Serial communication and interval timer integration problems

Thanks for the answer. I'm new to this ans studying by myself.

I'm not using sys_clk_timer nor timerstamp_timer. Is it necessary to create them in QSYS and define in Nios IDE?

In examples I've noticed that usually interrupt handling functions defined as static and some variables defined as volatile. When do I have to use this definitions?

I'm also using timers for a fan control: PWM and tachometer. Timer for a PWM is very dynamic, but still it works without any problems.