external monitor blanks on 10 second cycle

Bug #317144 reported by charles.figura on 2009-01-14
Affects Status Importance Assigned to Milestone
xserver-xorg-video-intel (Ubuntu)

Bug Description

Binary package hint: xserver-xorg-video-intel

System: Ubuntu Intrepid (updated from hardy), up-to-date as of 2009/01/14 on Dell Latitude D620 with Intel 945GM video, 1440x900 display.
Problem: External monitor appears to configure correctly automatically, but blanks to black for about 2 seconds every 10 seconds. About 8 seconds of visibility, 2 seconds of black. 10 second cycle is pretty solid, no creep over long time - about an hour of watching. There DOESN'T appear to be any problems/flicker with the laptop display itself.

/var/log/Xorg.0.log shows no errors (that I can see), and /etc/X11/xorg.conf is effectively empty, nothing particular to my system.

charles.figura (charles-figura) wrote :
charles.figura (charles-figura) wrote :
Geir Ove Myhr (gomyhr) wrote :

Are you using KDE? I suspect this is (yet another) duplicate of bug 278471. Basically, a few monitors go black when information about it is being probed (known as DDC or EDID). The current KDE version has a daemon that probes this information every 10 seconds. Some lines are also dumped to Xorg.0.log at the same time, and you seem to have the same lines repeating over and over again in that file (that happens to everyone, see bug 299492, but only some monitors blink).

To verify that this is what happens, you can run
`while true; do wc -l /var/log/Xorg.0.log; sleep 1; done` (without ``)
This will show print the number of lines in Xorg.0.log every second. You can stop it with Ctrl+C. If it increases just when the monitor blinks, it's a good indication that this is the culprit.

Another detail I noticed is that when I run
`sudo get-edid | parse-edid`
(you will need the read-edid package for this) one of the lines I get is
 Screen is not blanked during DDC transfer
So it seems the montor has a means to advertise that it is blanked during DDC transfers. Possibly yours will do that.

As a possible workaround, you can take a look at the first comment of bug 296481.

If you don't use KDE or otherwise don't think this is duplicate of bug 278471, please include the output of the command `lspci -vvnn`.

Changed in xserver-xorg-video-intel:
status: New → Incomplete
charles.figura (charles-figura) wrote :

Geir -
That's it. I ran both tests that you sugggested, and saw both indicators.
And shutting down the RandR service did, indeed, stop the blinking - the display worked well.

I think I can confirm that my circumstances sound like bug 278471, though with the difference that I'm seeing blanking, not artifacts.

Geir Ove Myhr (gomyhr) wrote :

Great that it solved the problem for you. I'm marking this as a duplicate of bug 278471. The exact type of blinking may be different between different monitors, but the real problem is that KDE keeps probing the DDC information (even though information is available that says that the screen will blank when this is done).

Changed in xserver-xorg-video-intel:
status: Incomplete → Confirmed
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