From: ovek AT arcticnet DOT no (Ove Kaaven)
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Newbie needs Help! Allegro + W95   :-(
Date: Thu, 09 Jan 1997 09:55:46 GMT
Organization: Vplan Programvare AS
Lines: 16
Message-ID: <5b2fb7$cps$1@troll.powertech.no>
References: <32d1828e DOT 750845 AT news DOT demon DOT co DOT uk> <q01J6aAwwq0yEw3v AT talula DOT demon DOT co DOT uk>
NNTP-Posting-Host: alwayscold.darkness.arcticnet.no
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Shawn Hargreaves <Shawn AT talula DOT demon DOT co DOT uk> wrote:

>The problem is, I think, with the vsync() call. Win95 seems very erratic
>in it's handling of retrace syncing. Sometimes it works, sometimes it
>doesn't, which is very irritating (if only IBM had seen fit to include a
>retrace interrupt in the VGA design!).

This may not have been in the *original* IBM VGA card, but according
to my old book in programming for PC video subsystems, the EGA, the
VGA, and the MCGA supports generating a Vertical Interrupt on IRQ2
whenever vertical retrace starts, and explains how this is done. On
the EGA/VGA, these interrupts appears to be controlled by the CRTC
Vertical Retrace End register (CRTC register 11h) bits 4 and 5, though
I haven't really studied this in detail.