A Dynamic Voltage Scaling Algorithm for Sporadic Tasks

Dynamic voltage scaling (DVS) algorithms save energy by scaling down the processor frequency when the processor is not fully loaded. Many algorithms have been proposed for periodic and aperiodic task models but none support the canonical sporadic task model. A DVS algorithm, called DVSST, is presented that can be used with sporadic tasks in conjunction with preemptive EDF scheduling. The algorithm is proven to guarantee each task meets its deadline while saving the maximum amount of energy possible with processor frequency scaling. DVSST was implemented in the μC/OS-II real-time operating system for embedded systems and its overhead was measured using a stand-alone Rabbit 2000 test board. Though theoretically optimal, the actual power savings realized with DVSST is a function of the sporadic task set and the processor’s DVS support. It is shown that the DVSST algorithm achieves 83% of the theoretical power savings for a Robotic Highway Safety Marker real-time application. The difference between the theoretical power savings and the actual power savings is due to the limited number of frequency levels the Rabbit 2000 processor supports.