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1 | Video Mode Selection Support 2.13 | ||
2 | (c) 1995--1999 Martin Mares, <mj@ucw.cz> | ||
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 hhanemaa@cs.ruu.nl, 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. | ||