radeon vs. flaky DDC / EDID of Samsung 214T

Csillag Kristof csillag.kristof at united-consult.hu
Tue Sep 8 19:43:01 PDT 2009

Dear all,

I am trying to use a Samsung SyncMaster 214T monitor
with a radeon-based graphics solution (RS690M to be
more specific.)

If I connect it via VGA, everything is fine 
- except the image quality, of course. 
(See attached log.)

However, when connected via DVI, the monitor is
not detected neither by the BIOS at boot time,
nor by Xorg. (See attached log.)

I have also tried to run get-edid,
but it fails to produce any output.
(It also works fine when connected via VGA.)

   * * *

I am sure that the monitor can be forced to work:
if I got the DVI output configured (by having 
a different monitor connected at boot time or 
at X start time), and than remove the original
monitor, and connect the 214T,
both the linux console and Xorg works.

        * * *

The problem is definitely with the monitor:
if I connect the same monitor to an Nvidia card
(using the proprietary driver), the monitor 
can be detected via DDC, but the EDID 
can not be properly read. The only way
to use the monitor properly with Nvidia is
to capture the EDID while connected via VGA,
and forcing the Nvidia to use the captured EDID
info when using the monitor via DVI,
by using the CustomEDID option in
the xorg.conf file.

    * * *

I would like to use this monitor with 
my radeon card, via DVI. How do I do that?

I have tried to fiddle around the various options
(IgnoreEDID, noDDC), but the monitor is still
not detected. Is there a way to force driving the
output in a specified way, regardless of the DDC

I remember fglxr has something like "MonitorLayout"
which can be used to force monitor types,
but I would like to stay with the Radeon driver.

Thank you for your help:

    Kristof Csillag


I have also checked it with RadeonHD: the autodetection
fails the same way, but I can force monitor output on DVI
by specifying a modeline in the monitor section, and
assigning a monitor with an option.

However, the outputted signal does not seem to be correct.
(The monitor does not say the usual "PP" when asked about
for the current mode, and the image is twitching.)

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