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jtwdyp 11-19-2012 05:26 PM

info needed about kms kernel arg "video=VGA-1:1280x1024-24@75"
 
I'm a multi-booter running several different linux distribution on multiple computers. I also have trouble remembering how I solved something before. especially when it seems that the method needed changes depending on the distro and/or hardware involved. So I'm trying to build myself a visual aid for designating screen resolution and/or text font size on the {tty} consoles.

I can never read the default. I miss using vga=normal...


there is a method I've heard of for kms where the kernel argument to set 1280x1024 resolution using 24 bps {kbps?} at 75Hz is supposed to be
Code:

video=VGA-1:1280x1024-24@75
I can easily put up with the default long enough to peek inside E17's video resolution module to check the available resolution and Hz settings.But that wouldn't tell me the bps, {Or is it really kbps? I mean the 24bps I got from the example I saw in some wiki sounds awful slow to me.} So since I'm usualy setting up linux on some salvaged computer with zero documentation, I would need either to be able to omit the bps value:
Code:

video=VGA-1:1280x1024@75
Or have a reliable method of determining what it is.

Can I omit the "-25" as in the 2nd code example?

How can I extract the bps value from the info Linux detects for use with the resolution settings inside the desktop environment?

andrewthomas 11-20-2012 09:18 PM

Quote:

Originally Posted by https://wiki.archlinux.org/index.php/Kernel_Mode_Setting

At first, note that for any method you use, you should always disable:

Any "vga=" options in your bootloader as these will conflict with the native resolution enabled by KMS.
Any "video=" lines that enable a framebuffer that conflicts with the driver.
Any other framebuffer drivers

bps? are you referring to the depth? bits per pixel

jtwdyp 11-22-2012 03:30 PM

Quote:

Originally Posted by andrewthomas (Post 4833687)
bps? are you referring to the depth? bits per pixel

Don't really know... I just found the method via google search


Quote:

Originally Posted by http://en.gentoo-wiki.com/wiki/Kernel_Mode_Setting
Forcing a Resolution

If you get a black screen, an incorrect resolution or want to specify the resolution to use, you can force a resolution on the kernel command-line. This can be useful if KMS auto detection fails with rare/incorrect EDID from the monitor.

When using a driver utilizing Kernel Mode Setting, you do not specify any driver name in the video= parameter. For example, setting the screen resolution to 1280x1024, 24bps at 75Hz would be just:
video=1280x1024-24@75


If it doesn't seem to have any effect, you may need to specify the output interface explictly:
video=VGA-1:1280x1024-24@75

The gentoo wiki seems to expect people to know what 24bps is...

TobiSGD 11-22-2012 06:03 PM

That must be a typo, usually it is referred to as 24 bpp, not 24 bps. bpp is the short form for bits per pixel and defines the color depth (~16,7 million colors in the case of 24bpp).

jtwdyp 11-23-2012 12:35 PM

Quote:

Originally Posted by TobiSGD (Post 4835120)
That must be a typo, usually it is referred to as 24 bpp, not 24 bps. bpp is the short form for bits per pixel and defines the color depth (~16,7 million colors in the case of 24bpp).

so then using this chart as a guide:

Quote:

Originally Posted by http://forums.gentoo.org/viewtopic.php?t=49036
| 640x480 800x600 1024x768 1280x1024
----+-------------------------------------
256 | 0x301 0x303 0x305 0x307
32k | 0x310 0x313 0x316 0x319
64k | 0x311 0x314 0x317 0x31A
16M | 0x312 0x315 0x318 0x31B

video=1280x1024-24@75 is roughly equivelent to vga=0x31B...

Though I had no idea how 16M resolved to 24... untill your description led me to a google search for:
Code:

"bits per pixel" "color depth"
Which led me to: https://en.wikipedia.org/wiki/Color_depth
From which I extracted that 16M is roughly equivelent to 2^24... And if I understand it that should mean that:
video=1024x768-16@75 is roughly equivelent to vga=0x317
video=800x600-15@75 is roughly equivelent to vga=0x315
video=640x480-8@75 is roughly equivelent to vga=0x301[/code]
All of which indicate a 75Hz refresh rate though so on my laptop where the available refresh rate for it is 60Hz, the equivelent of vga=0x305 would be:
Code:

video=1024x768-8@60
Is that right?


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