a circuit for providing commutation control signals to a commutator for a polyphase brushless dc motor in a mass data storage device includes an accumulator to accumulate a digital count that is proportional or related to a phase difference between the commutation control signals and a motor bemf . a digital variable frequency oscillator generates an oscillator output signal of frequency proportional to the digital count to reset the accumulator after a predetermined time determined by the frequency . the circuit may also include a digital filter between the digital accumulator and the digital variable frequency oscillator to generate a magnitude signal of magnitude proportional to the accumulated count for delivery to the variable frequency oscillator to control the frequency thereof .