grub (vga = ) parameters

[Federico Voges]

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On 24 Sep 2002 11:24:20 +0100, Bob Raymond wrote:

>On Tue, 2002-09-24 at 04:24, Keith Morse wrote:
>> On 23 Sep 2002, Bob Raymond wrote:
>> 
>> > That should be 1024x768 at 16 bit color.  I use 794, which is 1280x1024
>> > at 16 bit color.
>> 
>> 
>> Oooooo. slicker still.  But..  How did you know?  Trial and error?
>
>792 I knew from using SuSE- when I selected 1024x768 on the install of
>7.3, I looked at /etc/lilo.conf aftewards.  vga was set to 792.  I
>honestly can't remember how I got 794, and I'd really like to take
>advantage of my 17 in. Trinitron and my great high-schooler's eyes, and
>set it to 1600x1200 with 16 bit color, maybe even 24 or 32 if I can
>figure it out.  I run my desktop at 1600x1200 with 24 bit color, anyway.
>
>Does someone want me to research this a bit more and write a step by
>step for it with a nice index of all the modes say from 640x480 to
>2048x1536 (the current high point for most consumer graphics cards, not
>that I'm sure vesafb goes that high)?
>
>Bob Raymond
>

- From Documentation/fb/vesafb.txt (in the kernel src dir):

How to use it?
==============

Switching modes is done using the vga=... boot parameter.  Read
Documentation/svga.txt for details.

You should compile in both vgacon (for text mode) and vesafb (for
graphics mode). Which of them takes over the console depends on
whenever the specified mode is text or graphics.

The graphic modes are NOT in the list which you get if you boot with
vga=ask and hit return. The mode you wish to use is derived from the
VESA mode number. Here are those VESA mode numbers:

    | 640x480  800x600  1024x768 1280x1024
- ----+-------------------------------------
256 |  0x101    0x103    0x105    0x107   
32k |  0x110    0x113    0x116    0x119   
64k |  0x111    0x114    0x117    0x11A   
16M |  0x112    0x115    0x118    0x11B   

The video mode number of the Linux kernel is the VESA mode number plus
0x200.
 
 Linux_kernel_mode_number = VESA_mode_number + 0x200

So the table for the Kernel mode numbers are:

    | 640x480  800x600  1024x768 1280x1024
- ----+-------------------------------------
256 |  0x301    0x303    0x305    0x307   
32k |  0x310    0x313    0x316    0x319   
64k |  0x311    0x314    0x317    0x31A   
16M |  0x312    0x315    0x318    0x31B   

To enable one of those modes you have to specify "vga=ask" in the
lilo.conf file and rerun LILO. Then you can type in the desired
mode at the "vga=ask" prompt. For example if you like to use 
1024x768x256 colors you have to say "305" at this prompt.

If this does not work, this might be because your BIOS does not support
linear framebuffers or because it does not support this mode at all.
Even if your board does, it might be the BIOS which does not.  VESA
BIOS
Extensions v2.0 are required, 1.2 is NOT sufficient.  You will get a
"bad mode number" message if something goes wrong.

1. Note: LILO cannot handle hex, for booting directly with 
         "vga=mode-number" you have to transform the numbers to
decimal.
2. Note: Some newer versions of LILO appear to work with those hex
values,
         if you set the 0x in front of the numbers.


Just convert those hex numbers to decimal and you'll find where that
792/794 came from ;)

Bye!
Federico Voges
Socio gerente

Intrasoft
Malabia 2137 14 A
(1425) Buenos Aires
Argentina

Te/Fax: 54-11-4833-5182
e-mail: fvoges at intrasoft.com.ar
Web: http://www.intrasoft.com.ar

PGP Public Key Fingerprint: A536 4595 EB6F D197  FBC1 5C3A 145C 2516

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