Documentation/admin-guide/svga.rst

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.. include:: <isonum.txt>

=================================
Video Mode Selection Support 2.13
=================================

:Copyright: |copy| 1995--1999 Martin Mares, <mj@ucw.cz>

Intro
~~~~~

This small document describes the "Video Mode Selection" feature which
allows the use of various special video modes supported by the video BIOS. Due
to usage of the BIOS, the selection is limited to boot time (before the
kernel decompression starts) and works only on 80X86 machines that are
booted through BIOS firmware (as opposed to through UEFI, kexec, etc.).

.. note::

   Short intro for the impatient: Just use vga=ask for the first time,
   enter ``scan`` on the video mode prompt, pick the mode you want to use,
   remember its mode ID (the four-digit hexadecimal number) and then
   set the vga parameter to this number (converted to decimal first).

The video mode to be used is selected by a kernel parameter which can be
specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..."
option of LILO (or some other boot loader you use) or by the "xrandr" utility
(present in standard Linux utility packages). You can use the following values
of this parameter::

   NORMAL_VGA - Standard 80x25 mode available on all display adapters.

   EXTENDED_VGA	- Standard 8-pixel font mode: 80x43 on EGA, 80x50 on VGA.

   ASK_VGA - Display a video mode menu upon startup (see below).

   0..35 - Menu item number (when you have used the menu to view the list of
      modes available on your adapter, you can specify the menu item you want
      to use). 0..9 correspond to "0".."9", 10..35 to "a".."z". Warning: the
      mode list displayed may vary as the kernel version changes, because the
      modes are listed in a "first detected -- first displayed" manner. It's
      better to use absolute mode numbers instead.

   0x.... - Hexadecimal video mode ID (also displayed on the menu, see below
      for exact meaning of the ID). Warning: LILO doesn't support
      hexadecimal numbers -- you have to convert it to decimal manually.

Menu
~~~~

The ASK_VGA mode causes the kernel to offer a video mode menu upon
bootup. It displays a "Press <RETURN> to see video modes available, <SPACE>
to continue or wait 30 secs" message. If you press <RETURN>, you enter the
menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in
the standard 80x25 mode.

The menu looks like::

	Video adapter: <name-of-detected-video-adapter>
	Mode:    COLSxROWS:
	0  0F00  80x25
	1  0F01  80x50
	2  0F02  80x43
	3  0F03  80x26
	....
	Enter mode number or ``scan``: <flashing-cursor-here>

<name-of-detected-video-adapter> tells what video adapter did Linux detect
-- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA
with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection

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