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106
A Dynamic Voltage Scaling Algorithm for DynamicPriority Hard RealTime Systems Using Slack Time Analysis
 In Proceedings of Design Automation and Test in Europe
, 2002
"... Dynamic voltage scaling (DVS), which adjusts the clock speed and supply voltage dynamically, is an effective technique in reducing the energy consumption of embedded realtime systems. The energy efficiency of a DVS algorithm largely depends on the performance of the slack estimation method used in i ..."
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Cited by 84 (12 self)
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Dynamic voltage scaling (DVS), which adjusts the clock speed and supply voltage dynamically, is an effective technique in reducing the energy consumption of embedded realtime systems. The energy efficiency of a DVS algorithm largely depends on the performance of the slack estimation method used in it. In this paper, we propose a novel DVS algorithm for periodic hard realtime tasks based on an improved slack estimation algorithm. Unlike the existing techniques, the proposed method takes full advantage of the periodic characteristics of the realtime tasks under prioritydriven scheduling such as EDF. Experimental results show that the proposed algorithm reduces the energy consumption by 20#40% over the existing DVS algorithm. The experiment results also show that our algorithm based on the improved slack estimation method gives comparable energy savings to the DVS algorithm based on the theoretically optimal (but impractical) slack estimation method.
Static and dynamic variable voltage scheduling algorithms for realtime heterogeneous distributed embedded systems
 In the 15th International Conference on VLSI Design (VLSID’02
, 2002
"... This paper addresses the problem of static and dynamic variable voltage scheduling of multirate periodic task graphs (i.e., tasks with precedence relationships) and aperiodic tasks in heterogeneous distributed realtime embedded systems. Such an embedded system may contain generalpurpose processor ..."
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Cited by 55 (0 self)
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This paper addresses the problem of static and dynamic variable voltage scheduling of multirate periodic task graphs (i.e., tasks with precedence relationships) and aperiodic tasks in heterogeneous distributed realtime embedded systems. Such an embedded system may contain generalpurpose processors, fieldprogrammable gate arrays (FPGAs) and applicationspecific integrated circuits (ASICs). Variable voltage scheduling is performed only on generalpurpose processors. The static scheduling algorithm constructs a variable voltage schedule via heuristics based on critical path analysis and task execution order refinement. The algorithm redistributes the slack in the initial schedule and refines task execution order in an efficient manner. The variable voltage schedule guarantees all the hard deadlines and precedence relationships of periodic tasks. The dynamic scheduling algorithm is also based on an initially valid static schedule. The objective of the online scheduling algorithm is to provide besteffort service to soft aperiodic tasks, as well as to reduce the system power consumption by determining clock frequencies (and correspondingly supply voltages) for different tasks at runtime, while still guaranteeing the deadlines and precedence relationships of hard realtime periodic tasks. 1.
EnergyAware Adaptive Checkpointing in Embedded RealTime Systems
, 2003
"... We present an integrated approach that provides fault tolerance and dynamic power management for a realtime task executing in an embedded system. Fault tolerance is achieved through an adaptive checkpointing scheme that dynamically adjusts the checkpointing interval during task execution. Adaptive ..."
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Cited by 53 (6 self)
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We present an integrated approach that provides fault tolerance and dynamic power management for a realtime task executing in an embedded system. Fault tolerance is achieved through an adaptive checkpointing scheme that dynamically adjusts the checkpointing interval during task execution. Adaptive checkpointing is then combined with a dynamic voltage scaling scheme to achieve power reduction. The resulting energyaware adaptive checkpointing scheme uses a dynamic voltage scaling criterion that is based not only on the slack in task execution but also on the occurrences of faults during task execution. Simulation results show that compared to previous methods, the proposed approach significantly reduces power consumption and increases the likelihood of timely task completion in the presence of faults.
Variable Voltage Task Scheduling Algorithms for Minimizing Energy/Power
, 1999
"... In this paper we propose variable voltage task scheduling algorithms that minimize energy or minimize peak power for the case when the task arrival times, deadline times, execution times, periods and switching activities are given. We consider aperiodic (earliest due date, earliest deadline first), ..."
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Cited by 45 (2 self)
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In this paper we propose variable voltage task scheduling algorithms that minimize energy or minimize peak power for the case when the task arrival times, deadline times, execution times, periods and switching activities are given. We consider aperiodic (earliest due date, earliest deadline first), as well as periodic (rate monotonic, earliest deadline first) scheduling algorithms. We use the Lagrange multiplier method to theoretically determine the relation between the task voltages such that the energy or peak power is minimum, and then develop an iterative algorithm that tries to satisfy the relation. We propose two implementations of the iterative algorithm: a low complexity one and an exact one. The asymptotic complexity of the existing scheduling algorithms change very mildly with the application of the proposed algorithms. We show experimentally (random experiments as well as reallife cases), that the voltage assignment obtained by the proposed low complexity algorithm is very close to that of the optimal energy (0.1% error) and optimal peak power (1% error) assignment. Furthermore, we consider the e#ect of the delay to change the converter voltage and the clock frequency.
Minimum Energy FixedPriority Scheduling for Variable Voltage Processors
, 2002
"... To fully exploit the benefit of variable voltage processors, voltage schedules must be designed in the context of work load requirement. In this paper, we present an approach to finding the leastenergy voltage schedule for executing realtime jobs on such a processor according to a fixed priority, p ..."
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Cited by 40 (3 self)
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To fully exploit the benefit of variable voltage processors, voltage schedules must be designed in the context of work load requirement. In this paper, we present an approach to finding the leastenergy voltage schedule for executing realtime jobs on such a processor according to a fixed priority, preemptive policy. The significance of our approach is that the theoretical limit in terms of energy saving for such systems is established, which can thus serve as the standard to evaluate the performance of various heuristic approaches. Two algorithms for deriving the optimal voltage schedule are provided. The first one explores fundamental properties of voltage schedules while the second one builds on the first one to further reduce the computational cost. Experimental results are shown to compare the results of this paper with previous ones.
EnergyEfficient Mapping and Scheduling for DVS Enabled Distributed Embedded Systems
 In Proc. DATE02
, 2002
"... In this paper, we present an efficient twostep iterative synthesis approach for distributed embedded systems containing dynamic voltage scalable processing elements (DVSPEs), based on genetic algorithms. The approach partitions, schedules, and voltage scales multirate specifications given as task ..."
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Cited by 35 (5 self)
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In this paper, we present an efficient twostep iterative synthesis approach for distributed embedded systems containing dynamic voltage scalable processing elements (DVSPEs), based on genetic algorithms. The approach partitions, schedules, and voltage scales multirate specifications given as task graphs with multiple deadlines. A distinguishing feature of the proposed synthesis is the utilisation of a generalised DVS method. In contrast to previous techniques, which ”simply ” exploit available slack time, this generalised technique additionally considers the PE power profile during a refined voltage selection to further increase the energy savings. Extensive experiments are conducted to demonstrate the efficiency of the proposed approach. We report up to 43.2 % higher energy reductions compared to previous DVS scheduling approaches based on constructive techniques and total energy savings of up to 82.9 % for mapping and scheduling optimised DVS systems. 1. Introduction and Related
Energy Reduction Techniques for Multimedia Applications with Tolerance to Deadline Misses
 in ACM/IEEE Design Automation Conference (DAC), 2003
, 2003
"... Many embedded systems such as PDAs require processing of the given applications with rigid power budget. However, they are able to tolerate occasional failures due to the imperfect human visual/auditory systems. The problem we address in this paper is how to utilize such tolerance to reduce multimed ..."
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Cited by 34 (10 self)
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Many embedded systems such as PDAs require processing of the given applications with rigid power budget. However, they are able to tolerate occasional failures due to the imperfect human visual/auditory systems. The problem we address in this paper is how to utilize such tolerance to reduce multimedia system's energy consumption for providing guaranteed quality of service at the user level in terms of completion ratio. We explore a range of o#ine and online strategies that take this tolerance into account in conjunction with the modest nondeterminism in application's execution time. First, we give a simple beste#ort approach that achieves the maximum completion ratio; then we propose an enhanced online beste#ort energy minimization (BEEM) approach and a hybrid o#ine/online minimume #ort (O ME) approach. We prove that BEEM maintains the maximum completion ratio while consuming the provably least amount of energy and O ME guarantees the required completion ratio statistically. We apply both approaches to a variety of benchmark task graphs, most from popular DSP applications. Simulation results show that significant energy savings (38% for BEEM and 54% for O ME, both over the simple beste#ort approach) can be achieved while meeting the required completion ratio requirements.
What is the Limit of Energy Saving by Dynamic Voltage Scaling?
, 2001
"... Dynamic voltage scaling (DVS) is a technique that varies the supply voltage and clock frequency based on the computation load to provide desired performance with the minimal amount of energy consumption. It has been demonstrated as one of the most effective low power system design techniques, in pa ..."
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Cited by 34 (8 self)
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Dynamic voltage scaling (DVS) is a technique that varies the supply voltage and clock frequency based on the computation load to provide desired performance with the minimal amount of energy consumption. It has been demonstrated as one of the most effective low power system design techniques, in particular for real time systems. Previously, there are works on both ends of the DVS systems: the ideal variable voltage system which can change its voltage with no physical constraints, and the multiple voltage system which has a number of discrete voltages available simultaneously. In this paper, we study the DVS systems between these two extreme cases. We consider systems that can vary the operating voltage dynamically under various reallife physical constraints. Based on the system's different behavior during voltage transition, we define the feasible DVS system and the practical DVS system. We build mathematical model to analyze the potential of DVS on energy saving for these different systems. Finally, we simulate the behavior of a secure wireless communication networks with DVS systems. The results show that DVS results in energy reduction from 36% to 79%, and the real life DVS systems can be very close to the ideal system in energy saving.
A Realistic Variable Voltage Scheduling Model for RealTime Applications
 In Proc. ICCAD02
, 2002
"... Voltage scheduling is indispensable for exploiting the benefit of variable voltage processors. Though extensive research has been done in this area, current processor limitations such as transition overhead and voltage level discretization are often considered insignificant and are typically ignored ..."
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Cited by 34 (4 self)
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Voltage scheduling is indispensable for exploiting the benefit of variable voltage processors. Though extensive research has been done in this area, current processor limitations such as transition overhead and voltage level discretization are often considered insignificant and are typically ignored. We show that for hard, realtime applications, disregarding such details can lead to suboptimal or even invalid results. We propose two algorithms that guarantee valid solutions. The first is a greedy yet simple approach, while the second is more complex but significantly reduces energy consumption under certain conditions. Through experimental results on both real and randomly generated systems, we show the effectiveness of both algorithms, and explore what conditions make it beneficial to use the complex algorithm over the basic one. 1.
A dynamic voltage scaling algorithm for sporadic tasks
, 2003
"... Dynamic voltage scaling (DVS) algorithms save energy by scaling down the processor frequency when the processor is not fully loaded. Many algorithms have been proposed for periodic and aperiodic task models but none support the canonical sporadic task model. A DVS algorithm, called DVSST, is present ..."
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Cited by 33 (1 self)
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Dynamic voltage scaling (DVS) algorithms save energy by scaling down the processor frequency when the processor is not fully loaded. Many algorithms have been proposed for periodic and aperiodic task models but none support the canonical sporadic task model. A DVS algorithm, called DVSST, is presented that can be used with sporadic tasks in conjunction with preemptive EDF scheduling. The algorithm is proven to guarantee each task meets its deadline while saving the maximum amount of energy possible with processor frequency scaling. DVSST was implemented in the µC/OSII realtime operating system for embedded systems and its overhead was measured using a standalone Rabbit 2000 test board. Though theoretically optimal, the actual power savings realized with DVSST is a function of the sporadic task set and the processor’s DVS support. It is shown that the DVSST algorithm achieves 83 % of the theoretical power savings for a Robotic Highway Safety Marker realtime application. The difference between the theoretical power savings and the actual power savings is due to the limited number of frequency levels the Rabbit 2000 processor supports. 1