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diff --git a/Documentation/svga.txt b/Documentation/svga.txt new file mode 100644 index 000000000000..cd66ec836e4f --- /dev/null +++ b/Documentation/svga.txt @@ -0,0 +1,276 @@ + Video Mode Selection Support 2.13 + (c) 1995--1999 Martin Mares, <mj@ucw.cz> +-------------------------------------------------------------------------------- + +1. Intro +~~~~~~~~ + This small document describes the "Video Mode Selection" feature which +allows the use of various special video modes supported by the video BIOS. Due +to usage of the BIOS, the selection is limited to boot time (before the +kernel decompression starts) and works only on 80X86 machines. + + ** Short intro for the impatient: Just use vga=ask for the first time, + ** enter `scan' on the video mode prompt, pick the mode you want to use, + ** remember its mode ID (the four-digit hexadecimal number) and then + ** set the vga parameter to this number (converted to decimal first). + + The video mode to be used is selected by a kernel parameter which can be +specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..." +option of LILO (or some other boot loader you use) or by the "vidmode" utility +(present in standard Linux utility packages). You can use the following values +of this parameter: + + NORMAL_VGA - Standard 80x25 mode available on all display adapters. + + EXTENDED_VGA - Standard 8-pixel font mode: 80x43 on EGA, 80x50 on VGA. + + ASK_VGA - Display a video mode menu upon startup (see below). + + 0..35 - Menu item number (when you have used the menu to view the list of + modes available on your adapter, you can specify the menu item you want + to use). 0..9 correspond to "0".."9", 10..35 to "a".."z". Warning: the + mode list displayed may vary as the kernel version changes, because the + modes are listed in a "first detected -- first displayed" manner. It's + better to use absolute mode numbers instead. + + 0x.... - Hexadecimal video mode ID (also displayed on the menu, see below + for exact meaning of the ID). Warning: rdev and LILO don't support + hexadecimal numbers -- you have to convert it to decimal manually. + +2. Menu +~~~~~~~ + The ASK_VGA mode causes the kernel to offer a video mode menu upon +bootup. It displays a "Press <RETURN> to see video modes available, <SPACE> +to continue or wait 30 secs" message. If you press <RETURN>, you enter the +menu, if you press <SPACE> or wait 30 seconds, the kernel will boot up in +the standard 80x25 mode. + + The menu looks like: + +Video adapter: <name-of-detected-video-adapter> +Mode: COLSxROWS: +0 0F00 80x25 +1 0F01 80x50 +2 0F02 80x43 +3 0F03 80x26 +.... +Enter mode number or `scan': <flashing-cursor-here> + + <name-of-detected-video-adapter> tells what video adapter did Linux detect +-- it's either a generic adapter name (MDA, CGA, HGC, EGA, VGA, VESA VGA [a VGA +with VESA-compliant BIOS]) or a chipset name (e.g., Trident). Direct detection +of chipsets is turned off by default (see CONFIG_VIDEO_SVGA in chapter 4 to see +how to enable it if you really want) as it's inherently unreliable due to +absolutely insane PC design. + + "0 0F00 80x25" means that the first menu item (the menu items are numbered +from "0" to "9" and from "a" to "z") is a 80x25 mode with ID=0x0f00 (see the +next section for a description of mode IDs). + + <flashing-cursor-here> encourages you to enter the item number or mode ID +you wish to set and press <RETURN>. If the computer complains something about +"Unknown mode ID", it is trying to tell you that it isn't possible to set such +a mode. It's also possible to press only <RETURN> which leaves the current mode. + + The mode list usually contains a few basic modes and some VESA modes. In +case your chipset has been detected, some chipset-specific modes are shown as +well (some of these might be missing or unusable on your machine as different +BIOSes are often shipped with the same card and the mode numbers depend purely +on the VGA BIOS). + + The modes displayed on the menu are partially sorted: The list starts with +the standard modes (80x25 and 80x50) followed by "special" modes (80x28 and +80x43), local modes (if the local modes feature is enabled), VESA modes and +finally SVGA modes for the auto-detected adapter. + + If you are not happy with the mode list offered (e.g., if you think your card +is able to do more), you can enter "scan" instead of item number / mode ID. The +program will try to ask the BIOS for all possible video mode numbers and test +what happens then. The screen will be probably flashing wildly for some time and +strange noises will be heard from inside the monitor and so on and then, really +all consistent video modes supported by your BIOS will appear (plus maybe some +`ghost modes'). If you are afraid this could damage your monitor, don't use this +function. + + After scanning, the mode ordering is a bit different: the auto-detected SVGA +modes are not listed at all and the modes revealed by `scan' are shown before +all VESA modes. + +3. Mode IDs +~~~~~~~~~~~ + Because of the complexity of all the video stuff, the video mode IDs +used here are also a bit complex. A video mode ID is a 16-bit number usually +expressed in a hexadecimal notation (starting with "0x"). You can set a mode +by entering its mode directly if you know it even if it isn't shown on the menu. + +The ID numbers can be divided to three regions: + + 0x0000 to 0x00ff - menu item references. 0x0000 is the first item. Don't use + outside the menu as this can change from boot to boot (especially if you + have used the `scan' feature). + + 0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number + (as presented to INT 10, function 00) increased by 0x0100. + + 0x0200 to 0x08ff - VESA BIOS modes. The ID is a VESA mode ID increased by + 0x0100. All VESA modes should be autodetected and shown on the menu. + + 0x0900 to 0x09ff - Video7 special modes. Set by calling INT 0x10, AX=0x6f05. + (Usually 940=80x43, 941=132x25, 942=132x44, 943=80x60, 944=100x60, + 945=132x28 for the standard Video7 BIOS) + + 0x0f00 to 0x0fff - special modes (they are set by various tricks -- usually + by modifying one of the standard modes). Currently available: + 0x0f00 standard 80x25, don't reset mode if already set (=FFFF) + 0x0f01 standard with 8-point font: 80x43 on EGA, 80x50 on VGA + 0x0f02 VGA 80x43 (VGA switched to 350 scanlines with a 8-point font) + 0x0f03 VGA 80x28 (standard VGA scans, but 14-point font) + 0x0f04 leave current video mode + 0x0f05 VGA 80x30 (480 scans, 16-point font) + 0x0f06 VGA 80x34 (480 scans, 14-point font) + 0x0f07 VGA 80x60 (480 scans, 8-point font) + 0x0f08 Graphics hack (see the CONFIG_VIDEO_HACK paragraph below) + + 0x1000 to 0x7fff - modes specified by resolution. The code has a "0xRRCC" + form where RR is a number of rows and CC is a number of columns. + E.g., 0x1950 corresponds to a 80x25 mode, 0x2b84 to 132x43 etc. + This is the only fully portable way to refer to a non-standard mode, + but it relies on the mode being found and displayed on the menu + (remember that mode scanning is not done automatically). + + 0xff00 to 0xffff - aliases for backward compatibility: + 0xffff equivalent to 0x0f00 (standard 80x25) + 0xfffe equivalent to 0x0f01 (EGA 80x43 or VGA 80x50) + + If you add 0x8000 to the mode ID, the program will try to recalculate +vertical display timing according to mode parameters, which can be used to +eliminate some annoying bugs of certain VGA BIOSes (usually those used for +cards with S3 chipsets and old Cirrus Logic BIOSes) -- mainly extra lines at the +end of the display. + +4. Options +~~~~~~~~~~ + Some options can be set in the source text (in arch/i386/boot/video.S). +All of them are simple #define's -- change them to #undef's when you want to +switch them off. Currently supported: + + CONFIG_VIDEO_SVGA - enables autodetection of SVGA cards. This is switched +off by default as it's a bit unreliable due to terribly bad PC design. If you +really want to have the adapter autodetected (maybe in case the `scan' feature +doesn't work on your machine), switch this on and don't cry if the results +are not completely sane. In case you really need this feature, please drop me +a mail as I think of removing it some day. + + CONFIG_VIDEO_VESA - enables autodetection of VESA modes. If it doesn't work +on your machine (or displays a "Error: Scanning of VESA modes failed" message), +you can switch it off and report as a bug. + + CONFIG_VIDEO_COMPACT - enables compacting of the video mode list. If there +are more modes with the same screen size, only the first one is kept (see above +for more info on mode ordering). However, in very strange cases it's possible +that the first "version" of the mode doesn't work although some of the others +do -- in this case turn this switch off to see the rest. + + CONFIG_VIDEO_RETAIN - enables retaining of screen contents when switching +video modes. Works only with some boot loaders which leave enough room for the +buffer. (If you have old LILO, you can adjust heap_end_ptr and loadflags +in setup.S, but it's better to upgrade the boot loader...) + + CONFIG_VIDEO_LOCAL - enables inclusion of "local modes" in the list. The +local modes are added automatically to the beginning of the list not depending +on hardware configuration. The local modes are listed in the source text after +the "local_mode_table:" line. The comment before this line describes the format +of the table (which also includes a video card name to be displayed on the +top of the menu). + + CONFIG_VIDEO_400_HACK - force setting of 400 scan lines for standard VGA +modes. This option is intended to be used on certain buggy BIOSes which draw +some useless logo using font download and then fail to reset the correct mode. +Don't use unless needed as it forces resetting the video card. + + CONFIG_VIDEO_GFX_HACK - includes special hack for setting of graphics modes +to be used later by special drivers (e.g., 800x600 on IBM ThinkPad -- see +ftp://ftp.phys.keio.ac.jp/pub/XFree86/800x600/XF86Configs/XF86Config.IBM_TP560). +Allows to set _any_ BIOS mode including graphic ones and forcing specific +text screen resolution instead of peeking it from BIOS variables. Don't use +unless you think you know what you're doing. To activate this setup, use +mode number 0x0f08 (see section 3). + +5. Still doesn't work? +~~~~~~~~~~~~~~~~~~~~~~ + When the mode detection doesn't work (e.g., the mode list is incorrect or +the machine hangs instead of displaying the menu), try to switch off some of +the configuration options listed in section 4. If it fails, you can still use +your kernel with the video mode set directly via the kernel parameter. + + In either case, please send me a bug report containing what _exactly_ +happens and how do the configuration switches affect the behaviour of the bug. + + If you start Linux from M$-DOS, you might also use some DOS tools for +video mode setting. In this case, you must specify the 0x0f04 mode ("leave +current settings") to Linux, because if you don't and you use any non-standard +mode, Linux will switch to 80x25 automatically. + + If you set some extended mode and there's one or more extra lines on the +bottom of the display containing already scrolled-out text, your VGA BIOS +contains the most common video BIOS bug called "incorrect vertical display +end setting". Adding 0x8000 to the mode ID might fix the problem. Unfortunately, +this must be done manually -- no autodetection mechanisms are available. + + If you have a VGA card and your display still looks as on EGA, your BIOS +is probably broken and you need to set the CONFIG_VIDEO_400_HACK switch to +force setting of the correct mode. + +6. History +~~~~~~~~~~ +1.0 (??-Nov-95) First version supporting all adapters supported by the old + setup.S + Cirrus Logic 54XX. Present in some 1.3.4? kernels + and then removed due to instability on some machines. +2.0 (28-Jan-96) Rewritten from scratch. Cirrus Logic 64XX support added, almost + everything is configurable, the VESA support should be much more + stable, explicit mode numbering allowed, "scan" implemented etc. +2.1 (30-Jan-96) VESA modes moved to 0x200-0x3ff. Mode selection by resolution + supported. Few bugs fixed. VESA modes are listed prior to + modes supplied by SVGA autodetection as they are more reliable. + CLGD autodetect works better. Doesn't depend on 80x25 being + active when started. Scanning fixed. 80x43 (any VGA) added. + Code cleaned up. +2.2 (01-Feb-96) EGA 80x43 fixed. VESA extended to 0x200-0x4ff (non-standard 02XX + VESA modes work now). Display end bug workaround supported. + Special modes renumbered to allow adding of the "recalculate" + flag, 0xffff and 0xfffe became aliases instead of real IDs. + Screen contents retained during mode changes. +2.3 (15-Mar-96) Changed to work with 1.3.74 kernel. +2.4 (18-Mar-96) Added patches by Hans Lermen fixing a memory overwrite problem + with some boot loaders. Memory management rewritten to reflect + these changes. Unfortunately, screen contents retaining works + only with some loaders now. + Added a Tseng 132x60 mode. +2.5 (19-Mar-96) Fixed a VESA mode scanning bug introduced in 2.4. +2.6 (25-Mar-96) Some VESA BIOS errors not reported -- it fixes error reports on + several cards with broken VESA code (e.g., ATI VGA). +2.7 (09-Apr-96) - Accepted all VESA modes in range 0x100 to 0x7ff, because some + cards use very strange mode numbers. + - Added Realtek VGA modes (thanks to Gonzalo Tornaria). + - Hardware testing order slightly changed, tests based on ROM + contents done as first. + - Added support for special Video7 mode switching functions + (thanks to Tom Vander Aa). + - Added 480-scanline modes (especially useful for notebooks, + original version written by hhanemaa@cs.ruu.nl, patched by + Jeff Chua, rewritten by me). + - Screen store/restore fixed. +2.8 (14-Apr-96) - Previous release was not compilable without CONFIG_VIDEO_SVGA. + - Better recognition of text modes during mode scan. +2.9 (12-May-96) - Ignored VESA modes 0x80 - 0xff (more VESA BIOS bugs!) +2.10 (11-Nov-96)- The whole thing made optional. + - Added the CONFIG_VIDEO_400_HACK switch. + - Added the CONFIG_VIDEO_GFX_HACK switch. + - Code cleanup. +2.11 (03-May-97)- Yet another cleanup, now including also the documentation. + - Direct testing of SVGA adapters turned off by default, `scan' + offered explicitly on the prompt line. + - Removed the doc section describing adding of new probing + functions as I try to get rid of _all_ hardware probing here. +2.12 (25-May-98)- Added support for VESA frame buffer graphics. +2.13 (14-May-99)- Minor documentation fixes. |