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Thread: Dual-head newbie seeks info

  1. #1
    mini MURCer
    Join Date
    Oct 1999
    Noblesville, IN, USA

    Default Dual-head newbie seeks info


    I've got a dual-head (DH) G400MAX that I'm running on a RedHat v9 system with the current Matrox drivers for this card. Until now I've never actually had a need to use the second head. Now I do. Mind if I ask a few questions?

    1. Is it possiple to direct the output of a specific application to the 2nd monitor?

    2. Do the resolutions on both monitors have to be the same? How about the pixel depth? Refresh rate?

    3. I have an application the uses direct writes to video memory (the app uses the SVGALib library rather than XFree86 calls for displaying). Can the DH still work with direct writes to video memory? How do I know what address in video memory will be reflected on a given monitor?

    4. Is there any further reading I can do to get up to speed on the using DH with a G400MAX in XFree86 v4.3.0?


  2. #2
    Super MURCer Ribbit's Avatar
    Join Date
    Apr 2001


    Let's see if I can help....

    Under XFree86, there are two ways you can have dual-head. There is Xinerama mode, and there is what I'll call Independent mode. I believe there is a clone mode as well, but I've never used it. You say you're using the Matrox drivers, so I assume that Powerdesk can configure all this for you. (I use the XFree86 drivers.)

    In independent mode, the outputs are treated as two separate screens. They can have different resolutions, pixel depths, and refresh rates. The first screen will be called display :0.0 or just :0 (this is assuming your server is running as display :0) and the second will be called display :0.1. So in this mode you can have an application display to the second head with something like xclock -display :0.1.

    In Xinerama mode, the heads will be treated as one big display. They have to have the same pixel depth, but the resolutions and refresh rates can be different. You'll be able to move windows from one head to the other or even have them span both, but unless the application is specifically Xinerama-aware, it won't realise that there are actually two separate displays.

    As for question 3, I haven't tried it at all, but I believe the kernel framebuffer can drive both heads. If SVGALib has a framebuffer driver (rather than a native driver), you can probably make it work that way.

    Feel free to ask if you need something clarifying or if I've just confused you...
    Blah blah blah nick blah blah confusion, blah blah blah blah frog.

  3. #3


    a few additions. You can't exceed a 130MHz dotclock on the G400 second head. I max out at 1280x960x75Hz on the second head -- any higher refresh rate or resolution and it won't display. The display attributes need not be the same as the first head, but it is usually nicer to use it that way.<p>Also, you can't use hardware 3D if you use Xinerama. 3D works fine with the two-desktop dualhead (which is my setup). <p>Furthermore, neither 3D, mga_vid, nor Xv work on the second head. All that stuff needs to be done on the first head.

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