Example of a Safety-Critical Element With Deliberately Unreliable Function

Rainer Faller recounted an example of a 32-bit processor, intended to be used for some critical operations, in which a “Debug/Maintenance” mode had been built in to the critical software (henceforth SW). In this mode, various safety functions were inoperational, and indeed in response to “normal” inputs the SW could engage in behavior which was dangerous on the system level. This D/M mode was not described in the SW documentation, and was reachable only through a specific 32-bit number given as input to the SW. Examples of benign such operations in non-critical contexts are often known as “Easter Eggs”.