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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.
+
+.. 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 "vidmode" 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: rdev and LILO don'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
+of chipsets is turned off by default as it's inherently unreliable due to
+absolutely insane PC design.
+
+"0 0F00 80x25" means that the first menu item (the menu items are numbered
+from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the
+next section for a description of mode IDs).
+
+<flashing-cursor-here> encourages you to enter the item number or mode ID
+you wish to set and press <RETURN>. If the computer complains something about
+"Unknown mode ID", it is trying to tell you that it isn't possible to set such
+a mode. It's also possible to press only <RETURN> which leaves the current mode.
+
+The mode list usually contains a few basic modes and some VESA modes. In
+case your chipset has been detected, some chipset-specific modes are shown as
+well (some of these might be missing or unusable on your machine as different
+BIOSes are often shipped with the same card and the mode numbers depend purely
+on the VGA BIOS).
+
+The modes displayed on the menu are partially sorted: The list starts with
+the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and
+80x43), local modes (if the local modes feature is enabled), VESA modes and
+finally SVGA modes for the auto-detected adapter.
+
+If you are not happy with the mode list offered (e.g., if you think your card
+is able to do more), you can enter "scan" instead of item number / mode ID. The
+program will try to ask the BIOS for all possible video mode numbers and test
+what happens then. The screen will be probably flashing wildly for some time and
+strange noises will be heard from inside the monitor and so on and then, really
+all consistent video modes supported by your BIOS will appear (plus maybe some
+``ghost modes``). If you are afraid this could damage your monitor, don't use
+this function.
+
+After scanning, the mode ordering is a bit different: the auto-detected SVGA
+modes are not listed at all and the modes revealed by ``scan`` are shown before
+all VESA modes.
+
+Mode IDs
+~~~~~~~~
+
+Because of the complexity of all the video stuff, the video mode IDs
+used here are also a bit complex. A video mode ID is a 16-bit number usually
+expressed in a hexadecimal notation (starting with "0x"). You can set a mode
+by entering its mode directly if you know it even if it isn't shown on the menu.
+
+The ID numbers can be divided to those regions::
+
+ 0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use
+ outside the menu as this can change from boot to boot (especially if you
+ have used the ``scan`` feature).
+
+ 0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number
+ (as presented to INT 10, function 00) increased by 0x0100.
+
+ 0x0200 to 0x08ff - VESA BIOS modes. The ID is a VESA mode ID increased by
+ 0x0100. All VESA modes should be autodetected and shown on the menu.
+
+ 0x0900 to 0x09ff - Video7 special modes. Set by calling INT 0x10, AX=0x6f05.
+ (Usually 940=80x43, 941=132x25, 942=132x44, 943=80x60, 944=100x60,
+ 945=132x28 for the standard Video7 BIOS)
+
+ 0x0f00 to 0x0fff - special modes (they are set by various tricks -- usually
+ by modifying one of the standard modes). Currently available:
+ 0x0f00 standard 80x25, don't reset mode if already set (=FFFF)
+ 0x0f01 standard with 8-point font: 80x43 on EGA, 80x50 on VGA
+ 0x0f02 VGA 80x43 (VGA switched to 350 scanlines with a 8-point font)
+ 0x0f03 VGA 80x28 (standard VGA scans, but 14-point font)
+ 0x0f04 leave current video mode
+ 0x0f05 VGA 80x30 (480 scans, 16-point font)
+ 0x0f06 VGA 80x34 (480 scans, 14-point font)
+ 0x0f07 VGA 80x60 (480 scans, 8-point font)
+ 0x0f08 Graphics hack (see the VIDEO_GFX_HACK paragraph below)
+
+ 0x1000 to 0x7fff - modes specified by resolution. The code has a "0xRRCC"
+ form where RR is a number of rows and CC is a number of columns.
+ E.g., 0x1950 corresponds to a 80x25 mode, 0x2b84 to 132x43 etc.
+ This is the only fully portable way to refer to a non-standard mode,
+ but it relies on the mode being found and displayed on the menu
+ (remember that mode scanning is not done automatically).
+
+ 0xff00 to 0xffff - aliases for backward compatibility:
+ 0xffff equivalent to 0x0f00 (standard 80x25)
+ 0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50)
+
+If you add 0x8000 to the mode ID, the program will try to recalculate
+vertical display timing according to mode parameters, which can be used to
+eliminate some annoying bugs of certain VGA BIOSes (usually those used for
+cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the
+end of the display.
+
+Options
+~~~~~~~
+
+Build options for arch/x86/boot/* are selected by the kernel kconfig
+utility and the kernel .config file.
+
+VIDEO_GFX_HACK - includes special hack for setting of graphics modes
+to be used later by special drivers.
+Allows to set _any_ BIOS mode including graphic ones and forcing specific
+text screen resolution instead of peeking it from BIOS variables. Don't use
+unless you think you know what you're doing. To activate this setup, use
+mode number 0x0f08 (see the Mode IDs section above).
+
+Still doesn't work?
+~~~~~~~~~~~~~~~~~~~
+
+When the mode detection doesn't work (e.g., the mode list is incorrect or
+the machine hangs instead of displaying the menu), try to switch off some of
+the configuration options listed under "Options". If it fails, you can still use
+your kernel with the video mode set directly via the kernel parameter.
+
+In either case, please send me a bug report containing what _exactly_
+happens and how do the configuration switches affect the behaviour of the bug.
+
+If you start Linux from M$-DOS, you might also use some DOS tools for
+video mode setting. In this case, you must specify the 0x0f04 mode ("leave
+current settings") to Linux, because if you don't and you use any non-standard
+mode, Linux will switch to 80x25 automatically.
+
+If you set some extended mode and there's one or more extra lines on the
+bottom of the display containing already scrolled-out text, your VGA BIOS
+contains the most common video BIOS bug called "incorrect vertical display
+end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately,
+this must be done manually -- no autodetection mechanisms are available.
+
+History
+~~~~~~~
+
+=============== ================================================================
+1.0 (??-Nov-95) First version supporting all adapters supported by the old
+ setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels
+ and then removed due to instability on some machines.
+2.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost
+ everything is configurable, the VESA support should be much more
+ stable, explicit mode numbering allowed, "scan" implemented etc.
+2.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution
+ supported. Few bugs fixed. VESA modes are listed prior to
+ modes supplied by SVGA autodetection as they are more reliable.
+ CLGD autodetect works better. Doesn't depend on 80x25 being
+ active when started. Scanning fixed. 80x43 (any VGA) added.
+ Code cleaned up.
+2.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX
+ VESA modes work now). Display end bug workaround supported.
+ Special modes renumbered to allow adding of the "recalculate"
+ flag, 0xffff and 0xfffe became aliases instead of real IDs.
+ Screen contents retained during mode changes.
+2.3 (15-Mar-96) Changed to work with 1.3.74 kernel.
+2.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem
+ with some boot loaders. Memory management rewritten to reflect
+ these changes. Unfortunately, screen contents retaining works
+ only with some loaders now.
+ Added a Tseng 132x60 mode.
+2.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4.
+2.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on
+ several cards with broken VESA code (e.g., ATI VGA).
+2.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some
+ cards use very strange mode numbers.
+ - Added Realtek VGA modes (thanks to Gonzalo Tornaria).
+ - Hardware testing order slightly changed, tests based on ROM
+ contents done as first.
+ - Added support for special Video7 mode switching functions
+ (thanks to Tom Vander Aa).
+ - Added 480-scanline modes (especially useful for notebooks,
+ original version written by hhanemaa@cs.ruu.nl, patched by
+ Jeff Chua, rewritten by me).
+ - Screen store/restore fixed.
+2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA.
+ - Better recognition of text modes during mode scan.
+2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!)
+2.10(11-Nov-96) - The whole thing made optional.
+ - Added the CONFIG_VIDEO_400_HACK switch.
+ - Added the CONFIG_VIDEO_GFX_HACK switch.
+ - Code cleanup.
+2.11(03-May-97) - Yet another cleanup, now including also the documentation.
+ - Direct testing of SVGA adapters turned off by default, ``scan``
+ offered explicitly on the prompt line.
+ - Removed the doc section describing adding of new probing
+ functions as I try to get rid of _all_ hardware probing here.
+2.12(25-May-98) Added support for VESA frame buffer graphics.
+2.13(14-May-99) Minor documentation fixes.
+=============== ================================================================