Message-Id: <335F7F77.21A3@canvaslink.com>
Date: Thu, 24 Apr 1997 11:42:47 -0400
From: Tom Grandgent <tgrand AT canvaslink DOT com>
Reply-To: tgrand AT canvaslink DOT com
Organization: Canvas Link, Inc.
Mime-Version: 1.0
To: Christoph Kukulies <kuku AT gilberto DOT physik DOT rwth-aachen DOT de>
Cc: noss AT pupk DOT unibe DOT ch, djgpp AT delorie DOT com
Subject: Re: timer interrupt - sample code anyone?
References: <199704240849 DOT KAA21592 AT gilberto DOT physik DOT rwth-aachen DOT de>
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Precedence: bulk

Christoph Kukulies wrote:
> 
> > At 02:57 PM 4/23/97 -0400, you wrote:
> >
> > >Ok, I have a system of measuring the frame rate in my game that I
> > >think is pretty foolproof.  I have a variable called frame_count that
> > >is incremented at the end of every frame.  I then have an ISR which
> > >is called once per second.  In this ISR, I copy frame_count into
> > >a variable called fps, then I set frame_count back to 0.
> > >
> > >     Tom Grandgent
> >
> > And how do you detect the end of every frame?  From VGA specs I found on the
> > Web I read that bit 3 of 0x3CA is set during vertical retrace but I have not
> > been able to capture it.  Am I barking up the wrong tree?  Is there a
> 
> I think he is talking about frames that his program writes, not the
> VGA vsync framerate. Although buffer switching with the video framerate
> would be optimal, I think. Or am *I* now off tagret? ;)
> 
> Chris Christoph P. U. Kukulies kuku AT gil DOT physik DOT rwth-aachen DOT de

Yes, you are correct- I consider the end of the frame to be at the
bottom
of my main loop, after the frame has been drawn and I have flipped pages
(or copied the offscreen buffer to the screen, depending on what
animation
method is currently selected).

However, it's pretty easy to find vertical retrace.  This should wait
for
the vertical retrace:

while (inportb(0x3DA) & 1);

	Tom Grandgent
	tgrand AT canvaslink DOT com
	Canvas Link, Inc.