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Validation of Safety-Critical Distributed Real-Time Systems

A safety-critical distributed real-time system is an electronic system where a system failure may cause a severe hazard that will endanger human life or the environment. For the development of such systems, it is desirable to determine in an early development phase whether the system can cause such a hazardous event, before a hardware is built and before the system is in service. This thesis proposes methods and techniques to validate the behavior of such systems using a simulation model in an early development phase. The simulation model represents the system architecture (hardware and software) as specified in the design specification. The system model is based on a strict distinction between the application software that represents the desired functionality of the system, and the hardware and software platform which executes the application software. This strict distinction gives insights into complex interactions between hardware and software components of the system. It allows to evaluate fault-tolerant system architectures in the presence of errors caused by faults of hardware elements or interferences. The principle of the validation of a system proposed in this thesis is as follows: a test bench stimulates the system model with realistic and safety relevant test scenarios. An observer system monitors signals produced by the system and evaluates whether or not the systems reaction violates any predefined conditions. The conditions represent safety requirements that the system must fulfill to operate safely in its environment. An essential part of the validation is the fault injection. This technique provokes errors caused by faults of hardware elements or interferences during a test scenario. The observer system assesses the systems reaction to those errors and reports if the system violates any of the predefined conditions. This thesis presents a case study of a brake-by-wire system of an automobile. The case study shows how the proposed techniques and methods can support the development of an electronic system in an early development phase. The test scenarios reveal that the brake-by-wire system will not meet the safety requirements if it is built as specified in the design specification.