1 2What is vesafb? 3=============== 4 5This is a generic driver for a graphic framebuffer on intel boxes. 6 7The idea is simple: Turn on graphics mode at boot time with the help 8of the BIOS, and use this as framebuffer device /dev/fb0, like the m68k 9(and other) ports do. 10 11This means we decide at boot time whenever we want to run in text or 12graphics mode. Switching mode later on (in protected mode) is 13impossible; BIOS calls work in real mode only. VESA BIOS Extensions 14Version 2.0 are required, because we need a linear frame buffer. 15 16Advantages: 17 18 * It provides a nice large console (128 cols + 48 lines with 1024x768) 19 without using tiny, unreadable fonts. 20 * You can run XF68_FBDev on top of /dev/fb0 (=> non-accelerated X11 21 support for every VBE 2.0 compliant graphics board). 22 * Most important: boot logo :-) 23 24Disadvantages: 25 26 * graphic mode is slower than text mode... 27 28 29How to use it? 30============== 31 32Switching modes is done using the vga=... boot parameter. Read 33Documentation/svga.txt for details. 34 35You should compile in both vgacon (for text mode) and vesafb (for 36graphics mode). Which of them takes over the console depends on 37whenever the specified mode is text or graphics. 38 39The graphic modes are NOT in the list which you get if you boot with 40vga=ask and hit return. The mode you wish to use is derived from the 41VESA mode number. Here are those VESA mode numbers: 42 43 | 640x480 800x600 1024x768 1280x1024 44----+------------------------------------- 45256 | 0x101 0x103 0x105 0x107 4632k | 0x110 0x113 0x116 0x119 4764k | 0x111 0x114 0x117 0x11A 4816M | 0x112 0x115 0x118 0x11B 49 50The video mode number of the Linux kernel is the VESA mode number plus 510x200. 52 53 Linux_kernel_mode_number = VESA_mode_number + 0x200 54 55So the table for the Kernel mode numbers are: 56 57 | 640x480 800x600 1024x768 1280x1024 58----+------------------------------------- 59256 | 0x301 0x303 0x305 0x307 6032k | 0x310 0x313 0x316 0x319 6164k | 0x311 0x314 0x317 0x31A 6216M | 0x312 0x315 0x318 0x31B 63 64To enable one of those modes you have to specify "vga=ask" in the 65lilo.conf file and rerun LILO. Then you can type in the desired 66mode at the "vga=ask" prompt. For example if you like to use 671024x768x256 colors you have to say "305" at this prompt. 68 69If this does not work, this might be because your BIOS does not support 70linear framebuffers or because it does not support this mode at all. 71Even if your board does, it might be the BIOS which does not. VESA BIOS 72Extensions v2.0 are required, 1.2 is NOT sufficient. You will get a 73"bad mode number" message if something goes wrong. 74 751. Note: LILO cannot handle hex, for booting directly with 76 "vga=mode-number" you have to transform the numbers to decimal. 772. Note: Some newer versions of LILO appear to work with those hex values, 78 if you set the 0x in front of the numbers. 79 80X11 81=== 82 83XF68_FBDev should work just fine, but it is non-accelerated. Running 84another (accelerated) X-Server like XF86_SVGA might or might not work. 85It depends on X-Server and graphics board. 86 87The X-Server must restore the video mode correctly, else you end up 88with a broken console (and vesafb cannot do anything about this). 89 90 91Refresh rates 92============= 93 94There is no way to change the vesafb video mode and/or timings after 95booting linux. If you are not happy with the 60 Hz refresh rate, you 96have these options: 97 98 * configure and load the DOS-Tools for your the graphics board (if 99 available) and boot linux with loadlin. 100 * use a native driver (matroxfb/atyfb) instead if vesafb. If none 101 is available, write a new one! 102 * VBE 3.0 might work too. I have neither a gfx board with VBE 3.0 103 support nor the specs, so I have not checked this yet. 104 105 106Configuration 107============= 108 109The VESA BIOS provides protected mode interface for changing 110some parameters. vesafb can use it for palette changes and 111to pan the display. It is turned off by default because it 112seems not to work with some BIOS versions, but there are options 113to turn it on. 114 115You can pass options to vesafb using "video=vesa:option" on 116the kernel command line. Multiple options should be separated 117by comma, like this: "video=vesa:ypan,invers" 118 119Accepted options: 120 121invers no comment... 122 123ypan enable display panning using the VESA protected mode 124 interface. The visible screen is just a window of the 125 video memory, console scrolling is done by changing the 126 start of the window. 127 pro: * scrolling (fullscreen) is fast, because there is 128 no need to copy around data. 129 * You'll get scrollback (the Shift-PgUp thing), 130 the video memory can be used as scrollback buffer 131 kontra: * scrolling only parts of the screen causes some 132 ugly flicker effects (boot logo flickers for 133 example). 134 135ywrap Same as ypan, but assumes your gfx board can wrap-around 136 the video memory (i.e. starts reading from top if it 137 reaches the end of video memory). Faster than ypan. 138 139redraw scroll by redrawing the affected part of the screen, this 140 is the safe (and slow) default. 141 142vgapal Use the standard vga registers for palette changes. 143 This is the default. 144pmipal Use the protected mode interface for palette changes. 145 146mtrr setup memory type range registers for the vesafb framebuffer. 147 148vram:n remap 'n' MiB of video RAM. If 0 or not specified, remap memory 149 according to video mode. (2.5.66 patch/idea by Antonino Daplas 150 reversed to give override possibility (allocate more fb memory 151 than the kernel would) to 2.4 by tmb@iki.fi) 152 153 154Have fun! 155 156 Gerd 157 158-- 159Gerd Knorr <kraxel@goldbach.in-berlin.de> 160 161Minor (mostly typo) changes 162by Nico Schmoigl <schmoigl@rumms.uni-mannheim.de> 163