New Strategies for Ensuring Time and Value Correctness in Dependable Real-time Systems

Dependable real-time embedded systems are typically composed of tasks with multiple criticality levels allocated to a number of heterogeneous computing nodes connected by heterogeneous networks. The heterogeneous nature of the hardware, results in a varying level of vulnerability to different types of hardware failures. For example, a computing node with effective shielding shows higher resistance to failures caused by transient faults, such as radiation or temperature changes, than an unshielded node. Similarly, resistance to failures caused by permanent faults can vary depending on the manufacturing procedures used. Task vulnerability to different types of errors, potentially leading to a system failure, varies from task to task, and depends on several factors, such as the hardware on which the task runs and communicates, the software architecture and the implementation quality of the software. This variance, the different criticality levels of tasks, and the real-time requirements, necessitate novel fault-tolerance approaches to be developed and used, in order to meet the stringent dependability requirements of resource-constrained real-time systems. In this thesis, we provide four major contributions in the area of dependable real-time systems. Firstly, we describe an error classification for real-time embedded systems and address error propagation aspects. The goal of this work is to perform the analysis on a given system, in order to find bottlenecks towards satisfying dependability requirements, and to provide guidelines on the usage of appropriate error detection and fault tolerance mechanisms. Secondly, we present a time-redundancy approach to provide a-priori guarantees in fixed-priority scheduling (FPS) such that the system will be able to tolerate a single value error per every critical task instance, while keeping the potential costs minimized. Our third contribution is a novel approach, Voting on Time and Value (VTV), which extends the N-modular redundancy approach by explicitly coni Copyright © Hüseyin Aysan, 2009 ISSN 1651-9256 ISBN 978-91-86135-28-7 Printed by Mälardalen University, Västerås, Sweden