Re: GNAT R/T Annex and Win95

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

Marin David Condic, 407.796.8997, M/S 731-93 wrote:
> 
>     Here's an interesting question which we've been thinking about
>     around here a lot:
> 
>     Do you consider Windows NT capable of being a "realtime" operating
>     system? (It doesn't seem to be advertised as such.... yet.)
> 

A straight NT question in an Ada group, huh? Oh well...

When you say "real-time", typically I think of a system with a clock
which is capable of generating software iterrupts every 10msec or
better, and some way of knowing when you have failed to service
an interrupt.

According to my NT book, there are two ways to do Timers with NT. The
first uses the SetTimer system call. This will put a WM_TIMER event
in the thread's normal message queue.  The resolution is ABOUT 55
milliseconds, but there can be message queue delays. Not very useful.

The second is the "Multimedia Timer". This timer allows you to define
a callback that will get called directly by an interrupt, without any
message queue processing overhead. The resolution is said to be 
"about 16 (Intel) milliseconds". Whatever that means, you can get the
exact resolution on your system via a call to "timeGetDevCaps". (Oddly
enough, Microsoft's example uses a resolution of 5 milliseconds) This
is a little more useful, but still not what we would like to see. 

-- 
T.E.D.          
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