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aa4d5203 | 1 | .. include:: <isonum.txt> |
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3 | ================================= |
4 | Video Mode Selection Support 2.13 | |
5 | ================================= | |
6 | ||
7 | :Copyright: |copy| 1995--1999 Martin Mares, <mj@ucw.cz> | |
8 | ||
9 | Intro | |
10 | ~~~~~ | |
11 | ||
12 | This small document describes the "Video Mode Selection" feature which | |
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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 | ||
aa4d5203 | 17 | .. note:: |
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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 | |
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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 | |
aa4d5203 | 28 | of this parameter:: |
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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 | ||
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47 | Menu |
48 | ~~~~ | |
49 | ||
50 | The ASK_VGA mode causes the kernel to offer a video mode menu upon | |
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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 | ||
aa4d5203 | 56 | The menu looks like:: |
1da177e4 | 57 | |
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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> | |
1da177e4 | 66 | |
aa4d5203 | 67 | <name-of-detected-video-adapter> tells what video adapter did Linux detect |
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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 | ||
aa4d5203 | 74 | "0 0F00 80x25" means that the first menu item (the menu items are numbered |
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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 | ||
aa4d5203 | 78 | <flashing-cursor-here> encourages you to enter the item number or mode ID |
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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 | ||
aa4d5203 | 83 | The mode list usually contains a few basic modes and some VESA modes. In |
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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 | ||
aa4d5203 | 89 | The modes displayed on the menu are partially sorted: The list starts with |
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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 | ||
aa4d5203 | 94 | If you are not happy with the mode list offered (e.g., if you think your card |
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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 | |
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100 | ``ghost modes``). If you are afraid this could damage your monitor, don't use |
101 | this function. | |
1da177e4 | 102 | |
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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 | |
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105 | all VESA modes. |
106 | ||
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107 | Mode IDs |
108 | ~~~~~~~~ | |
109 | ||
110 | Because of the complexity of all the video stuff, the video mode IDs | |
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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 | ||
aa4d5203 | 115 | The ID numbers can be divided to those regions:: |
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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 | |
aa4d5203 | 119 | have used the ``scan`` feature). |
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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 | ||
aa4d5203 | 154 | If you add 0x8000 to the mode ID, the program will try to recalculate |
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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 | ||
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160 | Options |
161 | ~~~~~~~ | |
162 | ||
163 | Some options can be set in the source text (in arch/i386/boot/video.S). | |
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164 | All of them are simple #define's -- change them to #undef's when you want to |
165 | switch them off. Currently supported: | |
166 | ||
aa4d5203 | 167 | CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched |
1da177e4 | 168 | off by default as it's a bit unreliable due to terribly bad PC design. If you |
aa4d5203 | 169 | really want to have the adapter autodetected (maybe in case the ``scan`` feature |
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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 | ||
aa4d5203 | 174 | CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work |
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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 | ||
aa4d5203 | 178 | CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there |
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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 | ||
aa4d5203 | 184 | CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching |
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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 | ||
aa4d5203 | 189 | CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The |
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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 | ||
aa4d5203 | 196 | CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA |
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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 | ||
aa4d5203 | 201 | CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes |
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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 | ||
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209 | Still doesn't work? |
210 | ~~~~~~~~~~~~~~~~~~~ | |
211 | ||
212 | When the mode detection doesn't work (e.g., the mode list is incorrect or | |
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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 | ||
aa4d5203 | 217 | In either case, please send me a bug report containing what _exactly_ |
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218 | happens and how do the configuration switches affect the behaviour of the bug. |
219 | ||
aa4d5203 | 220 | If you start Linux from M$-DOS, you might also use some DOS tools for |
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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 | ||
aa4d5203 | 225 | If you set some extended mode and there's one or more extra lines on the |
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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 | ||
aa4d5203 | 231 | If you have a VGA card and your display still looks as on EGA, your BIOS |
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232 | is probably broken and you need to set the CONFIG_VIDEO_400_HACK switch to |
233 | force setting of the correct mode. | |
234 | ||
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235 | History |
236 | ~~~~~~~ | |
237 | ||
238 | =============== ================================================================ | |
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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 hhanemaa@cs.ruu.nl, patched by | |
274 | Jeff Chua, rewritten by me). | |
275 | - Screen store/restore fixed. | |
aa4d5203 | 276 | 2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. |
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277 | - Better recognition of text modes during mode scan. |
278 | 2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) | |
aa4d5203 | 279 | 2.10(11-Nov-96) - The whole thing made optional. |
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280 | - Added the CONFIG_VIDEO_400_HACK switch. |
281 | - Added the CONFIG_VIDEO_GFX_HACK switch. | |
282 | - Code cleanup. | |
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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`` | |
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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. | |
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288 | 2.12(25-May-98) Added support for VESA frame buffer graphics. |
289 | 2.13(14-May-99) Minor documentation fixes. | |
290 | =============== ================================================================ |