C. M. Woodside

Software CAD: a revolutionary approach

A research project is described in which an experimental software CAD environment called the Carleton embedded system design environment (CAEDE), oriented toward embedded systems and Ada, was developed to provide a demonstration of the concept and to serve as a research testbed. The major contribution of CAEDE is a demonstration of a visual paradigm which combines semantic depth and syntactic shallowness, relative to Ada, in a manner that makes it possible for the embedded-system designer to work in terms of abstract machines while still thinking Ada. A secondary contribution is the identification of Prolog as a promising approach for supporting tool development in an environment which supports the visual paradigm. Also described are experimental tools for temporal analysis, performance analysis, and the generation of skeleton Ada code. >

The rejection rate for tasks with random arrivals, deadlines, and preemptive scheduling

A means of approximating light-traffic performance of RAD (random-arrivals-with-deadlines) systems for four basic preemptive scheduling policies is presented. The design goal is to keep congestion low enough to make the probability of rejection acceptably small. These designs must have low processor utilization. The study analyzes rejection probabilities at utilizations up to 20% and rejection probabilities up to about 10% for various well-known preemptive scheduling disciplines (shortest job first, earliest due date, and least laxity first), as well as first-come, first-served. Good approximations for the rejection probability and for a number of other properties, such as the distribution of time-to-go at rejection, are found. >

TimeBench: a CAD tool for real-time system design

This paper provides an overview of TimeBench, a prototype CAD tool for designing real-time systems, as well as some experiences gained through building and using it. TimeBench aims to support a true engineering design process for real-time systems in a largely graphical working environment. The environment includes support for design synthesis, analysis, and system generation, with equal emphasis on the design of operational structure and the design of temporal behavior. Its main features include: (1) a hybrid graphical---textual design description notation (MachineCharts, Abstract Controller Machines, and MachineChart Language), (2) design experimentation through an embedded interpreter and behavior visualization tools to animate designs, (3) further design evaluation through a performance modelling tool based on fast approximate analystic methods, and (4) a code generation system than can be tailored to produce code for a desired environment.

An overview and example of application of CAEDE: a new, experimental design environment for Ada

CAEDE is an experimental, integrated, iconic design environment which supports (1) a structured design methodology based on Buhrs System Design With Ada book (2) an iconic design entry system, (3) a design data base, and (4) design tools. The design data base is automatically represented in Prolog and the majority of the design tools are written in Prolog. Tools are currently available for structural and temporal analysis, and for source code generation. This paper describes both the ideas behind CAEDE and an example of a CAEDE tools written in Prolog for representing and analyzing the temporal behaviour of Ada tasking designs, without having to program them in Ada first.

Modeling the coverage and effectiveness of fault-management architectures in layered distributed systems

Increasingly, fault-tolerant distributed software applications use a separate architecture for failure detection instead of coding the mechanisms inside the application itself. Such a structure removes the intricacies of the failure detection mechanisms from the application, and avoids repeating them in every program. However, successful system reconfiguration now depends on the management architecture (which does both fault detection and reconfiguration), and on management subsystem failures, as well as on the application. This paper presents an approach which computes the architecture-based system reconfiguration coverage simultaneously with its performability.

Dependable LQNS: a performability modeling tool for layered systems

Dependable LQNS is a software tool for modeling and evaluating performability of fault-tolerant layered distributed applications that use a separate architecture for failure detection and reconfiguration. It takes into account the effects of management architecture, application software architecture, failure of management and application components in the dependability computation. It uses a combination of minpath algorithms, AND-OR graphs, noncoherent fault trees and Layered Queueing modeling in the analysis.