Re: Boeing 787 integer overflow

[Dennis Lee Bieber <wlfraed@ix.netcom.com>]

On Mon, 04 May 2015 10:28:59 +0200, Georg Bauhaus
<bauhaus@futureapps.invalid> declaimed the following:

>On 04.05.15 01:54, robin.vowels@gmail.com wrote:
>>> A software fix might be nice, such as increasing the counter to 64 bits to
>>> >push the overflow time out to something ridiculous,
>> That isn't the solution.
>> The solution is to have an appropriate error handler.
>
>If the variable has system-wide effects, I think error
>handling would require a little more than a few lines of
>code for overflow. Also provided that detecting overflow can
>be made fast enough in the first place.
>
>So, if the bit size could be increased without affecting
>the system in other ways, this looks like a much cheaper
>solution to me.

	Hardware changes are unlikely...  Would probably entail a multiple
man-year effort to design and certify a new processor board, along with new
software on the board to handle the changes in the hardware... 

	I wouldn't be overly surprised to find the actual flight operations
don't care about the roll-over... It could be something as simple as a
poorly written built-in test algorithm that gets run periodically (every 5
minutes say). Maybe a test for counter operation that relies upon "current
value > previous value"; which, upon finding a current value suddenly less
than the value the last time it ran, declares the unit faulty and shuts it
down.

	The stop-gap directive seems to be to perform an action that resets the
counter and the test values (since just restarting the software woud pick
up the values that had been in play).

-- 
	Wulfraed                 Dennis Lee Bieber         AF6VN
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