Abstract: Digital circuitry synchronizes clock signals in a digital circuit. A value of a reference clock is sampled at a plurality of points near a transition point of a generated clock. It is determined whether the reference clock transitioned from a first state to a second state before, after or within an acceptable range of a transition point of the generated clock. Upon determining that the reference clock transitioned before the transition point of the generated clock, one period of the generated clock is shortened. Upon determining that the reference clock transitioned after the transition point of the generated clock, one period of the generated clock is lengthened.