JOURNAL OF COMPUTERS, VOL. 7, NO. 1, JANUARY 2012 147 Battery and Power Consumption of Pocket PCs Assim Sagahyroon Department of Computer Science and Engineering American University of Sharjah, UAE Email:[email protected] Abstract—Due to the increased functionality in today’s display. Energy consumption characterization in portable devices, battery life and energy consumption handheld devices for popular GUI platforms from the continue to be a major concern for both designers and users. hardware, software, and application perspectives was Unfortunately battery technology is not keeping pace with discussed in [4]. Such characterization provides a basis the energy requirements of these devices and therefore for further research on GUI energy optimization. The energy-efficient hardware design techniques, software optimization, energy management, and the design of power consumption of videos encoded using various efficient communication protocols continue to be explored codec standards and played on handheld devices was by researches as viable means that would assist in the presented in [2]. Experiments were performed to explore efficient use of the energy resources of these mobile devices. the effects of the choice of codec standards, file formats, In this paper, using results obtained from a number of and encoding parameters on power consumed. Since the experiments, we investigate battery utilization and power incorporation of 3D graphics in handhelds poses several consumption of two pocket PCs. Using benchmarks that are serious challenges to the hardware designer, an analysis representative of typical workloads, and by varying the of the power consumption of mobile 3D graphics operating conditions of these devices we were able to explore pipelines and the effects of various 3D graphics factors the impact of a number of features available in these devices on battery life and the power consumed. such as resolution, frame rate, level of detail, lighting and Characterizing the consumption of these devices provides a texture maps on power consumption was presented in [5]. platform for further research and contribute to the design In recent years and improve the energy budget usage of improved and energy-efficient future mobile computing of portable units, several energy management techniques devices. have been investigated at different levels of system design – starting from silicon at the bottom to application Index Terms —portable devices, battery life, power design at the top, with communication protocols and consumption. operating system in between [6 – 9]. The primary objective of these techniques was to find means and I. INTRODUCTION methods to reduce the power consumption of mobile Mobile devices are increasingly becoming an integral devices and extend the battery life time. part of our daily life contributing to an ever growing Therefore and in view of the slow battery capacity ubiquitous computing environment. Hence, users will growth, it is becoming increasingly important to develop continue to expect more functionality from these devices. techniques to achieve high energy efficiency for handheld Enhanced features and the complex operations performed mobile devices. Designers must strive to maximize the by these portable devices are rapidly draining their amount of service work that the system can accomplish limited system energy budget. Battery lifetime is perhaps taking into consideration today’s battery capacity one of the most important characteristics of a portable constraints. An analysis of the power consumption computer. For many users, doubling the battery lifetime requirements and an understanding of battery may be far more important than doubling the clock performance as the only energy source in these devices is frequency. A main concern is the fact that improvements essential, and offers both users and designers critical in battery capacity have not kept pace with the information that would assist in efficient system usage improvements in microelectronics technology [1]. and in bringing to the market energy-efficient designs. Reducing power consumption and prolonging battery-life Initial and partial results of the work presented here is a major concern for designers. Battery capacity grows were presented at APCCS [10]. In this paper an very slowly, about 5 to 10% every year, which is not expanded and elaborate version of this work is presented. adequate when we take into consideration the energy The aim is to experiment with two portable devices, demand of handheld devices [2]. An understanding of namely the Compaq iPAQ 3950 and the HP iPAQ the power consumption behavior of these devices and the Rx3715 and assess their battery utilization as well as impact of the different operating modes and scenarios on power consumption characteristics. The methodology battery life is critical for the design of energy used in this work is applicable to most handheld devices. efficient devices. The rest of the paper is organized as follows: section In [3], an attempt was made to study the power usage 2 describes the experiment environment and the of an IBM ThinkPad R40 laptop. The authors run a set of experimental setup as well the theoretical framework that experiments to measure the power consumption of forms the basis for the measurements taken. The various various key components such as CPU, hard disk and loads or benchmark software used is discussed in section © 2012 ACADEMY PUBLISHER doi:10.4304/jcp.7.1.147-155 148 JOURNAL OF COMPUTERS, VOL. 7, NO. 1, JANUARY 2012 3. Experimental results are presented in section 4. The modulation in the signal. The oscilloscope also had a paper is concluded in section 5. built-in floppy disk to store and retreive waveforms and setups. The waveforms could be saved as a picture, II. EXPERIMENT ENVIRONMENT spreadsheet file, MathCAD or internal format. To prevent overcharging of the battery due to a spike The methodology used and the procedural steps taken upon connecting the Pocket PC directly to the power to collect data that reflects battery usage, and the source, a protection circuit is used. The circuit diagram is consumption characteristics are described in the of the complete setup is shown in figure 2. following subsections. A. Experimental Setting The experimental setup or testbed consisted of the following components: the pocket PCs, the measurement apparatus and the software or benchmarks to be run to gauge the consumption. The setup is shown in Figure 1. Figure 2. Circuit Diagram In steady state, the power P of the pocket computer can be computed as follows: P = V * I Figure 1. Experimental Setup Where V is the battery voltage and I is the current drawn by the computer. In this work, a digital multimeter The Compaq iPAQ 3950 unit uses an Intel XScale was used to measure the voltage across the battery processor. The speed is 400MHz and RAM is 64MB. It terminals. To measure the current, a small resistor R is comes with an SD/MMC slot for extra memory. It has a positioned in series with the lithium battery. The voltage transflective TFT display. Audio capabilities include across the resistor VR is sampled using the oscilloscope; microphone, speaker and a headphone jack. The only using Kirchoff’s law (I = VR/R ), we can compute the mode of wireless communication is through infrared. The current drawn by the pocket computer. The instantaneous operating system used is Windows Pocket PC. power is then computed by multiplying this current with The HP iPAQ Rx3715 unit uses a Samsung 2440 the supply voltage. This is similar to the approach utilized Processor. The speed is 400MHz and 152 MB of memory in [11] to assess the power characteristics of the Itsy is available to the user. It also has a SD memory card platform. support for any extra memory if required. The display is The oscilloscope was configured to perform a a 3.5 inch transflective color QVGA, 240 X 320 pixels, predefined number (N) of measurements while 64K color support. The backlight can be modified so as calculating the voltage across the battery. In our case, we to change its brightness. For audio capabilities there is an set N at 500. At the end of every acquisition which is a integrated microphone, speaker, 3.5 mm stereo set of N measurements the average is calculated. headphone jack, MP3 stereo through audio jack. The For a total of N measurements taken ∆ units of time communication features include Infrared with a data apart, an estimate of the average power is computed using transfer speed up to 115.2 Kbps, Bluetooth with a 10 the following equation: meter range and WiFi capabilities. The Operating system N used by it is Windows CE. PAVG = 1/N Σi P(i) We used as well a Tektronix TDS 3032 Digital III. SOFTWARE BENCHMARKS Phosphor Oscilloscope. It has two channels, a bandwidth of 300MHz, and maximum sample rate of 2.5GS/s. It has In this work we experimented with a variety of workloads the capability of acquiring a maximum of 10,000 points representing a wide range of tasks and at the same time waveforms to capture horizontal detail. The signal capable of stressing different components within the PC. processing features include averaging the input signal to The applications used include: remove the uncorrelated noise and improve the measurement accuracy. If the signal appears noisy, the A. The Pocket PC Benchmark v1.02 waveform intensity knob could be increased to see the noise more easily. The display features include a color The application [12] tests the Pocket PC from different LCD and digital phosphor to clearly display intensity points of view such as calculations and heap management © 2012 ACADEMY PUBLISHER JOURNAL OF COMPUTERS, VOL. 7, NO. 1, JANUARY 2012 149 performance. It can execute three types of benchmarks, Each single battery test is carried out for the whole namely, CPU Benchmark, Graphics Benchmark and Flat battery lifetime period . File Benchmark. The benchmarks can be executed on a Finally, the XCPUScalar software is used to loop count from 1 to 1000.