Based on kernel version 4.3. Page generated on 2015-11-02 12:51 EST.
1 Video Mode Selection Support 2.13 2 (c) 1995--1999 Martin Mares, <firstname.lastname@example.org> 3 -------------------------------------------------------------------------------- 4 5 1. Intro 6 ~~~~~~~~ 7 This small document describes the "Video Mode Selection" feature which 8 allows the use of various special video modes supported by the video BIOS. Due 9 to usage of the BIOS, the selection is limited to boot time (before the 10 kernel decompression starts) and works only on 80X86 machines. 11 12 ** Short intro for the impatient: Just use vga=ask for the first time, 13 ** enter `scan' on the video mode prompt, pick the mode you want to use, 14 ** remember its mode ID (the four-digit hexadecimal number) and then 15 ** set the vga parameter to this number (converted to decimal first). 16 17 The video mode to be used is selected by a kernel parameter which can be 18 specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..." 19 option of LILO (or some other boot loader you use) or by the "vidmode" utility 20 (present in standard Linux utility packages). You can use the following values 21 of this parameter: 22 23 NORMAL_VGA - Standard 80x25 mode available on all display adapters. 24 25 EXTENDED_VGA - Standard 8-pixel font mode: 80x43 on EGA, 80x50 on VGA. 26 27 ASK_VGA - Display a video mode menu upon startup (see below). 28 29 0..35 - Menu item number (when you have used the menu to view the list of 30 modes available on your adapter, you can specify the menu item you want 31 to use). 0..9 correspond to "0".."9", 10..35 to "a".."z". Warning: the 32 mode list displayed may vary as the kernel version changes, because the 33 modes are listed in a "first detected -- first displayed" manner. It's 34 better to use absolute mode numbers instead. 35 36 0x.... - Hexadecimal video mode ID (also displayed on the menu, see below 37 for exact meaning of the ID). Warning: rdev and LILO don't support 38 hexadecimal numbers -- you have to convert it to decimal manually. 39 40 2. Menu 41 ~~~~~~~ 42 The ASK_VGA mode causes the kernel to offer a video mode menu upon 43 bootup. It displays a "Press <RETURN> to see video modes available, <SPACE> 44 to continue or wait 30 secs" message. If you press <RETURN>, you enter the 45 menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in 46 the standard 80x25 mode. 47 48 The menu looks like: 49 50 Video adapter: <name-of-detected-video-adapter> 51 Mode: COLSxROWS: 52 0 0F00 80x25 53 1 0F01 80x50 54 2 0F02 80x43 55 3 0F03 80x26 56 .... 57 Enter mode number or `scan': <flashing-cursor-here> 58 59 <name-of-detected-video-adapter> tells what video adapter did Linux detect 60 -- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA 61 with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection 62 of chipsets is turned off by default (see CONFIG_VIDEO_SVGA in chapter 4 to see 63 how to enable it if you really want) as it's inherently unreliable due to 64 absolutely insane PC design. 65 66 "0 0F00 80x25" means that the first menu item (the menu items are numbered 67 from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the 68 next section for a description of mode IDs). 69 70 <flashing-cursor-here> encourages you to enter the item number or mode ID 71 you wish to set and press <RETURN>. If the computer complains something about 72 "Unknown mode ID", it is trying to tell you that it isn't possible to set such 73 a mode. It's also possible to press only <RETURN> which leaves the current mode. 74 75 The mode list usually contains a few basic modes and some VESA modes. In 76 case your chipset has been detected, some chipset-specific modes are shown as 77 well (some of these might be missing or unusable on your machine as different 78 BIOSes are often shipped with the same card and the mode numbers depend purely 79 on the VGA BIOS). 80 81 The modes displayed on the menu are partially sorted: The list starts with 82 the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and 83 80x43), local modes (if the local modes feature is enabled), VESA modes and 84 finally SVGA modes for the auto-detected adapter. 85 86 If you are not happy with the mode list offered (e.g., if you think your card 87 is able to do more), you can enter "scan" instead of item number / mode ID. The 88 program will try to ask the BIOS for all possible video mode numbers and test 89 what happens then. The screen will be probably flashing wildly for some time and 90 strange noises will be heard from inside the monitor and so on and then, really 91 all consistent video modes supported by your BIOS will appear (plus maybe some 92 `ghost modes'). If you are afraid this could damage your monitor, don't use this 93 function. 94 95 After scanning, the mode ordering is a bit different: the auto-detected SVGA 96 modes are not listed at all and the modes revealed by `scan' are shown before 97 all VESA modes. 98 99 3. Mode IDs 100 ~~~~~~~~~~~ 101 Because of the complexity of all the video stuff, the video mode IDs 102 used here are also a bit complex. A video mode ID is a 16-bit number usually 103 expressed in a hexadecimal notation (starting with "0x"). You can set a mode 104 by entering its mode directly if you know it even if it isn't shown on the menu. 105 106 The ID numbers can be divided to three regions: 107 108 0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use 109 outside the menu as this can change from boot to boot (especially if you 110 have used the `scan' feature). 111 112 0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number 113 (as presented to INT 10, function 00) increased by 0x0100. 114 115 0x0200 to 0x08ff - VESA BIOS modes. The ID is a VESA mode ID increased by 116 0x0100. All VESA modes should be autodetected and shown on the menu. 117 118 0x0900 to 0x09ff - Video7 special modes. Set by calling INT 0x10, AX=0x6f05. 119 (Usually 940=80x43, 941=132x25, 942=132x44, 943=80x60, 944=100x60, 120 945=132x28 for the standard Video7 BIOS) 121 122 0x0f00 to 0x0fff - special modes (they are set by various tricks -- usually 123 by modifying one of the standard modes). Currently available: 124 0x0f00 standard 80x25, don't reset mode if already set (=FFFF) 125 0x0f01 standard with 8-point font: 80x43 on EGA, 80x50 on VGA 126 0x0f02 VGA 80x43 (VGA switched to 350 scanlines with a 8-point font) 127 0x0f03 VGA 80x28 (standard VGA scans, but 14-point font) 128 0x0f04 leave current video mode 129 0x0f05 VGA 80x30 (480 scans, 16-point font) 130 0x0f06 VGA 80x34 (480 scans, 14-point font) 131 0x0f07 VGA 80x60 (480 scans, 8-point font) 132 0x0f08 Graphics hack (see the CONFIG_VIDEO_HACK paragraph below) 133 134 0x1000 to 0x7fff - modes specified by resolution. The code has a "0xRRCC" 135 form where RR is a number of rows and CC is a number of columns. 136 E.g., 0x1950 corresponds to a 80x25 mode, 0x2b84 to 132x43 etc. 137 This is the only fully portable way to refer to a non-standard mode, 138 but it relies on the mode being found and displayed on the menu 139 (remember that mode scanning is not done automatically). 140 141 0xff00 to 0xffff - aliases for backward compatibility: 142 0xffff equivalent to 0x0f00 (standard 80x25) 143 0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50) 144 145 If you add 0x8000 to the mode ID, the program will try to recalculate 146 vertical display timing according to mode parameters, which can be used to 147 eliminate some annoying bugs of certain VGA BIOSes (usually those used for 148 cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the 149 end of the display. 150 151 4. Options 152 ~~~~~~~~~~ 153 Some options can be set in the source text (in arch/i386/boot/video.S). 154 All of them are simple #define's -- change them to #undef's when you want to 155 switch them off. Currently supported: 156 157 CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched 158 off by default as it's a bit unreliable due to terribly bad PC design. If you 159 really want to have the adapter autodetected (maybe in case the `scan' feature 160 doesn't work on your machine), switch this on and don't cry if the results 161 are not completely sane. In case you really need this feature, please drop me 162 a mail as I think of removing it some day. 163 164 CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work 165 on your machine (or displays a "Error: Scanning of VESA modes failed" message), 166 you can switch it off and report as a bug. 167 168 CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there 169 are more modes with the same screen size, only the first one is kept (see above 170 for more info on mode ordering). However, in very strange cases it's possible 171 that the first "version" of the mode doesn't work although some of the others 172 do -- in this case turn this switch off to see the rest. 173 174 CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching 175 video modes. Works only with some boot loaders which leave enough room for the 176 buffer. (If you have old LILO, you can adjust heap_end_ptr and loadflags 177 in setup.S, but it's better to upgrade the boot loader...) 178 179 CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The 180 local modes are added automatically to the beginning of the list not depending 181 on hardware configuration. The local modes are listed in the source text after 182 the "local_mode_table:" line. The comment before this line describes the format 183 of the table (which also includes a video card name to be displayed on the 184 top of the menu). 185 186 CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA 187 modes. This option is intended to be used on certain buggy BIOSes which draw 188 some useless logo using font download and then fail to reset the correct mode. 189 Don't use unless needed as it forces resetting the video card. 190 191 CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes 192 to be used later by special drivers (e.g., 800x600 on IBM ThinkPad -- see 193 ftp://ftp.phys.keio.ac.jp/pub/XFree86/800x600/XF86Configs/XF86Config.IBM_TP560). 194 Allows to set _any_ BIOS mode including graphic ones and forcing specific 195 text screen resolution instead of peeking it from BIOS variables. Don't use 196 unless you think you know what you're doing. To activate this setup, use 197 mode number 0x0f08 (see section 3). 198 199 5. Still doesn't work? 200 ~~~~~~~~~~~~~~~~~~~~~~ 201 When the mode detection doesn't work (e.g., the mode list is incorrect or 202 the machine hangs instead of displaying the menu), try to switch off some of 203 the configuration options listed in section 4. If it fails, you can still use 204 your kernel with the video mode set directly via the kernel parameter. 205 206 In either case, please send me a bug report containing what _exactly_ 207 happens and how do the configuration switches affect the behaviour of the bug. 208 209 If you start Linux from M$-DOS, you might also use some DOS tools for 210 video mode setting. In this case, you must specify the 0x0f04 mode ("leave 211 current settings") to Linux, because if you don't and you use any non-standard 212 mode, Linux will switch to 80x25 automatically. 213 214 If you set some extended mode and there's one or more extra lines on the 215 bottom of the display containing already scrolled-out text, your VGA BIOS 216 contains the most common video BIOS bug called "incorrect vertical display 217 end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately, 218 this must be done manually -- no autodetection mechanisms are available. 219 220 If you have a VGA card and your display still looks as on EGA, your BIOS 221 is probably broken and you need to set the CONFIG_VIDEO_400_HACK switch to 222 force setting of the correct mode. 223 224 6. History 225 ~~~~~~~~~~ 226 1.0 (??-Nov-95) First version supporting all adapters supported by the old 227 setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels 228 and then removed due to instability on some machines. 229 2.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost 230 everything is configurable, the VESA support should be much more 231 stable, explicit mode numbering allowed, "scan" implemented etc. 232 2.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution 233 supported. Few bugs fixed. VESA modes are listed prior to 234 modes supplied by SVGA autodetection as they are more reliable. 235 CLGD autodetect works better. Doesn't depend on 80x25 being 236 active when started. Scanning fixed. 80x43 (any VGA) added. 237 Code cleaned up. 238 2.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX 239 VESA modes work now). Display end bug workaround supported. 240 Special modes renumbered to allow adding of the "recalculate" 241 flag, 0xffff and 0xfffe became aliases instead of real IDs. 242 Screen contents retained during mode changes. 243 2.3 (15-Mar-96) Changed to work with 1.3.74 kernel. 244 2.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem 245 with some boot loaders. Memory management rewritten to reflect 246 these changes. Unfortunately, screen contents retaining works 247 only with some loaders now. 248 Added a Tseng 132x60 mode. 249 2.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4. 250 2.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on 251 several cards with broken VESA code (e.g., ATI VGA). 252 2.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some 253 cards use very strange mode numbers. 254 - Added Realtek VGA modes (thanks to Gonzalo Tornaria). 255 - Hardware testing order slightly changed, tests based on ROM 256 contents done as first. 257 - Added support for special Video7 mode switching functions 258 (thanks to Tom Vander Aa). 259 - Added 480-scanline modes (especially useful for notebooks, 260 original version written by email@example.com, patched by 261 Jeff Chua, rewritten by me). 262 - Screen store/restore fixed. 263 2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. 264 - Better recognition of text modes during mode scan. 265 2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) 266 2.10 (11-Nov-96)- The whole thing made optional. 267 - Added the CONFIG_VIDEO_400_HACK switch. 268 - Added the CONFIG_VIDEO_GFX_HACK switch. 269 - Code cleanup. 270 2.11 (03-May-97)- Yet another cleanup, now including also the documentation. 271 - Direct testing of SVGA adapters turned off by default, `scan' 272 offered explicitly on the prompt line. 273 - Removed the doc section describing adding of new probing 274 functions as I try to get rid of _all_ hardware probing here. 275 2.12 (25-May-98)- Added support for VESA frame buffer graphics. 276 2.13 (14-May-99)- Minor documentation fixes.