Re: GNAT R/T Annex and Win95

[Wiljan Derks <W.Derks@nl.cis.philips.com>]

Theodore E. Dennison wrote:
> 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.
> 

This remark gives the wrong impression for NT. Gnat uses things
like waitforsingleobject in its tasking implementation. For this service
one can specify a time in milliseconds, but as far as I know and any intel
system it has a resolution of 10ms.
Normally services like this one will be use for timing on NT.

> 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.

I did not really use the multimedia timers upto now but I think one can
get resolutions upto 1 ms. I called the function timeGetDevCaps and it
reports me a minimum of 1 and a maximum of 1000000 milliseconds for
multimedia timer resolution range.

Wiljan