Mark Nicholson

Pipelined processors and worst case execution times

The calculation of worst case execution time (WCET) is a fundamental requirement of almost all scheduling approaches for hard real-time systems. Due to their unpredictability, hardware enhancements such as cache and pipelining are often ignored in attempts to find WCET of programs. This results in estimations that are excessively pessimistic. In this article a simple instruction pipeline is modeled so that more accurate estimations are obtained. The model presented can be used with any schedulability analysis that allows sections of nonpreemptable code to be included. Our results indicate the WCET overestimates at basic block level can be reduced from over 20% to less than 2%, and that the overestimates for typical structured real-time programs can be reduced by 17%–40%.

Health Monitoring for Reconfigurable Integrated Control Systems

The next generation of control systems are likely to be characterised by much higher integration, where common / shared computer resources perform multiple system functions. It is possible to reconfigure such systems to provide continued functionality when an element of the system fails. To achieve this aim a number of pre-requisites must be in-place: the ability to determine when a failure has occurred, the appropriate configuration to move to and the ability to safely transfer from one configuration to another. This paper concentrates on the first of these in the form of health monitoring systems for IMS. The approach takes into account the potentially safety critical nature of the applications and the nature of these computer systems.

Exploring the Possibilities Towards a Preliminary Safety Case for IMA Blueprints

The Aim of this paper is to show how a safety argument could be constructed for the use of blueprints in platforms using Integrated Modular Avionics (IMA). It is assumed that the IMA system will contain safety-critical elements. Given current safety analysis techniques, there is no certainty that this can be achieved satisfactorily.

Computer Safety For Modern Bridge Systems

Computer Based Systems (CBS) and Integrated Bridge Systems (IBS) are being introduced. They provide enhanced navigation capabilities and promote ship safety. However, they are highly complex and are becoming the primary source of data/information used to navigate ships. CBS issues have arisen that challenge current safety assurance and certification practices. This paper explores the potential contribution of System Safety Engineering including technical, operational management and crew capability contributions to CBS/IBS safety. A six step roadmap for the production of best practice guidance for the safe development and operation of such systems is presented.