Re: The rate you do the things you do...

["Theodore E. Dennison" <dennison@escmail.orl.mmc.com>]

David Weller wrote:
> 
> I have a feeling this will raise more questions than answers, but here
>  goes...
> 
> I'm trying to cut through the hype and understand whether Windows NT
> can support "simulation software" rates in the 30-60Hz range.  We have
> a, um, enthusiastic MS supporter that sez, "Sure, no problem!".
> Before I expend labor hours attempting to prove them wrong (or right,
> for that matter), I'd be interested in feedback from anybody else in
> this community that has gone through such a venture yet.  We're not
> looking for hairy details, just a general range for now (tops out at
> 10Hz? 5Hz?).  I personally am VERY leery of a "business-based" OS
> being able to support real-time scheduling rates, but we have a lot of
> management pressure to examine PC-based COTS products for future
> approaches.  This ain't my idea, folks, but I do have a professional
> responsibility to shoot it down^H^H^H^H^H^H^H^H^H^H^H^H^H examine its
> potential :-)


I've been using NT for about a year now for a "real-time" project with a
1HZ update rate (any sneers you have at 1HZ real-time, I share with you).

One thing I have found, though, is that NT supports an equivalent to a
real-time clock. It is called the "Multimedia timer". Its highest 
effective resolution is about 55 milliseconds (good for up to 18 Hz, if
my math is good). It calls a user-specified routine at interrupt 
priority (higher than any process. All of NT's other timing mechanisms
are message-based, which is unacceptable for a hard real-time application.

If you need better than 18 Hz (and it looks like you do) you would have
to find a third-party real-time clock with NT drivers. Good luck!
(tell me if you find one).

Don't be so quick to dismiss NT though. The more I work with it, the
more impressed I am. Internally, it is very Unix-like. I'd wager that
your average VMS or Unix (non-GUI) application could be ported to 
WindowsNT with minimal effort.

-- 
T.E.D.          
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