905 Works

Code Generation for Streaming: an Access/Execute Mechanism

Manuel Benitez & Jack Davidson
Access/execute architectures have several advantages over more traditional architectures. Because address generation and memory access are decoupled from operand use, memory latencies are tolerated better, there is more potential for concurrent operation, and it permits the use of specialized hardware to facilitate fast address generation. This paper describes the code generation and optimization algorithms that are used in an optimizing compiler for an architecture that contains explicit hardware support for the access/execute model of computation....

Gate - A Genetic Algorithm for Compacting Randomly Generated Test Sets

J Aylor, J Cohoon, E Feldhousen & B Johnson
A new technique. named GATE. is presented for the generation of compact test sets. GATE combines a previously proven method for random test pattern generation with the adaptive searching capabilities of genetic algorithms to produce very high quality test sets. A series of experiments demonstrated that our technique performed consistently better than the traditional method with respect to both fault coverage and test set size. 1‘ This research was supported in part by the Virginia...

WM Protection: The Base Mechanism

Wm Wulf & Anita Jones

A Real-Time Synchronization Scheme for Replicated Data in Distributed Database Systems

Sang Son & Spiros Kouloumbis
The design and implementation of time-critical schedulers for real-time distributed replicated database systems must satisfy two major requirements: transactions must be able to meet the timing constraints associated with them, and mutual and internal consistency of replicated data must be preserved. In this paper, we propose a new replication control algorithm, which integrates real~time scheduling and replication control. The algorithm adopts a token-based scheme for replication control and attempts to balance the criticality of realtime...

A Study of the Effects of Subprogram Inlining

Anne Holler
This dissertation examines subprogram inlining, a widely-known code optimization technique whose effects were not well understood prior to this study. For a set of test programs on several computer systems, the sizes and runtimes of executable files produced using a tool that automatically substitutes subprograms inline were compared with those of versions in which call sites were not expanded inline. Issues raised by this experiment's results led to the formulation of equations hypothesized to estimate...

Development of a Set of 'Closed Laboratories' for an Undergraduate Computer Science Curriculum

Wm Wulf
As a discipline, Computer Science has seen many dramatic changes in its brief history. Through new textbooks and an evolving curriculum, the content of undergraduate Computer Science education has for the most part kept pace with these changes. But the pedagogy has hardly changed. Not only is that pedagogy out of dat - - it is profoundly wrong. It emphasizes individual skill in writing short programs in a dead language, from scratch. This emphasis is...

Giving CANDY to Children: User-Tailored Gesture Input Driving An Articulator Based Speech Synthesizer

Randy Pausch & R Williams
The CANDY Project (Communication Assistance to Negate Disabilities in Youth) seeks to provide a realtime speech synthesizer for disabled individuals, particularly non-vocal children with cerebral palsy. Existing speech synthesizers convert user input into discrete linguistic or phonetic symbols which are converted into sound. Complicated sentences must be created by concatenating lower level symbols, precluding real-time conversational speech. We have developed an articulator-based speech synthesizer which simulates the motion of the human tongue and produces the...

Achieving Software Quality Through Reuse

JC Knight & Cass
Software reuse is advocated primarily as a technique to improve programmer productivity. Reuse permits various artifacts of software development to be used on more than one project in order to amortize their development costs. Productivity is not the only advantage of reuse although it is the most widely publicized. By incorporating reusable parts into a new product, the parts bring with them whatever qualities they possess, and these can contribute to the quality of the...

Portable Run-Time Support for Dynamic Object-Oriented Parallel Processing

Andrew Grimshaw, Jon Weissman & W Strayer
The object-oriented paradigm is a powerful tool for managing software complexity. A key question when the paradigm is applied to parallel computing is whether the associated overhead is so large as to defeat the high-performance objectives that motivate parallel computing. We show that high-performance and dynamic object-oriented parallel processing are not mutually exclusive. Our vehicle is Mentat, a portable, object-oriented parallel processing system developed at the University of Virginia. We present a brief overview of...

A Video Mail Distribution System for Networked Personal Computers

F Street & A Weaver
The Computer Networks Laboratory at the University of Virginia has used the Xpress TranSferProtocol (XTP) to construct the Xpress File System (XFS), a local area network peer-to-peer file sharing system for MS-DOS based IBM Personal Computers. XFS is usable for a variety of purposes, most notably the real time delivery of multimedia data streams. Using specialized hardware and software from Fluent Machines Inc., we have shown that XFS is capable of maintaining syffrcient file system...

A Delay Sensitive Error Control Scheme for Continuous Media Communications

Bert Dempsey, Jorg Liebeherr & Alfred Weaver
In this paper we present a new error control approach for continuous media communication protocols. Since continuous media data are inherently bursty, these protocols commonly use a control time for the first packet in a burst to ensure continuous playback in the presence of delay jitter. The retransmission scheme presented in this paper, which is called Slack Automatic Repeat Request (S-ARQ), is based on appropriately extending the control time for the first packet in a...

A Formal Semantics for Evaluating Crytographic Protocols

Alec Yasinsac & William Wulf
Much research in the field of network security is concentrated on the technology and application of cryptography. While the cryptographic methods are heavily investigated to ensure confidence in the security of the code, many cryptographic schemes are Vulnerable due to the protocols used to implement communication in a cryptographic environment. Much work has been done to develop secure protocols, but protocols, like software, are very difficult to verify. Recent research is aimed at finding methods...

An Analytic Model of SMC Performance

Sally McKee

A Fast Method for Generalized Starting Temperature Determination in Two-Stage Simulated Annealing Systems

James Varanelli & James Cohoon
Simulated annealing is a stochastic process that has proven to be an effective method for approximating globally optimum solutions to many types of combinatorial optimization problems, especially in the field of VLSI computer-ended design. The major drawback to the simulated annealing algorithm is its typically very long running times. Several methods have been proposed for accelerating the simulated annealing algorithm. One method is to replace a significant portion of the stochastic operations with a fast...

Laboratory Experience for an Introductory Computer Science Course

W Wulf & J Prey

Dynamically-Wiresized Elmore-Based Routing Constructions

Todd Hodes, Bernard McCoy & Gabriel Robins
We analyze the impact of wiresizing on the performance of Elmore-based routing constructions. Whereas previous wiresizing schemes are static (i.e., they wiresize an existing topology), we introduce a new dynamic Elmore-based wiresizing technique, which uses wiresizing considerations to drive the routing construction itself. Simulations show that dynamic wiresizing affords superior performance over static wiresizing, and also avoids topological degeneracies. Moreover, dynamically-wiresized Elmore-based routing constructions significantly outperform all previous methods in term of maximum sourcesink signal...

Mentat 2.6 Release Notes

The Group

A Model for Specification and Communication of Data for Distributed Multimedia Systems

Sang Son & Nipun Agarwal
As network technology provides the capability to handle multimedia traffic and the demand of multimedia services increases, protocols are required for effective communication of multimedia data in a distributed environment. Synchronization is one of the key issues in a multimedia system. Most of the current approaches do not support an integrated solution to the problem of synchronization. In this paper we propose a mechanism for synchronization of multimedia data in distributed environment where the accuracy...

Legion: The Next Logical Step Toward a Nationwide Virtual Computer

Andrew Grimshaw, William Wulf, James French, Alfred Weaver & Jr Reynolds
The coming of giga-bit networks makes possible the realization of a single nationwide virtual computer comprised of a variety of geographically distributed high-performance machines and workstations. To realize the potential that the physical infrastructure provides, software must be developed that is easy to use, supports large degrees of parallelism in applications code, and manages the complexity of the underlying physical system for the user. This paper describes our approach to constructing and exploiting such "metasystems"....

New Performance-Driven FPGA Routing Algorithms

Michael Alexander & Gabriel Robins
Motivated by the goal of increasing the performance of FPGA-based designs, we propose effective Steiner and arborescence FPGA routing algorithms. Our graphbased Steiner tree constructions have provably-good performance bounds and outperform the best known ones in practice, while our arborescence heuristics produce routing solutions with optimal source-sink pathlengths at a reasonably low wirelength penalty. We have incorporated our algorithms into an actual FPGA router which routed a number ofindustrial circuits using channel widths considerably smaller...

Scheduling Periodic Tasks in a Hard Real-Time Environment

Y Oh

Pattern Minefield Detection From Inexact Data

Gabe Robins & Brian Robinson

TMMAC: ATDMA Based Multi-Channel MAC Protocol Using a Single Radio Transreceiver for Mobile Ad Hoc Networks

Jingbin Zhang, Gang Zhou, Chengdu Huang, Ting Yan, Sang Son & John Stankovic
In this paper, we propose amedium access control (MAC) protocol called TMMAC for Mobile Ad Hoc Networks (MANETs). TMMAC requires only a single half-duplex radio transceiver on each node. In addition to explicit frequency negotiation which is adopted by the conventional multi-channel MAC protocols, TMMAC introduces lightweight explicit time negotiation. This two-dimension negotiation enables TMMAC to exploit the advantage of both frequency diversity and TDMA. Performance evaluation results show that TMMAC achieves up to 62%...

Tutorial on UVA SAFENET Lightweight Communications Architecture

Bert Dempsey, Jeffrey Michel & Alfred Weaver

SAFENET Internals

Bert Dempsey, John Fenton, Jeff Michel, Alex Waterman & Alfred Weaver

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