that also works if no high-resolution clocks are available look at "getnstimeofday".
Last edited by jschiwal; 01-29-2010 at 01:04 AM.