1.. include:: <isonum.txt> 2 3================================= 4Video Mode Selection Support 2.13 5================================= 6 7:Copyright: |copy| 1995--1999 Martin Mares, <mj@ucw.cz> 8 9Intro 10~~~~~ 11 12This small document describes the "Video Mode Selection" feature which 13allows the use of various special video modes supported by the video BIOS. Due 14to usage of the BIOS, the selection is limited to boot time (before the 15kernel decompression starts) and works only on 80X86 machines that are 16booted through BIOS firmware (as opposed to through UEFI, kexec, etc.). 17 18.. note:: 19 20 Short intro for the impatient: Just use vga=ask for the first time, 21 enter ``scan`` on the video mode prompt, pick the mode you want to use, 22 remember its mode ID (the four-digit hexadecimal number) and then 23 set the vga parameter to this number (converted to decimal first). 24 25The video mode to be used is selected by a kernel parameter which can be 26specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..." 27option of LILO (or some other boot loader you use) or by the "xrandr" utility 28(present in standard Linux utility packages). You can use the following values 29of this parameter:: 30 31 NORMAL_VGA - Standard 80x25 mode available on all display adapters. 32 33 EXTENDED_VGA - Standard 8-pixel font mode: 80x43 on EGA, 80x50 on VGA. 34 35 ASK_VGA - Display a video mode menu upon startup (see below). 36 37 0..35 - Menu item number (when you have used the menu to view the list of 38 modes available on your adapter, you can specify the menu item you want 39 to use). 0..9 correspond to "0".."9", 10..35 to "a".."z". Warning: the 40 mode list displayed may vary as the kernel version changes, because the 41 modes are listed in a "first detected -- first displayed" manner. It's 42 better to use absolute mode numbers instead. 43 44 0x.... - Hexadecimal video mode ID (also displayed on the menu, see below 45 for exact meaning of the ID). Warning: LILO doesn't support 46 hexadecimal numbers -- you have to convert it to decimal manually. 47 48Menu 49~~~~ 50 51The ASK_VGA mode causes the kernel to offer a video mode menu upon 52bootup. It displays a "Press <RETURN> to see video modes available, <SPACE> 53to continue or wait 30 secs" message. If you press <RETURN>, you enter the 54menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in 55the standard 80x25 mode. 56 57The menu looks like:: 58 59 Video adapter: <name-of-detected-video-adapter> 60 Mode: COLSxROWS: 61 0 0F00 80x25 62 1 0F01 80x50 63 2 0F02 80x43 64 3 0F03 80x26 65 .... 66 Enter mode number or ``scan``: <flashing-cursor-here> 67 68<name-of-detected-video-adapter> tells what video adapter did Linux detect 69-- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA 70with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection 71of chipsets is turned off by default as it's inherently unreliable due to 72absolutely insane PC design. 73 74"0 0F00 80x25" means that the first menu item (the menu items are numbered 75from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the 76next section for a description of mode IDs). 77 78<flashing-cursor-here> encourages you to enter the item number or mode ID 79you wish to set and press <RETURN>. If the computer complains something about 80"Unknown mode ID", it is trying to tell you that it isn't possible to set such 81a mode. It's also possible to press only <RETURN> which leaves the current mode. 82 83The mode list usually contains a few basic modes and some VESA modes. In 84case your chipset has been detected, some chipset-specific modes are shown as 85well (some of these might be missing or unusable on your machine as different 86BIOSes are often shipped with the same card and the mode numbers depend purely 87on the VGA BIOS). 88 89The modes displayed on the menu are partially sorted: The list starts with 90the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and 9180x43), local modes (if the local modes feature is enabled), VESA modes and 92finally SVGA modes for the auto-detected adapter. 93 94If you are not happy with the mode list offered (e.g., if you think your card 95is able to do more), you can enter "scan" instead of item number / mode ID. The 96program will try to ask the BIOS for all possible video mode numbers and test 97what happens then. The screen will be probably flashing wildly for some time and 98strange noises will be heard from inside the monitor and so on and then, really 99all consistent video modes supported by your BIOS will appear (plus maybe some 100``ghost modes``). If you are afraid this could damage your monitor, don't use 101this function. 102 103After scanning, the mode ordering is a bit different: the auto-detected SVGA 104modes are not listed at all and the modes revealed by ``scan`` are shown before 105all VESA modes. 106 107Mode IDs 108~~~~~~~~ 109 110Because of the complexity of all the video stuff, the video mode IDs 111used here are also a bit complex. A video mode ID is a 16-bit number usually 112expressed in a hexadecimal notation (starting with "0x"). You can set a mode 113by entering its mode directly if you know it even if it isn't shown on the menu. 114 115The ID numbers can be divided to those regions:: 116 117 0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use 118 outside the menu as this can change from boot to boot (especially if you 119 have used the ``scan`` feature). 120 121 0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number 122 (as presented to INT 10, function 00) increased by 0x0100. 123 124 0x0200 to 0x08ff - VESA BIOS modes. The ID is a VESA mode ID increased by 125 0x0100. All VESA modes should be autodetected and shown on the menu. 126 127 0x0900 to 0x09ff - Video7 special modes. Set by calling INT 0x10, AX=0x6f05. 128 (Usually 940=80x43, 941=132x25, 942=132x44, 943=80x60, 944=100x60, 129 945=132x28 for the standard Video7 BIOS) 130 131 0x0f00 to 0x0fff - special modes (they are set by various tricks -- usually 132 by modifying one of the standard modes). Currently available: 133 0x0f00 standard 80x25, don't reset mode if already set (=FFFF) 134 0x0f01 standard with 8-point font: 80x43 on EGA, 80x50 on VGA 135 0x0f02 VGA 80x43 (VGA switched to 350 scanlines with a 8-point font) 136 0x0f03 VGA 80x28 (standard VGA scans, but 14-point font) 137 0x0f04 leave current video mode 138 0x0f05 VGA 80x30 (480 scans, 16-point font) 139 0x0f06 VGA 80x34 (480 scans, 14-point font) 140 0x0f07 VGA 80x60 (480 scans, 8-point font) 141 0x0f08 Graphics hack (see the VIDEO_GFX_HACK paragraph below) 142 143 0x1000 to 0x7fff - modes specified by resolution. The code has a "0xRRCC" 144 form where RR is a number of rows and CC is a number of columns. 145 E.g., 0x1950 corresponds to a 80x25 mode, 0x2b84 to 132x43 etc. 146 This is the only fully portable way to refer to a non-standard mode, 147 but it relies on the mode being found and displayed on the menu 148 (remember that mode scanning is not done automatically). 149 150 0xff00 to 0xffff - aliases for backward compatibility: 151 0xffff equivalent to 0x0f00 (standard 80x25) 152 0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50) 153 154If you add 0x8000 to the mode ID, the program will try to recalculate 155vertical display timing according to mode parameters, which can be used to 156eliminate some annoying bugs of certain VGA BIOSes (usually those used for 157cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the 158end of the display. 159 160Options 161~~~~~~~ 162 163Build options for arch/x86/boot/* are selected by the kernel kconfig 164utility and the kernel .config file. 165 166VIDEO_GFX_HACK - includes special hack for setting of graphics modes 167to be used later by special drivers. 168Allows to set _any_ BIOS mode including graphic ones and forcing specific 169text screen resolution instead of peeking it from BIOS variables. Don't use 170unless you think you know what you're doing. To activate this setup, use 171mode number 0x0f08 (see the Mode IDs section above). 172 173Still doesn't work? 174~~~~~~~~~~~~~~~~~~~ 175 176When the mode detection doesn't work (e.g., the mode list is incorrect or 177the machine hangs instead of displaying the menu), try to switch off some of 178the configuration options listed under "Options". If it fails, you can still use 179your kernel with the video mode set directly via the kernel parameter. 180 181In either case, please send me a bug report containing what _exactly_ 182happens and how do the configuration switches affect the behaviour of the bug. 183 184If you start Linux from M$-DOS, you might also use some DOS tools for 185video mode setting. In this case, you must specify the 0x0f04 mode ("leave 186current settings") to Linux, because if you don't and you use any non-standard 187mode, Linux will switch to 80x25 automatically. 188 189If you set some extended mode and there's one or more extra lines on the 190bottom of the display containing already scrolled-out text, your VGA BIOS 191contains the most common video BIOS bug called "incorrect vertical display 192end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately, 193this must be done manually -- no autodetection mechanisms are available. 194 195History 196~~~~~~~ 197 198=============== ================================================================ 1991.0 (??-Nov-95) First version supporting all adapters supported by the old 200 setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels 201 and then removed due to instability on some machines. 2022.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost 203 everything is configurable, the VESA support should be much more 204 stable, explicit mode numbering allowed, "scan" implemented etc. 2052.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution 206 supported. Few bugs fixed. VESA modes are listed prior to 207 modes supplied by SVGA autodetection as they are more reliable. 208 CLGD autodetect works better. Doesn't depend on 80x25 being 209 active when started. Scanning fixed. 80x43 (any VGA) added. 210 Code cleaned up. 2112.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX 212 VESA modes work now). Display end bug workaround supported. 213 Special modes renumbered to allow adding of the "recalculate" 214 flag, 0xffff and 0xfffe became aliases instead of real IDs. 215 Screen contents retained during mode changes. 2162.3 (15-Mar-96) Changed to work with 1.3.74 kernel. 2172.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem 218 with some boot loaders. Memory management rewritten to reflect 219 these changes. Unfortunately, screen contents retaining works 220 only with some loaders now. 221 Added a Tseng 132x60 mode. 2222.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4. 2232.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on 224 several cards with broken VESA code (e.g., ATI VGA). 2252.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some 226 cards use very strange mode numbers. 227 - Added Realtek VGA modes (thanks to Gonzalo Tornaria). 228 - Hardware testing order slightly changed, tests based on ROM 229 contents done as first. 230 - Added support for special Video7 mode switching functions 231 (thanks to Tom Vander Aa). 232 - Added 480-scanline modes (especially useful for notebooks, 233 original version written by hhanemaa@cs.ruu.nl, patched by 234 Jeff Chua, rewritten by me). 235 - Screen store/restore fixed. 2362.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. 237 - Better recognition of text modes during mode scan. 2382.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) 2392.10(11-Nov-96) - The whole thing made optional. 240 - Added the CONFIG_VIDEO_400_HACK switch. 241 - Added the CONFIG_VIDEO_GFX_HACK switch. 242 - Code cleanup. 2432.11(03-May-97) - Yet another cleanup, now including also the documentation. 244 - Direct testing of SVGA adapters turned off by default, ``scan`` 245 offered explicitly on the prompt line. 246 - Removed the doc section describing adding of new probing 247 functions as I try to get rid of _all_ hardware probing here. 2482.12(25-May-98) Added support for VESA frame buffer graphics. 2492.13(14-May-99) Minor documentation fixes. 250=============== ================================================================ 251