DOUBLE13.DOC
Davor Slamnig (slama@slama.pub.hr)
11/94
DOUBLE13.EXE sets the VGA to mode 13h and puts it in
"big map" mode, providing 128K of video memory. This space is
large enough to contain two screen pages, which can be used for
double buffering. The program then does some page-flipping
and scrolling.
The process is much simpler and faster than using x-mode (but...)
The purpose of the test was/is to find how compatible this is
with various VGA cards.
So far, the (statistical) answer is, unfortunately:
"not very compatible".
Card: BIOS page flip: Register scroll:
------------------------------------------------------------------
Trident 8900 / 1M yes yes
Cirrus Logic 5428 24-bit VLB / 1M no no (*)
STB W32P PCI / 1M yes yes
Trident (?) TVGA BIOS D3.0 / 512K yes yes (**)
Tseng ET4000 8925CLK2B ? no
Paradise / 512K yes no
------------------------------------------------------------------
(*) Scroll doesn't work on Cirrus Logic CLDG 5422/5424/5426 either.
(**) Program crashes on exit.
About the program:
VGA is set to "big map" mode.
The video memory starts at a000h and is 128K long.
Page 2 begins at b000h. Page 1 one is filled with blue,
page 2 with red (system colors).
The program first switches pages using BIOS, then
does a smooth scroll through the pages using VGA
registers to change screen start address.
Note: The video mode is still 13h, packed -
one byte corresponds to one pixel.
What I'd like you to do is to run the program and
see whether it works on your card. Then mail or post
the result, and please include some info about your
card - the name, number and amount of RAM at least.
Also, I would like to hear about your improvements.
My address: slama@slama.pub.hr (Davor Slamnig).
Thanks to the people who tested the program so far:
Douglas B Clayton <dc6f+@andrew.cmu.edu>
rob@cimage.com (Rob Mcmillan)
mvalente@lnec.pt (Mario Valente)
tqf1397@is.nyu.edu (Timur Fanshteyn)
Rob Mcmillan (rob@cimage.com)
Nathan Hand <h9304891@student.anu.edu.au>