Optical scanning systems and methods of controlling a resonant scanning mirror are disclosed. A rotatable mirror may oscillate about a rotation axis in response to a drive signal. A reference source may provide a reference light beam directed to the rotatable mirror. A reference detector may be disposed to receive the reference light beam reflected from the rotatable mirror twice during each oscillation of the rotatable mirror. A controller may set both an amplitude and a frequency of the drive signal based on an output of the reference detector.