클럭 게이팅 및 플립 플롭 동시 최적화를 위한 설계 및 알고리즘

학위논문 (석사)-- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2019. 2. 김태환.본 논문에서는 표준 셀에서부터 배치 단계에 이르는 다양한 설계단에에서 칩의 동적 전력을 최적화 기법을 소개한다. 이 연구는 우선 데이터 구동형 (즉, 토글링 기반) 클럭 게이팅이 종래 클럭 게이팅 기법들에서 결코 다루어지지 않았던 플립 플 롭의 합성과 밀접하게 통합될 수 있는 방법을 연구한다. 우리의 관측의 핵심은 플립 플롭 셀의 일부 내부 부품이 클럭 게이팅 인에이블 신호를 생성 하기 위해 재사용 될 수 있다는 것이다. 이를 바탕으로 eXOR-FF 라고 불리는 새롭게 최적화된 플립 플롭 배선 구조를 제안합니다. 이 구조에서는 매 클럭 주기마다 내부 로직을 재사용 하여 클럭 게이팅을 통해 플립 플롭을 활성화할지 또는 비활성화할지 결정합니다. 모든 쌍의 플립 플롭 및 토글릴 감지 로직에서의 영역을 절약함에 따라서 누설 및 동적 전력의 절전 효과를 달성합니다. 그런 다음, 두 가지고유한 장점을 제공하는 배치/타이밍 인식 클럭 게이팅 탐색에 대한 포괄적인 방법론을 제안합니다. 해당 방 법론은 eXOR-FF 의 이점을 극대화하고, 전력 소비 및 타이밍 영향의 분해에 대한 정밀 분석을 수행하고 틀럭 게이팅 참색의 핵심 엔진을 비용기능으로 변환하는데 가장 적합합니다. ISCAS89, ITC89, ITC99 및 IWLS 2005의 벤치 마크 회로를 사용 한 실험을 통해 제안 된 방법이 이전의 데이터 구동 클록 게이팅 방식과 비교하여 총 전력을 5.6 % 및 면적으로 5.3 % 줄일 수 있음을 보여 주었다.In this paper, we introduce dynamic power optimization techniques applicable for various design stage from standard cell to placement stage. This work firstly investi�gates the problem of how designing data-driven (i.e., toggling based) clock gating can be closely integrated with the synthesis of flip-flops, which has never been addressed in the prior clock gating works. Our key observation is that some internal part of a flip-flop cell can be reused to generate its clock gating enable signal. Based on this, we propose a newly optimized flip-flop wiring structure, called eXOR-FF, in which an internal logic can be reused for every clock cycle to decide if the flip-flop is to be activated or inactivated through clock gating, thereby achieving area saving (thus, leakage as well as dynamic power saving) on every pair of flip-flop and its toggling detection logic. Then, we propose a comprehensive methodology of placement/timing�aware clock gating exploration that provides two unique strengths: best suited for max�imally exploiting the benefit of eXOR-FFs and precise analyses on the decomposition of power consumptions and timing impact, and translating them into cost functions in core engine of clock gating exploration. Through experiments with benchmark circuits in ISCAS89, ITC89, ITC99 and IWLS 2005, it is shown that our proposed method is able to reduce the total power by 5.6% and total cell area by 5.3% compared with the previous data-driven clock gating method in [1].Abstract Contents List of Tables List of Figures 1 Introduction 1.1 Power Consumption in CMOS Digital Design 1.2 Low Power Design Methodologies 1.3 Contribution of This Thesis 2 Preliminary and Motivations 6 2.1 Background 2.2 Observation on Area and Power Saving 2.3 Observation on Timing Impact 3 Redesign of Flip-flops Specialized for Clock Gating 3.1 Observation on Area Impact 4 Placement-aware Clock Gating Methodology Utilizing eXOR-FF Cells 4.1 Overall Design Flow 4.2 Cost Formulation for Conventional Clock Gating 4.3 Cost Formulation for Our Clock Gating using eXOR-FFs 5 Experiments 5.1 Experimental Setup 5.2 Experimental Results 5.3 Comparing with Industry Algorithm 6 Conclusion Abstract (In Korean)Maste

The impact of design techniques in the reduction of power consumption of SoCs Multimedia

Orientador: Guido Costa Souza de AraújoDissertação (mestrado) - Universidade Estadual de Campinas, Instituto de ComputaçãoResumo: A indústria de semicondutores sempre enfrentou fortes demandas em resolver problema de dissipação de calor e reduzir o consumo de energia em dispositivos. Esta tendência tem sido intensificada nos últimos anos com o movimento de sustentabilidade ambiental. A concepção correta de um sistema eletrônico de baixo consumo de energia é um problema de vários níveis de complexidade e exige estratégias sistemáticas na sua construção. Fora disso, a adoção de qualquer técnica de redução de energia sempre está vinculada com objetivos especiais e provoca alguns impactos no projeto. Apesar dos projetistas conheçam bem os impactos de forma qualitativa, as detalhes quantitativas ainda são incógnitas ou apenas mantidas dentro do 'know-how' das empresas. Neste trabalho, de acordo com resultados experimentais baseado num plataforma de SoC1 industrial, tentamos quantificar os impactos derivados do uso de técnicas de redução de consumo de energia. Nos concentramos em relacionar o fator de redução de energia de cada técnica aos impactos em termo de área, desempenho, esforço de implementação e verificação. Na ausência desse tipo de dados, que relacionam o esforço de engenharia com as metas de consumo de energia, incertezas e atrasos serão frequentes no cronograma de projeto. Esperamos que este tipo de orientações possam ajudar/guiar os arquitetos de projeto em selecionar as técnicas adequadas para reduzir o consumo de energia dentro do alcance de orçamento e cronograma de projetoAbstract: The semiconductor industry has always faced strong demands to solve the problem of heat dissipation and reduce the power consumption in electronic devices. This trend has been increased in recent years with the action of environmental sustainability. The correct conception of an electronic system for low power consumption is an issue with multiple levels of complexities and requires systematic approaches in its construction. However, the adoption of any technique for reducing the power consumption is always linked with some specific goals and causes some impacts on the project. Although the designers know well that these impacts can affect the design in a quality aspect, the quantitative details are still unkown or just be kept inside the company's know-how. In this work, according to the experimental results based on an industrial SoC2 platform, we try to quantify the impacts of the use of low power techniques. We will relate the power reduction factor of each technique to the impact in terms of area, performance, implementation and verification effort. In the absence of such data, which relates the engineering effort to the goals of power consumption, uncertainties and delays are frequent. We hope that such guidelines can help/guide the project architects in selecting the appropriate techniques to reduce the power consumption within the limit of budget and project scheduleMestradoCiência da ComputaçãoMestre em Ciência da Computaçã

Chapter One – An Overview of Architecture-Level Power- and Energy-Efficient Design Techniques

Power dissipation and energy consumption became the primary design constraint for almost all computer systems in the last 15 years. Both computer architects and circuit designers intent to reduce power and energy (without a performance degradation) at all design levels, as it is currently the main obstacle to continue with further scaling according to Moore's law. The aim of this survey is to provide a comprehensive overview of power- and energy-efficient “state-of-the-art” techniques. We classify techniques by component where they apply to, which is the most natural way from a designer point of view. We further divide the techniques by the component of power/energy they optimize (static or dynamic), covering in that way complete low-power design flow at the architectural level. At the end, we conclude that only a holistic approach that assumes optimizations at all design levels can lead to significant savings.Peer ReviewedPostprint (published version

Circuits and Systems Advances in Near Threshold Computing

Modern society is witnessing a sea change in ubiquitous computing, in which people have embraced computing systems as an indispensable part of day-to-day existence. Computation, storage, and communication abilities of smartphones, for example, have undergone monumental changes over the past decade. However, global emphasis on creating and sustaining green environments is leading to a rapid and ongoing proliferation of edge computing systems and applications. As a broad spectrum of healthcare, home, and transport applications shift to the edge of the network, near-threshold computing (NTC) is emerging as one of the promising low-power computing platforms. An NTC device sets its supply voltage close to its threshold voltage, dramatically reducing the energy consumption. Despite showing substantial promise in terms of energy efficiency, NTC is yet to see widescale commercial adoption. This is because circuits and systems operating with NTC suffer from several problems, including increased sensitivity to process variation, reliability problems, performance degradation, and security vulnerabilities, to name a few. To realize its potential, we need designs, techniques, and solutions to overcome these challenges associated with NTC circuits and systems. The readers of this book will be able to familiarize themselves with recent advances in electronics systems, focusing on near-threshold computing

Energy-efficient hardware design based on high-level synthesis

This dissertation describes research activities broadly concerning the area of High-level synthesis (HLS), but more specifically, regarding the HLS-based design of energy-efficient hardware (HW) accelerators. HW accelerators, mostly implemented on FPGAs, are integral to the heterogeneous architectures employed in modern high performance computing (HPC) systems due to their ability to speed up the execution while dramatically reducing the energy consumption of computationally challenging portions of complex applications. Hence, the first activity was regarding an HLS-based approach to directly execute an OpenCL code on an FPGA instead of its traditional GPU-based counterpart. Modern FPGAs offer considerable computational capabilities while consuming significantly smaller power as compared to high-end GPUs. Several different implementations of the K-Nearest Neighbor algorithm were considered on both FPGA- and GPU-based platforms and their performance was compared. FPGAs were generally more energy-efficient than the GPUs in all the test cases. Eventually, we were also able to get a faster (in terms of execution time) FPGA implementation by using an FPGA-specific OpenCL coding style and utilizing suitable HLS directives. The second activity was targeted towards the development of a methodology complementing HLS to automatically derive power optimization directives (also known as "power intent") from a system-level design description and use it to drive the design steps after HLS, by producing a directive file written using the common power format (CPF) to achieve power shut-off (PSO) in case of an ASIC design. The proposed LP-HLS methodology reduces the design effort by enabling designers to infer low power information from the system-level description of a design rather than at the RTL. This methodology required a SystemC description of a generic power management module to describe the design context of a HW module also modeled in SystemC, along with the development of a tool to automatically produce the CPF file to accomplish PSO. Several test cases were considered to validate the proposed methodology and the results demonstrated its ability to correctly extract the low power information and apply it to achieve power optimization in the backend flow

AN APPROACH FOR LOW LEAKAGE POWER BY POWER GATING STACK TECHNIQUE

Clock gating (CG) and power gating (PG) the two most widely used techniques to reduce dynamic power and leakage power respectively, are expected to be integrated together effectively. Normally, the implementation of CG leads to some redundant operations, which provides the opportunity to apply PG. In this brief, we have proposed an activity-driven fine-grained CG and PG integration. For the implementation of XOR-based CG we have intro-duce an optimized bus-specific-clock-gating (OBSC) scheme to improve traditional gating.It chooses only a subset of flip-flops (FFs) to be gated selectively, and the problem of gated FF selection is reduced from exponential complexity into linear. Then those combinational logics, which completely depend on the outputs of gated FFs, are performing redundant operations. They can be power gated, and the clock enable signal generated by OBSC is used as the sleep signal. A minimum average idle time concept is proposed to determine whether the insertion of PG will lead to energy reduction.The simulation results show that 25.07% dynamic power can be reduced by OBSC, and 50.19% active leakage power can be saved by PG

Modelling and Automated Implementation of Optimal Power Saving Strategies in Coarse-Grained Reconfigurable Architectures

This paper focuses on how to efficiently reduce power consumption in coarse-grained reconfigurable designs, to allow their effective adoption in heterogeneous architectures supporting and accelerating complex and highly variable multifunctional applications. We propose a design flow for this kind of architectures that, besides their automatic customization, is also capable of determining their optimal power management support. Power and clock gating implementation costs are estimated in advance, before their physical implementation, on the basis of the functional, technological, and architectural parameters of the baseline design. Experimental results, on 90 and 45 nm CMOS technologies, demonstrate that the proposed approach guides the designer towards optimal implementation

ASIC implemented MicroBlaze-based Coprocessor for Data Stream Management Systems

Indiana University-Purdue University Indianapolis (IUPUI)The drastic increase in Internet usage demands the need for processing data in real time with higher efficiency than ever before. Symbiote Coprocessor Unit (SCU), developed by Dr. Pranav Vaidya, is a hardware accelerator which has potential of providing data processing speedup of up to 150x compared with traditional data stream processors. However, SCU implementation is very complex, fixed, and uses an outdated host interface, which limits future improvement. Mr. Tareq S. Alqaisi, an MSECE graduate from IUPUI worked on curbing these limitations. In his architecture, he used a Xilinx MicroBlaze microcontroller to reduce the complexity of SCU along with few other modifications. The objective of this study is to make SCU suitable for mass production while reducing its power consumption and delay. To accomplish this, the execution unit of SCU has been implemented in application specific integrated circuit and modules such as ACG/OCG, sequential comparator, and D-word multiplier/divider are integrated into the design. Furthermore, techniques such as operand isolation, buffer insertion, cell swapping, and cell resizing are also integrated into the system. As a result, the new design attains 67.9435 µW of dynamic power as compared to 74.0012 µW before power optimization along with a small increase in static power, 39.47 ns of clock period as opposed to 52.26 ns before time optimization

Embedding Logic and Non-volatile Devices in CMOS Digital Circuits for Improving Energy Efficiency

abstract: Static CMOS logic has remained the dominant design style of digital systems for more than four decades due to its robustness and near zero standby current. Static CMOS logic circuits consist of a network of combinational logic cells and clocked sequential elements, such as latches and flip-flops that are used for sequencing computations over time. The majority of the digital design techniques to reduce power, area, and leakage over the past four decades have focused almost entirely on optimizing the combinational logic. This work explores alternate architectures for the flip-flops for improving the overall circuit performance, power and area. It consists of three main sections. First, is the design of a multi-input configurable flip-flop structure with embedded logic. A conventional D-type flip-flop may be viewed as realizing an identity function, in which the output is simply the value of the input sampled at the clock edge. In contrast, the proposed multi-input flip-flop, named PNAND, can be configured to realize one of a family of Boolean functions called threshold functions. In essence, the PNAND is a circuit implementation of the well-known binary perceptron. Unlike other reconfigurable circuits, a PNAND can be configured by simply changing the assignment of signals to its inputs. Using a standard cell library of such gates, a technology mapping algorithm can be applied to transform a given netlist into one with an optimal mixture of conventional logic gates and threshold gates. This approach was used to fabricate a 32-bit Wallace Tree multiplier and a 32-bit booth multiplier in 65nm LP technology. Simulation and chip measurements show more than 30% improvement in dynamic power and more than 20% reduction in core area. The functional yield of the PNAND reduces with geometry and voltage scaling. The second part of this research investigates the use of two mechanisms to improve the robustness of the PNAND circuit architecture. One is the use of forward and reverse body biases to change the device threshold and the other is the use of RRAM devices for low voltage operation. The third part of this research focused on the design of flip-flops with non-volatile storage. Spin-transfer torque magnetic tunnel junctions (STT-MTJ) are integrated with both conventional D-flipflop and the PNAND circuits to implement non-volatile logic (NVL). These non-volatile storage enhanced flip-flops are able to save the state of system locally when a power interruption occurs. However, manufacturing variations in the STT-MTJs and in the CMOS transistors significantly reduce the yield, leading to an overly pessimistic design and consequently, higher energy consumption. A detailed analysis of the design trade-offs in the driver circuitry for performing backup and restore, and a novel method to design the energy optimal driver for a given yield is presented. Efficient designs of two nonvolatile flip-flop (NVFF) circuits are presented, in which the backup time is determined on a per-chip basis, resulting in minimizing the energy wastage and satisfying the yield constraint. To achieve a yield of 98%, the conventional approach would have to expend nearly 5X more energy than the minimum required, whereas the proposed tunable approach expends only 26% more energy than the minimum. A non-volatile threshold gate architecture NV-TLFF are designed with the same backup and restore circuitry in 65nm technology. The embedded logic in NV-TLFF compensates performance overhead of NVL. This leads to the possibility of zero-overhead non-volatile datapath circuits. An 8-bit multiply-and- accumulate (MAC) unit is designed to demonstrate the performance benefits of the proposed architecture. Based on the results of HSPICE simulations, the MAC circuit with the proposed NV-TLFF cells is shown to consume at least 20% less power and area as compared to the circuit designed with conventional DFFs, without sacrificing any performance.Dissertation/ThesisDoctoral Dissertation Electrical Engineering 201

On Energy Efficient Computing Platforms

In accordance with the Moore's law, the increasing number of on-chip integrated transistors has enabled modern computing platforms with not only higher processing power but also more affordable prices. As a result, these platforms, including portable devices, work stations and data centres, are becoming an inevitable part of the human society. However, with the demand for portability and raising cost of power, energy efficiency has emerged to be a major concern for modern computing platforms. As the complexity of on-chip systems increases, Network-on-Chip (NoC) has been proved as an efficient communication architecture which can further improve system performances and scalability while reducing the design cost. Therefore, in this thesis, we study and propose energy optimization approaches based on NoC architecture, with special focuses on the following aspects. As the architectural trend of future computing platforms, 3D systems have many bene ts including higher integration density, smaller footprint, heterogeneous integration, etc. Moreover, 3D technology can signi cantly improve the network communication and effectively avoid long wirings, and therefore, provide higher system performance and energy efficiency. With the dynamic nature of on-chip communication in large scale NoC based systems, run-time system optimization is of crucial importance in order to achieve higher system reliability and essentially energy efficiency. In this thesis, we propose an agent based system design approach where agents are on-chip components which monitor and control system parameters such as supply voltage, operating frequency, etc. With this approach, we have analysed the implementation alternatives for dynamic voltage and frequency scaling and power gating techniques at different granularity, which reduce both dynamic and leakage energy consumption. Topologies, being one of the key factors for NoCs, are also explored for energy saving purpose. A Honeycomb NoC architecture is proposed in this thesis with turn-model based deadlock-free routing algorithms. Our analysis and simulation based evaluation show that Honeycomb NoCs outperform their Mesh based counterparts in terms of network cost, system performance as well as energy efficiency.Siirretty Doriast