Safety Features and Reasonableness Checks

This is in response to Pradeep's question here.

Pradeep indicates that in his project, Requirement related to WDT is a derived high-level requirement. I find that rather surprising. A good Systems document will address "Software Hanging So Help" situations. The Systems Requirement may not actually use the word WDT, but will definitely indicate that software needs to reboot the system if it hangs. Once that is done, the SRD will have a WDT related requirement that can be traced back to the Systems document.

Reasonableness Checks are part of safety related requirements. A good, precise definition of reasonableness checks is available here. It is a good method to prevent propogation of fault between sub-systems. For example, if your software reads data from a subsystem that computes Airspeed, do a simple range check to see if the computed AirSpeed falls within a "reasonable" range.  If yes, process the data. If not, raise a flag. Your design should accommodate such fault tolerance.

Comments

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[Pretreatment]

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