Re: Duration vs. Ada.Real_Time

[swhalen@micron.net (Steve Whalen)]

You think you had problems... did you read the NSA mongraph on the
WWII SIGSALY system? 
 
 http://www.nsa.gov/wwii/papers/start_of_digital_revolution.htm

In glancing at it again, I don't think their synchronization solution
would have helped you because they primarily relied on an external 
time source, but maybe some of their other tricks for maintaining
synchronization might be adaptable to your situation (somehow 
translating hardware / mechanical / analog into Ada!).

Steve

Marin David Condic <mcondic.auntie.spam@acm.org> wrote in
<3A82BC7B.8EF005AB@acm.org>: 

>Actually, the problem was a lot more specialized than what you seem to
>be gathering from my post. Basically, it was two separate, identical
>computers running identical software with independent 1.024mS
>interrupts. (No common time source or this would have been a source for
>common-mode failure) 
>
>Given the presence of watchdog timers in both boxes that had to be
>stroked on specific cycles and the need for each computer to be
>operating on identical sensor input, you wanted to have them sync'ed on
>the same cycle and starting each cycle with a high degree of precision.
>(I believe we settled on about 50uS as a jitter amount, so that was
>roughly the tolerance of the sync.)
>
>We had primitive communications between the two CPU's - a Manchester
>data link and a couple of discretes.
>
>We achieved sync by basically having the two machines look for each
>other on the discretes and one machine taking small delays until they
>both arrived at the same cycle. From there, we pulled a few other tricks
>involving delays until the machines were in fine sync. (BTW, the same
>basic problem happens with frequency-hopping radios where you don't have
>a common time source or you can't get the time source until you achieve
>coarse sync.) 
>
>Basically, we came up with a solution that worked, but I could never get
>over the feeling that some academic type had probably written a book or
>a paper discussing various methods of doing this which might have shed
>some light on better ideas.
>
>MDC

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---   Steve Whalen                  swhalen@micron.net   ---
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