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> From: Wayne Foletta <wayne@ELECTROTEK.COM>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: ROM checksum
> Date: Monday, January 12, 1998 12:23 PM
>
> Am I missing something? I thought the main purpose for ROM (or other
> data) checksums was to verify the contents was correctly programmed with
> a given code version. Faster than other checks (i.e. CRC) but just a
> check.

That is true however with embedded systems the question  is
if the ROM can be proven defective then what?  The answer depends
on the application. In John's original post he was making a point that
the ROM test routine for something like the 17Cxxx parts could be
placed in a more reliable ROM than the application is stored in.

My point was with (great) care in analyzing the failure modes
of the test routine it might be possible to accomplish the same goals
with regular ROM.

Fails safe code has to be carefully written. About a year ago a failsafe
system shut the engine down on a ocean going cargo ship because a
bearing was getting hot the result was an out of control ship that took out
a
dock, hotel and part of a shopping mall in New Orleans.

The same kind of thought needs to go into fail-safe modes for car engine
controllers and embedded systems used in medicine.


 Walter Banks