16240719
Formal Verification of Out-of-Order Execution Using Incremental Flushing
We present a two-part approach for verifying out-of-order execution. First, the complexity of out-of-order issue and scheduling is handled by creating an in-order abstraction of the out-of-order execution core. Second, incremental flushing addresses the complexity difficulties encountered by automated abstraction functions on very deep pipelines. We illustrate the techniques on a model of a simple out-of-order processor core.
14277112
A Methodology for Large-Scale Hardware Verification
We present a formal verification methodology for datapath-dominated hardware. This provides a systematic but flexible framework within which to organize the activities undertaken in large-scale verification efforts and to structure the associated code and proof-script artifacts. The methodology deploys a combination of model checking and lightweight theorem proving in higher-order logic, tightly integrated within a general-purpose functional programming language that allows the framework to be easily customized and also serves as a specification language. We illustrate the methodology--which has has proved highly effective in large-scale industrial trials--with the verification of an IEEE-compliant, extended precision floating-point adder.
16718437
Practical Formal Verification in Microprocessor Design
Practical application of formal methods requires more than advanced technology and tools; it requires an appropriate methodology. A verification methodology for data-path-dominated hardware combines model checking and theorem proving in a customizable framework. This methodology has been effective in large-scale industrial trials, including verification of an IEEE-compliant floating-point adder.
5421455
Self-Consistency Checking
We introduce the notion of self-consistency checking, a new methodology for applying formal methods in the debugging process. Intuitively, self-consistency checks functional consistency of a circuit in two different modes or environments. Self-consistency can (1) simplify property verification and (2) enable the use of symbolic simulation in the absence of a concrete specification. We present a correctness model for property verification with self-consistency checking and the formal framework for the technique. Finally, we provide illustrative examples and partial verification results using self-consistency checking on circuits with many thousands of latches.
16794414
A Framework for Microprocessor Correctness Statements
Most verifications of out-of-order microprocessors compare state-machine-based implementations and specifications, where the specification is based on the instruction-set architecture. The different efforts use a variety of correctness statements, implementations, and verification approaches. We present a framework for classifying correctness statements about safety that is independent of implementation representation and verification approach. We characterize the relationships between the different statements and illustrate how existing and classical approaches fit within this framework.
85258
Reducing Manual Abstraction in Formal Verification of Out-of-Order Execution
Several methods have recently been proposed for verifying processors with out-of-order execution. These methods use intermediate abstractions to decompose the verification process into smaller steps. Unfortunately, the process of manually creating intermediate abstractions is very laborious. We present an approach that dramatically reduces the need for an intermediate abstraction, so that only the scheduling logic of the implementation is abstracted. After the abstraction, we apply an enhanced incremental-flushing approach to verify the remaining circuitry by comparing the processor description against itself in a slightly simpler configuration. By induction, we demonstrate that any reachable configuration is equivalent to the simplest possible configuration. Finally, we prove correctness on the simplest configuration. The approach is illustrated with a simple example of an out-of-order execution core.
8968901
Birrell's distributed reference listing revisited
The Java RMI collector is arguably the most widely used distributed garbage collector. Its distributed reference listing algorithm was introduced by Birrell et al. in the context of Network Objects, where the description was informal and heavily biased toward implementation. In this article, we formalize this algorithm in an implementation-independent manner, which allows us to clarify weaknesses of the initial presentation. In particular, we discover cases critical to the correctness of the algorithm that were not accounted for by Birrell. We use our formalization to derive an invariant-based proof of correctness of the algorithm that avoids notoriously difficult temporal reasoning. Furthermore, we offer a novel graphical representation of the state transition diagram, which we use to provide intuitive explanations of the algorithm and to investigate its tolerance to faults in a systematic manner. Finally, we examine how the algorithm may be optimized, either by placing constraints on message channels or by tightening the coupling between the application program and distributed garbage collector.
15205488
Query word deletion prediction
Web search query logs contain traces of users' search modifications. One strategy users employ is deleting terms, presumably to obtain greater coverage. It is useful to model and automate term deletion when arbitrary searches are conjunctively matched against a small hand constructed collection, such as a hand-built hierarchy, or collection of high-quality pages matched with key phrases. Queries with no matches can have words deleted till a match is obtained. We provide algorithms which perform substantially better than the baseline in predicting which word should be deleted from a reformulated query, for increasing query coverage in the context of web search on small high-quality collections.
11914137
TREC-10 Experiments at University of Maryland CLIR and Video
The University of Maryland Researchers participated in both the Arabic-English Cross Language Information Retrieval (CLIR) and Video tracks of TREC-10. In the CLIR track, our goal was to explore effective monolingual Arabic IR techniques and effective query translation from English to Arabic for cross language IR. For the monolingual part, the use of the different index terms including words, stems, roots, and character n-grams were explored. For the English-Arabic CLIR, the use of MT, wordlist based translation, and non-dictionary words transliteration was explored. In the video track, we participated in the shot boundary detection, and known item search with the primary goals being to evaluate existing technology for shot detection and a new approach to extending simple visual image queries to video sequences. We present a general overview of the approaches, summarize the results in discuss how the algorithms are being extended.
572074
Building mosaics from video using MPEG motion vectors
Abstract : In this paper, we present a novel way of creating mosaics from an MPEG video sequence. Two original aspects of our work are that (1) we explicitly compute camera motion between frames and (2) we deduce the camera motion directly from the motion vectors encoded in the MPEG video stream. This enables us to create mosaics more simply and quickly than with other methods.
26305456
Tail Recursion without Space Leaks
The G-machine (Johnsson, 1987; Peyton Jones, 1987) is a compiled graph reduction machine for lazy functional languages. The G-machine compiler contains many optimizations to improve performance. One set of such optimizations is designed to improve the performance of tail recursive functions. Unfortunately, the abstract machine is subject to a space leak—objects are unnecessarily preserved by the garbage collector. This paper analyses why a particular form of space leak occurs in the G-machine, and presents some ideas for fixing this problem. This phenomena in other abstract machines is also examined briefly.