PieceTimer: A Holistic Timing Analysis Framework Considering Setup/Hold Time Interdependency Using A Piecewise Model

In static timing analysis, clock-to-q delays of flip-flops are considered as constants. Setup times and hold times are characterized separately and also used as constants. The characterized delays, setup times and hold times, are ap- plied in timing analysis independently to verify the perfor- mance of circuits. In reality, however, clock-to-q delays of flip-flops depend on both setup and hold times. Instead of being constants, these delays change with respect to different setup/hold time combinations. Consequently, the simple ab- straction of setup/hold times and constant clock-to-q delays introduces inaccuracy in timing analysis. In this paper, we propose a holistic method to consider the relation between clock-to-q delays and setup/hold time combinations with a piecewise linear model. The result is more accurate than that of traditional timing analysis, and the incorporation of the interdependency between clock-to-q delays, setup times and hold times may also improve circuit performance.Comment: IEEE/ACM International Conference on Computer-Aided Design (ICCAD), November 201

로직 및 피지컬 합성에서의 타이밍 분석과 최적화

학위논문 (박사) -- 서울대학교 대학원 : 공과대학 전기·정보공학부, 2020. 8. 김태환.Timing analysis is one of the necessary steps in the development of a semiconductor circuit. In addition, it is increasingly important in the advanced process technologies due to various factors, including the increase of process–voltage–temperature variation. This dissertation addresses three problems related to timing analysis and optimization in logic and physical synthesis. Firstly, most static timing analysis today are based on conventional fixed flip-flop timing models, in which every flip-flop is assumed to have a fixed clock-to-Q delay. However, setup and hold skews affect the clock-to-Q delay in reality. In this dissertation, I propose a mathematical formulation to solve the problem and apply it to the clock skew scheduling problems as well as to the analysis of a given circuit, with a scalable speedup technique. Secondly, near-threshold computing is one of the promising concepts for energy-efficient operation of VLSI systems, but wide performance variation and nonlinearity to process variations block the proliferation. To cope with this, I propose a holistic hardware performance monitoring methodology for accurate timing prediction in a near-threshold voltage regime and advanced process technology. Lastly, an asynchronous circuit is one of the alternatives to the conventional synchronous style, and asynchronous pipeline circuit especially attractive because of its small design effort. This dissertation addresses the synthesis problem of lightening two-phase bundled-data asynchronous pipeline controllers, in which delay buffers are essential for guaranteeing the correct handshaking operation but incurs considerable area increase.타이밍 분석은 반도체 회로 개발 필수 과정 중 하나로, 최신 공정일수록 공정-전압-온도 변이 증가를 포함한 다양한 요인으로 하여금 그 중요성이 커지고 있다. 본 논문에서는 로직 및 피지컬 합성과 관련하여 세 가지 타이밍 분석 및 최적화 문제에 대해 다룬다. 첫째로, 오늘날 대부분의 정적 타이밍 분석은 모든 플립-플롭의 클럭-출력 딜레이가 고정된 값이라는 가정을 바탕으로 이루어졌다. 하지만 실제 클럭-출력 딜레이는 해당 플립-플롭의 셋업 및 홀드 스큐에 영향을 받는다. 본 논문에서는 이러한 특성을 수학적으로 정리하였으며, 이를 확장 가능한 속도 향상 기법과 더불어 주어진 회로의 타이밍 분석 및 클럭 스큐 스케쥴링 문제에 적용하였다. 둘째로, 유사 문턱 연산은 초고집적 회로 동작의 에너지 효율을 끌어 올릴 수 있다는 점에서 각광받지만, 큰 폭의 성능 변이 및 비선형성 때문에 널리 활용되고 있지 않다. 이를 해결하기 위해 유사 문턱 전압 영역 및 최신 공정 노드에서 보다 정확한 타이밍 예측을 위한 하드웨어 성능 모니터링 방법론 전반을 제안하였다. 마지막으로, 비동기 회로는 기존 동기 회로의 대안 중 하나로, 그 중에서도 비동기 파이프라인 회로는 비교적 적은 설계 노력만으로도 구현 가능하다는 장점이 있다. 본 논문에서는 2위상 묶음 데이터 프로토콜 기반 비동기 파이프라인 컨트롤러 상에서, 정확한 핸드셰이킹 통신을 위해 삽입된 딜레이 버퍼에 의한 면적 증가를 완화할 수 있는 합성 기법을 제시하였다.1 INTRODUCTION 1 1.1 Flexible Flip-Flop Timing Model 1 1.2 Hardware Performance Monitoring Methodology 4 1.3 Asynchronous Pipeline Controller 10 1.4 Contributions of this Dissertation 15 2 ANALYSIS AND OPTIMIZATION CONSIDERING FLEXIBLE FLIP-FLOP TIMING MODEL 17 2.1 Preliminaries 17 2.1.1 Terminologies 17 2.1.2 Timing Analysis 20 2.1.3 Clock-to-Q Delay Surface Modeling 21 2.2 Clock-to-Q Delay Interval Analysis 22 2.2.1 Derivation 23 2.2.2 Additional Constraints 26 2.2.3 Analysis: Finding Minimum Clock Period 28 2.2.4 Optimization: Clock Skew Scheduling 30 2.2.5 Scalable Speedup Technique 33 2.3 Experimental Results 37 2.3.1 Application to Minimum Clock Period Finding 37 2.3.2 Application to Clock Skew Scheduling 39 2.3.3 Efficacy of Scalable Speedup Technique 43 2.4 Summary 44 3 HARDWARE PERFORMANCE MONITORING METHODOLOGY AT NTC AND ADVANCED TECHNOLOGY NODE 45 3.1 Overall Flow of Proposed HPM Methodology 45 3.2 Prerequisites to HPM Methodology 47 3.2.1 BEOL Process Variation Modeling 47 3.2.2 Surrogate Model Preparation 49 3.3 HPM Methodology: Design Phase 52 3.3.1 HPM2PV Model Construction 52 3.3.2 Optimization of Monitoring Circuits Configuration 54 3.3.3 PV2CPT Model Construction 58 3.4 HPM Methodology: Post-Silicon Phase 60 3.4.1 Transfer Learning in Silicon Characterization Step 60 3.4.2 Procedures in Volume Production Phase 61 3.5 Experimental Results 62 3.5.1 Experimental Setup 62 3.5.2 Exploration of Monitoring Circuits Configuration 64 3.5.3 Effectiveness of Monitoring Circuits Optimization 66 3.5.4 Considering BEOL PVs and Uncertainty Learning 68 3.5.5 Comparison among Different Prediction Flows 69 3.5.6 Effectiveness of Prediction Model Calibration 71 3.6 Summary 73 4 LIGHTENING ASYNCHRONOUS PIPELINE CONTROLLER 75 4.1 Preliminaries and State-of-the-Art Work 75 4.1.1 Bundled-data vs. Dual-rail Asynchronous Circuits 75 4.1.2 Two-phase vs. Four-phase Bundled-data Protocol 76 4.1.3 Conventional State-of-the-Art Pipeline Controller Template 77 4.2 Delay Path Sharing for Lightening Pipeline Controller Template 78 4.2.1 Synthesizing Sharable Delay Paths 78 4.2.2 Validating Logical Correctness for Sharable Delay Paths 80 4.2.3 Reformulating Timing Constraints of Controller Template 81 4.2.4 Minimally Allocating Delay Buffers 87 4.3 In-depth Pipeline Controller Template Synthesis with Delay Path Reusing 88 4.3.1 Synthesizing Delay Path Units 88 4.3.2 Validating Logical Correctness of Delay Path Units 89 4.3.3 Updating Timing Constraints for Delay Path Units 91 4.3.4 In-depth Synthesis Flow Utilizing Delay Path Units 95 4.4 Experimental Results 99 4.4.1 Environment Setup 99 4.4.2 Piecewise Linear Modeling of Delay Path Unit Area 99 4.4.3 Comparison of Power, Performance, and Area 102 4.5 Summary 107 5 CONCLUSION 109 5.1 Chapter 2 109 5.2 Chapter 3 110 5.3 Chapter 4 110 Abstract (In Korean) 127Docto

저전력 고성능 디지털 시스템을 위한 고신뢰도의 클럭 네트워크 설계 방법론

학위논문 (박사)-- 서울대학교 대학원 : 전기·컴퓨터공학부, 2015. 8. 김태환.오늘날의 회로 설계에서 공정변이가 회로 클럭의 타이밍의 변이에 미치는 영향은 매우 커짐에 따라, 전통적으로 사용되던 클럭 트리 구조를 기반으로 한 클럭 네트워크를 사용하는 것은 한계에 부딪히게 되었고, 이를 극복하기 위한 여러가지 기술들이 제안되었다. 본 논문에서는 변이에 강한 클럭 네트워크를 설계하기 위해, 연구 및 사용되고 있는 세 가지 기술에 대해 소개하고, 이들을 개선한 연구들을 제안한다. 첫째로, 이 논문에서는 클럭의 타이밍 문제를 회로 제작 이후 단계에서 조정할 수 있는 포스트 실리콘 조정 클럭 버퍼를 배치하는 문제에 대해 서술한다. 포스트 실리콘 조정 버퍼는 클럭의 지연시간을 회로가 제작된 이후의 단계에서 조정하 여 클럭의 타이밍 문제를 해결할 수 있지만, 버퍼 자체의 크기 때문에 최소한의 개수만 가장 효율적인 위치에 배치해야 하는 문제가 있다. 본 논문에서는 이전의 연구가 회로의 수율을 계산할 때 시간이 많이 걸리는 몬테-카를로 시뮬레이션을 사용하기 때문에 탐색 가능한 포스트 실리콘 조정 버퍼의 배치가 제한되는 문제가 있음을 지적한 후, 기존에 제안되었던 그래프 기반 회로 수율 계산 기법을 사용하여 효율적인 포스트 실리콘 조정 버퍼 배치를 찾을 수 있는 점진적이고 체계적인 방법을 제시한다. 다음은 클럭 시차 스케쥴링 방법에 대한 연구를 서술한다. 최근의 연구에서 제안되었던, 플립-플롭의 클럭에서 출력까지의 딜레이가 클럭의 준비시간과 유지시간에 의존한다는 유연한 플립-플롭 타이밍 모델 연구는 기존의 플립-플롭의 타이밍 특성들이 고정된 값이라는 가정에 기반한 정적 타이밍 분석의 정확성 문제를 해결할 수 있는 중요한 연구이다. 본 논문에서는 새로운 모델을 고려하여, 이전에 고전적인 플립-플롭 타이밍 특성 모델을 기반으로 진행되었던 클럭 시차 스케쥴링의 최적화 문제를 유연한 플립-플롭 타이밍 모델을 고려하여 해결하였다. 본 연구에서는 주어진 회로의 준비시간과 유지시간의 여유시간을 반복적이고 체계적으로 최대화하여 문제를 해결하였다. 마지막으로 클럭 스파인 네트워크의 합성을 자동화하는 문제에 대해 서술한다. 전통적인 클럭 트리 구조가 공정변이 문제를 해결하지 못했기 때문에 클럭 메쉬를 포함하는 다양한 대안적 구조가 제안되었다. 클럭 메쉬의 경우 공정변이에 의한 클럭 시차를 줄일 수 있었지만 이를 위해 와이어나 버퍼 등의 자원을 많이 소모하는 문제를 가지고 있다. 두 구조의 중간적 구조에는 클럭 트리의 노드를 연결하는 크로스 링크를 삽입하는 구조와 클럭 스파인 구조가 있다. 클럭 트리에 점진적인 수정을 가하여 만드는 크로스 링크와 달리, 클럭 스파인 구조는 트리나 이후에 제안된 메쉬와는 완전히 별개의 구조로, 이를 합성하는 방법도 매우 다르다. 그렇기 때문에 클럭 스파인을 합성하는 알고리즘은 필수적이라고 할 수 있으나, 합성 방법론이나 이를 자동화하는 방법에 관한 연구는 아직 없다. 본 논문에서는 우선, 클럭-게이팅을 지원하는 클럭 스파인을 주어진 클럭 시차 및 클럭 슬루 조건을 만족하면서 자원 및 전력 소모량을 최소화하는 문제에 대해 서술한다. 그리고, 회로에서 주어진 플립-플롭들을 클럭-게이팅 조건에서의 연관성을 고려하고 조직화하여 클럭 스파인을 삽입한 후, 클럭 시차 및 슬루 조건을 고려하여 버퍼를 삽입하는 알고리즘을 제안한다. 요약하면, 본 논문에서는 클럭의 타이밍 문제를 해결하기 위해 포스트-실리콘 조정 클럭 버퍼를 사용하는 테크닉과 클럭 시차 스케쥴링을 유연한 플립-플롭 타이밍 모델에서 적용하는 테크닉을 제시하고, 클럭의 타이밍 문제와 전력 소모 문제를 한번에 해결하기 위한 새로운 클럭 스파인 네트워크를 합성하는 자동화 알고리즘을 제시한다.As the process variation is dominating to cause the clock timing variation among chips to be much large, conventional clock tree based clock network is not able to guarantee the timing constraint of a digital system. To overcome the limitations of traditional clock design techniques, various techniques have been studied. This dissertation addresses three techniques that have been widely used for designing robust clock network and proposes developed methods. First, it is widely accepted that post-silicon tunable (PST) clock buffers can effectively resolve the clock timing violation. Since PST buffers, which can reset the clock delay to flip-flops after the chip is manufactured, impose a non-trivial implementation area and control circuitry, it is very important to minimally allocate PST buffers while satisfying the chip yield constraint. In this dissertation, we (1) develop a graph-based chip yield computation technique which can update yields very efficiently and accurately for incremental PST buffer allocation, based on which we (2) propose a systematic (bottom-up and top-down with refinement) PST buffer allocation algorithm that is able to fully explore the design space of PST buffer allocation. Second, clock skew scheduling is one of the essential steps that must be carefully performed during the design process. This dissertation addresses the clock skew optimization problem integrated with the consideration of the interdependent relation between the setup and hold skews, and clk-to-Q delay of flip-flops, so that the time margin is more accurately and reliably set aside over that of the previous methods, which have never taken the integrated problem into account. Precisely, based on an accurate flexible model of setup skew, hold skew, and clk-to-Q delay, we propose a stepwise clock skew scheduling technique in which at each iteration, the worst slack of setup and hold skews is systematically and incrementally relaxed to maximally extend the time margin. Lastly, clock tree with cross links and clock spine have an intermediate characteristics for skew tolerance and power consumption, compared to clock tree and clock mesh which are two extreme structures of clock network. Unlike the clock tree with links between clock nodes, which is a sort of an incremental modification of the structure of clock tree, clock spine network is a completely separated structure from the structures of tree and mesh. Consequently, it is necessary and essential to develop a synthesis algorithm for clock spines, which will be compatible to the existing synthesis algorithms of clock trees and clock meshes. To this end, this dissertation first addresses the problem of automating the synthesis of clock-gated clock spines with the objective of minimizing total clock power while meeting the clock skew and slew constraints. The key idea of our proposed synthesis algorithm is to identify and group the flip-flops with tight correlation of clock-gating operations together to form a spine while accurately predicting and maintaining clock skew and slew variations through the buffer insertion and stub allocation. In summary, this dissertation presents clock tuning techniques with consideration of post-silicon tuning, flexible flip-flop timing model, and clock-gated clock spine synthesis algorithm.Abstract i Chapter 1 INTRODUCTION 1 1.1 Clock Distribution Network . . . . . . . . . . . . . . . . . . . . . 1 1.2 Process Variation . . . . . . . . . . . . . . . . . . . . . . . . . . . 2 1.3 Flexible Flip-flop Timing Model . . . . . . . . . . . . . . . . . . . 3 1.4 Clock Spine . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3 1.5 Contributions of This Dissertation . . . . . . . . . . . . . . . . . 6 Chapter 2 POST-SILICON TUNABLE CLOCK BUFFER ALLOCATION BASED ON FAST CHIP YIELD COMPUTATION 8 2.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8 2.2 Systematic Exploration of PST Buffer Allocation . . . . . . . . . 10 2.2.1 Observations . . . . . . . . . . . . . . . . . . . . . . . . . 10 2.2.2 Problem Definition . . . . . . . . . . . . . . . . . . . . . . 15 2.2.3 Allocation Algorithm . . . . . . . . . . . . . . . . . . . . . 16 2.3 Fast Timing Yield Computation . . . . . . . . . . . . . . . . . . 17 2.3.1 Preliminaries . . . . . . . . . . . . . . . . . . . . . . . . . 17 2.3.2 Incremental Yield Computation . . . . . . . . . . . . . . . 22 2.4 Experimental Result . . . . . . . . . . . . . . . . . . . . . . . . . 24 2.5 PST Buffer Configuration Techniques . . . . . . . . . . . . . . . 31 2.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 32 Chapter 3 POST-SILICON TUNING BASED ON FLEXIBLE FLIP-FLOP TIMING 34 3.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 34 3.2 Preliminary and Definitions . . . . . . . . . . . . . . . . . . . . . 40 3.2.1 Flexible Flip-Flop Timing Model . . . . . . . . . . . . . . 40 3.2.2 Definitions . . . . . . . . . . . . . . . . . . . . . . . . . . 40 3.3 Motivational Examples . . . . . . . . . . . . . . . . . . . . . . . . 42 3.4 Clock Skew Scheduling for Slack Relaxation Based on Flexible Flip-Flop Timing . . . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.4.1 Overall Flow . . . . . . . . . . . . . . . . . . . . . . . . . 46 3.4.2 Finding Local Clock Skew Schedule . . . . . . . . . . . . 48 3.5 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . 51 3.6 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 57 Chapter 4 SYNTHESIS FOR POWER-AWARE CLOCK SPINES 61 4.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 61 4.2 Preliminaries and Motivation . . . . . . . . . . . . . . . . . . . . 64 4.2.1 Clock Spine . . . . . . . . . . . . . . . . . . . . . . . . . . 64 4.2.2 Activity Patterns . . . . . . . . . . . . . . . . . . . . . . . 67 4.2.3 Power Computation . . . . . . . . . . . . . . . . . . . . . 67 4.3 Algorithm for Clock Spine Synthesis . . . . . . . . . . . . . . . . 68 4.3.1 Problem Definition . . . . . . . . . . . . . . . . . . . . . . 68 4.3.2 Power-Aware Sink Clustering . . . . . . . . . . . . . . . . 70 4.3.3 Spine Relaxation . . . . . . . . . . . . . . . . . . . . . . . 77 4.3.4 Spine Buffer Allocation . . . . . . . . . . . . . . . . . . . 80 4.3.5 Top-Level Tree Construction . . . . . . . . . . . . . . . . 86 4.4 Experimental Results . . . . . . . . . . . . . . . . . . . . . . . . . 86 4.5 Summary . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 91 Chapter 5 CONCLUSION 95 5.1 Chapter 2 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.2 Chapter 3 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 95 5.3 Chapter 4 . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 96 Bibliography 97 초록 106Docto

Research Reports: 1989 NASA/ASEE Summer Faculty Fellowship Program

For the twenty-fifth consecutive year, a NASA/ASEE Summer Faculty Fellowship Program was conducted at the Marshall Space Flight Center (MSFC). The basic objectives of the programs are: (1) to further the professional knowledge of qualified engineering and science faculty members; (2) to stimulate an exchange of ideas between participants and NASA; (3) to enrich and refresh the research and teaching activities of the participants' institutions; and (4) to contribute to the research objectives of the NASA Centers. The Faculty Fellows spent ten weeks at MSFC engaged in a research project compatible with their interests and background and worked in collaboration with a NASA/MSFC colleague

Aeronautical engineering: A continuing bibliography with indexes (supplement 272)

This bibliography lists 719 reports, articles, and other documents introduced into the NASA scientific and technical information system in November, 1991. Subject coverage includes: design, construction and testing of aircraft and aircraft engines; aircraft components, equipment, and systems; ground support systems; and theoretical and applied aspects of aerodynamics and general fluid dynamics

Cumulative index to NASA Tech Briefs, 1986-1990, volumes 10-14

Tech Briefs are short announcements of new technology derived from the R&D activities of the National Aeronautics and Space Administration. These briefs emphasize information considered likely to be transferrable across industrial, regional, or disciplinary lines and are issued to encourage commercial application. This cumulative index of Tech Briefs contains abstracts and four indexes (subject, personal author, originating center, and Tech Brief number) and covers the period 1986 to 1990. The abstract section is organized by the following subject categories: electronic components and circuits, electronic systems, physical sciences, materials, computer programs, life sciences, mechanics, machinery, fabrication technology, and mathematics and information sciences

Six Decades of Flight Research: An Annotated Bibliography of Technical Publications of NASA Dryden Flight Research Center, 1946-2006

Titles, authors, report numbers, and abstracts are given for nearly 2900 unclassified and unrestricted technical reports and papers published from September 1946 to December 2006 by the NASA Dryden Flight Research Center and its predecessor organizations. These technical reports and papers describe and give the results of 60 years of flight research performed by the NACA and NASA, from the X-1 and other early X-airplanes, to the X-15, Space Shuttle, X-29 Forward Swept Wing, X-31, and X-43 aircraft. Some of the other research airplanes tested were the D-558, phase 1 and 2; M-2, HL-10 and X-24 lifting bodies; Digital Fly-By-Wire and Supercritical Wing F-8; XB-70; YF-12; AFTI F-111 TACT and MAW; F-15 HiDEC; F-18 High Alpha Research Vehicle, F-18 Systems Research Aircraft and the NASA Landing Systems Research aircraft. The citations of reports and papers are listed in chronological order, with author and aircraft indices. In addition, in the appendices, citations of 270 contractor reports, more than 200 UCLA Flight System Research Center reports, nearly 200 Tech Briefs, 30 Dryden Historical Publications, and over 30 videotapes are included