DRV10866 Starting position of FG output

Hi,

My customer is using DRV10866.
He has a issue about Starting position of FG output.
He uses FG signal to confirm position motor.
and he say that "DRV10866 has 3 point of starting(occurring) position of FG signal".

Could you let me know mechanism of FG frequency generator in DRV10866, please?
Can customer use FG signal as position detector?
->Customer want to know motor position by FG starting position and FG clock count.

Best regards,
Shimizu