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Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03001.. include:: <isonum.txt>
Linus Torvalds1da177e2005-04-16 15:20:36 -07002
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03003=================================
4Video Mode Selection Support 2.13
5=================================
6
7:Copyright: |copy| 1995--1999 Martin Mares, <mj@ucw.cz>
8
9Intro
10~~~~~
11
12This small document describes the "Video Mode Selection" feature which
Linus Torvalds1da177e2005-04-16 15:20:36 -070013allows the use of various special video modes supported by the video BIOS. Due
14to usage of the BIOS, the selection is limited to boot time (before the
15kernel decompression starts) and works only on 80X86 machines.
16
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030017.. note::
Linus Torvalds1da177e2005-04-16 15:20:36 -070018
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030019 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
24The video mode to be used is selected by a kernel parameter which can be
Linus Torvalds1da177e2005-04-16 15:20:36 -070025specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..."
26option 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
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030028of this parameter::
Linus Torvalds1da177e2005-04-16 15:20:36 -070029
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
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030047Menu
48~~~~
49
50The ASK_VGA mode causes the kernel to offer a video mode menu upon
Linus Torvalds1da177e2005-04-16 15:20:36 -070051bootup. It displays a "Press <RETURN> to see video modes available, <SPACE>
52to continue or wait 30 secs" message. If you press <RETURN>, you enter the
53menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in
54the standard 80x25 mode.
55
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030056The menu looks like::
Linus Torvalds1da177e2005-04-16 15:20:36 -070057
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030058 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>
Linus Torvalds1da177e2005-04-16 15:20:36 -070066
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030067<name-of-detected-video-adapter> tells what video adapter did Linux detect
Linus Torvalds1da177e2005-04-16 15:20:36 -070068-- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA
69with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection
Randy Dunlap0cf9bb62017-11-19 10:02:20 -080070of chipsets is turned off by default as it's inherently unreliable due to
Linus Torvalds1da177e2005-04-16 15:20:36 -070071absolutely insane PC design.
72
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030073"0 0F00 80x25" means that the first menu item (the menu items are numbered
Linus Torvalds1da177e2005-04-16 15:20:36 -070074from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the
75next section for a description of mode IDs).
76
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030077<flashing-cursor-here> encourages you to enter the item number or mode ID
Linus Torvalds1da177e2005-04-16 15:20:36 -070078you 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
80a mode. It's also possible to press only <RETURN> which leaves the current mode.
81
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030082The mode list usually contains a few basic modes and some VESA modes. In
Linus Torvalds1da177e2005-04-16 15:20:36 -070083case your chipset has been detected, some chipset-specific modes are shown as
84well (some of these might be missing or unusable on your machine as different
85BIOSes are often shipped with the same card and the mode numbers depend purely
86on the VGA BIOS).
87
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030088The modes displayed on the menu are partially sorted: The list starts with
Linus Torvalds1da177e2005-04-16 15:20:36 -070089the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and
9080x43), local modes (if the local modes feature is enabled), VESA modes and
91finally SVGA modes for the auto-detected adapter.
92
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030093If you are not happy with the mode list offered (e.g., if you think your card
Linus Torvalds1da177e2005-04-16 15:20:36 -070094is able to do more), you can enter "scan" instead of item number / mode ID. The
95program will try to ask the BIOS for all possible video mode numbers and test
96what happens then. The screen will be probably flashing wildly for some time and
97strange noises will be heard from inside the monitor and so on and then, really
98all consistent video modes supported by your BIOS will appear (plus maybe some
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -030099``ghost modes``). If you are afraid this could damage your monitor, don't use
100this function.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700101
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300102After scanning, the mode ordering is a bit different: the auto-detected SVGA
103modes are not listed at all and the modes revealed by ``scan`` are shown before
Linus Torvalds1da177e2005-04-16 15:20:36 -0700104all VESA modes.
105
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300106Mode IDs
107~~~~~~~~
108
109Because of the complexity of all the video stuff, the video mode IDs
Linus Torvalds1da177e2005-04-16 15:20:36 -0700110used here are also a bit complex. A video mode ID is a 16-bit number usually
111expressed in a hexadecimal notation (starting with "0x"). You can set a mode
112by entering its mode directly if you know it even if it isn't shown on the menu.
113
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300114The ID numbers can be divided to those regions::
Linus Torvalds1da177e2005-04-16 15:20:36 -0700115
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
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300118 have used the ``scan`` feature).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700119
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)
Randy Dunlap0cf9bb62017-11-19 10:02:20 -0800140 0x0f08 Graphics hack (see the VIDEO_GFX_HACK paragraph below)
Linus Torvalds1da177e2005-04-16 15:20:36 -0700141
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
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300153If you add 0x8000 to the mode ID, the program will try to recalculate
Linus Torvalds1da177e2005-04-16 15:20:36 -0700154vertical display timing according to mode parameters, which can be used to
155eliminate some annoying bugs of certain VGA BIOSes (usually those used for
156cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the
157end of the display.
158
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300159Options
160~~~~~~~
161
Randy Dunlap0cf9bb62017-11-19 10:02:20 -0800162Build options for arch/x86/boot/* are selected by the kernel kconfig
163utility and the kernel .config file.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700164
Randy Dunlap0cf9bb62017-11-19 10:02:20 -0800165VIDEO_GFX_HACK - includes special hack for setting of graphics modes
166to be used later by special drivers.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700167Allows to set _any_ BIOS mode including graphic ones and forcing specific
168text screen resolution instead of peeking it from BIOS variables. Don't use
169unless you think you know what you're doing. To activate this setup, use
Randy Dunlap0cf9bb62017-11-19 10:02:20 -0800170mode number 0x0f08 (see the Mode IDs section above).
Linus Torvalds1da177e2005-04-16 15:20:36 -0700171
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300172Still doesn't work?
173~~~~~~~~~~~~~~~~~~~
174
175When the mode detection doesn't work (e.g., the mode list is incorrect or
Linus Torvalds1da177e2005-04-16 15:20:36 -0700176the machine hangs instead of displaying the menu), try to switch off some of
Randy Dunlap0cf9bb62017-11-19 10:02:20 -0800177the configuration options listed under "Options". If it fails, you can still use
Linus Torvalds1da177e2005-04-16 15:20:36 -0700178your kernel with the video mode set directly via the kernel parameter.
179
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300180In either case, please send me a bug report containing what _exactly_
Linus Torvalds1da177e2005-04-16 15:20:36 -0700181happens and how do the configuration switches affect the behaviour of the bug.
182
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300183If you start Linux from M$-DOS, you might also use some DOS tools for
Linus Torvalds1da177e2005-04-16 15:20:36 -0700184video mode setting. In this case, you must specify the 0x0f04 mode ("leave
185current settings") to Linux, because if you don't and you use any non-standard
186mode, Linux will switch to 80x25 automatically.
187
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300188If you set some extended mode and there's one or more extra lines on the
Linus Torvalds1da177e2005-04-16 15:20:36 -0700189bottom of the display containing already scrolled-out text, your VGA BIOS
190contains the most common video BIOS bug called "incorrect vertical display
191end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately,
192this must be done manually -- no autodetection mechanisms are available.
193
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -0300194History
195~~~~~~~
196
197=============== ================================================================
Linus Torvalds1da177e2005-04-16 15:20:36 -07001981.0 (??-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.
2012.0 (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.
2042.1 (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.
2102.2 (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.
2152.3 (15-Mar-96) Changed to work with 1.3.74 kernel.
2162.4 (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.
2212.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4.
2222.6 (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).
2242.7 (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 hhanemaa@cs.ruu.nl, patched by
233 Jeff Chua, rewritten by me).
234 - Screen store/restore fixed.
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03002352.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700236 - Better recognition of text modes during mode scan.
2372.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!)
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03002382.10(11-Nov-96) - The whole thing made optional.
Linus Torvalds1da177e2005-04-16 15:20:36 -0700239 - Added the CONFIG_VIDEO_400_HACK switch.
240 - Added the CONFIG_VIDEO_GFX_HACK switch.
241 - Code cleanup.
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03002422.11(03-May-97) - Yet another cleanup, now including also the documentation.
243 - Direct testing of SVGA adapters turned off by default, ``scan``
Linus Torvalds1da177e2005-04-16 15:20:36 -0700244 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.
Mauro Carvalho Chehabaa4d5202017-05-17 09:00:17 -03002472.12(25-May-98) Added support for VESA frame buffer graphics.
2482.13(14-May-99) Minor documentation fixes.
249=============== ================================================================