[SystemSafety] Koopman replies to concerns over Toyota UA case

[Driscoll, Kevin R]

> accidentally make use of aliased variables 
To rub salt in the wound, these problems usually are hard to debug (i.e., “Who wrote those wrong values?“).  If there is a small range of illegal values that can be differentiated from legal values, the problem is not so bad.  But, Murphy ensures that the reverse is usually the case.  This is compounded by the fact that most debuggers and logic analyzers don’t have the capability to trigger on “memory address = shared variable address“, “write signal = true“, and “data value not in legal range“.

There is a similar widespread problem with VHDL.  Most(!) VHDL designers are ignorant of the fact they should be using std_ulogic versus std_logic typing. The latter is equivalent to shared variables and makes it hard to find unintentional contending drivers.  The IEEE standardization committees (through their laziness) actually encourages this bad behavior.

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