1998-02-23

The X-By-Wire Concept: Time-Triggered Information Exchange and Fail Silence Support by New System Services 980555

This paper presents the conceptual model and the fundamental mechanisms for software development in the context of the Brite-EuRam project Safety Related Fault Tolerant Systems in Vehicles (nick-named X-By-Wire). The objective of the X-By-Wire project is to achieve a framework for the introduction of safety related fault tolerant electronic systems without mechanical backup in vehicles.To achieve the required level of fault-tolerance, an X-By-Wire system must be designed as a distributed system comprising a number of fault-tolerant units connected by a reliable real-time communication system.For the communication system, the time-triggered TTP/C real-time communication protocol was selected. TTP/C provides fault-tolerance message transfer, state synchronization, reliable detection of node failures, a global time base, and a distributed membership service.Redundancy is used for masking failures of individual processor nodes and hardware peripherals. To keep the required number of processors low, the processor nodes must exhibit fail-silent behavior, i.e., produce either correct results or none at all.At the logical design level, the so called XBW-model was developed to combine the basic mechanisms for system design (BASEMENT and DFR). For the detailed software design of embedded distributed fault-tolerant hard real-time systems, the framework of the DFR meta object model is used. The model supports systematic error detection strategies for achie-ving fail-silence behavior at the node level and fault tolerance strategies for achieving fail-operational behavior at the system level. This eases the application software development for distributed fault-tolerant real-time systems considerably.Within the X-By-Wire project, a prototype of a steer-by-wire system is developed. This prototype will demonstrate the application of the principles, model, and mechanisms developed by the X-By-Wire partners.

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