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There are fouressential measures in the development of safety-critical systems. 1. Design of safe systems 2. Measures to minimizerandom hardware errors 3. Measures to minimizesystematic hardware and software erors 4. Organizationalmeasures (management of functional safety) Particularly inthe design of safe systems, the principle of Freedom of interference is apowerful measure. What’s this? The following blog provides an answer to thisquestion. The followingdiagram illustrates the principle: With the Freedom of Interference, it can be demonstratedthat a (Sub-) system with a less critical ASIL level (in the diagram ASIL A)can not influence a system with a more critical ASIL (in the diagram ASIL C).The goal is to prevent that a system with a higher error rate (= ASIL A) drivesa system in which a lower error rate (ASIL C) is required. The design onthe left shows that there is no way the ASIL A system could affect the ASIL Csystem. This means that the ASIL C system achieves the Freedom of Interferencewith respect to the ASIL A system. In the systemdesign, on the right, a data / control flow is present from the ASIL A to theASIL C system. As a result, the ASIL C system does not achieve the Freedom ofinterference, at least without any further analysis. The ASIL C system can beinfluenced by the ASIL A system. In this case, further design or verificationmeasures need to be taken in order to achieve the freedom of interference. Forexample, the ASIL C system could first check the correctness of the ASIL Asystem’s data. Taking into account this measure, the ASIL C component wouldachieve the Freedom of interference. In bothpresentations the system design was developed by the ASIL decomposition of anASIL D component. Therefore, the D is put into the parenthesis. ISO26262 makes„only“ the statement that sufficient independence must be achieved. In the nextblog you can read how this works in the actual project practice. I’ll be glad tohelp you also with any specific questions about your project. The HEICONStarter as well as the HEICON Consulting products are designed to solve suchopen points. Send an email to: info[at] http://blog./category/englische-blogs/
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