Architectural synthesis of timed asynchronous systems

Journal ArticleThis paper describes a new method for architectural synthesis of timed asynchronous systems. Due to the variable delays associated with asynchronous resources, implicit schedules are created by the addition of supplementary constraints between resources. Since the number of schedules grows exponentially with respect to the size of the given data flow graph, pruning techniques are introduced which dramatically improve run-time without significantly affecting the quality of the results. Using a combination of data and resource constraints, as well as an analysis of bounded delay information, our method determines the minimum number of resources and registers needed to implement a given schedule. Results are demonstrated using some high-level synthesis benchmark circuits and an industrial example

Latency Optimized Asynchronous Early Output Ripple Carry Adder based on Delay-Insensitive Dual-Rail Data Encoding

Asynchronous circuits employing delay-insensitive codes for data representation i.e. encoding and following a 4-phase return-to-zero protocol for handshaking are generally robust. Depending upon whether a single delay-insensitive code or multiple delay-insensitive code(s) are used for data encoding, the encoding scheme is called homogeneous or heterogeneous delay-insensitive data encoding. This article proposes a new latency optimized early output asynchronous ripple carry adder (RCA) that utilizes single-bit asynchronous full adders (SAFAs) and dual-bit asynchronous full adders (DAFAs) which incorporate redundant logic and are based on the delay-insensitive dual-rail code i.e. homogeneous data encoding, and follow a 4-phase return-to-zero handshaking. Amongst various RCA, carry lookahead adder (CLA), and carry select adder (CSLA) designs, which are based on homogeneous or heterogeneous delay-insensitive data encodings which correspond to the weak-indication or the early output timing model, the proposed early output asynchronous RCA that incorporates SAFAs and DAFAs with redundant logic is found to result in reduced latency for a dual-operand addition operation. In particular, for a 32-bit asynchronous RCA, utilizing 15 stages of DAFAs and 2 stages of SAFAs leads to reduced latency. The theoretical worst-case latencies of the different asynchronous adders were calculated by taking into account the typical gate delays of a 32/28nm CMOS digital cell library, and a comparison is made with their practical worst-case latencies estimated. The theoretical and practical worst-case latencies show a close correlation....Comment: arXiv admin note: text overlap with arXiv:1704.0761

Formal Model Engineering for Embedded Systems Using Real-Time Maude

This paper motivates why Real-Time Maude should be well suited to provide a formal semantics and formal analysis capabilities to modeling languages for embedded systems. One can then use the code generation facilities of the tools for the modeling languages to automatically synthesize Real-Time Maude verification models from design models, enabling a formal model engineering process that combines the convenience of modeling using an informal but intuitive modeling language with formal verification. We give a brief overview six fairly different modeling formalisms for which Real-Time Maude has provided the formal semantics and (possibly) formal analysis. These models include behavioral subsets of the avionics modeling standard AADL, Ptolemy II discrete-event models, two EMF-based timed model transformation systems, and a modeling language for handset software.Comment: In Proceedings AMMSE 2011, arXiv:1106.596

Doctor of Philosophy

dissertationAsynchronous design has a very promising potential even though it has largely received a cold reception from industry. Part of this reluctance has been due to the necessity of custom design languages and computer aided design (CAD) flows to design, optimize, and validate asynchronous modules and systems. Next generation asynchronous flows should support modern programming languages (e.g., Verilog) and application specific integrated circuits (ASIC) CAD tools. They also have to support multifrequency designs with mixed synchronous (clocked) and asynchronous (unclocked) designs. This work presents a novel relative timing (RT) based methodology for generating multifrequency designs using synchronous CAD tools and flows. Synchronous CAD tools must be constrained for them to work with asynchronous circuits. Identification of these constraints and characterization flow to automatically derive the constraints is presented. The effect of the constraints on the designs and the way they are handled by the synchronous CAD tools are analyzed and reported in this work. The automation of the generation of asynchronous design templates and also the constraint generation is an important problem. Algorithms for automation of reset addition to asynchronous circuits and power and/or performance optimizations applied to the circuits using logical effort are explored thus filling an important hole in the automation flow. Constraints representing cyclic asynchronous circuits as directed acyclic graphs (DAGs) to the CAD tools is necessary for applying synchronous CAD optimizations like sizing, path delay optimizations and also using static timing analysis (STA) on these circuits. A thorough investigation for the requirements of cycle cutting while preserving timing paths is presented with an algorithm to automate the process of generating them. A large set of designs for 4 phase handshake protocol circuit implementations with early and late data validity are characterized for area, power and performance. Benchmark circuits with automated scripts to generate various configurations for better understanding of the designs are proposed and analyzed. Extension to the methodology like addition of scan insertion using automatic test pattern generation (ATPG) tools to add testability of datapath in bundled data asynchronous circuit implementations and timing closure approaches are also described. Energy, area, and performance of purely asynchronous circuits and circuits with mixed synchronous and asynchronous blocks are explored. Results indicate the benefits that can be derived by generating circuits with asynchronous components using this methodology

A comparison of modular self-timed design styles

technical reportState-machine sequencing methods in modular 2-phase and 4-phase asynchronous handshake control are compared. Design styles are discussed, and the sequencers are tested against each other using a medium-scale minicomputer test design implemented in FPGAs. Seven 4-phase sequencers are tested. In these comparisons, 2- phase control is faster than 4-phase. Within the 4-phase designs, speed is enhanced when work is overlapped with handshake restoration. Performance of asynchronous and synchronous designs is compared

Self-timed design in GaAs - case study of a high-speed parallel multiplier

Journal ArticleAbstract-The problems with synchronous designs at high clock frequencies have been well documented. This makes an asynchronous approach attractive for high speed technologies like GaAs. We investigate the issues involved by describing the design of a parallel multiplier that can be part of a floating point multiplier. We first present a new architecture called the partial army of array (PAA) that is more regular than a partial tree approach while having the same latency. We then show how this architecture can be used in a self-timed implementation in the style of micropipelines. We next describe how we can design the final carry propagate adder using a new precharged logic family in GaAs that we developed as part of this project. We conclude with some genera1 observations on doing asynchronous design in GaAs

An A-FPGA architecture for relative timing based asynchronous designs

pre-printThis paper presents an asynchronous FPGA architecture that is capable of implementing relative timing based asynchronous designs. The architecture uses the Xilinx 7-Series architecture as a starting point and proposes modifications that would make it asynchronous design capable while keeping it fully functional for synchronous designs. Even though the architecture requires additional components, it is observed when implemented on the 64-nm node, the area of the slice was increases marginally by 7%. The architecture leaves configurable routing structures untouched and does not compromise on performance of the synchronous architecture

Practical advances in asynchronous design and in asynchronous/synchronous interfaces

Journal ArticleAsynchronous systems are being viewed as an increasingly viable alternative to purely synchronous systems. This paper gives an overview of the current state of the art in practical asynchronous circuit and system design in four areas: controllers, datapaths, processors, and the design of asynchronous/synchronous interfaces