forked from Minki/linux
1da177e4c3
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
168 lines
5.7 KiB
Plaintext
168 lines
5.7 KiB
Plaintext
|
|
What is vesafb?
|
|
===============
|
|
|
|
This is a generic driver for a graphic framebuffer on intel boxes.
|
|
|
|
The idea is simple: Turn on graphics mode at boot time with the help
|
|
of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
|
|
(and other) ports do.
|
|
|
|
This means we decide at boot time whenever we want to run in text or
|
|
graphics mode. Switching mode later on (in protected mode) is
|
|
impossible; BIOS calls work in real mode only. VESA BIOS Extensions
|
|
Version 2.0 are required, because we need a linear frame buffer.
|
|
|
|
Advantages:
|
|
|
|
* It provides a nice large console (128 cols + 48 lines with 1024x768)
|
|
without using tiny, unreadable fonts.
|
|
* You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
|
|
support for every VBE 2.0 compliant graphics board).
|
|
* Most important: boot logo :-)
|
|
|
|
Disadvantages:
|
|
|
|
* graphic mode is slower than text mode...
|
|
|
|
|
|
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.
|
|
|
|
X11
|
|
===
|
|
|
|
XF68_FBDev should work just fine, but it is non-accelerated. Running
|
|
another (accelerated) X-Server like XF86_SVGA might or might not work.
|
|
It depends on X-Server and graphics board.
|
|
|
|
The X-Server must restore the video mode correctly, else you end up
|
|
with a broken console (and vesafb cannot do anything about this).
|
|
|
|
|
|
Refresh rates
|
|
=============
|
|
|
|
There is no way to change the vesafb video mode and/or timings after
|
|
booting linux. If you are not happy with the 60 Hz refresh rate, you
|
|
have these options:
|
|
|
|
* configure and load the DOS-Tools for your the graphics board (if
|
|
available) and boot linux with loadlin.
|
|
* use a native driver (matroxfb/atyfb) instead if vesafb. If none
|
|
is available, write a new one!
|
|
* VBE 3.0 might work too. I have neither a gfx board with VBE 3.0
|
|
support nor the specs, so I have not checked this yet.
|
|
|
|
|
|
Configuration
|
|
=============
|
|
|
|
The VESA BIOS provides protected mode interface for changing
|
|
some parameters. vesafb can use it for palette changes and
|
|
to pan the display. It is turned off by default because it
|
|
seems not to work with some BIOS versions, but there are options
|
|
to turn it on.
|
|
|
|
You can pass options to vesafb using "video=vesafb:option" on
|
|
the kernel command line. Multiple options should be separated
|
|
by comma, like this: "video=vesafb:ypan,invers"
|
|
|
|
Accepted options:
|
|
|
|
invers no comment...
|
|
|
|
ypan enable display panning using the VESA protected mode
|
|
interface. The visible screen is just a window of the
|
|
video memory, console scrolling is done by changing the
|
|
start of the window.
|
|
pro: * scrolling (fullscreen) is fast, because there is
|
|
no need to copy around data.
|
|
* You'll get scrollback (the Shift-PgUp thing),
|
|
the video memory can be used as scrollback buffer
|
|
kontra: * scrolling only parts of the screen causes some
|
|
ugly flicker effects (boot logo flickers for
|
|
example).
|
|
|
|
ywrap Same as ypan, but assumes your gfx board can wrap-around
|
|
the video memory (i.e. starts reading from top if it
|
|
reaches the end of video memory). Faster than ypan.
|
|
|
|
redraw scroll by redrawing the affected part of the screen, this
|
|
is the safe (and slow) default.
|
|
|
|
|
|
vgapal Use the standard vga registers for palette changes.
|
|
This is the default.
|
|
pmipal Use the protected mode interface for palette changes.
|
|
|
|
mtrr setup memory type range registers for the vesafb framebuffer.
|
|
|
|
vremap:n
|
|
remap 'n' MiB of video RAM. If 0 or not specified, remap memory
|
|
according to video mode. (2.5.66 patch/idea by Antonino Daplas
|
|
reversed to give override possibility (allocate more fb memory
|
|
than the kernel would) to 2.4 by tmb@iki.fi)
|
|
|
|
vtotal:n
|
|
if the video BIOS of your card incorrectly determines the total
|
|
amount of video RAM, use this option to override the BIOS (in MiB).
|
|
|
|
Have fun!
|
|
|
|
Gerd
|
|
|
|
--
|
|
Gerd Knorr <kraxel@goldbach.in-berlin.de>
|
|
|
|
Minor (mostly typo) changes
|
|
by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>
|