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authorLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
committerLinus Torvalds <torvalds@ppc970.osdl.org>2005-04-16 15:20:36 -0700
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tree0bba044c4ce775e45a88a51686b5d9f90697ea9d /Documentation/fb/vesafb.txt
downloadlinux-1da177e4c3f41524e886b7f1b8a0c1fc7321cac2.tar.gz
Linux-2.6.12-rc2v2.6.12-rc2
Initial git repository build. I'm not bothering with the full history, even though we have it. We can create a separate "historical" git archive of that later if we want to, and in the meantime it's about 3.2GB when imported into git - space that would just make the early git days unnecessarily complicated, when we don't have a lot of good infrastructure for it. Let it rip!
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+
+What is vesafb?
+===============
+
+This is a generic driver for a graphic framebuffer on intel boxes.
+
+The idea is simple: Turn on graphics mode at boot time with the help
+of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k
+(and other) ports do.
+
+This means we decide at boot time whenever we want to run in text or
+graphics mode. Switching mode later on (in protected mode) is
+impossible; BIOS calls work in real mode only. VESA BIOS Extensions
+Version 2.0 are required, because we need a linear frame buffer.
+
+Advantages:
+
+ * It provides a nice large console (128 cols + 48 lines with 1024x768)
+ without using tiny, unreadable fonts.
+ * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11
+ support for every VBE 2.0 compliant graphics board).
+ * Most important: boot logo :-)
+
+Disadvantages:
+
+ * graphic mode is slower than text mode...
+
+
+How to use it?
+==============
+
+Switching modes is done using the vga=... boot parameter. Read
+Documentation/svga.txt for details.
+
+You should compile in both vgacon (for text mode) and vesafb (for
+graphics mode). Which of them takes over the console depends on
+whenever the specified mode is text or graphics.
+
+The graphic modes are NOT in the list which you get if you boot with
+vga=ask and hit return. The mode you wish to use is derived from the
+VESA mode number. Here are those VESA mode numbers:
+
+ | 640x480 800x600 1024x768 1280x1024
+----+-------------------------------------
+256 | 0x101 0x103 0x105 0x107
+32k | 0x110 0x113 0x116 0x119
+64k | 0x111 0x114 0x117 0x11A
+16M | 0x112 0x115 0x118 0x11B
+
+The video mode number of the Linux kernel is the VESA mode number plus
+0x200.
+
+ Linux_kernel_mode_number = VESA_mode_number + 0x200
+
+So the table for the Kernel mode numbers are:
+
+ | 640x480 800x600 1024x768 1280x1024
+----+-------------------------------------
+256 | 0x301 0x303 0x305 0x307
+32k | 0x310 0x313 0x316 0x319
+64k | 0x311 0x314 0x317 0x31A
+16M | 0x312 0x315 0x318 0x31B
+
+To enable one of those modes you have to specify "vga=ask" in the
+lilo.conf file and rerun LILO. Then you can type in the desired
+mode at the "vga=ask" prompt. For example if you like to use
+1024x768x256 colors you have to say "305" at this prompt.
+
+If this does not work, this might be because your BIOS does not support
+linear framebuffers or because it does not support this mode at all.
+Even if your board does, it might be the BIOS which does not. VESA BIOS
+Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a
+"bad mode number" message if something goes wrong.
+
+1. Note: LILO cannot handle hex, for booting directly with
+ "vga=mode-number" you have to transform the numbers to decimal.
+2. Note: Some newer versions of LILO appear to work with those hex values,
+ if you set the 0x in front of the numbers.
+
+X11
+===
+
+XF68_FBDev should work just fine, but it is non-accelerated. Running
+another (accelerated) X-Server like XF86_SVGA might or might not work.
+It depends on X-Server and graphics board.
+
+The X-Server must restore the video mode correctly, else you end up
+with a broken console (and vesafb cannot do anything about this).
+
+
+Refresh rates
+=============
+
+There is no way to change the vesafb video mode and/or timings after
+booting linux. If you are not happy with the 60 Hz refresh rate, you
+have these options:
+
+ * configure and load the DOS-Tools for your the graphics board (if
+ available) and boot linux with loadlin.
+ * use a native driver (matroxfb/atyfb) instead if vesafb. If none
+ is available, write a new one!
+ * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0
+ support nor the specs, so I have not checked this yet.
+
+
+Configuration
+=============
+
+The VESA BIOS provides protected mode interface for changing
+some parameters. vesafb can use it for palette changes and
+to pan the display. It is turned off by default because it
+seems not to work with some BIOS versions, but there are options
+to turn it on.
+
+You can pass options to vesafb using "video=vesafb:option" on
+the kernel command line. Multiple options should be separated
+by comma, like this: "video=vesafb:ypan,invers"
+
+Accepted options:
+
+invers no comment...
+
+ypan enable display panning using the VESA protected mode
+ interface. The visible screen is just a window of the
+ video memory, console scrolling is done by changing the
+ start of the window.
+ pro: * scrolling (fullscreen) is fast, because there is
+ no need to copy around data.
+ * You'll get scrollback (the Shift-PgUp thing),
+ the video memory can be used as scrollback buffer
+ kontra: * scrolling only parts of the screen causes some
+ ugly flicker effects (boot logo flickers for
+ example).
+
+ywrap Same as ypan, but assumes your gfx board can wrap-around
+ the video memory (i.e. starts reading from top if it
+ reaches the end of video memory). Faster than ypan.
+
+redraw scroll by redrawing the affected part of the screen, this
+ is the safe (and slow) default.
+
+
+vgapal Use the standard vga registers for palette changes.
+ This is the default.
+pmipal Use the protected mode interface for palette changes.
+
+mtrr setup memory type range registers for the vesafb framebuffer.
+
+vremap:n
+ remap 'n' MiB of video RAM. If 0 or not specified, remap memory
+ according to video mode. (2.5.66 patch/idea by Antonino Daplas
+ reversed to give override possibility (allocate more fb memory
+ than the kernel would) to 2.4 by tmb@iki.fi)
+
+vtotal:n
+ if the video BIOS of your card incorrectly determines the total
+ amount of video RAM, use this option to override the BIOS (in MiB).
+
+Have fun!
+
+ Gerd
+
+--
+Gerd Knorr <kraxel@goldbach.in-berlin.de>
+
+Minor (mostly typo) changes
+by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de>