| .. 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 | |
| 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. | |
| =============== ================================================================ |