| |
| 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 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,inverse" |
| |
| Accepted options: |
| |
| inverse use inverse color map |
| |
| 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:n setup memory type range registers for the vesafb framebuffer |
| where n: |
| 0 - disabled (equivalent to nomtrr) (default) |
| 1 - uncachable |
| 2 - write-back |
| 3 - write-combining |
| 4 - write-through |
| |
| If you see the following in dmesg, choose the type that matches the |
| old one. In this example, use "mtrr:2". |
| ... |
| mtrr: type mismatch for e0000000,8000000 old: write-back new: write-combining |
| ... |
| |
| nomtrr disable mtrr |
| |
| 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> |