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hothead
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PostPosted: Thu Sep 23, 2004 7:11 pm    Post subject: livecd 2004.2 - change framebuffer resolution Reply with quote

If you want to change the resolution when booting from the livecd read the following

You can change the resolution if you boot with the normal 2.4 Kernel (named 'gentoo'),
by adding the vga-parameter to commandline. In this case the value of the vga-parameter has to be decimal not hexadecimal because the livecd boots with syslinux.

For example my commandline, when I boot from livecd with a resolution of 1280x1024 @ 16bit:

Code:
gentoo dokeymap vga=794


Background information

ILO, GRUB, and syslinux (Linux bootloaders) all want their VGA values in decimal. The Linux kernel vga boot parameter wants VGA values in hexdecimal. To give you a starting point for conversion, 785 decimal is 0x311 hexdecimal, or a 640x480 16 bit color framebuffer.

When you use the vga=parameter in GRUB, LILO, or syslinux, use the decimal number listed below that represents the video mode you want to use; for example, 640x480x16 is 0x311 hexdecimal, so the vga parameter should be vga=785.

Quote:
From /usr/src/linux/Documentation/svga.txt:

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).


How to convert from hexadecimal to decimal and the other way around

convert hexadecimal (0x301) to decimal
Code:
echo "ibase=16;301" | bc
769


convert decimal (769) to hexadecimal
Code:
echo "obase=16;769" | bc
301


VESA mode numbers

Code:
    | 640x480  800x600  1024x768 1280x1024
----+-------------------------------------
256 |  0x101    0x103    0x105    0x107
32k |  0x110    0x113    0x116    0x119
64k |  0x111    0x114    0x117    0x11A
16M |  0x112    0x115    0x118    0x11B


video mode number of the Linux kernel (VESA mode number plus 0x200)

Code:
    | 640x480  800x600  1024x768 1280x1024
----+-------------------------------------
256 |  0x301    0x303    0x305    0x307
32k |  0x310    0x313    0x316    0x319
64k |  0x311    0x314    0x317    0x31A
16M |  0x312    0x315    0x318    0x31B


VGA values in decimal

This is the section you need to select the mode from that fits your needs.

Code:
             | 640x480  800x600  1024x768 1280x1024
-------------+------------------------------------
256 colors   |  769       771      773       775
15 bit / 32k |  784       787      799       793
16 bit / 64k |  785       788      791       794
32 bit / 16M |  786       789      792       795


The 15bit values are rarely supported and needed. Take 16 or 32bit values.


Hope this can help someone out there!

Ruben
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mudrii
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PostPosted: Thu Oct 07, 2004 2:37 am    Post subject: Reply with quote

THX for very usefull HOWTO it realy helps :-)
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Sadako
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PostPosted: Thu Oct 07, 2004 3:31 pm    Post subject: Reply with quote

Useful explanation, but is there any way to get a 1400 x 1050 mode?
All the others look crap on my notebook.
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hothead
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PostPosted: Sat Oct 09, 2004 10:01 pm    Post subject: Reply with quote

I've not tested the values myself, but maybe you can try it and tell me if its working:

VESA mode numbers

Code:

       | 1400x1050
-------+----------
16 bit |   0x142
24 bit |   0x143


video mode numerge of the Linux kernel
Code:

      | 1400x1050
-------+----------
16 bit |   0x342
24 bit |   0x343

VGA values in decimal
Code:

       | 1400x1050
-------+----------
16 bit |  834
24 bit |  835


Hope this helps!

Ruben
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