MacBook vs. projector saga

January 22nd, 2009 | Tags:

I’ve finally found reliable workarounds for a long-standing issue where my Intel MacBook doesn’t work with most projectors.

The error message when trying to use xrandr to force output via VGA looks like:

$ xrandr --output VGA --auto
xrandr: cannot find crtc for output VGA

It seems the driver has a bug where it thinks it has the hardware available to drive the LCD panel, DVI and analogue VGA outputs at the same time, when it can in fact only handle two of these. xrandr shows three displays enabled:

Screen 0: minimum 320 x 200, current 1024 x 768, maximum 1280 x 1280
VGA connected (normal left inverted right x axis y axis)
   1024x768       60.0
   800x600        60.3
   640x480        59.9
LVDS connected 1024x768+0+0 (normal left inverted right x axis y axis) 286mm x 179mm
   1280x800       59.9 +
   1024x768       60.0*
   800x600        60.3
   640x480        59.9
TMDS-1 connected 1024x768+0+0 (normal left inverted right x axis y axis) 0mm x 0mm
   1024x768       60.0*
   800x600        60.3
   640x480        59.9
TV disconnected (normal left inverted right x axis y axis)

I’m guessing this might have something to do with both analogue and digital signals being sent out the same connector. In any case, the fix is to disable ‘TMDS-1′.

This can be done during an active session:

$ xrandr --output TMDS-1 --off

$ xrandr --output VGA --auto

The X server can also be configured to disable ‘TMDS-1′ during startup. On F10, you need to first create an xorg.conf. I ended up doing this:

# yum install system-config-display

# system-config-display

and just quit, which seems to cause /etc/X11/xorg.conf to be generated.

I edited the file, adding the “Option” line to the “Device” section:

Section "Device"
	Identifier  "Videocard0"
	Driver      "intel"
	Option      "monitor-TMDS-1" "dvi"

then, I added this section:

Section "Monitor"
        Identifier "dvi"
        Option "Disable"  "true"

which all seems to work ok for me and is about as obvious as quantum supergravity.


LCA has been great fun so far — more later.

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