Safety Aspects and Real-Time Systems

Very often we can find the following definition of real time systems  

Vehicle real time systems in the context of functional safety could be classified by the consequence of missing a deadline  

It could not be considered, that chassis systems considered as hard real-time, power-train systems as firm real-time and interior system are soft real time systems. ISO 26262 defines the fault-tolerant-time-interval as the basic criterion to specify safety-related timing-specific requirements. This interval defines a period of time, within faults should be controlled by the system (see also Chap. 3 of this book). The consequences of a missing deadline can only be evaluated by the consequences of the fault-error propagation in the latter, consequences of the possible hazard due to resulting malfunctions. 

The example with the light system shows that also veiy often the average time of fulfilling a deadline and the distance to the worst case time could be seen as a criterion for a soft or hard real-time system. The time-distance shows how probable or frequent the potential is to miss a given deadline (Figs. 5.2 and 5.3). 

If a real-time deadline is allocated to a safety-related function the deadlines must be met, regardless of the system load. This heavily impacts the software architecture, design, realization, and implementation. 

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