The present invention relates to processing apparatus utilising dynamic scaling of voltage (DVS), and in particular although not exclusively to a controller for such apparatus. The invention is especially applicable to software defined radio (SDR), but is not so limited and may be applied to other re-configurable electronic systems. The present invention provides a controller for a processing apparatus having a plurality of processing resources, at least some of said resources having controllable supply voltage and/or frequency; the controller comprising: means for scheduling operations on said resources, at least some of said operations having a predetermined deadline by which the operation must be performed; means for determining a voltage and/or frequency profile for a said operation having a said deadline; and means for instructing the resources to perform said operations according to said schedule and said profile.