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Dynamic Voltage Scaling (DVS) and Dynamic Power Management (DPM) techniques form the basis of numerous energy management schemes proposed for real-time embedded systems. DVS targets reducing the dynamic CPU energy consumption, while DPM attempts to reduce theenergy consumption of idle devices by putting them to low-power states over sufficiently long intervals. It is imperative that the system-wide energy management schemes efficiently integrate DVS and DPM while exploiting the subtle trade-off dimensions. In this paper, we develop and propose a unified framework for periodic real-time tasks where DVS and DPM are judiciously combined. The framework, called DFR-EDF, assumes a general system-level energy model and includes both static and dynamic(online) components. The static part is based on the extension of the recently proposed Device Forbidden Regions (DFRs) approach to Earliest-Deadline-First (EDF) scheduling. The online component integrates the predictive DPM techniques and offers a generalized slack reclaiming mechanism that can be used by DVS and DPM simultaneously. Our experimental evaluation indicates significant gains of DFR-EDF at the system-level compared to the state-of-the-art solutions. Finally, this research effort makes another contribution by formally showing that optimally solving the DPM problem in periodic real-time execution settings is NP-Hard in the strong sense, even in the absence of DVS.