From: michael DOT mauch AT gmx DOT de (Michael Mauch)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Intermittent Run-Time of DJGPP App under Win95
Date: Thu, 27 Nov 1997 13:12:03 +0100
Organization: Gerhard-Mercator-Universitaet -GH- Duisburg
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On 26 Nov 1997 19:21:57 GMT, George Foot <mert0407 AT sable DOT ox DOT ac DOT uk>
wrote:

> Why do you use real mode calls for this?

Because I never thought that Int 2Fh supports protected mode.

>  I thought there was a speed penalty in doing so.

Yes, of course it is better to use a simple protected mode call than to
go from protected mode to real mode and then back to protected mode
again.

>  I don't suppose this is that significant since
> our timing resolution is milliseconds, though.

Yes, but I think it is significant for the 840 nanoseconds timer
(function 0x100 of the VTD API). And there are no drawbacks with your
direct method, are there any? Are there any chances that the VTD code
gets paged out sometimes (I don't think so), so that the lcall could
fail?

>  it didn't work quite properly for the registry access VxD
> though.  [The calls worked fine, and valid error codes were returned;
> I just couldn't pass parameters to it properly.]

But I guess you would have had the same problems if you had used the
DPMI way, wouldn't you?
 
> If you want to see code showing what I mean, look in vtd.c in this zip
> file:  http://users.ox.ac.uk/~mert0407/downloads/vtd.zip.  I wrote
> this before finding out what the different functions in the VTD were
> for, so please excuse the erroneous guesses in some of the comments ;).

Yes, thank you, it works fine here on Win95 and WfW3.11. vtd_init()
fails without problems on plain DOS 7, just like it is supposed to do.

Regards...
		Michael