Re: Processor Synchronization

[Marin David Condic <condicma@bogon.pwfl.com>]

The Bohemian Monk wrote:
> 
> After reading all the thread ... damn guys wake up.  A processor as
> simple as the 8088 has bus sync signals to allow multiple processors on
> a single buss, or a single memory.  Software does little for
> multiprocessing, hardware does the most, unless you program embedded in
> something like Forth.  With non-buss-master processesors you can use a
> PAL to envoke wait-states based on buss signals, all in hardware with
> simple memory table semaphores for access control.
> 
I'll try not to condescend, but boy is it tempting! :-)

Our style of computer system for jet and rocket engines is not nearly
that easy to do. The requirements won't allow for it. This box is
strapped to the side of a really hot vibration generator and having it
stop operating for any reason is considered "A Bad Thing". In the case
of rockets, it is considered "A Really Bad Thing". And the rockets will
take you out to where you can introduce your box to a bunch of gamma
rays - just to make life interesting for your EEPROMs, etc., and to keep
you appropriately humble. Due to the high reliability requirement, the
systems are dual redundant and each channel has to be able to take
immediate control if the other side is detected to have passed on to
meet its maker.

A real easy way to get in trouble and have to answer lots of
embarrassing questions and probably start looking for a new career in
the exciting world of the fast food industry is to have built completely
redundant systems except for one common link - a clock or interrupt line
for synchronization. If that chip or foil trace or wire should happen to
break, all your dual redundancy was for naught. Hence, we have to pull
some stunts to keep the two sides in synch.

Anyway - if you know of any texts or papers discussing techniques for
tightly synching two or more independent processors, please pass them
along. Thanks.

MDC
-- 
Marin David Condic
Real Time & Embedded Systems, Propulsion Systems Analysis
United Technologies, Pratt & Whitney, Large Military Engines
M/S 731-95, P.O.B. 109600, West Palm Beach, FL, 33410-9600
Ph: 561.796.8997         Fx: 561.796.4669
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