Peter R. Croll

Automating the development of distributed control software

The Development Framework translates application-specific system specifications into parallel, hard real-time implementations, using methods that are both familiar to developers and optimal for the application. The Development Framework approach applies CASE tools-as well as several new tools-to the development of distributed systems, so designers can concentrate on the control-engineering aspects of their systems. The approach addresses three development phases: specification, software design, and implementation. In the specification phase, the control engineer refines behavioral requirements through simulation and analysis, thereby verifying that the system meets its functional requirements prior to implementation. Once the simulated behavior is satisfactory, the specified behavior is translated into a design. Finally, our tools produce source code, either by automatically generating it or by drawing it from a library. We describe the new and existing tools we apply during each phase. We then demonstrate our approach using an example of a linearized roll-pitch-yaw autopilot and airframe model.<<ETX>>

Improving the quality of Software Engineering courses through University Based Industrial Projects

Through the use of University Based Industrial Projects, students at Sheffield University have been gaining the advantages of industrial contact, while still studying full time. This paper discusses the experience gained, within the Department of Computer Science, from running Industrial projects and other initiatives, focusing specifically on a second year project called the ‘Software Hut’. A set of guidelines, and good practice, derived from over ten years experience, are described and discussed. The implications of changes in client requirements and the effect of increasing class size are considered and possible solutions are proposed.

A Prototype Development Framework for Hybrid Control System Design

Abstract Hybrid control systems are a combination of real-time control law and discrete-state logic. This paper describes how a Development Framework for control systems software has been adapted so that it may also handle discrete events such as mode switching. The Framework provides a highly automated path from a control engineering specification to a distributed system implementation. Simulink, an extension to Matlab, is used to specify control laws, and a statecharts tool, Statemate, is used to specify and model discrete-state components. The design phase of the Development Framework supports the integration of the two sets of specification. An inverted pendulum control system is introduced as a simple example of a hybrid system implemented using the Framework. The translation of statecharts to dataflow notations is described for the example system. General translation rules are also presented.

Three Domain Voting In Real-time Distributed Control Systems

An intelligent and robust voting service for real-time distributed control systems is proposed. Three novel features of the voter are described. Firstly, the voter is distributed using a primary site algorithm. This algorithm is used to coordinate the voter elements ensuring service is provided even in the presence of single faults. Secondly, the voter is capable of selecting a correct result in certain cases of disagreement. This is achieved by moniroring the temporal behaviour and reliability of the application modules in addition to the comparison of numerical result values, a.n approach called Three Domain Voting. Thirdly, inclusion of a voting service in a Framework of tools for the design of real-time distributed control sofiare is discussed. The Frame work allows control engineers to specify their problem in a familiar application speciJic manner. The tools then provide a highly transparent transformation to an executable implementation.

Engineering safety-related parallel systems

A growing number of safety-related applications are dependent on software for their control. High performance and redundancy requirements in modern control systems can be satisfied by parallel processing. This paper considers the requirements for the software engineering of safe parallel systems and the specific problems that need to be addressed: safe state analysis and temporal analysis. The benefits to be gained from utilizing commercial CASE tools and extending them to facilitate the required analysis are detailed.

Dependable, intelligent voting for real-time control software

Abstract An intelligent and dependable voting mechanism for use in real-time control applications is presented. Strategies proposed by current safety standards advocate N-version software to minimize the effects of undetected software design faults (bugs). This requires diversity in design but presents a problem in that truly diverse code produces diverse results; that is, differences in output values, timeliness and reliability. Reaching a consensus requires an intelligent voter, especially when non-stop operation is demanded, e.g. in aerospace applications. This paper, therefore, firstly considers the applicable safety standards and the requirements for an intelligent voter service. The use of replicated voters to improve reliability is examined and a mechanism to ensure non-stop operation is presented. The formal mathematical analysis used to verify the crucial behavioural properties of the voting service design is detailed. Finally, the use of neural nets and genetic algorithms to create N- version redundant voters, is considered.

Towards Safer Industrial Computer Controlled Systems

A study of 21 incidents involving electrical, electronic and/or programmable electronic safety-related systems in small manufacturing enterprises, originally investigated by the Health and Safety Laboratory, has revealed that 40% of contributory faults are due to inadequate specification of system or safety requirements. Consequently the HAZAPS methodology and supporting software tool is proposed as a useful step forward in producing safer industrial computer controlled systems. The tool is demonstrated using a case study and suggestions are made for its improvement.

Development framework approach to heterogeneous system design for control systems

Abstract An integrated environment of software development tools, known as the Development Framework, which automates the design process for complex real-time embedded control systems, is introduced. The approach favoured here is to maximise the use of commercially available tools that are well understood by current industrial practitioners. Where necessary, new tools are introduced both in unifying the automated method and for supporting specialist functions. Introduced here is one such specialist example: support for the design of heterogeneous systems. This paper details the work on heterogeneity, and demonstrates how the essential properties of the Development Framework have been preserved. Thus, the Framework presents a unified methodology and an open system architecture. Finally, what should be learnt from this for building future techniques and tools for complex real-time control systems is discussed.

Modelling the client-server behaviour of parallel real-time systems using Petri nets

Guaranteeing the timeliness of a parallel hard real-time system, requires knowledge of its communication behaviour. Analysis of the communication structure can identify potential livelock and deadlock in parallel systems. An approach which describes the communications of parallel systems, called a client-server behaviour graph, is given which enables a Petri net model of a complete system to be built in a compositional manner, reducing the state explosion problem in the identification of both deadlocks and livelocks.<<ETX>>

Safe and Deterministic Real-Time Programming in a Nondeterministic Parallel Processing System

Abstract The application of parallel processing to real-time control applications is discussed. The approach to handling timing constraints in hard real-time systems will need to include message passing. A router design is outlined which can satisfy these requirements and offer a degree of fault-tolerance. The behaviour of this design is verified using formal methods which give a higher reliance for safety related applications.