linux/Documentation/fb/vesafb.txt
<<
>>
Prefs
   1
   2What is vesafb?
   3===============
   4
   5This is a generic driver for a graphic framebuffer on intel boxes.
   6
   7The idea is simple:  Turn on graphics mode at boot time with the help
   8of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
   9(and other) ports do.
  10
  11This means we decide at boot time whenever we want to run in text or
  12graphics mode.  Switching mode later on (in protected mode) is
  13impossible; BIOS calls work in real mode only.  VESA BIOS Extensions
  14Version 2.0 are required, because we need a linear frame buffer.
  15
  16Advantages:
  17
  18 * It provides a nice large console (128 cols + 48 lines with 1024x768)
  19   without using tiny, unreadable fonts.
  20 * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
  21   support for every VBE 2.0 compliant graphics board).
  22 * Most important: boot logo :-)
  23
  24Disadvantages:
  25
  26 * graphic mode is slower than text mode...
  27
  28
  29How to use it?
  30==============
  31
  32Switching modes is done using the vga=... boot parameter.  Read
  33Documentation/svga.txt for details.
  34
  35You should compile in both vgacon (for text mode) and vesafb (for
  36graphics mode). Which of them takes over the console depends on
  37whenever the specified mode is text or graphics.
  38
  39The graphic modes are NOT in the list which you get if you boot with
  40vga=ask and hit return. The mode you wish to use is derived from the
  41VESA mode number. Here are those VESA mode numbers:
  42
  43    | 640x480  800x600  1024x768 1280x1024
  44----+-------------------------------------
  45256 |  0x101    0x103    0x105    0x107   
  4632k |  0x110    0x113    0x116    0x119   
  4764k |  0x111    0x114    0x117    0x11A   
  4816M |  0x112    0x115    0x118    0x11B   
  49
  50The video mode number of the Linux kernel is the VESA mode number plus
  510x200.
  52 
  53 Linux_kernel_mode_number = VESA_mode_number + 0x200
  54
  55So the table for the Kernel mode numbers are:
  56
  57    | 640x480  800x600  1024x768 1280x1024
  58----+-------------------------------------
  59256 |  0x301    0x303    0x305    0x307   
  6032k |  0x310    0x313    0x316    0x319   
  6164k |  0x311    0x314    0x317    0x31A   
  6216M |  0x312    0x315    0x318    0x31B   
  63
  64To enable one of those modes you have to specify "vga=ask" in the
  65lilo.conf file and rerun LILO. Then you can type in the desired
  66mode at the "vga=ask" prompt. For example if you like to use 
  671024x768x256 colors you have to say "305" at this prompt.
  68
  69If this does not work, this might be because your BIOS does not support
  70linear framebuffers or because it does not support this mode at all.
  71Even if your board does, it might be the BIOS which does not.  VESA BIOS
  72Extensions v2.0 are required, 1.2 is NOT sufficient.  You will get a
  73"bad mode number" message if something goes wrong.
  74
  751. Note: LILO cannot handle hex, for booting directly with 
  76         "vga=mode-number" you have to transform the numbers to decimal.
  772. Note: Some newer versions of LILO appear to work with those hex values,
  78         if you set the 0x in front of the numbers.
  79
  80X11
  81===
  82
  83XF68_FBDev should work just fine, but it is non-accelerated.  Running
  84another (accelerated) X-Server like XF86_SVGA might or might not work.
  85It depends on X-Server and graphics board.
  86
  87The X-Server must restore the video mode correctly, else you end up
  88with a broken console (and vesafb cannot do anything about this).
  89
  90
  91Refresh rates
  92=============
  93
  94There is no way to change the vesafb video mode and/or timings after
  95booting linux.  If you are not happy with the 60 Hz refresh rate, you
  96have these options:
  97
  98 * configure and load the DOS-Tools for the graphics board (if
  99   available) and boot linux with loadlin.
 100 * use a native driver (matroxfb/atyfb) instead if vesafb.  If none
 101   is available, write a new one!
 102 * VBE 3.0 might work too.  I have neither a gfx board with VBE 3.0
 103   support nor the specs, so I have not checked this yet.
 104
 105
 106Configuration
 107=============
 108
 109The VESA BIOS provides protected mode interface for changing
 110some parameters.  vesafb can use it for palette changes and
 111to pan the display.  It is turned off by default because it
 112seems not to work with some BIOS versions, but there are options
 113to turn it on.
 114
 115You can pass options to vesafb using "video=vesafb:option" on
 116the kernel command line.  Multiple options should be separated
 117by comma, like this: "video=vesafb:ypan,invers"
 118
 119Accepted options:
 120
 121invers  no comment...
 122
 123ypan    enable display panning using the VESA protected mode 
 124        interface.  The visible screen is just a window of the
 125        video memory, console scrolling is done by changing the
 126        start of the window.
 127        pro:    * scrolling (fullscreen) is fast, because there is
 128                  no need to copy around data.
 129                * You'll get scrollback (the Shift-PgUp thing),
 130                  the video memory can be used as scrollback buffer
 131        kontra: * scrolling only parts of the screen causes some
 132                  ugly flicker effects (boot logo flickers for
 133                  example).
 134
 135ywrap   Same as ypan, but assumes your gfx board can wrap-around 
 136        the video memory (i.e. starts reading from top if it
 137        reaches the end of video memory).  Faster than ypan.
 138
 139redraw  scroll by redrawing the affected part of the screen, this
 140        is the safe (and slow) default.
 141
 142
 143vgapal  Use the standard vga registers for palette changes.
 144        This is the default.
 145pmipal  Use the protected mode interface for palette changes.
 146
 147mtrr:n  setup memory type range registers for the vesafb framebuffer
 148        where n:
 149              0 - disabled (equivalent to nomtrr) (default)
 150              1 - uncachable
 151              2 - write-back
 152              3 - write-combining
 153              4 - write-through
 154
 155        If you see the following in dmesg, choose the type that matches the
 156        old one. In this example, use "mtrr:2".
 157...
 158mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining
 159...
 160
 161nomtrr  disable mtrr
 162
 163vremap:n
 164        remap 'n' MiB of video RAM. If 0 or not specified, remap memory
 165        according to video mode. (2.5.66 patch/idea by Antonino Daplas
 166        reversed to give override possibility (allocate more fb memory
 167        than the kernel would) to 2.4 by tmb@iki.fi)
 168
 169vtotal:n
 170        if the video BIOS of your card incorrectly determines the total
 171        amount of video RAM, use this option to override the BIOS (in MiB).
 172
 173Have fun!
 174
 175  Gerd
 176
 177--
 178Gerd Knorr <kraxel@goldbach.in-berlin.de>
 179
 180Minor (mostly typo) changes 
 181by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>
 182
lxr.linux.no kindly hosted by Redpill Linpro AS, provider of Linux consulting and operations services since 1995.