# Odd flip timestamps

**URL:** <https://psychtoolbox.discourse.group/t/odd-flip-timestamps/370>\
**Category:** Uncategorized\
**Created:** [January 4, 2017, 2:34pm UTC](https://psychtoolbox.discourse.group/t/odd-flip-timestamps/370 "2017-01-04T14:34:10Z")\
**Posts on this page:** 2\
**Page:** 1

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**Author:** ![andreaswidmann](https://avatars.discourse-cdn.com/v4/letter/a/77aa72/32.png) [@andreaswidmann](https://psychtoolbox.discourse.group/u/andreaswidmann)\
**Post date:** [January 4, 2017, 2:34pm UTC](https://psychtoolbox.discourse.group/t/odd-flip-timestamps/370/1 "2017-01-04T14:34:10Z")

</div>

Dear Mario and list,  
  
while programming a new experiment where we want to precisely sync auditory and visual stimuli I stumbled across some confusing oddities in the flip timestamping in our lab (I hope this is not a very stupid question):  
  
From the diagnostic PTB output (see below) I assumed that our system (Ubuntu 16.04 low-latency kernel, older nVidia Quadro NVS 290 card, nouveau driver, newest PTB) supports beamposition queries. However, the VBLTimeStamp returned by Screen('Flip‘, …) always equals the StimulusOnsetTime. On the other hand, the corresponding beampos is not -1 as I would have expected in case of missing support for beamposition queries from your explanation in the FAQ ([https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ:-Explanation-of-Flip-Timestamps)](https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ:-Explanation-of-Flip-Timestamps)) but consistently between 774 and 776.  
  
More importantly, the returned VBLTimeStamp is consistently \*later\* than the corresponding FlipTimestamp (by ~400 to 450 µS). The FlipTimestamp itself has only very small deviations from a GetSecs timestamp taken after Flip (\< 50 µS).  
  
\* Is this expected behavior and my mental concept is flawed (i.e., doesn’t the VBLTimeStamp reflect VBL onset and should thus be earlier than FlipTimestamp)?  
\* Or did I misconfigure something?  
\* Or is this a limitation of our admittedly somewhat older graphics card (working flawlessly otherwise)?  
\* And finally, to compute true StimulusOnsetTime on this system would it be safe to apply the equation to compute VBL duration used in PredictVisualOnsetForTime?  
  
Thanks a lot! Best,  
Andreas  
  
  
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PTB-INFO: Support status on this operating system release: Linux 4.4.0-57-lowlatency 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.  
  
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<div class="post-metadata">

**Author:** ![andreaswidmann](https://avatars.discourse-cdn.com/v4/letter/a/77aa72/32.png) [@andreaswidmann](https://psychtoolbox.discourse.group/u/andreaswidmann)\
**Post date:** [January 4, 2017, 5:58pm UTC](https://psychtoolbox.discourse.group/t/odd-flip-timestamps/370/2 "2017-01-04T17:58:49Z")

</div>

Dear Mario,  
  
thanks a lot for the detailed response and fixing my outdated mental concept! I will add your explanation to the FAQ page, ok?  
  
Sorry, your explanation triggered two additional questions:  
  
\* At the end of PredictVisualOnsetForTime() the VBL duration is calculated and added to the estimated vbl time (if beamposition queries are supported). Wouldn’t that systematically overestimate expected stimulus onset time if VBLTimestamp already reflects real stimulus onset on OpenML systems? (the observed offset was the reason to start looking at the timestamps in more detail)  
  
\* And if I want to send a TTL trigger with the visual stimulus onset optimally I wait until VBLTimestamp if it is later than FlipTimestamp/GetSecs() on OpenML systems? Actually, wasn’t aware of that yet.  
  
And yes, we verify audio-video sync with oscilloscope and photodiode.  
  
Thank you! Best regards  
Andreas  
  

> \> these results look all perfect. I guess that FAQ is simply not quite up to date. It was written sometime before 2010, before we had the improved timestamping on Linux + FOSS drivers. It describes the beamposition timestamping used on Windows, OSX with AMD and NVidia cards + PsychtoolboxKernelDriver, and Linux with proprietary NVidia driver.  
> \>   
> \> On Linux with open-source drivers we use the OS builtin timestamping, which implements the OpenML OML\_sync\_control extension, and is generally superior to PTB's mechanism. On Intel, AMD and NVidia graphics cards, as well as the RaspberryPi and a couple of other embedded gpu's, the current algorithm is essentially a substantially improved version of PTB's mechanism, but other implementations would be possible as long as they satisfy the OML\_sync\_control spec to a sufficient degree.  
> \>   
> \> With OpenML timestamping, the returned timestamps are always visual stimulus onset timestamps, ie. the 2nd return argument of Flip, the time when the first new top-left stimulus pixel gets send out to the display. VBLTimestamp is set == stimulus onset timestamp, so the rule VBLTimestamp \<= StimulusOnsetTimestamp holds. In theory we could calculate and return the VBLTimestamp from StimulusOnsetTimestamp, but in practice i can not think of any situation where this would provide a benefit.  
> \>   
> \> FlipTimestamp, which is not much more than a GetSecs taken at end of Flip, can and often will be earlier than StimulusOnsetTimestamp, as flip processing usually already completes while the display is still in VBLANK, preparing for display of the new stimulus frame, that's why StimulusOnsetTimestamp == VBLTimestamp \> FlipTimestamp.  
> \>   
> \> PTB would fall back to the older beamposition timestamping if it would detect a problem with the OpenML timestamping. We have something like up to 4-fold redundancy on Linux with open-source drivers when it comes to visual timing and also extra mechanisms to detect and correct/compensate for trouble compared to other OS'es. The Screen Preference setting VBLTimestampingmode 0 (or 1?) would force you back on beamposition timestamping.  
> \>   
> \> -\> Wrt. PredictVisualOnsetForTime(), yes that's what you should use to predict visual onset, and feed into PsychPortAudio as target time for good audio-video sync. In fact, i changed PsychPortAudioTimingTest.m - our example of doing and testing audio-video sync - in the latest Beta update to demonstrate that approach via PredictVisualOnsetForTime().  
> \>   
> \> -\> One thing to keep in mind is that you should still test audio-video sync independently once for your setup before running data collection, as there is no way to detect purely in software if the audio timing works correctly. Also there can still be an unavoidable fixed offset between requested and true audio onset/offset, dependent on audio hardware. However, that offset is fixed, can be eliminated by calibration and was not ever observed by myself anywhere to be larger than ~1 msec. And Linux gets tested for proper audio-timing by myself with a Datapixx (via PsychPortAudioTimingTest and PsychPortAudioDatapixxTimingtest) for each kernel release at least on some typical onboard sound chips like in your machine and so far never failed in over 6 years of testing.  
> \>   
> \> Happy testing,  
> \> -mario  
> \>   
> \>   
> \> while programming a new experiment where we want to precisely sync auditory and visual stimuli I stumbled across some confusing oddities in the flip timestamping in our lab (I hope this is not a very stupid question):  
> \>   
> \> From the diagnostic PTB output (see below) I assumed that our system (Ubuntu 16.04 low-latency kernel, older nVidia Quadro NVS 290 card, nouveau driver, newest PTB) supports beamposition queries. However, the VBLTimeStamp returned by Screen('Flip‘, …) always equals the StimulusOnsetTime. On the other hand, the corresponding beampos is not -1 as I would have expected in case of missing support for beamposition queries from your explanation in the FAQ ([https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ:-Explanation-of-Flip-Timestamps)](https://github.com/Psychtoolbox-3/Psychtoolbox-3/wiki/FAQ:-Explanation-of-Flip-Timestamps)) but consistently between 774 and 776.  
> \>   
> \> More importantly, the returned VBLTimeStamp is consistently \*later\* than the corresponding FlipTimestamp (by ~400 to 450 µS). The FlipTimestamp itself has only very small deviations from a GetSecs timestamp taken after Flip (\< 50 µS).  
> \>   
> \> \* Is this expected behavior and my mental concept is flawed (i.e., doesn’t the VBLTimeStamp reflect VBL onset and should thus be earlier than FlipTimestamp)?  
> \> \* Or did I misconfigure something?  
> \> \* Or is this a limitation of our admittedly somewhat older graphics card (working flawlessly otherwise)?  
> \> \* And finally, to compute true StimulusOnsetTime on this system would it be safe to apply the equation to compute VBL duration used in PredictVisualOnsetForTime?  
> \>   
> \> Thanks a lot! Best,  
> \> Andreas  
> \>   
> \>   
> \> RandR: 1024x768\_100.00 (0xa9) 112.2MHz  
> \> h: width 1024 start 1096 end 1200 total 1376 skew 0  
> \> v: height 768 start 771 end 775 total 816  
> \>   
> \>   
> \> PTB-INFO: This is Psychtoolbox-3 for GNU/Linux X11, under GNU/Octave 64-Bit (Version 3.0.14 - Build date: Dec 22 2016).  
> \> PTB-INFO: Support status on this operating system release: Linux 4.4.0-57-lowlatency 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-DEBUG: Checking PCI device [Intel Corporation 4 Series Chipset DRAM Controller] with class x00060000 ...  
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> \> PTB-DEBUG: Checking PCI device [Intel Corporation 4 Series Chipset Serial KT Controller] with class x00070002 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82567LM-3 Gigabit Network Connection] with class x00020000 ...  
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> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB UHCI Controller #6] with class x000c0300 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB2 EHCI Controller #2] with class x000c0320 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) HD Audio Controller] with class x00040300 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) PCI Express Port 1] with class x00060400 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) PCI Express Port 2] with class x00060400 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB UHCI Controller #1] with class x000c0300 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB UHCI Controller #2] with class x000c0300 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB UHCI Controller #3] with class x000c0300 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) USB2 EHCI Controller #1] with class x000c0320 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801 PCI Bridge] with class x00060401 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD (ICH10D) LPC Interface Controller] with classx00060100 ...  
> \> PTB-DEBUG: Checking PCI device [Intel Corporation 82801JD/DO (ICH10 Family) SATA AHCI Controller] with class x00010601 ...  
> \> PTB-DEBUG: Checking PCI device [NVIDIA Corporation G86 [Quadro NVS 290]] with class x00030000 ...  
> \> PTB-INFO: NVIDIA Corporation - G86 [Quadro NVS 290] GPU found. Trying to establish low-level access...  
> \> PTB-DEBUG: Mapping GPU BAR address 0xf2000000 ...  
> \> PTB-DEBUG: Mapping 0x1000000 bytes...  
> \> PTB-INFO: Connected to NVidia G86 [Quadro NVS 290] GPU of NV-050 family with 2 display heads. Beamposition timestamping enabled.  
> \> PTB-INFO: Using old-style override-redirect setup path for onscreen window creation.  
> \> PTB-INFO: GLX Visual info depths is 24 bits  
> \> PTB-INFO: Running on Mesa version 11.2.0  
> \> PTB-INFO: This combo of X-Server and Mesa is considered safe for use under DRI3/Present.  
> \> PTB-INFO: Using GLEW version 2.0.0 for automatic detection of OpenGL extensions...  
> \> PTB-INFO: Using GLX\_MESA\_swap\_control extension for control of vsync.  
> \> PTB-INFO: INTEL\_swap\_event support for additional swap completion correctness checks enabled.  
> \> PTB-DEBUG: PPM file magic is P6  
> \> -\> Ok  
> \> # CREATOR: GIMP PNM Filter Version 1.1  
> \> PTB-DEBUG: Recognized splash image of 656 x 304 pixels, maxlevel 255. Loading...  
> \>   
> \>   
> \> OpenGL-Vendor / renderer / version are: nouveau - Gallium 0.4 on NV86 - 3.0 Mesa 11.2.0  
> \>   
> \>   
> \> OpenGL-Extensions are: GL\_ARB\_multisample GL\_EXT\_abgr GL\_EXT\_bgra GL\_EXT\_blend\_color GL\_EXT\_blend\_minmax GL\_EXT\_blend\_subtract GL\_EXT\_copy\_texture GL\_EXT\_polygon\_offset GL\_EXT\_subtexture GL\_EXT\_texture\_object GL\_EXT\_vertex\_array GL\_EXT\_compiled\_vertex\_array GL\_EXT\_texture GL\_EXT\_texture3D GL\_IBM\_rasterpos\_clipGL\_ARB\_point\_parameters GL\_EXT\_draw\_range\_elements GL\_EXT\_packed\_pixels GL\_EXT\_point\_parameters GL\_EXT\_rescale\_normal GL\_EXT\_separate\_specular\_color GL\_EXT\_texture\_edge\_clamp GL\_SGIS\_generate\_mipmap GL\_SGIS\_texture\_border\_clamp GL\_SGIS\_texture\_edge\_clamp GL\_SGIS\_texture\_lod GL\_ARB\_framebuffer\_sRGB GL\_ARB\_multitexture GL\_EXT\_framebuffer\_sRGB GL\_IBM\_multimode\_draw\_arrays GL\_IBM\_texture\_mirrored\_repeat GL\_ARB\_texture\_cube\_map GL\_ARB\_texture\_env\_add GL\_ARB\_transpose\_matrix GL\_EXT\_blend\_func\_separate GL\_EXT\_fog\_coord GL\_EXT\_multi\_draw\_arrays GL\_EXT\_secondary\_color GL\_EXT\_texture\_env\_add GL\_EXT\_texture\_filter\_anisotropic GL\_EXT\_texture\_lod\_bias GL\_INGR\_blend\_func\_separate GL\_NV\_blend\_square GL\_NV\_light\_max\_exponent GL\_NV\_texgen\_reflection GL\_NV\_texture\_env\_combine4 GL\_S3\_s3tc GL\_SUN\_multi\_draw\_arrays GL\_ARB\_texture\_border\_clamp GL\_ARB\_texture\_compression GL\_EXT\_framebuffer\_object GL\_EXT\_texture\_compression\_s3tc GL\_EXT\_texture\_env\_combine GL\_EXT\_texture\_env\_dot3 GL\_MESA\_window\_pos GL\_NV\_packed\_depth\_stencil GL\_NV\_texture\_rectangleGL\_ARB\_depth\_texture GL\_ARB\_occlusion\_query GL\_ARB\_shadow GL\_ARB\_texture\_env\_combine GL\_ARB\_texture\_env\_crossbar GL\_ARB\_texture\_env\_dot3 GL\_ARB\_texture\_mirrored\_repeat GL\_ARB\_window\_pos GL\_EXT\_stencil\_two\_side GL\_EXT\_texture\_cube\_map GL\_NV\_depth\_clamp GL\_NV\_fog\_distance GL\_APPLE\_packed\_pixels GL\_APPLE\_vertex\_array\_object GL\_ARB\_draw\_buffers GL\_ARB\_fragment\_program GL\_ARB\_fragment\_shader GL\_ARB\_shader\_objects GL\_ARB\_vertex\_program GL\_ARB\_vertex\_shader GL\_ATI\_draw\_buffers GL\_ATI\_texture\_env\_combine3 GL\_ATI\_texture\_float GL\_EXT\_depth\_bounds\_test GL\_EXT\_shadow\_funcs GL\_EXT\_stencil\_wrap GL\_MESA\_pack\_invert GL\_NV\_primitive\_restart GL\_ARB\_depth\_clamp GL\_ARB\_fragment\_program\_shadow GL\_ARB\_half\_float\_pixel GL\_ARB\_occlusion\_query2 GL\_ARB\_point\_sprite GL\_ARB\_shading\_language\_100 GL\_ARB\_sync GL\_ARB\_texture\_non\_power\_of\_two GL\_ARB\_vertex\_buffer\_object GL\_ATI\_blend\_equation\_separate GL\_EXT\_blend\_equation\_separate GL\_OES\_read\_format GL\_ARB\_color\_buffer\_float GL\_ARB\_pixel\_buffer\_object GL\_ARB\_texture\_compression\_rgtc GL\_ARB\_texture\_float GL\_ARB\_texture\_rectangle GL\_ATI\_texture\_compression\_3dc GL\_EXT\_packed\_float GL\_EXT\_pixel\_buffer\_object GL\_EXT\_texture\_compression\_dxt1 GL\_EXT\_texture\_compression\_rgtc GL\_EXT\_texture\_mirror\_clamp GL\_EXT\_texture\_rectangle GL\_EXT\_texture\_sRGB GL\_EXT\_texture\_shared\_exponent GL\_ARB\_framebuffer\_object GL\_EXT\_framebuffer\_blit GL\_EXT\_framebuffer\_multisample GL\_EXT\_packed\_depth\_stencil GL\_ARB\_vertex\_array\_object GL\_ATI\_separate\_stencil GL\_ATI\_texture\_mirror\_once GL\_EXT\_draw\_buffers2 GL\_EXT\_draw\_instanced GL\_EXT\_gpu\_program\_parameters GL\_EXT\_texture\_array GL\_EXT\_texture\_compression\_latc GL\_EXT\_texture\_integer GL\_EXT\_texture\_sRGB\_decode GL\_EXT\_timer\_query GL\_OES\_EGL\_image GL\_AMD\_performance\_monitor GL\_ARB\_copy\_buffer GL\_ARB\_depth\_buffer\_float GL\_ARB\_draw\_instanced GL\_ARB\_half\_float\_vertex GL\_ARB\_instanced\_arrays GL\_ARB\_map\_buffer\_range GL\_ARB\_texture\_rg GL\_ARB\_texture\_swizzle GL\_ARB\_vertex\_array\_bgra GL\_EXT\_texture\_swizzle GL\_EXT\_vertex\_array\_bgra GL\_NV\_conditional\_render GL\_AMD\_conservative\_depth GL\_ARB\_ES2\_compatibility GL\_ARB\_blend\_func\_extended GL\_ARB\_debug\_output GL\_ARB\_draw\_elements\_base\_vertex GL\_ARB\_explicit\_attrib\_location GL\_ARB\_fragment\_coord\_conventions GL\_ARB\_provoking\_vertex GL\_ARB\_sampler\_objects GL\_ARB\_seamless\_cube\_map GL\_ARB\_shader\_texture\_lod GL\_ARB\_texture\_multisample GL\_ARB\_texture\_rgb10\_a2ui GL\_ARB\_uniform\_buffer\_object GL\_ARB\_vertex\_type\_2\_10\_10\_10\_rev GL\_EXT\_provoking\_vertex GL\_EXT\_texture\_snorm GL\_MESA\_texture\_signed\_rgba GL\_NV\_texture\_barrier GL\_ARB\_get\_program\_binary GL\_ARB\_robustness GL\_ARB\_separate\_shader\_objects GL\_ARB\_shader\_bit\_encoding GL\_ARB\_timer\_query GL\_NV\_vdpau\_interop GL\_ANGLE\_texture\_compression\_dxt3 GL\_ANGLE\_texture\_compression\_dxt5 GL\_ARB\_base\_instance GL\_ARB\_compressed\_texture\_pixel\_storage GL\_ARB\_conservative\_depth GL\_ARB\_internalformat\_query GL\_ARB\_map\_buffer\_alignment GL\_ARB\_shading\_language\_420pack GL\_ARB\_shading\_language\_packing GL\_ARB\_texture\_storage GL\_EXT\_framebuffer\_multisample\_blit\_scaled GL\_EXT\_transform\_feedback GL\_AMD\_shader\_trinary\_minmax GL\_ARB\_ES3\_compatibility GL\_ARB\_arrays\_of\_arrays GL\_ARB\_clear\_buffer\_object GL\_ARB\_copy\_image GL\_ARB\_explicit\_uniform\_location GL\_ARB\_invalidate\_subdata GL\_ARB\_program\_interface\_query GL\_ARB\_stencil\_texturing GL\_ARB\_texture\_query\_levels GL\_ARB\_texture\_storage\_multisample GL\_ARB\_texture\_view GL\_ARB\_vertex\_attrib\_binding GL\_KHR\_debug GL\_ARB\_buffer\_storage GL\_ARB\_clear\_texture GL\_ARB\_multi\_bind GL\_ARB\_texture\_mirror\_clamp\_to\_edge GL\_ARB\_texture\_stencil8 GL\_ARB\_vertex\_type\_10f\_11f\_11f\_rev GL\_EXT\_shader\_integer\_mix GL\_ARB\_clip\_control GL\_ARB\_conditional\_render\_inverted GL\_ARB\_derivative\_control GL\_ARB\_get\_texture\_sub\_image GL\_ARB\_pipeline\_statistics\_query GL\_ARB\_shader\_texture\_image\_samples GL\_ARB\_texture\_barrier GL\_EXT\_polygon\_offset\_clamp GL\_KHR\_context\_flush\_control  
> \>   
> \> PTB-DEBUG: Linux X11 backend with FOSS drivers - Enabling locked pixeltoken-write + flush workaround for XLib thread-safety.  
> \> PTB-DEBUG: Interrogating Low-level renderer capabilities for onscreen window with handle 10:  
> \> Indicator variables: FBO's 1, ATI\_texture\_float 1, ARB\_texture\_float 1, Vendor nouveau, Renderer Gallium 0.4 on NV86.  
> \> Indicator variables: maxcolorattachments = 8, maxrectangletexturesize = 8192, maxnativealuinstructions = 16384.  
> \> GPU supports non-power-of-two textures.  
> \> Hardware supports signed normalized textures of 16 bpc integer format.  
> \> Basic framebuffer objects with rectangle texture rendertargets supported --\> RGBA8 rendertargets with blending.  
> \> Framebuffer objects support fast blitting between each other.  
> \> Framebuffer objects support anti-aliasing via multisampling.  
> \> Framebuffer objects support single-pass multisample resolve blits and image rescaling.  
> \> Hardware supports floating point textures of 16bpc and 32bpc float format.  
> \> Assuming NV30 core or later...  
> \> Assuming NV40 core or later (maxcolattachments=8): Hardware supports floating point blending and filtering on 16bpc float format.  
> \> Hardware also supports floating point framebuffers of 16bpc and 32bpc float format.  
> \> Hardware supports full 32 bit floating point precision shading.  
> \> Assuming G80 core or later (maxtexsize=8192): Hardware supports full floating point blending and filtering on 16bpc and 32bpc float format.  
> \> Assuming hardware supports native OpenGL primitive smoothing (points, lines).  
> \> PTB-Info: Running on 'The X.Org Foundation' XServer, Vendor release 11804000.  
> \> OML\_sync\_control indicators: glXGetSyncValuesOML=0x7f6c1bcd4c40 , glXWaitForMscOML=0x7f6c1bcd4d80, glXWaitForSbcOML=0x7f6c1bcd4e50, glXSwapBuffersMscOML=0x7f6c1bcd4cb0  
> \> OML\_sync\_control indicators: glxewIsSupported() says 1.  
> \> System supports OpenML OML\_sync\_control extension for high-precision scheduled swaps and timestamping.  
> \> OpenML OML\_sync\_control extension enabled for all scheduled swaps.  
> \> PTB-DEBUG: Interrogation done.  
> \>   
> \> RandR: 1024x768\_100.00 (0xa9) 112.2MHz  
> \> h: width 1024 start 1096 end 1200 total 1376 skew 0  
> \> v: height 768 start 771 end 775 total 816  
> \> RandR: 1024x768\_100.00 (0xa9) 112.2MHz  
> \> h: width 1024 start 1096 end 1200 total 1376 skew 0  
> \> v: height 768 start 771 end 775 total 816  
> \> PTB-DEBUG: glClear splash image top-left reference pixel: 255 255 255  
> \> PTB-INFO: Threshold Settings for successfull video refresh calibration are: maxStdDev = 0.200000 msecs,maxDeviation = 10.000000 %, minSamples = 50, maxDuration = 5.000000 secs.  
> \> PTB-DEBUG: Screen 1 [head 1]: vbl\_start = 812 vbl\_end = 44 vactive = 816.  
> \> PTB-INFO: Screen 1 [head 1]: Applying beamposition corrective offsets: vblbias = 44, vbltotal = 816.  
> \>   
> \>   
> \> PTB-DEBUG: Output of all acquired samples of calibration run follows:  
> \> PTB-DEBUG: Sample 0: 0.000000  
> \> PTB-DEBUG: Sample 1: 0.010005  
> \> PTB-DEBUG: Sample 2: 0.010005  
> \> PTB-DEBUG: Sample 3: 0.010006  
> \> PTB-DEBUG: Sample 4: 0.010005  
> \> PTB-DEBUG: Sample 5: 0.010005  
> \> PTB-DEBUG: Sample 6: 0.010005  
> \> PTB-DEBUG: Sample 7: 0.010005  
> \> PTB-DEBUG: Sample 8: 0.010006  
> \> PTB-DEBUG: Sample 9: 0.010005  
> \> PTB-DEBUG: Sample 10: 0.010005  
> \> PTB-DEBUG: Sample 11: 0.010005  
> \> PTB-DEBUG: Sample 12: 0.010005  
> \> PTB-DEBUG: Sample 13: 0.010005  
> \> PTB-DEBUG: Sample 14: 0.010005  
> \> PTB-DEBUG: Sample 15: 0.010006  
> \> PTB-DEBUG: Sample 16: 0.010005  
> \> PTB-DEBUG: Sample 17: 0.010005  
> \> PTB-DEBUG: Sample 18: 0.010005  
> \> PTB-DEBUG: Sample 19: 0.010005  
> \> PTB-DEBUG: Sample 20: 0.010007  
> \> PTB-DEBUG: Sample 21: 0.010005  
> \> PTB-DEBUG: Sample 22: 0.010005  
> \> PTB-DEBUG: Sample 23: 0.010005  
> \> PTB-DEBUG: Sample 24: 0.010005  
> \> PTB-DEBUG: Sample 25: 0.010005  
> \> PTB-DEBUG: Sample 26: 0.010006  
> \> PTB-DEBUG: Sample 27: 0.010005  
> \> PTB-DEBUG: Sample 28: 0.010005  
> \> PTB-DEBUG: Sample 29: 0.010005  
> \> PTB-DEBUG: Sample 30: 0.010005  
> \> PTB-DEBUG: Sample 31: 0.010005  
> \> PTB-DEBUG: Sample 32: 0.010005  
> \> PTB-DEBUG: Sample 33: 0.010005  
> \> PTB-DEBUG: Sample 34: 0.010005  
> \> PTB-DEBUG: Sample 35: 0.010005  
> \> PTB-DEBUG: Sample 36: 0.010005  
> \> PTB-DEBUG: Sample 37: 0.010005  
> \> PTB-DEBUG: Sample 38: 0.010005  
> \> PTB-DEBUG: Sample 39: 0.010005  
> \> PTB-DEBUG: Sample 40: 0.010005  
> \> PTB-DEBUG: Sample 41: 0.010005  
> \> PTB-DEBUG: Sample 42: 0.010005  
> \> PTB-DEBUG: Sample 43: 0.010006  
> \> PTB-DEBUG: Sample 44: 0.010005  
> \> PTB-DEBUG: Sample 45: 0.010006  
> \> PTB-DEBUG: Sample 46: 0.010005  
> \> PTB-DEBUG: Sample 47: 0.010005  
> \> PTB-DEBUG: Sample 48: 0.010005  
> \> PTB-DEBUG: Sample 49: 0.010006  
> \> PTB-DEBUG: Sample 50: 0.010005  
> \> PTB-DEBUG: End of calibration data for this run...  
> \>   
> \>   
> \>   
> \> PTB-INFO: OpenGL-Renderer is nouveau :: Gallium 0.4 on NV86 :: 3.0 Mesa 11.2.0  
> \> PTB-INFO: VBL startline = 768 , VBL Endline = 815  
> \> PTB-INFO: Measured monitor refresh interval from beamposition = 10.005163 ms [99.948400 Hz].  
> \> PTB-INFO: Will try to use OS-Builtin OpenML sync control support for accurate Flip timestamping.  
> \> PTB-INFO: Measured monitor refresh interval from VBLsync = 10.005183 ms [99.948195 Hz]. (50 valid samples taken, stddev=0.000490 ms.)  
> \> PTB-INFO: Reported monitor refresh interval from operating system = 10.002901 ms [99.971001 Hz].  
> \> PTB-INFO: Small deviations between reported values are normal and no reason to worry.  
> \> PTB-INFO: Support for fast OffscreenWindows enabled.  
> \>   
> \>   
> \>   
> \>