Failing systems that did not use a date function
' K.M.,
<Would you post an example of the type of Embedded failure you are looking at
please.>
This email I received from Roleigh Martin, an expert in this area, might answer
your question.
"I was a little disappointed in that one spokesman who said they had nothing to worry in
their hardware, because their devices do not work at the date level. That showed
ignorance of how these devices sometimes work.
There are plenty of electronic devices who only CARE about millisecond
intervals, but whose electronics for calculating the millisecond difference pulls a time
value from a computer clock that might look like this to the software:
YYMMDDHHMMSSTHK where
YY=2 digit year
MM=2 digit month
DD=2 digit day
HH=2 digit hour (military time)
SS=2 digit seconds
T= 1 digit tenths of a second
H= 1 digit hundredths of a second
K= 1 digit thousandths of a second
and the device figures out the gap in time (in milliseconds from)
invoking a built-in function that sends two values of
YYMMDDHHMMSSTHK, called YYMMDDHHMMSSTHK[present],
YYMMDDHHMMSSTHK[past]
and the device always assumes that
YYMMDDHHMMSSTHK[present] minus YYMMDDHHMMSSTHK[past] = positive
number
difference
However the above assumption will fail in 1/1/2000 if the past value is before
1/1/2000.
So anytime I hear a spokesman say, there is no worry because we only deal in
milliseconds, etc., I consider that spokesman ignorant of what is the nature of the
beast.
NOW, NOT ALL DEVICES WORK THIS WAY -- some only deal in ticks, and
represent a past tick with a positive integer, and a future tick with a larger integer, and
true "time" is never dealt with -- those devices will have no problems.
Also devices such as the above that accomodate the century rollover will work. Those
devices that represent the year as 4 digits will work. And in some cases, some devices
will not encounter such subtractions that lead to negative numbers, because they might not
be "doing anything" on the rollover and their history span might be only "seconds or
minutes ago".
But some devices will fail and have been proven to fail."
Roleigh Martin
ourworld.compuserve.com
From:
Message 3255685 |
