Video Mode Selection Support 2.13 (c) 1995--1999 Martin Mares, -------------------------------------------------------------------------------- 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 to see video modes available, to continue or wait 30 secs" message. If you press , you enter the menu, if you press or wait 30 seconds, the kernel will boot up in the standard 80x25 mode. The menu looks like: Video adapter: Mode: COLSxROWS: 0 0F00 80x25 1 0F01 80x50 2 0F02 80x43 3 0F03 80x26 .... Enter mode number or `scan':

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). encourages you to enter the item number or mode ID you wish to set and press . 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 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 -- usual