: Processors used in portable systems must provide highly energy-efficient operation, due to the importance of battery weight and size, without compromising high performance when the user requires it. The user-dependent modes of operation of a processor in portable systems are described and separate metrics for energy efficiency for each of them are found to be required. A variety of well known low-power techniques are re-evaluated against these metrics and in some cases are not found to be appropriate leading to a set of energy-efficient design principles. Also, the importance of idle energy reduction and the joint optimization of hardware and software will be examined for achieving the ultimate in lowenergy, high-performance design. 1. Introduction The recent explosive growth in portable electronics requires energy conscious design, without sacrificing performance. Simply increasing the battery capacity is not sufficient because the battery has become a significant fraction of the t...

Portable systems demand energy efficiency in order to maximize battery life. IRAM architectures, which combine DRAM and a processor on the same chip in a DRAM process, are more energy efficient than conventional systems. The high density of DRAM permits a much larger amount of memory on-chip than a traditional SRAM cache design in a logic process. This allows most or all IRAM memory accesses to be satisfied on-chip. Thus there is much less need to drive high-capacitance off-chip buses, which contribute significantly to the energy consumption of a system. To quantify this advantage we apply models of energy consumption in DRAM and SRAM memories to results from cache simulations of applications reflective of personal productivity tasks on low power systems. We find that IRAM memory hierarchies consume as little as 22% of the energy consumed by a conventional memory hierarchy for memoryintensive applications, while delivering comparable performance. Furthermore, the energy consumed by a s...

In this paper we identify the most prominent problems of wireless multimedia networking and present several state-of-the-art solutions with a focus on energy efficiency. Three key problems in networked wireless multimedia systems are 1) the need to maintain a minimum quality of service over time-varying channels, 2) to operate with limited energy resources, and 3) to operate in a heterogeneous environment. We identify two main principles to solve these problems. The first principle is that energy efficiency should involve all layers of the system. Second, Quality of Service is an essential mechanism for mobile multimedia systems not only to give users an adequate level of service, but also as a tool to achieve an energy-efficient system. Due to the dynamic wireless environment, adaptability of the system will be a key issue in achieving this. Keywords -- energy efficiency, wireless networking, mobile computing, quality of service. 1 Introduction Advances in technology enabl...

Portable products are being used increasingly. Because these systems are battery powered, reducing power consumption is vital. In this report we give the properties of low power design and techniques to exploit them on the architecture of the system. We focus on: minimizing capacitance, avoiding unnecessary and wasteful activity, and reducing voltage and frequency. We review energy reduction techniques in the architecture and design of a hand-held computer and the wireless communication system, including error control, system decomposition, communication and MAC protocols, and low power short range networks.

Portable products such as pagers, cordless and digital cellular telephones, personal audio equipment, and laptop computers are increasingly being used. Because these applications are battery powered, reducing power consumption is vital. In this report we first give a survey of techniques for accomplishing energy reduction on the hardware level such as: low voltage components, use of sleep or idle modes, dynamic control of the processor clock frequency, clocking regions, and disabling unused peripherals. Systemdesign techniques include minimizing external accesses, minimizing logic state transitions, and system partitioning using application-specific coprocessors. Then we review energy reduction techniques in the design of operating systems, including communication protocols, caching, scheduling and QoS management. Finally, we give an overview of policies to optimize the code of the application for energy consumption and make it aware of power management functions. Applications play a c...

Portable products such as pagers, cordless and digital cellular telephones, personal audio equipment, and laptop computers are being used increasingly. Because these applications are battery powered, reducing power consumption is vital. In this report we first give the properties of low power design and techniques to exploit them on the hardware level such as: minimize capacitance, avoid wasteful activity, and reduce voltage and frequency. We will then elaborate on low power system-design techniques in which the main themes are to avoid wasteful activity at system level and to exploit locality of reference. Finally we review energy reduction techniques in the design of a wireless communication system, including system decomposition, communication and MAC protocols, and low power short range networks. 1 Introduction The requirement of portability of hand-held computers and portable devices places severe restrictions on size and power consumption. Even though battery technology is impr...

Introduction The portability requirement of hand-held computers and other portable devices places severe restrictions on size and power consumption. Even though battery technology is improving continuously and processors and displays are rapidly improving in terms of power consumption, battery life and battery weight are issues that will have a marked influence on how hand-held computers can be used. These devices often require realtime processing capabilities, and thus demand high throughput. Power consumption is becoming the limiting factor in the amount of functionality that can be placed in these devices. More extensive and continuous use of network services will only aggravate this problem since communication consumes relatively much energy. Research is needed to provide policies for careful management of the energy consumption while still providing the appearance of continuous connections to system services and applications. In this chapter we will explore sources of energy c