1,726 research outputs found
Parallel symbolic state-space exploration is difficult, but what is the alternative?
State-space exploration is an essential step in many modeling and analysis
problems. Its goal is to find the states reachable from the initial state of a
discrete-state model described. The state space can used to answer important
questions, e.g., "Is there a dead state?" and "Can N become negative?", or as a
starting point for sophisticated investigations expressed in temporal logic.
Unfortunately, the state space is often so large that ordinary explicit data
structures and sequential algorithms cannot cope, prompting the exploration of
(1) parallel approaches using multiple processors, from simple workstation
networks to shared-memory supercomputers, to satisfy large memory and runtime
requirements and (2) symbolic approaches using decision diagrams to encode the
large structured sets and relations manipulated during state-space generation.
Both approaches have merits and limitations. Parallel explicit state-space
generation is challenging, but almost linear speedup can be achieved; however,
the analysis is ultimately limited by the memory and processors available.
Symbolic methods are a heuristic that can efficiently encode many, but not all,
functions over a structured and exponentially large domain; here the pitfalls
are subtler: their performance varies widely depending on the class of decision
diagram chosen, the state variable order, and obscure algorithmic parameters.
As symbolic approaches are often much more efficient than explicit ones for
many practical models, we argue for the need to parallelize symbolic
state-space generation algorithms, so that we can realize the advantage of both
approaches. This is a challenging endeavor, as the most efficient symbolic
algorithm, Saturation, is inherently sequential. We conclude by discussing
challenges, efforts, and promising directions toward this goal
Next-state equation generation for asynchronous sequential circuits - normal mode
This paper describes the known methods of generating next-state equations for asynchronous sequential circuits operating in normal fundamental mode. First, the methods that have been previously developed by other authors are explained and correlated in a simple and uniform language in order that the subtle differences of these approaches can be seen. This review is then followed by a development of a new method for generating minimal next-state equations which has some advantages over the previous methods. From the comparison of the previous known methods, it is noted that any one of these methods may be desirable for certain designs since each has some advantages that the others do not have. However, these methods also have limitations in that some methods can only be used with particular types of assignments. Also, as flow tables become larger the amount of work required to use some of these methods becomes excessive and tedious. The method developed here is a simple and straightforward approach which can be used for any unicode, single transition time assignment and will easily lend itself to computer application. The heart of this method emanates from the role that the Karnaugh map plays in the conventional approach for generating the next-state equations. The main advantage of this method seems to be its capability and proficiency in handling large flow tables --Abstract, pages ii-iii
Decomposition of sequential and concurrent models
Le macchine a stati finiti (FSM), sistemi di transizioni (TS) e le reti di Petri (PN) sono importanti modelli formali per la progettazione di sistemi. Un problema fodamentale è la conversione da un modello all'altro. Questa tesi esplora il mondo delle reti di Petri e della decomposizione di sistemi di transizioni. Per quanto riguarda la decomposizione dei sistemi di transizioni, la teoria delle regioni rappresenta la colonna portante dell'intero processo di decomposizione, mirato soprattutto a decomposizioni che utilizzano due sottoclassi delle reti di Petri: macchine a stati e reti di Petri a scelta libera. Nella tesi si dimostra che una proprietà chiamata ``chiusura rispetto all'eccitazione" (excitation-closure) è sufficiente per produrre un insieme di reti di Petri la cui sincronizzazione è bisimile al sistema di transizioni (o rete di Petri di partenza, se la decomposizione parte da una rete di Petri), dimostrando costruttivamente l'esistenza di una bisimulazione. Inoltre, è stato implementato un software che esegue la decomposizione dei sistemi di transizioni, per rafforzare i risultati teorici con dati sperimentali sistematici. Nella seconda parte della dissertazione si analizza un nuovo modello chiamato MSFSM, che rappresenta un insieme di FSM sincronizzate da due primitive specifiche (Wait State - Stato d'Attesa e Transition Barrier - Barriera di Transizione). Tale modello trova un utilizzo significativo nella sintesi di circuiti sincroni a partire da reti di Petri a scelta libera. In particolare vengono identificati degli errori nell'approccio originale, fornendo delle correzioni.Finite State Machines (FSMs), transition systems (TSs) and Petri nets (PNs) are important models of computation ubiquitous in formal methods for modeling systems. Important problems involve the transition from one model to another. This thesis explores Petri nets, transition systems and Finite State Machines decomposition and optimization. The first part addresses decomposition of transition systems and Petri nets, based on the theory of regions, representing them by means of restricted PNs, e.g., State Machines (SMs) and Free-choice Petri nets (FCPNs). We show that the property called ``excitation-closure" is sufficient to produce a set of synchronized Petri nets bisimilar to the original transition system or to the initial Petri net (if the decomposition starts from a PN), proving by construction the existence of a bisimulation. Furthermore, we implemented a software performing the decomposition of transition systems, and reported extensive experiments. The second part of the dissertation discusses Multiple Synchronized Finite State Machines (MSFSMs) specifying a set of FSMs synchronized by specific primitives: Wait State and Transition Barrier. It introduces a method for converting Petri nets into synchronous circuits using MSFSM, identifies errors in the initial approach, and provides corrections
NEW METHODS FOR PSEUDOEXHAUSTIVE TESTING
Pseudoexhaustive testing of combinational circuits has become of great importance
recently. These methods are keeping most of the benefits of the classical exhaustive testing which
check every combination of the input signals, but they need a considerably shorter sequence of
test patterns. In this paper we give a survey of pseudoexhaustive testing. Two new code
construction methods are presented: a systematic procedure to generate an effective exhaustive
code for every two dimensional subspace of the inputs; and an extension of the codes from the k
dimensional space to k+1. The efficiency of the new methods is compared to the ones described
in the literature
An Efficient Design Methodology for Complex Sequential Asynchronous Digital Circuits
Asynchronous digital logic as a design alternative offers a smaller circuit area and lower power consumption but suffers from increased complexity and difficulties related to logic hazards and elements synchronization. The presented work proposes a design methodology based on the speed-independent sequential logic theory, oriented toward asynchronous hardware implementation of complex multi-step algorithms. Targeting controller-centric devices that perform data-driven non-linear execution, the methodology offers a CSP language-based controller workflow description approach and the specification of a project implementation template supported by a two-stage design process. First, the CSP layer describes complex speed-independent controller behavior offering better scalability and maintainability than the STG model. Second, the component-oriented design template specifies functional elements\u27 structural organization and emphasizes the divide-and-conquer philosophy, streamlining large and complex devices\u27 design and maintenance. Finally, the implementation process is divided into two stages: a rapid development and functional verification stage and a synthesizable codebase stage. Additionally, a case study design of a split-transaction MESI cache coherency controller and its analysis are presented to validate the proposed methodology. The testing phase compares synthesized and routed gate-level asynchronous and synchronous implementations. For models synthesized to work with the same speed, the asynchronous circuit area is 20% smaller with lower power consumption at approximately 18% of the synchronous reference. The synchronous version synthesized for performance is 3.5 times faster, at the cost of a large increase in area and power usage. The results prove the methodology\u27s ability to deliver working complex asynchronous circuits competitive in the chip area and power characteristics
Dataflow computers: a tutorial and survey
Journal ArticleThe demand for very high performance computer has encouraged some researchers in the computer science field to consider alternatives to the conventional notions of program and computer organization. The dataflow computer is one attempt to form a new collection of consistent systems ideas to improve both computer performance and to alleviate the software design problems induced by the construction of highly concurrent programs
Energy-Efficient Digital Circuit Design using Threshold Logic Gates
abstract: Improving energy efficiency has always been the prime objective of the custom and automated digital circuit design techniques. As a result, a multitude of methods to reduce power without sacrificing performance have been proposed. However, as the field of design automation has matured over the last few decades, there have been no new automated design techniques, that can provide considerable improvements in circuit power, leakage and area. Although emerging nano-devices are expected to replace the existing MOSFET devices, they are far from being as mature as semiconductor devices and their full potential and promises are many years away from being practical.
The research described in this dissertation consists of four main parts. First is a new circuit architecture of a differential threshold logic flipflop called PNAND. The PNAND gate is an edge-triggered multi-input sequential cell whose next state function is a threshold function of its inputs. Second a new approach, called hybridization, that replaces flipflops and parts of their logic cones with PNAND cells is described. The resulting \hybrid circuit, which consists of conventional logic cells and PNANDs, is shown to have significantly less power consumption, smaller area, less standby power and less power variation.
Third, a new architecture of a field programmable array, called field programmable threshold logic array (FPTLA), in which the standard lookup table (LUT) is replaced by a PNAND is described. The FPTLA is shown to have as much as 50% lower energy-delay product compared to conventional FPGA using well known FPGA modeling tool called VPR.
Fourth, a novel clock skewing technique that makes use of the completion detection feature of the differential mode flipflops is described. This clock skewing method improves the area and power of the ASIC circuits by increasing slack on timing paths. An additional advantage of this method is the elimination of hold time violation on given short paths.
Several circuit design methodologies such as retiming and asynchronous circuit design can use the proposed threshold logic gate effectively. Therefore, the use of threshold logic flipflops in conventional design methodologies opens new avenues of research towards more energy-efficient circuits.Dissertation/ThesisDoctoral Dissertation Computer Science 201
Compositional approach to design of digital circuits
PhD ThesisIn this work we explore compositional methods for design of digital circuits with
the aim of improving existing methodoligies for desigh reuse. We address compositionality
techniques looking from both structural and behavioural perspectives.
First we consider the existing method of handshake circuit optimisation via control
path resynthesis using Petri nets, an approach using structural composition. In
that approach labelled Petri net parallel composition plays an important role and
we introduce an improvement to the parallel composition algorithm, reducing the
number of redundant places in the resulting Petri net representations. The proposed
algorithm applies to labelled Petri nets in general and can be applied outside of the
handshake circuit optimisation use case.
Next we look at the conditional partial order graph (CPOG) formalism, an approach
that allows for a convenient representation of systems consisting of multiple
alternative system behaviours, a phenomenon we call behavioural composition. We
generalise the notion of CPOG and identify an algebraic structure on a more general
notion of parameterised graph. This allows us to do equivalence-preserving manipulation
of graphs in symbolic form, which simplifies specification and reasoning about
systems defined in this way, as displayed by two case studies.
As a third contribution we build upon the previous work of CPOG synthesis used
to generate binary encoding of microcontroller instruction sets and design the corresponding
instruction decoder logic. The proposed CPOG synthesis technique solves
the optimisation problem for the general case, reducing it to Boolean satisfiability
problem and uses existing SAT solving tools to obtain the result.This work was
supported by a studentship from Newcastle University EECE school, EPSRC grant
EP/G037809/1 (VERDAD) and EPSRC grant EP/K001698/1 (UNCOVER).
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