Re: ADA os talk

["Marin David Condic" <dont.bother.mcondic.auntie.spam@[acm.org>]

We used VMS on engine test stands to collect & process temperature/pressure
sensor data in real time. I wasn't in on developing the software, but the
requirements were that you could detect the interrupt and have a predictable
latency to when you got to the ISR, even if other apps were running. (You
had to record the data points at even time intervals - as you say, not
necessarily "fast" but predictable.) We were able to run GUI apps at the
same time an engine test was going on - albeit with the probability that
mouse/window response was going to degrade, but it didn't stop the realtime
app from getting serviced when it needed to.

IIRC, VMS itself didn't guarantee realtime behavior, but if you took some
smart guys and let them study it long enough, they could figure out how to
get VMS to do what you wanted it to do. We accomplished the same sort of
thing with MS-DOS because basically, you could get your real time app to
move MS-DOS aside and just take over.

What would be nice is to have a workstation OS that didn't require you to
become an expert or circumvent the OS to do realtime - just declare a
process to be "realtime" and know that it can get certain services with
certain predictable latencies and be sure that it has priority over anything
else. (Dangerous, but necessary for realtime programming.)

MDC
--
Marin David Condic
Senior Software Engineer
Pace Micro Technology Americas    www.pacemicro.com
Enabling the digital revolution
e-Mail:    marin.condic@pacemicro.com
Web:      http://www.mcondic.com/


"Larry Kilgallen" <Kilgallen@SpamCop.net> wrote in message
news:MIj1nYP7aabe@eisner.encompasserve.org...
>
> I would say VMS is a good example, if you agree that:
>
> Just because there are a lot of applications that are
> missing from the GUI interface, that does not mean
> there is a technical (as distinguished from marketing)
> limit preventing their presence.
>
> You cannot really get the GUI performance you have come
> to expect while realtime processes are running.
>
> You do have to set process priorities appropriately, and of
> course the definiton of realtime is that events are handled
> within some predictable timeframe.  Certainly someone can
> define their timeframe requirements tighter than VMS can
> handle, but they could also define those requirements
> tighter than can be handled by the hardware -- any hardware.