A clock frequency is controlled by determining a cumulative duty cycle according to a ratio of a cumulative time, during an interval, that the clock frequency has a frequency greater than or equal to a design frequency threshold value to a duration of the interval. A frequency of the clock frequency is controlled to be a first frequency value when the cumulative duty cycle is less than a first duty cycle threshold; and controlled to be a second frequency value substantially less than the first frequency value when the cumulative duty cycle is greater than a second duty cycle threshold. The second duty cycle threshold is greater than or equal to the first duty cycle threshold.
