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svga.txt: standardize document format
Each text file under Documentation follows a different format. Some doesn't even have titles! Change its representation to follow the adopted standard, using ReST markups for it to be parseable by Sphinx: - Use standard notation for titles; - Use the note mark; - mark literal blocks; - adjust identation; - mark the table. Acked-By: Martin Mares <mj@ucw.cz> Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com> Signed-off-by: Jonathan Corbet <corbet@lwn.net>
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Mauro Carvalho Chehab
Jonathan Corbet
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aa4d520358
@ -1,24 +1,31 @@
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Video Mode Selection Support 2.13
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(c) 1995--1999 Martin Mares, <mj@ucw.cz>
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--------------------------------------------------------------------------------
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.. include:: <isonum.txt>
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1. Intro
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~~~~~~~~
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This small document describes the "Video Mode Selection" feature which
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=================================
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Video Mode Selection Support 2.13
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=================================
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:Copyright: |copy| 1995--1999 Martin Mares, <mj@ucw.cz>
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Intro
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~~~~~
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This small document describes the "Video Mode Selection" feature which
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allows the use of various special video modes supported by the video BIOS. Due
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to usage of the BIOS, the selection is limited to boot time (before the
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kernel decompression starts) and works only on 80X86 machines.
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** Short intro for the impatient: Just use vga=ask for the first time,
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** enter `scan' on the video mode prompt, pick the mode you want to use,
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** remember its mode ID (the four-digit hexadecimal number) and then
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** set the vga parameter to this number (converted to decimal first).
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.. note::
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The video mode to be used is selected by a kernel parameter which can be
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Short intro for the impatient: Just use vga=ask for the first time,
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enter ``scan`` on the video mode prompt, pick the mode you want to use,
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remember its mode ID (the four-digit hexadecimal number) and then
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set the vga parameter to this number (converted to decimal first).
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The video mode to be used is selected by a kernel parameter which can be
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specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..."
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option of LILO (or some other boot loader you use) or by the "vidmode" utility
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(present in standard Linux utility packages). You can use the following values
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of this parameter:
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of this parameter::
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NORMAL_VGA - Standard 80x25 mode available on all display adapters.
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@ -37,77 +44,79 @@ of this parameter:
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for exact meaning of the ID). Warning: rdev and LILO don't support
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hexadecimal numbers -- you have to convert it to decimal manually.
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2. Menu
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~~~~~~~
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The ASK_VGA mode causes the kernel to offer a video mode menu upon
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Menu
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~~~~
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The ASK_VGA mode causes the kernel to offer a video mode menu upon
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bootup. It displays a "Press <RETURN> to see video modes available, <SPACE>
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to continue or wait 30 secs" message. If you press <RETURN>, you enter the
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menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in
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the standard 80x25 mode.
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The menu looks like:
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The menu looks like::
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Video adapter: <name-of-detected-video-adapter>
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Mode: COLSxROWS:
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0 0F00 80x25
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1 0F01 80x50
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2 0F02 80x43
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3 0F03 80x26
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....
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Enter mode number or `scan': <flashing-cursor-here>
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Video adapter: <name-of-detected-video-adapter>
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Mode: COLSxROWS:
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0 0F00 80x25
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1 0F01 80x50
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2 0F02 80x43
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3 0F03 80x26
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....
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Enter mode number or ``scan``: <flashing-cursor-here>
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<name-of-detected-video-adapter> tells what video adapter did Linux detect
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<name-of-detected-video-adapter> tells what video adapter did Linux detect
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-- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA
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with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection
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of chipsets is turned off by default (see CONFIG_VIDEO_SVGA in chapter 4 to see
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how to enable it if you really want) as it's inherently unreliable due to
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absolutely insane PC design.
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"0 0F00 80x25" means that the first menu item (the menu items are numbered
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"0 0F00 80x25" means that the first menu item (the menu items are numbered
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from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the
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next section for a description of mode IDs).
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<flashing-cursor-here> encourages you to enter the item number or mode ID
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<flashing-cursor-here> encourages you to enter the item number or mode ID
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you wish to set and press <RETURN>. If the computer complains something about
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"Unknown mode ID", it is trying to tell you that it isn't possible to set such
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a mode. It's also possible to press only <RETURN> which leaves the current mode.
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The mode list usually contains a few basic modes and some VESA modes. In
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The mode list usually contains a few basic modes and some VESA modes. In
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case your chipset has been detected, some chipset-specific modes are shown as
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well (some of these might be missing or unusable on your machine as different
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BIOSes are often shipped with the same card and the mode numbers depend purely
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on the VGA BIOS).
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The modes displayed on the menu are partially sorted: The list starts with
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The modes displayed on the menu are partially sorted: The list starts with
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the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and
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80x43), local modes (if the local modes feature is enabled), VESA modes and
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finally SVGA modes for the auto-detected adapter.
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If you are not happy with the mode list offered (e.g., if you think your card
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If you are not happy with the mode list offered (e.g., if you think your card
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is able to do more), you can enter "scan" instead of item number / mode ID. The
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program will try to ask the BIOS for all possible video mode numbers and test
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what happens then. The screen will be probably flashing wildly for some time and
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strange noises will be heard from inside the monitor and so on and then, really
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all consistent video modes supported by your BIOS will appear (plus maybe some
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`ghost modes'). If you are afraid this could damage your monitor, don't use this
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function.
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``ghost modes``). If you are afraid this could damage your monitor, don't use
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this function.
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After scanning, the mode ordering is a bit different: the auto-detected SVGA
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modes are not listed at all and the modes revealed by `scan' are shown before
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After scanning, the mode ordering is a bit different: the auto-detected SVGA
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modes are not listed at all and the modes revealed by ``scan`` are shown before
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all VESA modes.
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3. Mode IDs
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~~~~~~~~~~~
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Because of the complexity of all the video stuff, the video mode IDs
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Mode IDs
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~~~~~~~~
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Because of the complexity of all the video stuff, the video mode IDs
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used here are also a bit complex. A video mode ID is a 16-bit number usually
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expressed in a hexadecimal notation (starting with "0x"). You can set a mode
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by entering its mode directly if you know it even if it isn't shown on the menu.
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The ID numbers can be divided to three regions:
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The ID numbers can be divided to those regions::
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0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use
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outside the menu as this can change from boot to boot (especially if you
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have used the `scan' feature).
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have used the ``scan`` feature).
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0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number
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(as presented to INT 10, function 00) increased by 0x0100.
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@ -142,53 +151,54 @@ The ID numbers can be divided to three regions:
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0xffff equivalent to 0x0f00 (standard 80x25)
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0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50)
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If you add 0x8000 to the mode ID, the program will try to recalculate
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If you add 0x8000 to the mode ID, the program will try to recalculate
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vertical display timing according to mode parameters, which can be used to
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eliminate some annoying bugs of certain VGA BIOSes (usually those used for
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cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the
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end of the display.
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4. Options
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~~~~~~~~~~
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Some options can be set in the source text (in arch/i386/boot/video.S).
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Options
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~~~~~~~
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Some options can be set in the source text (in arch/i386/boot/video.S).
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All of them are simple #define's -- change them to #undef's when you want to
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switch them off. Currently supported:
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CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched
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CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched
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off by default as it's a bit unreliable due to terribly bad PC design. If you
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really want to have the adapter autodetected (maybe in case the `scan' feature
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really want to have the adapter autodetected (maybe in case the ``scan`` feature
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doesn't work on your machine), switch this on and don't cry if the results
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are not completely sane. In case you really need this feature, please drop me
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a mail as I think of removing it some day.
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CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work
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CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work
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on your machine (or displays a "Error: Scanning of VESA modes failed" message),
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you can switch it off and report as a bug.
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CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there
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CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there
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are more modes with the same screen size, only the first one is kept (see above
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for more info on mode ordering). However, in very strange cases it's possible
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that the first "version" of the mode doesn't work although some of the others
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do -- in this case turn this switch off to see the rest.
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CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching
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CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching
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video modes. Works only with some boot loaders which leave enough room for the
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buffer. (If you have old LILO, you can adjust heap_end_ptr and loadflags
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in setup.S, but it's better to upgrade the boot loader...)
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CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The
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CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The
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local modes are added automatically to the beginning of the list not depending
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on hardware configuration. The local modes are listed in the source text after
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the "local_mode_table:" line. The comment before this line describes the format
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of the table (which also includes a video card name to be displayed on the
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top of the menu).
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CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA
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CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA
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modes. This option is intended to be used on certain buggy BIOSes which draw
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some useless logo using font download and then fail to reset the correct mode.
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Don't use unless needed as it forces resetting the video card.
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CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes
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CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes
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to be used later by special drivers (e.g., 800x600 on IBM ThinkPad -- see
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ftp://ftp.phys.keio.ac.jp/pub/XFree86/800x600/XF86Configs/XF86Config.IBM_TP560).
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Allows to set _any_ BIOS mode including graphic ones and forcing specific
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@ -196,33 +206,36 @@ text screen resolution instead of peeking it from BIOS variables. Don't use
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unless you think you know what you're doing. To activate this setup, use
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mode number 0x0f08 (see section 3).
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5. Still doesn't work?
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~~~~~~~~~~~~~~~~~~~~~~
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When the mode detection doesn't work (e.g., the mode list is incorrect or
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Still doesn't work?
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~~~~~~~~~~~~~~~~~~~
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When the mode detection doesn't work (e.g., the mode list is incorrect or
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the machine hangs instead of displaying the menu), try to switch off some of
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the configuration options listed in section 4. If it fails, you can still use
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your kernel with the video mode set directly via the kernel parameter.
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In either case, please send me a bug report containing what _exactly_
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In either case, please send me a bug report containing what _exactly_
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happens and how do the configuration switches affect the behaviour of the bug.
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If you start Linux from M$-DOS, you might also use some DOS tools for
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If you start Linux from M$-DOS, you might also use some DOS tools for
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video mode setting. In this case, you must specify the 0x0f04 mode ("leave
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current settings") to Linux, because if you don't and you use any non-standard
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mode, Linux will switch to 80x25 automatically.
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If you set some extended mode and there's one or more extra lines on the
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If you set some extended mode and there's one or more extra lines on the
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bottom of the display containing already scrolled-out text, your VGA BIOS
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contains the most common video BIOS bug called "incorrect vertical display
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end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately,
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this must be done manually -- no autodetection mechanisms are available.
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If you have a VGA card and your display still looks as on EGA, your BIOS
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If you have a VGA card and your display still looks as on EGA, your BIOS
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is probably broken and you need to set the CONFIG_VIDEO_400_HACK switch to
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force setting of the correct mode.
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6. History
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~~~~~~~~~~
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History
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~~~~~~~
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=============== ================================================================
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1.0 (??-Nov-95) First version supporting all adapters supported by the old
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setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels
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and then removed due to instability on some machines.
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@ -263,14 +276,15 @@ force setting of the correct mode.
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2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA.
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- Better recognition of text modes during mode scan.
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2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!)
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2.10 (11-Nov-96)- The whole thing made optional.
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2.10(11-Nov-96) - The whole thing made optional.
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- Added the CONFIG_VIDEO_400_HACK switch.
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- Added the CONFIG_VIDEO_GFX_HACK switch.
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- Code cleanup.
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2.11 (03-May-97)- Yet another cleanup, now including also the documentation.
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- Direct testing of SVGA adapters turned off by default, `scan'
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2.11(03-May-97) - Yet another cleanup, now including also the documentation.
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- Direct testing of SVGA adapters turned off by default, ``scan``
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offered explicitly on the prompt line.
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- Removed the doc section describing adding of new probing
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functions as I try to get rid of _all_ hardware probing here.
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2.12 (25-May-98)- Added support for VESA frame buffer graphics.
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2.13 (14-May-99)- Minor documentation fixes.
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2.12(25-May-98) Added support for VESA frame buffer graphics.
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2.13(14-May-99) Minor documentation fixes.
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=============== ================================================================
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