SYNCHRONIZATION TROUBLE Linux mirrorred displays

1
Hi,

I'm sorry to write another post about Synchronization problems but I can't find the solution for this.

This error inconsistent sometimes Psychtoolbox can  be set up with no errors but about half the time I get a warning symbol and the following error message;

WARNING: Mismatch between measured monitor refresh intervals! This indicates problems with rasterbeam position queries.


----- ! PTB - WARNING: SYNCHRONIZATION TROUBLE ! ----

Graphs attached

I have read the BeamPositionQueries section but can't see an obvious fix as I'm linux user;

I am running Ubuntu 14.04
The graphics card shown is
VGA compatible controller: NVIDIA Corporation G73 [GeForce 7600 GS]
and the driver is
NVIDIA accelerated graphics driver (version 304).
I am using the digital outputs to 2 different monitors - the displays are mirrored;
a Liyama 19" (E1902S)
and an Acer 23" TL232

When I run the PerceptualVBLSyncTest the screen flashes Homogenously. A yellow line appears toward the top of the screen (about 10mm from top). Interestingly this line only appears when there is synchronization trouble - as I said half the time I don't get this error and in this case there is no yellow line.

also I very occasionally have got the error
WARNING: Couldn't compute a reliable estimate of monitor refresh interval! Trouble with VBL syncing?!?
 after which the code crashes

(Full text generated by VBLSynctest and PerceptualVBLSyncTest is pasted below)

Any suggestions much appreciated

Ed




When I run VBLSynctest


ans =

     0



PTB-INFO: This is Psychtoolbox-3 for GNU/Linux X11, under Matlab 64-Bit (Version 3.0.11 - Build date: Aug 16 2014).
PTB-INFO: Support status on this operating system release: Linux 3.13.0-39-generic Supported.
PTB-INFO: Type 'PsychtoolboxVersion' for more detailed version information.
PTB-INFO: Most parts of the Psychtoolbox distribution are licensed to you under terms of the MIT License, with
PTB-INFO: some restrictions. See file 'License.txt' in the Psychtoolbox root folder for the exact licensing conditions.

PTB-INFO: NVIDIA Corporation - G73 [GeForce 7600 GS] GPU found. Trying to establish low-level access...
PTB-INFO: Connected to NVidia G73 [GeForce 7600 GS] GPU of NV-40 family with 2 display heads. Beamposition timestamping enabled.
PTB-INFO: Overriding unreliable measured vblank endline 1066 by low-level value 1065 read directly from GPU.


PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce 7600 GS/PCIe/SSE2 :: 2.1.2 NVIDIA 304.123
PTB-INFO: VBL startline = 1024 , VBL Endline = 1065
PTB-INFO: Measured monitor refresh interval from beamposition = 12.961529 ms [77.151393 Hz].
PTB-INFO: Will use beamposition query for accurate Flip time stamping.
PTB-INFO: Measured monitor refresh interval from VBLsync = 16.660237 ms [60.023155 Hz]. (50 valid samples taken, stddev=0.008064 ms.)
PTB-INFO: Reported monitor refresh interval from operating system = 16.661390 ms [60.019001 Hz].
PTB-INFO: Small deviations between reported values are normal and no reason to worry.

WARNING: Mismatch between measured monitor refresh intervals! This indicates problems with rasterbeam position queries.


----- ! PTB - WARNING: SYNCHRONIZATION TROUBLE ! ----

One or more internal checks (see Warnings above) indicate that
queries of rasterbeam position are not properly working for your setup.

Psychtoolbox will work around this by using a different timing algorithm,
but it will cause Screen('Flip') to report less accurate/robust timestamps
for stimulus timing.
Read 'help BeampositionQueries' for more info and troubleshooting tips.


PTB-INFO: Support for fast OffscreenWindows enabled.
The refresh interval reported by the operating system is 16.66667 ms.
Measured refresh interval, as reported by "GetFlipInterval" is 16.66024 ms. (nsamples = 0, stddev = 0.00000 ms)

ans =

     1

PTB missed 0 out of 600 stimulus presentation deadlines.
One missed deadline is ok and an artifact of the measurement.
PTB completed 0 stimulus presentations before the requested target time.
Have a look at the plots for more details...


When I run  PerceptualVBLSyncTest. The screen flashes are homogenous with a yellow line right new the top of the screen.

PTB-INFO: This is Psychtoolbox-3 for GNU/Linux X11, under Matlab 64-Bit (Version 3.0.11 - Build date: Aug 16 2014).
PTB-INFO: Support status on this operating system release: Linux 3.13.0-39-generic Supported.
PTB-INFO: Type 'PsychtoolboxVersion' for more detailed version information.
PTB-INFO: Most parts of the Psychtoolbox distribution are licensed to you under terms of the MIT License, with
PTB-INFO: some restrictions. See file 'License.txt' in the Psychtoolbox root folder for the exact licensing conditions.

PTB-INFO: NVIDIA Corporation - G73 [GeForce 7600 GS] GPU found. Trying to establish low-level access...
PTB-INFO: Connected to NVidia G73 [GeForce 7600 GS] GPU of NV-40 family with 2 display heads. Beamposition timestamping enabled.


PTB-INFO: OpenGL-Renderer is NVIDIA Corporation :: GeForce 7600 GS/PCIe/SSE2 :: 2.1.2 NVIDIA 304.123
PTB-INFO: VBL startline = 1024 , VBL Endline = 1065
PTB-INFO: Measured monitor refresh interval from beamposition = 13.190858 ms [75.810079 Hz].
PTB-INFO: Will use beamposition query for accurate Flip time stamping.
PTB-INFO: Measured monitor refresh interval from VBLsync = 16.661463 ms [60.018740 Hz]. (50 valid samples taken, stddev=0.017310 ms.)
PTB-INFO: Reported monitor refresh interval from operating system = 16.661390 ms [60.019001 Hz].
PTB-INFO: Small deviations between reported values are normal and no reason to worry.

WARNING: Mismatch between measured monitor refresh intervals! This indicates problems with rasterbeam position queries.


----- ! PTB - WARNING: SYNCHRONIZATION TROUBLE ! ----

One or more internal checks (see Warnings above) indicate that
queries of rasterbeam position are not properly working for your setup.

Psychtoolbox will work around this by using a different timing algorithm,
but it will cause Screen('Flip') to report less accurate/robust timestamps
for stimulus timing.
Read 'help BeampositionQueries' for more info and troubleshooting tips.


PTB-INFO: Support for fast OffscreenWindows enabled.



and occasssionally I get this error

WARNING: Couldn't compute a reliable estimate of monitor refresh interval! Trouble with VBL syncing?!?


----- ! PTB - ERROR: SYNCHRONIZATION FAILURE ! ----

One or more internal checks (see Warnings above) indicate that synchronization
of Psychtoolbox to the vertical retrace (VBL) is not working on your setup.

This will seriously impair proper stimulus presentation and stimulus presentation timing!
Please read 'help SyncTrouble' for information about how to solve or work-around the problem.
You can force Psychtoolbox to continue, despite the severe problems, by adding the command
Screen('Preference', 'SkipSyncTests', 1); at the top of your script, if you really know what you are doing.