An apparatus and a method of controlling a processor clock frequency are provided. The apparatus comprises a hardware counter to count write accesses to a memory buffer during a predetermined period of time, a hardware comparator to compare a number of write accesses counted by the hardware counter with at least one predetermined threshold value, the hardware comparator further to generate a control signal, the control signal being dependent on a result of a comparison of a number of write accesses counted by the hardware counter with at least one predetermined threshold value performed by the hardware comparator, and a clock frequency setting circuit to set a clock frequency of a processor depending on the control signal.