Based on kernel version 4.15. Page generated on 2018-01-29 10:01 EST.
1 .. include:: <isonum.txt> 2 3 ================================= 4 Video Mode Selection Support 2.13 5 ================================= 6 7 :Copyright: |copy| 1995--1999 Martin Mares, <email@example.com> 8 9 Intro 10 ~~~~~ 11 12 This small document describes the "Video Mode Selection" feature which 13 allows the use of various special video modes supported by the video BIOS. Due 14 to usage of the BIOS, the selection is limited to boot time (before the 15 kernel decompression starts) and works only on 80X86 machines. 16 17 .. note:: 18 19 Short intro for the impatient: Just use vga=ask for the first time, 20 enter ``scan`` on the video mode prompt, pick the mode you want to use, 21 remember its mode ID (the four-digit hexadecimal number) and then 22 set the vga parameter to this number (converted to decimal first). 23 24 The video mode to be used is selected by a kernel parameter which can be 25 specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..." 26 option of LILO (or some other boot loader you use) or by the "vidmode" utility 27 (present in standard Linux utility packages). You can use the following values 28 of this parameter:: 29 30 NORMAL_VGA - Standard 80x25 mode available on all display adapters. 31 32 EXTENDED_VGA - Standard 8-pixel font mode: 80x43 on EGA, 80x50 on VGA. 33 34 ASK_VGA - Display a video mode menu upon startup (see below). 35 36 0..35 - Menu item number (when you have used the menu to view the list of 37 modes available on your adapter, you can specify the menu item you want 38 to use). 0..9 correspond to "0".."9", 10..35 to "a".."z". Warning: the 39 mode list displayed may vary as the kernel version changes, because the 40 modes are listed in a "first detected -- first displayed" manner. It's 41 better to use absolute mode numbers instead. 42 43 0x.... - Hexadecimal video mode ID (also displayed on the menu, see below 44 for exact meaning of the ID). Warning: rdev and LILO don't support 45 hexadecimal numbers -- you have to convert it to decimal manually. 46 47 Menu 48 ~~~~ 49 50 The ASK_VGA mode causes the kernel to offer a video mode menu upon 51 bootup. It displays a "Press <RETURN> to see video modes available, <SPACE> 52 to continue or wait 30 secs" message. If you press <RETURN>, you enter the 53 menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in 54 the standard 80x25 mode. 55 56 The menu looks like:: 57 58 Video adapter: <name-of-detected-video-adapter> 59 Mode: COLSxROWS: 60 0 0F00 80x25 61 1 0F01 80x50 62 2 0F02 80x43 63 3 0F03 80x26 64 .... 65 Enter mode number or ``scan``: <flashing-cursor-here> 66 67 <name-of-detected-video-adapter> tells what video adapter did Linux detect 68 -- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA 69 with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection 70 of chipsets is turned off by default as it's inherently unreliable due to 71 absolutely insane PC design. 72 73 "0 0F00 80x25" means that the first menu item (the menu items are numbered 74 from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the 75 next section for a description of mode IDs). 76 77 <flashing-cursor-here> encourages you to enter the item number or mode ID 78 you wish to set and press <RETURN>. If the computer complains something about 79 "Unknown mode ID", it is trying to tell you that it isn't possible to set such 80 a mode. It's also possible to press only <RETURN> which leaves the current mode. 81 82 The mode list usually contains a few basic modes and some VESA modes. In 83 case your chipset has been detected, some chipset-specific modes are shown as 84 well (some of these might be missing or unusable on your machine as different 85 BIOSes are often shipped with the same card and the mode numbers depend purely 86 on the VGA BIOS). 87 88 The modes displayed on the menu are partially sorted: The list starts with 89 the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and 90 80x43), local modes (if the local modes feature is enabled), VESA modes and 91 finally SVGA modes for the auto-detected adapter. 92 93 If you are not happy with the mode list offered (e.g., if you think your card 94 is able to do more), you can enter "scan" instead of item number / mode ID. The 95 program will try to ask the BIOS for all possible video mode numbers and test 96 what happens then. The screen will be probably flashing wildly for some time and 97 strange noises will be heard from inside the monitor and so on and then, really 98 all consistent video modes supported by your BIOS will appear (plus maybe some 99 ``ghost modes``). If you are afraid this could damage your monitor, don't use 100 this function. 101 102 After scanning, the mode ordering is a bit different: the auto-detected SVGA 103 modes are not listed at all and the modes revealed by ``scan`` are shown before 104 all VESA modes. 105 106 Mode IDs 107 ~~~~~~~~ 108 109 Because of the complexity of all the video stuff, the video mode IDs 110 used here are also a bit complex. A video mode ID is a 16-bit number usually 111 expressed in a hexadecimal notation (starting with "0x"). You can set a mode 112 by entering its mode directly if you know it even if it isn't shown on the menu. 113 114 The ID numbers can be divided to those regions:: 115 116 0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use 117 outside the menu as this can change from boot to boot (especially if you 118 have used the ``scan`` feature). 119 120 0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number 121 (as presented to INT 10, function 00) increased by 0x0100. 122 123 0x0200 to 0x08ff - VESA BIOS modes. The ID is a VESA mode ID increased by 124 0x0100. All VESA modes should be autodetected and shown on the menu. 125 126 0x0900 to 0x09ff - Video7 special modes. Set by calling INT 0x10, AX=0x6f05. 127 (Usually 940=80x43, 941=132x25, 942=132x44, 943=80x60, 944=100x60, 128 945=132x28 for the standard Video7 BIOS) 129 130 0x0f00 to 0x0fff - special modes (they are set by various tricks -- usually 131 by modifying one of the standard modes). Currently available: 132 0x0f00 standard 80x25, don't reset mode if already set (=FFFF) 133 0x0f01 standard with 8-point font: 80x43 on EGA, 80x50 on VGA 134 0x0f02 VGA 80x43 (VGA switched to 350 scanlines with a 8-point font) 135 0x0f03 VGA 80x28 (standard VGA scans, but 14-point font) 136 0x0f04 leave current video mode 137 0x0f05 VGA 80x30 (480 scans, 16-point font) 138 0x0f06 VGA 80x34 (480 scans, 14-point font) 139 0x0f07 VGA 80x60 (480 scans, 8-point font) 140 0x0f08 Graphics hack (see the VIDEO_GFX_HACK paragraph below) 141 142 0x1000 to 0x7fff - modes specified by resolution. The code has a "0xRRCC" 143 form where RR is a number of rows and CC is a number of columns. 144 E.g., 0x1950 corresponds to a 80x25 mode, 0x2b84 to 132x43 etc. 145 This is the only fully portable way to refer to a non-standard mode, 146 but it relies on the mode being found and displayed on the menu 147 (remember that mode scanning is not done automatically). 148 149 0xff00 to 0xffff - aliases for backward compatibility: 150 0xffff equivalent to 0x0f00 (standard 80x25) 151 0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50) 152 153 If you add 0x8000 to the mode ID, the program will try to recalculate 154 vertical display timing according to mode parameters, which can be used to 155 eliminate some annoying bugs of certain VGA BIOSes (usually those used for 156 cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the 157 end of the display. 158 159 Options 160 ~~~~~~~ 161 162 Build options for arch/x86/boot/* are selected by the kernel kconfig 163 utility and the kernel .config file. 164 165 VIDEO_GFX_HACK - includes special hack for setting of graphics modes 166 to be used later by special drivers. 167 Allows to set _any_ BIOS mode including graphic ones and forcing specific 168 text screen resolution instead of peeking it from BIOS variables. Don't use 169 unless you think you know what you're doing. To activate this setup, use 170 mode number 0x0f08 (see the Mode IDs section above). 171 172 Still doesn't work? 173 ~~~~~~~~~~~~~~~~~~~ 174 175 When the mode detection doesn't work (e.g., the mode list is incorrect or 176 the machine hangs instead of displaying the menu), try to switch off some of 177 the configuration options listed under "Options". If it fails, you can still use 178 your kernel with the video mode set directly via the kernel parameter. 179 180 In either case, please send me a bug report containing what _exactly_ 181 happens and how do the configuration switches affect the behaviour of the bug. 182 183 If you start Linux from M$-DOS, you might also use some DOS tools for 184 video mode setting. In this case, you must specify the 0x0f04 mode ("leave 185 current settings") to Linux, because if you don't and you use any non-standard 186 mode, Linux will switch to 80x25 automatically. 187 188 If you set some extended mode and there's one or more extra lines on the 189 bottom of the display containing already scrolled-out text, your VGA BIOS 190 contains the most common video BIOS bug called "incorrect vertical display 191 end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately, 192 this must be done manually -- no autodetection mechanisms are available. 193 194 History 195 ~~~~~~~ 196 197 =============== ================================================================ 198 1.0 (??-Nov-95) First version supporting all adapters supported by the old 199 setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels 200 and then removed due to instability on some machines. 201 2.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost 202 everything is configurable, the VESA support should be much more 203 stable, explicit mode numbering allowed, "scan" implemented etc. 204 2.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution 205 supported. Few bugs fixed. VESA modes are listed prior to 206 modes supplied by SVGA autodetection as they are more reliable. 207 CLGD autodetect works better. Doesn't depend on 80x25 being 208 active when started. Scanning fixed. 80x43 (any VGA) added. 209 Code cleaned up. 210 2.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX 211 VESA modes work now). Display end bug workaround supported. 212 Special modes renumbered to allow adding of the "recalculate" 213 flag, 0xffff and 0xfffe became aliases instead of real IDs. 214 Screen contents retained during mode changes. 215 2.3 (15-Mar-96) Changed to work with 1.3.74 kernel. 216 2.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem 217 with some boot loaders. Memory management rewritten to reflect 218 these changes. Unfortunately, screen contents retaining works 219 only with some loaders now. 220 Added a Tseng 132x60 mode. 221 2.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4. 222 2.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on 223 several cards with broken VESA code (e.g., ATI VGA). 224 2.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some 225 cards use very strange mode numbers. 226 - Added Realtek VGA modes (thanks to Gonzalo Tornaria). 227 - Hardware testing order slightly changed, tests based on ROM 228 contents done as first. 229 - Added support for special Video7 mode switching functions 230 (thanks to Tom Vander Aa). 231 - Added 480-scanline modes (especially useful for notebooks, 232 original version written by firstname.lastname@example.org, patched by 233 Jeff Chua, rewritten by me). 234 - Screen store/restore fixed. 235 2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. 236 - Better recognition of text modes during mode scan. 237 2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) 238 2.10(11-Nov-96) - The whole thing made optional. 239 - Added the CONFIG_VIDEO_400_HACK switch. 240 - Added the CONFIG_VIDEO_GFX_HACK switch. 241 - Code cleanup. 242 2.11(03-May-97) - Yet another cleanup, now including also the documentation. 243 - Direct testing of SVGA adapters turned off by default, ``scan`` 244 offered explicitly on the prompt line. 245 - Removed the doc section describing adding of new probing 246 functions as I try to get rid of _all_ hardware probing here. 247 2.12(25-May-98) Added support for VESA frame buffer graphics. 248 2.13(14-May-99) Minor documentation fixes. 249 =============== ================================================================