Re: Few questions on embedded stuff
From: Ed Beroset (beroset_at_mindspring.com)
Date: 06/29/04
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Date: Tue, 29 Jun 2004 02:38:27 GMT
Joerg wrote:
> Hi Ed,
>
>> particularly energetic gamma particle flips just one single bit in RAM
>> from a zero to a one.
[...]
>
> Absolutely agree. Even rad hard stuff will have a chance to fail. Not
> using a WDT is like driving around without a safety belt. Some of us
> might live to be 90 that way, others not. All it takes is a tire blowing
> at 65mph.
OTOH, some of us drive 90mph and hope to reach 65. ;-)
> What I don't like are designs that rely on WDT for regular operation.
Yes, and I think that's always the fear of using WDT's -- that they'll
be abused. Also, one participant in this thread already noted that a
WDT is most useful if enough of the context is saved to be able to
forensically analyze what went wrong. It's a technically sound comment,
but it's not always possible in the case that an external WDT is used
and tied to the microprocessor's reset line. In many cases, the reset
itself wipes out all traces of evidence and makes diagnosis impossible.
In such cases, and depending on the application, it may be preferable
for the device to fail visibly than to reset and continue quietly. Like
most engineering, it requires an analysis of the tradeoffs for the
particular problem at hand...
Ed
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