Based on kernel version 4.13.3. Page generated on 2017-09-23 13:56 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 (see CONFIG_VIDEO_SVGA in chapter 4 to see 71 how to enable it if you really want) as it's inherently unreliable due to 72 absolutely insane PC design. 73 74 "0 0F00 80x25" means that the first menu item (the menu items are numbered 75 from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the 76 next section for a description of mode IDs). 77 78 <flashing-cursor-here> encourages you to enter the item number or mode ID 79 you 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 81 a mode. It's also possible to press only <RETURN> which leaves the current mode. 82 83 The mode list usually contains a few basic modes and some VESA modes. In 84 case your chipset has been detected, some chipset-specific modes are shown as 85 well (some of these might be missing or unusable on your machine as different 86 BIOSes are often shipped with the same card and the mode numbers depend purely 87 on the VGA BIOS). 88 89 The modes displayed on the menu are partially sorted: The list starts with 90 the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and 91 80x43), local modes (if the local modes feature is enabled), VESA modes and 92 finally SVGA modes for the auto-detected adapter. 93 94 If you are not happy with the mode list offered (e.g., if you think your card 95 is able to do more), you can enter "scan" instead of item number / mode ID. The 96 program will try to ask the BIOS for all possible video mode numbers and test 97 what happens then. The screen will be probably flashing wildly for some time and 98 strange noises will be heard from inside the monitor and so on and then, really 99 all 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 101 this function. 102 103 After scanning, the mode ordering is a bit different: the auto-detected SVGA 104 modes are not listed at all and the modes revealed by ``scan`` are shown before 105 all VESA modes. 106 107 Mode IDs 108 ~~~~~~~~ 109 110 Because of the complexity of all the video stuff, the video mode IDs 111 used here are also a bit complex. A video mode ID is a 16-bit number usually 112 expressed in a hexadecimal notation (starting with "0x"). You can set a mode 113 by entering its mode directly if you know it even if it isn't shown on the menu. 114 115 The 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 CONFIG_VIDEO_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) 153 154 If you add 0x8000 to the mode ID, the program will try to recalculate 155 vertical display timing according to mode parameters, which can be used to 156 eliminate some annoying bugs of certain VGA BIOSes (usually those used for 157 cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the 158 end of the display. 159 160 Options 161 ~~~~~~~ 162 163 Some options can be set in the source text (in arch/i386/boot/video.S). 164 All of them are simple #define's -- change them to #undef's when you want to 165 switch them off. Currently supported: 166 167 CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched 168 off by default as it's a bit unreliable due to terribly bad PC design. If you 169 really want to have the adapter autodetected (maybe in case the ``scan`` feature 170 doesn't work on your machine), switch this on and don't cry if the results 171 are not completely sane. In case you really need this feature, please drop me 172 a mail as I think of removing it some day. 173 174 CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work 175 on your machine (or displays a "Error: Scanning of VESA modes failed" message), 176 you can switch it off and report as a bug. 177 178 CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there 179 are more modes with the same screen size, only the first one is kept (see above 180 for more info on mode ordering). However, in very strange cases it's possible 181 that the first "version" of the mode doesn't work although some of the others 182 do -- in this case turn this switch off to see the rest. 183 184 CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching 185 video modes. Works only with some boot loaders which leave enough room for the 186 buffer. (If you have old LILO, you can adjust heap_end_ptr and loadflags 187 in setup.S, but it's better to upgrade the boot loader...) 188 189 CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The 190 local modes are added automatically to the beginning of the list not depending 191 on hardware configuration. The local modes are listed in the source text after 192 the "local_mode_table:" line. The comment before this line describes the format 193 of the table (which also includes a video card name to be displayed on the 194 top of the menu). 195 196 CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA 197 modes. This option is intended to be used on certain buggy BIOSes which draw 198 some useless logo using font download and then fail to reset the correct mode. 199 Don't use unless needed as it forces resetting the video card. 200 201 CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes 202 to be used later by special drivers (e.g., 800x600 on IBM ThinkPad -- see 203 ftp://ftp.phys.keio.ac.jp/pub/XFree86/800x600/XF86Configs/XF86Config.IBM_TP560). 204 Allows to set _any_ BIOS mode including graphic ones and forcing specific 205 text screen resolution instead of peeking it from BIOS variables. Don't use 206 unless you think you know what you're doing. To activate this setup, use 207 mode number 0x0f08 (see section 3). 208 209 Still doesn't work? 210 ~~~~~~~~~~~~~~~~~~~ 211 212 When the mode detection doesn't work (e.g., the mode list is incorrect or 213 the machine hangs instead of displaying the menu), try to switch off some of 214 the configuration options listed in section 4. If it fails, you can still use 215 your kernel with the video mode set directly via the kernel parameter. 216 217 In either case, please send me a bug report containing what _exactly_ 218 happens and how do the configuration switches affect the behaviour of the bug. 219 220 If you start Linux from M$-DOS, you might also use some DOS tools for 221 video mode setting. In this case, you must specify the 0x0f04 mode ("leave 222 current settings") to Linux, because if you don't and you use any non-standard 223 mode, Linux will switch to 80x25 automatically. 224 225 If you set some extended mode and there's one or more extra lines on the 226 bottom of the display containing already scrolled-out text, your VGA BIOS 227 contains the most common video BIOS bug called "incorrect vertical display 228 end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately, 229 this must be done manually -- no autodetection mechanisms are available. 230 231 If you have a VGA card and your display still looks as on EGA, your BIOS 232 is probably broken and you need to set the CONFIG_VIDEO_400_HACK switch to 233 force setting of the correct mode. 234 235 History 236 ~~~~~~~ 237 238 =============== ================================================================ 239 1.0 (??-Nov-95) First version supporting all adapters supported by the old 240 setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels 241 and then removed due to instability on some machines. 242 2.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost 243 everything is configurable, the VESA support should be much more 244 stable, explicit mode numbering allowed, "scan" implemented etc. 245 2.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution 246 supported. Few bugs fixed. VESA modes are listed prior to 247 modes supplied by SVGA autodetection as they are more reliable. 248 CLGD autodetect works better. Doesn't depend on 80x25 being 249 active when started. Scanning fixed. 80x43 (any VGA) added. 250 Code cleaned up. 251 2.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX 252 VESA modes work now). Display end bug workaround supported. 253 Special modes renumbered to allow adding of the "recalculate" 254 flag, 0xffff and 0xfffe became aliases instead of real IDs. 255 Screen contents retained during mode changes. 256 2.3 (15-Mar-96) Changed to work with 1.3.74 kernel. 257 2.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem 258 with some boot loaders. Memory management rewritten to reflect 259 these changes. Unfortunately, screen contents retaining works 260 only with some loaders now. 261 Added a Tseng 132x60 mode. 262 2.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4. 263 2.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on 264 several cards with broken VESA code (e.g., ATI VGA). 265 2.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some 266 cards use very strange mode numbers. 267 - Added Realtek VGA modes (thanks to Gonzalo Tornaria). 268 - Hardware testing order slightly changed, tests based on ROM 269 contents done as first. 270 - Added support for special Video7 mode switching functions 271 (thanks to Tom Vander Aa). 272 - Added 480-scanline modes (especially useful for notebooks, 273 original version written by firstname.lastname@example.org, patched by 274 Jeff Chua, rewritten by me). 275 - Screen store/restore fixed. 276 2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. 277 - Better recognition of text modes during mode scan. 278 2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) 279 2.10(11-Nov-96) - The whole thing made optional. 280 - Added the CONFIG_VIDEO_400_HACK switch. 281 - Added the CONFIG_VIDEO_GFX_HACK switch. 282 - Code cleanup. 283 2.11(03-May-97) - Yet another cleanup, now including also the documentation. 284 - Direct testing of SVGA adapters turned off by default, ``scan`` 285 offered explicitly on the prompt line. 286 - Removed the doc section describing adding of new probing 287 functions as I try to get rid of _all_ hardware probing here. 288 2.12(25-May-98) Added support for VESA frame buffer graphics. 289 2.13(14-May-99) Minor documentation fixes. 290 =============== ================================================================