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.

Abstract—A microprocessor system is presented in which the supply voltage and clock frequency can be dynamically varied so that the system can deliver high throughput when required while significantly extending battery life during the low speed periods. The system consists of a dc-dc switching regulator, an ARM V4 microprocessor with a 16-kB cache, a bank of 64-kB SRAM ICs, and an I/O interface IC. The four custom chips were fabricated in a standard 0.6- m 3-metal CMOS process. The system can dynamically vary the supply voltage from 1.2 to 3.8 V in less than 70 s. This provides a throughput range of 6–85 MIPS with an energy consumption of 0.54–5.6 mW/MIP yielding an effective energy efficiency as high as 26 200 MIPS/W. Index Terms—Adaptive processor, energy efficient, low power, variable voltage. I.

Low power has emerged as a principal theme in today's electronics industry. The need for low power has caused a major paradigm shift in which power dissipation is as important as performance and area. This article presents an in-depth survey of CAD methodologies and techniques for designing low power digital CMOS circuits and systems and describes the many issues facing designers at architectural, logic and physical levels of design abstraction. It reviews some of the techniques and tools that have been proposed to overcome these difficulties and outlines the future challenges that must be met to design low power, high performance systems.

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The energy efficiency of systems-on-a-chip can be much improved if one were to vary the supply voltage dynamically at run time. In this paper we describe the synthesis of systems-on-a-chip based on core processors, while treating voltage (and correspondingly, the clock frequency) as a variable to be scheduled along with the computation tasks during the static scheduling step. In addition to describing the complete synthesis design flow for these variable voltage systems, we focus on the problem of doing the voltage scheduling while taking into account the inherent limitation on the rates at which the voltage and clock frequency can be changed by the power supply controllers and clock generators. Taking these limits on rate of change into account is crucial since changing the voltage by even a volt may take time equivalent to 100s to 10,000s of instructions on modern processors. We present both an exact but impractical formulation of this scheduling problem as a set of non-linear equations, as well as a heuristic approach based on reduction to an optimally solvable restricted ordered scheduling problem. Using various task mixes drawn from a set of nine real-life applications, our results show that we are able to reduce power consumption to within 7% of the lower bound obtained by imposing no limit at the rate of change of voltage and clock frequencies.

The growing class of portable systems, such as personal computing and communication devices, has resulted in a new set of system design requirements, mainly characterized by dominant importance of power minimization and design reuse. The energy efficiency of systems-on-a-chip (SOC) could be much improved if one were to vary the supply voltage dynamically at run time. We develop the design methodology for the lowpower core-based real-time SOC based on dynamically variable voltage hardware. The key challenge is to develop effective scheduling techniques that treat voltage as a variable to be determined, in addition to the conventional task scheduling and allocation. Our synthesis technique also addresses the selection of the processor core and the determination of the instruction and data cache size and configuration so as to fully exploit dynamically variable voltage hardware, which results in significantly lower power consumption for a set of target applications than existing techniques. The highlight of the proposed approach is the nonpreemptive scheduling heuristic, which results in solutions very close to optimal ones for many test cases. The effectiveness of the approach is demonstrated on a variety of modern industrialstrength multimedia and communication applications.

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This paper presents a digital power supply controller for variable frequency and voltage circuits. By using a ring oscillator as a method of predicting circuit performance, the regulated voltage is set to the minimum required to operate at a reference frequency which maximizes energy efficiency. Our initial test silicon, implemented with a fixed frequency controller, is analyzed and reveals that the controller’s power consumption is a major limitation for such a design. To make the controller power dissipation scale with the CV2f power of the load, we introduce a new architecture with variable frequency control, which allows the control-ler’s supply and frequency to scale along with the load device.

The application of adaptive power-supply regulation is extended to serial links. The adaptive supply maximizes the energy -efficiency of the I/O circuits and serves as a global bias to scale the link properties optimally with the bitrate. Parallelism in transceivers and the use of multiphase clocks increase the bitrate to a multiple of the clock frequency and, hence, enable the lowfrequency low-voltage operation to reduce power while meeting the specified bitrate. Two key designs to enable this power saving are presented: parallelized transceivers for low-voltage operation and dual-loop architecture phase/delay-locked loop for multiphase clock distribution. A prototype chip fabricated in 0.25- m CMOS process operates at 0.65--5.0 Gb/s while dissipating 9.7--380 mW.

The paper describes a closed-loop controller for adaptive voltage scaling (AVS) where the supply voltage to a standard-cell ASIC is dynamically adjusted to the minimum value required for the desired system speed. The controller includes a clock generator that provides a low-jitter clock to the ASIC at all steady-state operating points and through transients. To speed up the voltage transient response to step changes in clock frequency, the controller is based on a multiple-tap resettable delay line. A chip including the AVS controller and a dual 16-bit MAC application has been fabricated in a standard 0.5 µ CMOS process. The area taken by the AVS controller is 0.12 mm². Experimental results demonstrate operation over the application clock frequency range from 80 kHz to 20 MHz, and a 38 µs transient response for a step change in speed from standby to maximum throughput operation.