This reminds me of a particular hardware system I'm familiar with whose design specified "dual power supplies". However late in the acceptance process it was discovered that the condition of one power supply up and one power supply down causes the system to lock up. (My guess would be a phantom current path between the powered and un-powered halves causing an unintended circuit state. Or perhaps just a software bug; maybe the one-supply-down notification code path was never tested.)
The vendor simply changed the procedures to say the user must use a two-fingers procedure to simultaneously flip both power supply switches on or both off at once. It bothers me that we still don't know WHY the original problem happened. How do we know there isn't electrical damage occurring during the brief period between the two switch contacts (since no human can do that perfectly)? If it's a software problem, what is the most time one power supply can be up and one down before the bug is triggered? That's not been characterized, to my knowledge.
But in the context of this thread, what's relevant is to avoid addressing the problem the vendor changed the meaning of "dual power supplies" from an OR condition to an AND condition! They met the letter of the spec while completely violating the spirit of the requirement.
The vendor simply changed the procedures to say the user must use a two-fingers procedure to simultaneously flip both power supply switches on or both off at once. It bothers me that we still don't know WHY the original problem happened. How do we know there isn't electrical damage occurring during the brief period between the two switch contacts (since no human can do that perfectly)? If it's a software problem, what is the most time one power supply can be up and one down before the bug is triggered? That's not been characterized, to my knowledge.
But in the context of this thread, what's relevant is to avoid addressing the problem the vendor changed the meaning of "dual power supplies" from an OR condition to an AND condition! They met the letter of the spec while completely violating the spirit of the requirement.