Xref: news2.mv.net comp.os.msdos.djgpp:5532
From: brucef AT central DOT co DOT nz (Bruce Foley)
Newsgroups: comp.os.msdos.djgpp
Subject: VESA problems
Date: Sat, 29 Jun 1996 21:42:03 GMT
Organization: Internet Company of New Zealand
Lines: 39
Message-ID: <4r4bdr$4mc@status.gen.nz>
NNTP-Posting-Host: brucef.central.co.nz
To: djgpp AT delorie DOT com
DJ-Gateway: from newsgroup comp.os.msdos.djgpp

Hi.  Up until recently I have used the Vertical Non-display rather
than the Vertical Retrace to sync with the graphics card.
For those that don't know, the VN uses the display enable
bit (DE) to figure out when it is OK to start writing to the screen.

However I have started using VESA (1.2 in my case) and I have
found that when calling my vertical non-display routines I get a
total mind-lock on the computer.  I switched to the simpler VR and
that seems to work fine.  Why?  Does the DE work differently
in VESA mode? (I have a Mach 64).  This problem is made all the
more difficult by virtue of the fact that I am using a new toolset
and have not learnt to use the new debugger (which is command
line based) -though I guess this is a good reason to start.

Finally, a question about graphics cards.  You may have wondered
why I am using VESA 1.2 when when VESA 2 offers so much more
in a protected mode environment.  The answer is that my card
only natively supports 1.2 and I have been unable to get Display
Doctors UNIVBE to work.  When it does the graphics mode testing
I get a mind-lock.  Trying to use the manual overrides does not
prevent this from happening.  I would also note that my card is
a 1Meg Mach 64 and yet I have never been able to get more than
256 colors or again, a blank screen & total mind-lock results.
I am thinking I would like to upgrade my card to a new one.
Can anyone suggest a card that offers great performance and
native Vesa 2 compliance?

Thanks, Bruce.

PS.  I have just written a small program that displays the details
returned from the vesa info block, including a list of all available
modes.  It then allows you to select a mode at which point you
get a detailed display of the mode info block.  I have found this
program to be useful while studying the VESA specification.
It is written in DJGPP, and if anyone is just starting out (like me)
and would like a copy of the source/executable, feel free to
give me a yell.