LAUNCHXL-F28069M: In the InstaSPIN FOC lab11a, How is the mainISR called? & What is the sample time?

I am using the launchpad F28069M and DRV8305 inverter to control a PMSM without any sensor.

First, based on the lab 11a,  the mainISR calls almost all the controller function, but I cannot find anything to call the mainISR itself in the main void.  How is the mainISR called?

Second, I want to set a timing-varing speed reference, such like a real-time sine wave, to replace the original constant reference. Therefore, I add the code to generate real-time sine wave with denfining corresponding variables at the begin of proj_lab11a.c .

SineWave = sin (nTs);           

Should I add this code in the forever loop or  in the mainISR？If in the forever loop, I think, n will be  the counts of loop, then what should be the sample time Ts?

If in the mainISR, I think, n will be  the counts of mainISR. Similarly, what should be the sample time Ts?

Thank you very much!