800x480 under X11

techuser — Sun, 06 Jan 2008 17:12:55 +0000

Keywords:

Recently my car PC display started playing up. I couldn't get it to display the native 800x480, although more usual resolutions like 800x600 were working okay (just unreadably small or blurry on a 7" screen in a car!).

To cut three weeks short, it appears that Mandriva (2008.0) started listening to the TFT's DDC information - the codes that tell the PC what resolutions the monitor supports. Now it turns out that the CTF700 I have never reports the correct resolution. It reports either 800x600 or 640x480, so Xorg thought it was doing the correct thing.

The answer is to turn off DDC in Xorg and set the resolutions manually (or, in my case restore the previously working backup and change that so DDC is ignored).

To do this, add:
Option "NoDDCValue"
to the Device section of /etc/X11/xorg.conf.

I actually stumbled on this by looking at the old Via Unichrome driver notes. It does seem quite obvious now I think about the symptoms... I suppose some update I did in December changed something, although Mandriva 2008.0 is still not yet running 100% correctly - the last to work well was 2006.0, but that had poor wireless support for anything but WEP.

The last issue I'm trying to sort now is a kernel bug - on each suspend/resume, the event drivers aren't being released properly and continue to count up in /dev/input/eventNN / inputNN. This eventually causes evdev (for the touchscreen) to fail (all slots taken, leaving the machine unusable. The heavy-handed fix I've got for this is to check for my custom udev generated symlink /etc/input/touchscreen every five minutes, and if it's missing to reboot the machine. Hardly the best thing to do.

The evdev problem looks like this, notice the high input number, which was normally less than ten:

Jan 1 17:08:51 localhost kernel: evdev: no more free evdev devices Jan 1 17:08:51 localhost kernel: input: failed to attach handler evdev to device input72, error: -23

Technological Wanderings - x11

800x480 under X11