patch-1.3.75 linux/Documentation/svga.txt

• Lines: 219
• Date: Sat Mar 16 14:50:05 1996
• Orig file: v1.3.74/linux/Documentation/svga.txt
• Orig date: Thu Jan 1 02:00:00 1970

diff -u --recursive --new-file v1.3.74/linux/Documentation/svga.txt linux/Documentation/svga.txt
@@ -0,0 +1,218 @@
+			Video Mode Selection Support 2.2
+	      (c) 1995, 1996 Martin Mares, <mj@k332.feld.cvut.cz>
+--------------------------------------------------------------------------------
+
+1. Intro
+~~~~~~~~
+   This small document describes the "Video Mode Selection" feature which
+allows to use various special video modes supported by the video BIOS. Due
+to usage of the BIOS, the selection is limited to the boot time (before the
+kernel decompression starts and works only on 80X86 machines.
+
+   IF YOU USE THIS FEATURE, I'LL BE MUCH PLEASED IF YOU SEND ME A MAIL
+DESCRIBING YOUR EXPERIENCE WITH IT. BUG REPORTS ARE ALSO WELCOME.
+
+   The video mode to be used is selected by a kernel paramater which can be
+specified in the kernel Makefile (the SVGA_MODE=... line) or by the "vga=..."
+option of LILO or by the "vidmode" utility (present in standard Linux utility
+packages). You can use the following settings 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 with
+the standard 80x25 mode set.
+
+   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: <flashing-cursor-here>
+
+   <name-of-detected-video-adapter> should contain a name of your video adapter
+or the chip in it or at least whether it's an EGA or VGA or VESA VGA (VGA with
+a VESA-compliant BIOS in it). If it doesn't match your configuration, tell me
+and I'll try to fix it somehow (you know, hardware detection is a real pain
+on PC's).
+
+   "0  0F00  80x25" tells 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 the mode ID's).
+
+   <flashing-cursor-here> encourages you to write the item number or mode ID
+you wish to set and press <RETURN>. If the computer complains something about
+"Unknown mode ID", it tries to explain you that it isn't possible to set such
+a mode. It's also possible to press only <RETURN> which forces the current
+mode to be used.
+
+   The mode list may be a bit inaccurate on your machine (it isn't possible
+to autodetect all existing video cards and their mutations). Some of the
+modes may be unsettable, some of them might work incorrectly with Linux
+(the common case is mirroring of first few lines at the bottom of the screen
+because of BIOS bugs) or there can exist modes which are not displayed. If
+you think the list doesn't match your configuration, let me know and I'll try
+to add your configuration to the next version of the mode selector.
+
+   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 enter "scan" instead of item number / mode ID, the program will try
+to scan your video modes in a slightly aggresive, but much more accurate way.
+This should reveal all video modes supported by your BIOS. During this process,
+the screen will flash wildly and strange things will appear. If you are afraid
+this could damage your monitor, don't use this functions. After scanning, the
+mode ordering is a bit different: the auto-detected SVGA modes are not listed
+at all and the modes revealed by the scan are shown before the VESA modes.
+
+3. Mode ID's
+~~~~~~~~~~~~
+   Because of the complexity of all the video stuff, the video mode ID's
+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"). The ID numbers
+can be divided to three regions:
+
+   0x0000 to 0x00ff - menu item references. 0x0000 is the first item.
+
+   0x0100 to 0x017f - standard BIOS modes. The ID is a BIOS video mode number
+	(as presented to INT 10, function 00) increased by 0x0100. You can
+	use any mode numbers even if not shown on the menu.
+
+   0x0200 to 0x04ff - VESA BIOS modes. The ID is a VESA mode ID increased by
+	0x0200. All VESA modes should be autodetected and shown on the menu.
+
+   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
+
+   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.
+
+   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 BIOS'es -- 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. If your card is
+detected incorrectly, you can switch this off.
+
+   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. Duplicate
+entries (those with the same screen size) are deleted except for the first one
+(see the previous section for more information on mode ordering). However,
+it's possible that the first variant doesn't work, while 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. Useful and probably harmless.
+
+   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
+by 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).
+
+5. Adding more cards
+~~~~~~~~~~~~~~~~~~~~
+   If you have a card not detected by the driver and you are a good programmer,
+feel free to add it to the source and send me a diff. It's very simple: You
+have to add a new entry to the svga_table consisting of a pointer to your mode
+table and a pointer to your detection routine. The order of entries in the
+svga_table defines the order of probing. Please use only reliable detection
+routines which are known to identify _only_ the card in question.
+
+   The detection routine is called with BP pointing to your mode table and
+ES containing 0xc000. If you want, you may alter BP allowing to select an
+appropriate mode table according to model ID detected. If the detection fails,
+return BP=0.
+
+   The mode table consists of lines containing a (BIOS mode number, rows,
+columns) triple and is finished by single zero byte followed by NUL-terminated
+adapter name.
+
+6. 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 the 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 use anything other, the 80x25
+mode will be used automatically.
+
+   If you set some SVGA mode and there's one or more extra lines on the
+bottom of the display containing already scrolled-out lines, 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.
+
+7. 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 ID's.
+		Screen contents retained during mode changes.
+2.3 (15-Mar-96)	Changed to work with 1.3.74 kernel.