Re: Multi Head video cards

[Helge H. <hel...@hi...>]

Vineesh wrote:

>Hi,
> Is there any usefull link which describes the Multi head setup with
>frame buffers under the 2.6.9 or 2.6.7 and fedora core3 ?
>regards 
>   vineesh
>  
>
Take a look at archives for this mailing list, you'll find descriptions for
such a setup except that it isn't for fedora core3.

It isn't all that hard, assuming you already know how to set up an xserver
for fc3. 

Hardware:
Two sets of keyboards & mice, connected to the pc somehow.
A dualhead card, such as a G550.  Note that not all dualhead
cards supports a framebuffer for the second head, but the
matrox happens to do so.

Software:
A kernel with the ruby patch, and framebuffer support turned on for
the second head.  Optionally use fbcon for the second head,
but this may be broken.

A xserver.  A plain xserver will do for a dualhead setup on a G550.
A setup with two graphichs cards has an added requirement: a
xserver with the prefbusid/isolatedevice patch.  This is not necessary
with only one "device".

Setup:
Compile the patched kernel, and boot it. Verify that the second keyboard
attach to VT17 by issuing
cat /dev/tty17
Then check to see that you get some text by typing it in at the other
keyboard and press enter on it.  Don't proceed until this works,
you may have to experiment with the "dumbcon" kernel parameter.

First head:
Install ordinary xserver support for the card.  Make sure you don't
use the second head too, don't run xinerama.

Second head:
If you're using a matrox, it probably shows the same desktop as
the first head.  Get the "matroxset" utility and use it so the second head
shows the second framebuffer.  (It is not initialized yet, so it will
probably be black or full of crazy lines.)

Note that the first xserver use the config file
/etc/X11/XF86Config-4  (x.org use a different name)
Make a copy, such as XF86Config-4-fbdev in the
same directory.  Then modify it to be a config file
for your second head:

In the InputDevice section, change the mouse device to
whatever device your second mouse uses instead of the first.

In the Device section, specify the framebuffer driver instead of
the matrox driver.  Like this:
        Driver          "fbdev"
        Option          "UseFBDev"              "true"
        Option          "fbdev"                 "/dev/fb/1"

Finally, set up your system to start the second xserver.
FC3 probably does this a bit different than debian which I use.
Find wherever your default xserver is started  (gdm? xdm? kdm?)
and add an entry for the second server.

My first xserver starts with such a command:
/usr/X11R6/bin/X :0 vt7  -deferglyphs 16 -nolisten tcp -dpi 100
and the second one like this:
/usr/X11R6/bin/X :1 vt17 -deferglyphs 16 -nolisten tcp -xf86config 
XF86Config-4-fbdev

For testing purposes, try this last command on the command line.

Optimization:
It makes sense to run a font server such as xfs, and _not_ let the
xservers handle fonts themselves.  After all, you're running two
xservers now but both can use the same fontserver.  Having both xservers
handling fonts duplicates functionality.

Problems:
You will probably notice that any resolution change (or restarting)
of the first accelerated xserver will mess up the display for the second
one using the framebuffer.  This is fixable by re-running
matroxset.  Now, typing in a matroxset command isn't easy
when you can't see the screen, so I fixed this by setting up a hotkey
for my matroxset script in the window manager setup.  Details for doing
this depends entirely on what window manager you use.
A setup with several graphichs cards doesn't have this problem.


Helge Hafting