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Old 08-06-2009, 08:26 AM   #1
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Xorg configuration with unknown resolution second monitor and virtual screen

Hi. First time poster on here but have found loads of answers previously on LQ, so hopefully someone can help with the problem I'm stuck on!

What I'm trying to get
- A virtual screen in X which spans two monitors
- First monitor is 800x600
- Second monitor is right of this, and is an unknown/non fixed resolution

What I've got so far
- I've got the virtual screen (added the Virtual line in the xorg.conf with the maximum resolution I want)
- First monitor comes up fine (Its a LCD panel at 800x600)
- Second monitor comes up, but not in its native resolution
The second monitor I'm testing with at the moment can support up to 1024*768, but is coming up as 800x600:

Originally Posted by Xorg log
(II) intel(0): Output VGA using initial mode 800x600
What I've tried:
- If I add a preferredmode option into the xorg.conf file, I can get it to display at 1024*768, but if I then connect a 1440*900 screen up, it will still do 1024*768 as I've "preferred" that mode.
- I've added a list of "modes" of the resolutions that I want it to be able to work with, but even with those there it will still use the 800x600 option. Not sure if thats along the right line though and I just haven't put it in the right place yet.

I'm not that experienced with the whole xorg config system, but it is as though when trying to find a mode for the screen to work with ( I get a bunch of correct modelines from the monitor in the Xorg.log file which match up with what I'd expect, and has 1024*768 in there), it is comparing the resolution with that of the *virtual* screen, not the individual screens making up the virtual one. I have a second graphics card in place and that only has one monitor attached and happily autodetects the correct resolution, which is why I think it is something to do with the "virtual" resolution not matching. Is there any way I can give pairs of possible resolution modes, for example: "800x600 800x600" "800x600 1024x768", "800x600 1440x900" sort of thing?

Let me know if I've missed out any bits of information that would help!

Thanks in advance

Old 08-06-2009, 10:56 AM   #2
Registered: Oct 2007
Distribution: Arch x86_64
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What version of x11 are you running? The newer ones should be able to detect resolutions automagically. You will however, need to set up Xinerama (or TwinView, on your own)
Old 08-06-2009, 11:14 AM   #3
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Version info:

X.Org X Server 1.4.2
Release Date: 11 June 2008
X Protocol Version 11, Revision 0
Build Operating System: Linux Debian (xorg-server 2:1.4.2-10.lenny2)
Current Operating System: Linux #17 Fri Jul 24 17:17:41 BST 2009 i686
Build Date: 08 June 2009 09:12:57AM
As I stated in the original post - it happily autodetects the monitor resolutions available as they show up in the Xorg.log file, it just doesn't want to use them if its part of the virtual monitor.
For info: The two gfx cards I am using are an intel i810 and a sis V7 card.

Last edited by Wol; 08-06-2009 at 11:28 AM. Reason: added more info.
Old 08-09-2009, 10:29 AM   #4
Registered: Oct 2007
Distribution: Arch x86_64
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How are you making out with this? Are you able to use each monitor separately on the intended video card?
Old 08-10-2009, 03:27 AM   #5
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I'm able to use all three monitors (2 on the primary gfx card, one on the secondary one) happily and get outputs on them. The single monitor on the secondary graphics card autodetects the resolution happily, but the monitor on the primary graphics card (which is part of the Virtual screen) won't. Same make and model of monitor on both. I can hard code the resolutions in the xorg.conf and they work at those resolutions, but the problem is that the system thats being deployed needs to be able to support lots of different resolutions, so I can't hard code a specific resolution. I can hard code a list though if necessary.

Primary graphics card
- LVDS output - 800x600 lcd panel - Works at 800x600
- VGA output - A monitor with an unknown resolution - >>> Will default to 800x600 even if the native res is higher <<<
Secondary Graphics Card
- VGA output - A monitor with an unknown resolution - Works at native res


dual, monitor, virtual, xorg

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