Switching on external monitors works now. Most of the time with success (except some VGA monitors when using the wrong x and y dimensions or wrong Hz. It stopped working lately – now I found out why (I bought a dock which enables the use of DVI)!
The Radeon X300 seems to have ‘two crtc‘ interfaces only. And one is always used when the LVDS (laptop builtin display) is enabled (in use). So one is left. Since i use DVI-0 on one workplace and VGA-0 on the other i usually was forced to reset X to make things work, since i wasn’t aware of the resource limitation. The error which came up was:
% xrandr –auto –output VGA-0 –mode 1024×768
xrandr: cannot find crtc for output VGA-0
The solution is easy. Just disable (in this case) DVI-0 output. Next enable VGA-0 output again.
xrandr –output DVI-0 –off
xrandr –auto –output VGA-0 –mode 1280×1024 –right-of LVDS
Usability wise this problem is a result of a missing resource counter (maybe it exists) but still the interface ‘xrandr’ was not very helpful in diagnosing the issue. I would have expected an error message as:
xrandr: no free crct for output VGA-0 left. you can only enable two devices at a time, maybe disable one to enable the other.
- 00:00.0 Host bridge: Intel Corporation Mobile 915GM/PM/GMS/910GML Express Processor to DRAM Controller (rev 03)
- 01:00.0 VGA compatible controller: ATI Technologies Inc M22 [Mobility Radeon X300]
- 00:01.0 PCI bridge: Intel Corporation Mobile 915GM/PM Express PCI Express Root Port (rev 03)