For question1, The user can use the GUI to adjust the location of zero and gain in the frequency domain to get desired loop gain bandwidth and phase margin. And the filter gain and zero in the digital domain is calculated by the GUI according on the compensator in the Filter setting window.
For question 2, P1 and P2 are not using linear format as Read_PIN command, they are using their own format. The equation is
P=Register_value*1.6*0.75*(R1+R2)/(212*R2*Rsense)
Rsense is the current sensing resistor, R1 is the top equivalent resistor of the equivalent voltage divider for VAC and R2 is the bottom equivalent resistor of the equivalent voltage divider for VAC