X386: Plain VGA 16-color mode

X386: Plain VGA 16-color mode

Post by Per M. Bothn » Mon, 20 Jul 1992 06:22:00



Is anyone working on enhancing X386 to support vanilla
VGA systems (640*480, 16 colors)?  (I have a laptop, so
I want to make X work using the existing VGA controller.)

If no-one else is working on it, I might give it a try.
(In an earlier life, I backed X servers for a while.)

My understanding is that the VGA has 4 independent bit-planes
so the cfb (color frame-buffer) code isn't useful.  But a reasonable
approach might be to just call the approriate mfb (monochrone
frame-buffer) once per bit-plane, at least as a first cut.

 
 
 

X386: Plain VGA 16-color mode

Post by william E Davids » Wed, 22 Jul 1992 04:30:52



|>
|> Is anyone working on enhancing X386 to support vanilla
|> VGA systems (640*480, 16 colors)?  (I have a laptop, so
|> I want to make X work using the existing VGA controller.)
|>
|> If no-one else is working on it, I might give it a try.
|> (In an earlier life, I backed X servers for a while.)

  If you do this, you could do the world a real favor and be sure the 16
color mode works in the general case. The ET4000 will support
1280x1024x16 on almost every card (I tried some MS-windows drivers on
4-5 cards I had around, and all worked. Many time resolution would be
more useful than colors when opening a lot of text windows.

  Someday I hope to hear that someone has hacked a hicolor 800x600 X for
all the checp hicolor cards around.
--
bill davidsen, GE Corp. R&D Center; Box 8; Schenectady NY 12345
        It never ceases to amaze me that otherwise rational people, able to
        understand calculus, compound interest, and the income tax form, can
        continue to believe that poker is a game of chance.

 
 
 

X386: Plain VGA 16-color mode

Post by Kevin Cummin » Thu, 23 Jul 1992 03:48:16




> |>
> |> Is anyone working on enhancing X386 to support vanilla
> |> VGA systems (640*480, 16 colors)?  (I have a laptop, so
> |> I want to make X work using the existing VGA controller.)
> |>
> |> If no-one else is working on it, I might give it a try.
> |> (In an earlier life, I backed X servers for a while.)

>   If you do this, you could do the world a real favor and be sure the 16
> color mode works in the general case. The ET4000 will support
> 1280x1024x16 on almost every card (I tried some MS-windows drivers on
> 4-5 cards I had around, and all worked. Many time resolution would be
> more useful than colors when opening a lot of text windows.

Yes, yes, yes!  Just a small point to remember here, video cards with up to 256K
of memory (yes, this includes EGA!) should all be somewhat compatible with
regards to video memory access up though 800x600x16!  (I still own, but no longer
use, an EGA card that was 800x600x16 compatible.)  The video graphics library I
used under DOS uses the same routines (after video selection is done) for 16 color
EGA graphics as for 16 color VGA graphics.  After 800x600, you require 512K of
video memory (OK, really 384K), but the bitmap for 1024x768x16 requires 96K of
addressable memory which will require some bank switching since all of the
addressable memory can't be fit between A0000 and AFFFF.  1280x1024 requires 160K
of addressable memory (3 banks) and 1M of real video memory (well, 640K, OK?).

Quote:>   Someday I hope to hear that someone has hacked a hicolor 800x600 X for
> all the checp hicolor cards around.

Hopefully compatible with 640x480x32K as well!

For those who prefer to look at tables:

Board           Required        Bitmap  Numer of        Total Video Memory
Types           Resolution:     memory: 64K Banks:      Required        On Board
EGA             640x200x16      16000   1                63K             64K
EGA             640x350x16      28000   1               110K            128K
VGA             640x400x16      32000   1               125K            128K
SEGA/VGA        640x480x16      37.5K   1               150K            256K
SEGA/SVGA       800x600x16      58.6K   1               234K            256K
SVGA            1024x768x16     96K     2               384K            512K
SVGA            1152x900x16     126K    2               506K            512K
SVGA            1280x1024x16    160K    3               640K            1M

XGA             640x480x32K     600K?   10?             600K            1M
???             800x600x32K     937.5K? 15?             937.5K          1M

Please note that none of the above entries takes into account anything about
sync rates required to attain those resolutions, just the memory required to
support them.  And certain video chip sets may not support all of the resoltuions
listed above (like the S3 chip doesn't support 1152x900x16 or 800x600x32K).

The table for 256 color modes is left as an exercise to the reader.  Remember
that most 256 color modes are byte mapped, not planear! and require 8 times the
addressable memory in the byte map as the corresponding 16 color mode!  And the
32K color modes require twice as much memory as the 256 color modes.  I also
think I read that the 32K color modes require that each two byte color pixel value
be written to memory as two seperate bytes in different memory banks.  I beleive
that is how the S3 chip works.  Does the ET4000 work the same way?

=================================================================
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1. How to set Xwindows into VGA 16-color mode ?

I also envisage having the same problem as my video card is not on the list
of Linux supported cards.  I would appreciate it if the answer could be
posted in the group...

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