Dynamic power management (DPM) is a design methodology for dynamically reconfiguring systems to provide the requested services and performance levels with a minimum number of active components or a minimum load on such components. DPM encompasses a set of techniques that achieves energy-efficient computation by selectively turning off (or reducing the performance of) system components when they are idle (or partially unexploited). In this paper, we survey several approaches to system-level dynamic power management. We first describe how systems employ power-manageable components and how the use of dynamic reconfiguration can impact the overall power consumption.We then analyze DPM implementation issues in electronic systems, and we survey recent initiatives in standardizing the hardware/software interface to enable software-controlled power management of hardware components.

Battery lifetime extension is a primary design objective for portable systems. We introduce the concept of battery-driven dynamic power management, which strives to enhance lifetime by automatically adapting discharge rate and current profiles to battery charge state.

Energy-efficient design of battery-powered systems demands optimizations in both hardware and software. We present a modular approach for enhancing instruction level simulators with cycle-accurate simulation of energy dissipation in embedded systems. Our methodology has tightly coupled component models thus making our approach more accurate. Performance and energy computed by our simulator are within a 5% tolerance of hardware measurements on the SmartBadge. We show how the simulation methodology can be used for hardware design exploration aimed at enhancing the SmartBadge with real-time MPEG video feature. In addition, we present a profiler that relates energy consumption to the source code. Using the profiler we can quickly and easily redesign the MP3 audio decoder software to run in real time on the SmartBadge with low energy consumption. Performance increase of 92% and energy consumption decrease of 77% over the original executable specification have been achieved.

For portable applications, long battery lifetime is the ultimate design goal. Therefore, the availability of battery and voltage converter models providing accurate estimates of battery lifetime is key for system-level low-power design frameworks. In this paper, we introduce a discrete-time model for the complete power supply subsystem that closely approximates the behavior of its circuit-level continuous-time counterpart. The model is abstract and efficient enough to enable event-driven simulation of digital systems described at a very high level of abstraction and that includes, among their components, also the power supply. The model gives the designer the possibility of estimating battery lifetime during system-level design exploration, as shown by the results we have collected on meaningful case studies. In addition, it is flexible and it can thus be employed for different battery chemistries.

Abstract-In this paper, we describe a software-controlled approach for adaptively minimizing energy in embedded systems for real-time multimedia processing. Energy is optimized by clock speed setting: the software controller dynamically adjusts processor clock speed to the frame rate (FR) requirements of the incoming multimedia stream. The speed-setting policy is based on a system model that correlates clock speed with best case, average case, and worst case sustainable FRs, accounting for data dependency in multimedia streams. The technique has been implemented in a energy-efficient MPEG3 real-time decoder algorithm designed for wearable devices as a case study. The target system is the Hewlett-Packard SmartBadgeIII prototype system based on the StrongARM1100 processor. Hardware measurements show that computational energy can be drastically reduced (up to 40%) with respect to fixed-frequency operation.