A processing apparatus uses dynamic scaling of voltage (DVS) and includes a controller. This is particularly applicable to software defined radio (SDR), but may also be for other reconfigurable electronic systems. The controller includes a plurality of processing resources at least some of which have controllable supply voltage and/or frequency. The controller schedules operations on the resources, at least some of which have a predetermined deadline by which the operation must be performed, determines a voltage and/or frequency profile for an operation having a deadline, and instructs the resources to perform operations according to the schedule and the profile. The profile is determined by a voltage frequency profile calculator, for a processing resource for a predetermined task. The calculator determines metrics characterizing a probability distribution of cycle counts for completing the task using the resource, and determines a voltage profile for the next task depending on the metrics.