Energy Efficient Code Research Articles

An energy-efficient method of supporting flexible special instructions in an embedded processor with compact ISA

In application-specific processor design, a common approach to improve performance and efficiency is to use special instructions that execute complex operation patterns. However, in a generic embedded processor with compact Instruction Set Architecture (ISA), these special instructions may lead to large overhead such as: ( i ) more bits are needed to encode the extra opcodes and operands, resulting in wider instructions; ( ii ) more Register File (RF) ports are required to provide the extra operands to the function units. Such overhead may increase energy consumption considerably. In this article, we propose to support flexible operation pair patterns in a processor with a compact 24-bit RISC-like ISA using: ( i ) a partially reconfigurable decoder that exploits the pattern locality to reduce opcode space requirement; ( ii ) a software-controlled bypass network to reduce operand encoding bit and RF port requirement. An energy-aware compiler backend is designed for the proposed architecture that performs pattern selection and bypass-aware scheduling to generate energy-efficient codes. Though the proposed design imposes extra constraints on the operation patterns, the experimental results show that for benchmark applications from different domains, the average dynamic instruction count is reduced by over 25%, which is only about 2% less than the architecture without such constraints. The proposed architecture reduces total energy by an average of 15.8% compared to the RISC baseline, while the one without constraints achieves almost no improvement due to its high overhead. When high performance is required, the proposed architecture is able to achieve a speedup of 13.8% with 13.1% energy reduction compared to the baseline by introducing multicycle SFU operations.

Temporal whitening by power-law adaptation in neocortical neurons

Spike-frequency adaptation (SFA) is widespread in the CNS, but its function remains unclear. In neocortical pyramidal neurons, adaptation manifests itself by an increase in the firing threshold and by adaptation currents triggered after each spike. Combining electrophysiological recordings in mice with modeling, we found that these adaptation processes lasted for more than 20 s and decayed over multiple timescales according to a power law. The power-law decay associated with adaptation mirrored and canceled the temporal correlations of input current received in vivo at the somata of layer 2/3 somatosensory pyramidal neurons. These findings suggest that, in the cortex, SFA causes temporal decorrelation of output spikes (temporal whitening), an energy-efficient coding procedure that, at high signal-to-noise ratio, improves the information transfer.

Energy Efficient Scalable Video Coding Based Cooperative Multicast Scheme with Selective Layer Forwarding

Scalable Video Coding (SVC) based multicast schemes have been researched for many years in efforts to simultaneously achieve high throughput and good fairness, which have a trade-off relationship in multicast communication. In an SVC based multicast, all group members in a good channel condition can receive both base layer and enhancement layer information and thus can recover high quality video, while other group members receive the base layer information for guaranteeing basic quality video. However, this causes differentiation of video quality between group members with varying channel conditions, and average video quality is consequently degraded. We propose an Energy Efficient SVC based cooperative multicast (EE-SVC-CM) scheme with selective layer forwarding as a novel approach to mitigate this problem. The performance results reveal that the proposed scheme enhances the overall energy efficiency (throughput per watt) with reduced unnecessary relay power consumption.

A Novel Optical Code RAKE Receiver Using a Multiport Encoder/Decoder

We propose an energy efficient optical code (OC) receiver, based on a RAKE configuration, using a single passive multiport encoder/decoder (E/D). We numerically demonstrate the crosstalk signals are used to enhance the energy efficiency and the label recognition performance, using only a combiner and optical delay lines (ODL), without any additional photo detector (PD). We numerically analyze the system performance and experimentally investigate the influence of the beat noise, that can be eliminated.

Energy-Efficient Code by Refactoring

The rising number of mobile devices increase the interest in longer battery durations. To increase battery duration, researchers try to improve e.g. different hardware components, such as processors and GPS for lower energy consumption. Frequently, software optimization possibilities to save energy are forgotten. Hence, an approach is shown to reduce energy consumption of applications by reengineering. Therefor, energy-wasteful code in applications is searched by code analysis and then restructured to optimize their energy consumption. Energy savings are validated by different energy measurements techniques.

Half-Wits

This work analyzes the stochastic behavior of writing to embedded flash memory at voltages lower than recommended by a microcontroller’s specifications in order to reduce energy consumption. Flash memory integrated within a microcontroller typically requires the entire chip to operate on a common supply voltage almost twice as much as what the CPU portion requires. Our software approach allows the flash memory to tolerate a lower supply voltage so that the CPU may operate in a more energy-efficient manner. Energy-efficient coding algorithms then cope with flash memory writes that behave unpredictably. Our software-only coding algorithms ( in-place writes, multiple-place writes, RS-Berger codes , and slow writes ) enable reliable storage at low voltages on unmodified hardware by exploiting the electrically cumulative nature of half-written data in write-once bits. For a sensor monitoring application using the MSP430, coding with in-place writes reduces the overall energy consumption by 34%. In-place writes are competitive when the time spent on low-voltage operations such as computation are at least four times greater than the time spent on writes to flash memory. Our evaluation shows that tightly maintaining the digital abstraction for storage in embedded flash memory comes at a significant cost to energy consumption with minimal gain in reliability. We find our techniques most effective for embedded workloads that have significant duty cycling, rare writes, or energy harvesting.

Multi bit random and burst error correction code with crosstalk avoidance for reliable on chip interconnection links

We propose an energy efficient error control code for the on chip interconnection link capable of correcting any type of error patterns including random and burst errors up to five (i.e. 1, 2, 3, 4, and 5 errors). The proposed code is based on single error correction–double error detection (SEC–DED) extended Hamming code and standard triplication error correction scheme. Using single error correction–double error detection (SEC–DED) extended Hamming code and standard triplication error correction scheme a new decoding algorithm is proposed to correct multiple errors up to five in on-chip interconnection link. Triplication error correction scheme provides crosstalk avoidance by reducing the coupling capacitance of the interconnection wire. The proposed code provides high reliability compared to other error control codes. The performance of the proposed code is evaluated for codec area, codec power, codec delay, residual flit error rate, link swing voltage and link power. For the given reliability requirement of 10−5 and 10−20, the proposed code achieves low residual flit error rate and low swing voltage. The low swing voltage results in the reduction of the link power consumption up to 68% compared to the existing error control codes for on chip interconnection link. The low residual flit error rate and low link power make the proposed code appropriate for on chip interconnection link.

Effects of energy-efficiency building codes in the energy savings and emissions of carbon dioxide

This study estimated the effects of energy-efficiency building codes—IECC 2003 and IECC 2006—in residential energy consumption, using the American Community Survey 2007. This study detected violations of the assumption of independence of observation, corrected them by applying a hierarchical estimation technique, and measured the state’s heterogeneity. We found that households can save about 1.8 % of electricity, 1.3 % of natural gas, and 2.8 % of heating oil with the application of these energy efficiency codes, with corresponding reductions in the emissions of the global warming gas, CO2 of about 7.54 million metric tons per year if all homes apply these codes. For the pressing requirements of energy security and the limiting the emissions of CO2 for climate change mitigation, these energy efficiency codes can be an effective environmental policy measure for residential sector.

Warm Body Temperature Facilitates Energy Efficient Cortical Action Potentials

The energy efficiency of neural signal transmission is important not only as a limiting factor in brain architecture, but it also influences the interpretation of functional brain imaging signals. Action potential generation in mammalian, versus invertebrate, axons is remarkably energy efficient. Here we demonstrate that this increase in energy efficiency is due largely to a warmer body temperature. Increases in temperature result in an exponential increase in energy efficiency for single action potentials by increasing the rate of Na+ channel inactivation, resulting in a marked reduction in overlap of the inward Na+, and outward K+, currents and a shortening of action potential duration. This increase in single spike efficiency is, however, counterbalanced by a temperature-dependent decrease in the amplitude and duration of the spike afterhyperpolarization, resulting in a nonlinear increase in the spike firing rate, particularly at temperatures above approximately 35°C. Interestingly, the total energy cost, as measured by the multiplication of total Na+ entry per spike and average firing rate in response to a constant input, reaches a global minimum between 37–42°C. Our results indicate that increases in temperature result in an unexpected increase in energy efficiency, especially near normal body temperature, thus allowing the brain to utilize an energy efficient neural code.

Adaptation of California’s electricity sector to climate change

Climate change is likely to pose considerable new challenges to California’s electricity sector. This paper primarily focuses on the adaptation challenges of an important component of the energy arena: electricity demand in the residential and commercial sectors and electricity supply. The primary challenge to California’s electricity sector will likely be the increase in demand for air conditioning as a result of rising temperatures. In addition, renewable energy sources, which are an increasing share of the electricity portfolio, are particularly vulnerable to climate change. Many of the key players have been actively considering the implications of climate change. Because electricity generation accounts for nearly 30% of greenhouse gas emissions, this sector has been a target of the state’s efforts to reduce emissions. Fortunately, many of the same tools can simultaneously improve the sector’s resilience to a changing climate. Demand management strategies and supply diversification are both important strategies. Local governments can play a central role in encouraging the adoption of more energy efficient building codes and the use of more renewable sources, such as solar energy. The positive steps taken by many local governments are encouraging. Steps to increase public awareness are an important, often missing component, however. Increases in research, development, and demonstration to improve system resiliency and develop new energy conservation tools are also needed.

Assessment of building energy-saving policies and programs in China during the 11th Five-Year Plan

China’s 11th Five-Year Plan (FYP) sets an ambitious target to reduce the energy intensity per unit of gross domestic product by 20% from 2005 to 2010 (NDRC 2006). In the building sector, the primary energy-saving target allocated during the 11 FYP period is 100 Mtce. Savings are expected to be achieved through the strengthening of enforcement of building energy efficiency codes, existing building retrofits and heat supply system reform, followed by energy management of government office buildings and large-scale public buildings, adoption of renewable energy sources. To date, China has reported that it achieved the half of the 20% intensity reduction target by the end of 2008; however, little has been made clear on the status and the impact of the building programs. There has also been lack of description on methodology for calculating the savings and baseline definition, and no total savings that have been officially reported to date. This paper intends to provide both quantitative and qualitative assessment of the key policies and programs in building sector that China has instituted in its quest to fulfill the national goal. Overall, this paper concludes that the largest improvement for building energy efficiency were achieved in new buildings; the program to improve the energy management in government and large scale public buildings are in line with the target; however, the progress in the area of existing building retrofits, particularly heating supply system reform lags behind the stated goal by a large amount.

The Process for Adopting an Energy Efficiency Code in Existing Homes: A Case Study of Boulder, Colorado's SmartRegs Program

On January 3, 2011 Boulder, Colorado implemented the SmartRegsordinances, becoming the first city in the country to require energyretrofits for rental properties. SmartRegs is an update to the housing andrental licensing code while adding baseline efficiency requirements forrental housing. This study analyzes the process the City of Boulderendured to adopt SmartRegs by performing a content analysis of publicmeeting minutes and conducting interviews with decision makers toidentify barriers and success factors. A key finding is early involvementof one or more people committed to energy efficiency and reachingcompromise is necessary to adopt such requirements in an economicallydriven and adversarial environment.

Low-cost green building practice in China: Library of Shandong Transportation College

This paper introduces the design idea and technique utilized in the Library of Shandong Transportation College, which ranked 1st in the National Green Buildings Innovation Award in China in March 2007 due to its low cost and climate-oriented green strategy during its design and construction phase, including land saving, energy efficiency, water conservation, and so on. Originally, the place was a landfill site with an odor pool. After reconstruction, it was changed into the construction site of the library with an area of 7000 m2 and a scenery pond. With the integrated use of passive shading, daylighting, ventilation with atriums, high-insulation materials, underground duct ventilation, and the substitution of cooling tower with the pond water, the HVAC load design indexes are 59 W/m2 and 21.8 W/m2 for space cooling and heating, respectively, much lower than the newly issued Chinese energy efficient design code for public buildings. Moreover, a set of measures is utilized for water conversation, material saving, and improvement of indoor environmental quality. After three years of operation, the real effect has been validated by electricity meter and field measurement. The total initial cost for the building with the above mentioned integrated technologies was only RMB 2150 per square meter, which was worth spending in China due to the climatic adaptability and the relative low cost.

Towards update-conscious compilation for energy-efficient code dissemination in WSNs

Postdeployment code dissemination in wireless sensor networks (WSN) is challenging, as the code has to be transmitted via energy-expensive wireless communication. In this article, we propose novel update-conscious compilation (UCC) techniques to achieve energy efficiency. By integrating the compilation decisions in generating the old binary, an update-conscious compiler strives to match the old decisions, which improves the binary code similarity, reduces the amount of transmitted data to remote sensors, and thus, consumes less energy. In this article, we develop update-conscious register allocation and data layout algorithms. Our experimental results show great improvements over the traditional, update-oblivious approaches.

Advice tool for early design stages of intelligent facades based on energy and visual comfort approach

Increased awareness on environmental issues, together with requirements imposed by implementation of energy efficiency codes, has generated the need for tools that evaluate thermal performance of buildings. Their objective is to ensure compliance and certification. However, existing computer models are still rudimentary with many limitations for use in early design stages of any architectural project. They require exact data in a stage when designers consider conceptual ideas from a range of options rather than precise details and numbers. Design tools that suggest solutions based on ideas are rare. This disadvantage can be seen in the planning of intelligent facades, where the number of possible configurations can be overwhelming and decisions made in early stages have profound effects on energy and comfort performance. This paper presents NewFacades, a model that helps pass from ideas to significant concepts in the design of intelligent facades. It uses energy and visual comfort strategies abstracted from a prescriptive energy code for hot climates to suggest a range of good starting solutions. Designers can have energy and visual comfort estimations to these alternatives through an advanced stage energy simulation program such as EnergyPlus, or explore them further with other tools. Methods used by the tool are presented here in the context of sample cases. By working on energy principles or relying on local existing energy standards, the model can be extended to all types of climates.

Adaptive Multilevel Code Update Protocol for Real-Time Sensor Operating Systems

In wireless sensor networks each sensor node has very limited resources, and it is very difficult to find and collect them. For this reason, updating or adding programs in sensor nodes must be performed via a communication channel at run-time. Many code update protocols have been developed for sensor networks, ranging from function-level update to full-image replacement. However, they provide only a fixed level of code update protocols. These protocols require manual selection of an appropriate protocol because they do not consider a cost analysis of the update protocols. In addition, they do not consider real-time response while updating codes. In this paper, we present an adaptive multilevel code update protocol (AMCUP) for real-time sensor operating systems. AMCUP enables energy-efficient code update via support for multilevel protocols (i.e., full-image, module-level, function-level, and instruction-level). It adaptively selects a protocol which meets deadline of applications and consumes less energy based on a cost analysis of several protocols. Our simulation and experimental results show that AMCUP can reduce energy consumption and execution time compared with existing single-level code update protocols while meeting deadline of the running applications.

Motion Adaptation Enhances Object-Induced Neural Activity in Three-Dimensional Virtual Environment

Many response characteristics of neurons sensitive to visual motion depend on stimulus history and change during prolonged stimulation. Although the changes are usually regarded as adaptive, their functional significance is still not fully understood. With experimenter-defined stimuli, previous research on motion adaptation has mainly focused on enhancing the detection of changes in the stimulus domain, on preventing output saturation and on energy efficient coding. Here we will analyze in the blowfly visual system the functional significance of motion adaptation under the complex stimulus conditions encountered in the three-dimensional world. Identified motion sensitive neurons are confronted with seminatural optic flow as is seen by semi-free-flying animals as well as targeted modifications of it. Motion adaptation is shown to enhance object-induced neural responses in a three-dimensional environment although the overall neuronal response amplitude decreases during prolonged motion stimulation.

Energy limitation as a selective pressure on the evolution of sensory systems

Evolution of animal morphology, physiology and behaviour is shaped by the selective pressures to which they are subject. Some selective pressures act to increase the benefits accrued whilst others act to reduce the costs incurred, affecting the cost/benefit ratio. Selective pressures therefore produce a trade-off between costs and benefits that ultimately influences the fitness of the whole organism. The nervous system has a unique position as the interface between morphology, physiology and behaviour; the final output of the nervous system is the behaviour of the animal, which is a product of both its morphology and physiology. The nervous system is under selective pressure to generate adaptive behaviour, but at the same time is subject to costs related to the amount of energy that it consumes. Characterising this trade-off between costs and benefits is essential to understanding the evolution of nervous systems, including our own. Within the nervous system, sensory systems are the most amenable to analysing costs and benefits, not only because their function can be more readily defined than that of many central brain regions and their benefits quantified in terms of their performance, but also because recent studies of sensory systems have begun to directly assess their energetic costs. Our review focuses on the visual system in particular, although the principles we discuss are equally applicable throughout the nervous system. Examples are taken from a wide range of sensory modalities in both vertebrates and invertebrates. We aim to place the studies we review into an evolutionary framework. We combine experimentally determined measures of energy consumption from whole retinas of rabbits and flies with intracellular measurements of energy consumption from single fly photoreceptors and recently constructed energy budgets for neural processing in rats to assess the contributions of various components to neuronal energy consumption. Taken together, these studies emphasize the high costs of maintaining neurons at rest and whilst signalling. A substantial proportion of neuronal energy consumption is related to the movements of ions across the neuronal cell membrane through ion channels, though other processes such as vesicle loading and transmitter recycling also consume energy. Many of the energetic costs within neurons are linked to 3Na(+)/2K(+) ATPase activity, which consumes energy to pump Na(+) and K(+) ions across the cell membrane and is essential for the maintenance of the resting potential and its restoration following signalling. Furthermore, recent studies in fly photoreceptors show that energetic costs can be related, via basic biophysical relationships, to their function. These findings emphasize that neurons are subject to a law of diminishing returns that severely penalizes excess functional capacity with increased energetic costs. The high energetic costs associated with neural tissue favour energy efficient coding and wiring schemes, which have been found in numerous sensory systems. We discuss the role of these efficient schemes in reducing the costs of information processing. Assessing evidence from a wide range of vertebrate and invertebrate examples, we show that reducing energy expenditure can account for many of the morphological features of sensory systems and has played a key role in their evolution.

Nonlinear coding and estimation for correlated data in wireless sensor networks

The problem of designing simple and energy efficient nonlinear distributed source-channel codes is considered. By demonstrating similarities between this problem and the problem of bandwidth expansion, a structure for source-channel codes is presented and analyzed. Based on this analysis an understanding about desirable properties for such a system is gained and used to produce an explicit source-channel code which is then analyzed and simulated. One of the main advantages of the proposed scheme is that it is implementable for many sources, contrary to most existing nonlinear distributed source-channel coding systems.

UCC

Wireless sensor networks (WSN), composed of a large number of low-cost, battery-powered sensors, have recently emerged as promising computing platforms for many non-traditional applications. The preloaded code on remote sensors often needs to be updated after deployment in order for the WSN to adapt to the changing demands from the users. Post-deployment code dissemination is challenging as the data are transmitted via battery-powered wireless communication. Recent studies show that the energy for sending a single bit is about the same as executing 1000 instructions in aWSN. Therefore it is important to achieve energy efficiency in code dissemination. In this paper, we propose novel update-conscious compilation(UCC) techniques for energy-efficient code dissemination in WSNs. An update-conscious compiler, when compiling the modified code, includes the compilation decisions that were made when generating the old binary. The compiler employs a detailed energy model and strives to match the old decisions for a more energy-efficient result. In most cases, matching the previous decisions improves the binary code similarity, reduces the amount of data to be transmitted to remote sensors, and thus, consumes less energy. In this paper, we develop update-conscious register allocation and data layout algorithms. Our experimental results show that they can achieve great improvements over the traditional, update-oblivious approaches.