I recently discovered that using the DVI adapter with the Macbook Pro wasn’t as easy as I thought. The MBP comes with a DVI connector, which is great, and it works just fine when you plug a DVI monitor into it. However, when doing presentations, you almost always have to use a regular VGA connector. Even though the driver (nvidia) could see the screen, it refused to display anything.
Now I’ve finally worked out a solution, and luckily it’s not that complicated. The trick is that even though the monitor is recognized, it is still treated as a DVI monitor. In order to get the driver to treat it as a normal VGA monitor, add this to xorg.conf:
Option “ConnectedMonitor” “DFP-0,DFP-1,CRT-0”
Option “MetaModes” “DFP-0: 1440×900, DFP-1: 1680×1050; DFP-0: 1440×900, CRT-0: 1280×1024”
Of course, the modes should be adjusted according to the setup. The MetaModes line should contain the valid combinations, separated by ;. In this case, I’ve specified that the internal display should always run at 1440×900, and then I either have a DVI monitor connected at 1680×1050 or a VGA monitor at 1280×1024. Of course, it’s also possible just to specify one monitor if you’re not using TwinView.
The trick now is that when running in X, xrandr can be used to switch between the monitors. When running xrandr, it should display something like this:
Screen 0: minimum 1280 x 900, current 1440 x 900, maximum 2720 x 1024
default connected 1440×900+0+0 (normal left inverted right) 0mm x 0mm
1440×900 50.0* 51.0 54.0
2720×1024 52.0 50.0
The tricky part now is that the nvidia driver “hides” the monitor configuration in the refresh rate. For example, the 1280×1024 resolution has only one rate, which means that this resolution is unique to one monitor. Switching to this mode with ‘xrandr -s 1280×1024’ will enable the VGA monitor and disable the internal display.
However, the mode 2720×1024 has two refresh rates, 52 and 50. Unfortunately there’s no easy way of telling it, but the 52 rate is with the internal display and the VGA monitor on, while the 50 is with only the internal display on (and a larger desktop, something you probably don’t want to use). Switching on the VGA monitor then requires two arguments: xrandr -s 2720×1024 –rate 52.
This isn’t the easiest to work with, so I’ve created a small Perl script which can query the nvidia driver directly to find the available modes, and then call xrandr. Download the script here. To use it, the X11::Protocol Perl package must be installed, and of course xrandr and the nvidia driver. To use the script, simply call it without any arguments to get a list of the supported resolutions and monitors. Select a configuration by calling the script with -s