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Re: Enabling framebuffer, more than a kernel recompile?



On Fri, Oct 26, 2001 at 01:48:17PM -0400, Noah Meyerhans wrote:
| On Fri, Oct 26, 2001 at 12:00:53PM -0400, dman wrote:
| > | What other step(s) am I misssing?
| > 
| > Add "vga=0x31A" to your kernel command line.  This will give you
| > 1280x1024x16.  See the docs for the values of the other modes.
| > 
| 
| I don't think that parameter affects the framebuffer, though.  That is a

It does, see below.

| a VGA mode setting, and you can have a VGA text console without enabling
| a framebuffer.  Framebuffer parameters look something like
| "video=tdfx:1024x768".  

Supposedly that's what you do for the accelerated framebuffers
(matrox, etc) but that doesn't seem to work for vesafb.

| See Documentation/fb/modedb.txt in your kernel
| source tree.  Docs for what you're describing are in
| Documentation/svga.txt, and that exists independently the
| framebuffer support in the kernel.
| 
| I suppose I could be wrong, as I've only recently started playing
| with the framebuffer, but I know that you could pass 'vga=xyz'
| options to the kernel long before framebuffer support existed.

Yeah -- some numbers are for VGA text modes and some are for the VESA
framebuffer.

Here's a section of
/usr/share/doc/kernel-doc-2.4.8/Documentation/fb/vesafb.txt.gz :

-----------------------
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.
-----------------------

Now you don't need to hunt it down in the docs yourself :-).

-D



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