NIOS II C code tips?

i know but it's for a small research project in a class of mine. I did a pwm model using quartus and VHDL code and i need to do one using SOPC Builder and NIOS to compare the timing analysis results between the two.

the system itself is very simple i have 8 input PIO to fix the duty cycle wanted and one output and while the c code itself is very easy i can't find any document that explain how to write a c project for NIOS from Zero or how to write the C code in NIOS (like using IOWR and IORD for example). we find one in Chinese so it wasn't very helpful although the illustration in it did make things a little clear...