- Report #: NT TR 600
- Approved: December 2005
- Author(s): Johan Hedberg, Andreas Söderberg, Timo Malm, Maarit Kivipuro, Håkan Sivencrona
This report gives an overview of safety considerations relating to distributed embedded systems. Some principles of safety-related distributed systems are shown, and the design process is described. The design process is related to the safety lifecycle introduced in IEC 61508. The most important phases in the process are risk assessment, design and safety validation.
Embedded distributed systems have seen a vast increase in use and application during the last two decades. Concepts such as CAN and Profibus have become well-known standards for many real-time engineers. However, in new applications, where safety is a critical issue, the need for ultra-dependable systems has been expressed. One step to reach these ultra dependable systems has been to shift the communication paradigm from event-triggered to time triggered. Time triggered systems provide a more stable base for the implementation of dependability. This report briefly presents the “future” time triggered paradigm and some different properties of the concept and specific communication issues. Different topologies and implementations are discussed in order to give the reader an indication of the different possibilities that exist when a time triggered system later is being built and evaluated. The report also shortly describes the following time triggered communication protocols: TTP/C, FlexRay and TTCAN.
The report describes the difference in validation of systems built on time triggered systems compared to traditional communication such as CAN, Fieldbus etc and also gives examples of validation methods to handle the requirements on dependability and redundancy.
The validation methods cover aspects from the bus level up to the system level. It presents the influence of the changing to time triggered paradigm and the partitioning of processors and communication mean.
It also includes a check lists as an aid to decide about which communication concept to choose.
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