flat assembler
Message board for the users of flat assembler.

Index > DOS > how to tune screen refresh rate under dos vbe 2.0?

Author
Thread Post new topic Reply to topic
cylo



Joined: 06 Nov 2004
Posts: 20
cylo 06 Nov 2004, 17:54
hello!

i have programed a little graphic program with the svga.bgi unit for msdos (640x480x256 up to 1024x768x256)... but it is always fixed at 60Hz.

the program runs on a single board computer with a vesa vbe v2.0 compatible grafic chip.

i didnt figure out how to get this run at 75Hz or higher... Crying or Very sad

if i install windows i can go up to 1280x1024@85Hz... but i need dos! Embarassed

any idea?
Post 06 Nov 2004, 17:54
View user's profile Send private message Reply with quote
neonz



Joined: 02 Aug 2003
Posts: 62
Location: Latvia
neonz 06 Nov 2004, 18:07
VBE 2.0 does not have standartized API for changing refresh rate. VBE 3.0 have API for changing refresh but it is supported only by very new adapters (3dfx, nVidia, etc...).
Post 06 Nov 2004, 18:07
View user's profile Send private message Visit poster's website Reply with quote
cylo



Joined: 06 Nov 2004
Posts: 20
cylo 06 Nov 2004, 18:27
so the only way is to program the chip directly? what registers i have to look for?
Post 06 Nov 2004, 18:27
View user's profile Send private message Reply with quote
MCD



Joined: 21 Aug 2004
Posts: 602
Location: Germany
MCD 29 Nov 2004, 18:02
Lookily, many standard VGA-registers are accessible in VESA-modes too.
You tweak a bit around and test what changing of standard VGA-registers makes what changings in your VESA mode.

I used this way to emulate a vesa 512*384 mode starting from a 640*480/400 mode by simply writing something to miscellaneous output register, but this requires somewhat experimenting with graphics card, and when writing wrong things, the screen will often become blank. (Ctrl+C/Break or Ctrl+Alt+Delete Wink )

Another thing I did was changing the refresh rate of the standard vga 80*25/50 text mode by just setting a vesamode BEFORE setting to a textmode => this changes external pixel clock, which must be enabled in some VGA CRTC-register.

But all of these tweaking should be accomplished with lots of testing on many different machines, since I'm not sure how they work on other PCs, e.g. they are not (well) documented. (I think so)

_________________
MCD - the inevitable return of the Mad Computer Doggy

-||__/
.|+-~
.|| ||


Last edited by MCD on 29 Nov 2004, 18:04; edited 1 time in total
Post 29 Nov 2004, 18:02
View user's profile Send private message Reply with quote
MCD



Joined: 21 Aug 2004
Posts: 602
Location: Germany
MCD 29 Nov 2004, 18:03
I assume that you have a copy of Ralf Brown's Interrupt list. A "must-read"
Post 29 Nov 2004, 18:03
View user's profile Send private message Reply with quote
Display posts from previous:
Post new topic Reply to topic

Jump to:  


< Last Thread | Next Thread >
Forum Rules:
You cannot post new topics in this forum
You cannot reply to topics in this forum
You cannot edit your posts in this forum
You cannot delete your posts in this forum
You cannot vote in polls in this forum
You cannot attach files in this forum
You can download files in this forum


Copyright © 1999-2024, Tomasz Grysztar. Also on GitHub, YouTube.

Website powered by rwasa.