Synch trouble on linux Ubuntu 18.04 with GeForce GTX 1650 nvidia GPU

Hardware
2

Hi Lilian,

Your Psychtoolbox is way too old to recognize your graphics card. Updating to the latest 3.0.16 beta for Octave from NeuroDebian should solve that:

http://neuro.debian.net/pkgs/octave-psychtoolbox-3.html#pkg-octave-psychtoolbox-3

I have the same GTX1650 is my most modern NVidia card, so i know that it works with current PTB at least on Ubuntu 20.04-LTS. Ie. timestamping is fine and accurate, timing is usually fine.

Maybe the problem resolves itself after the PTB update. Otherwise, the proper mapping is probably one that only changes the index of the display engine, what is called GPU-CRTC in that output e.g., something like

Screen(‘Preference’, ‘ScreenToHead’, 0, 0, 1);
Screen(‘Preference’, ‘ScreenToHead’, 1, 0, 0);

Usually the 3rd number is what goes wrong as it can’t be auto-detected by PTB on NVidia hardware, and so it uses a heuristic that may or may not be right for any given setup.

Given that the diagnostics of VBLSyncTest relies on precise timestamps and you don’t have these with the broken timestamping, VBLSyncTest may miss problems.

Timing should work out of the box on the standard GNOME or Ubuntu desktop setup if i remember correctly. On KDE with a multi-display setup you may need to disable the compositor, e.g., SHIFT+ALT+F12, or change the setting in the KDE control center.

If it doesn’t work consistently out of the box then either it is some temporary system overload/timing jitter, or some NVidia proprietary graphics driver bug or incompatibility and there isn’t anything we could do about it. Maybe upgrade/downgrade the driver and hope for the best? Maybe upgrade to Ubuntu 20.04-LTS and hope for the best? Seems to work on my 20.04-LTS system with the 445.something driver.

Yes, they are discouraged, exactly because of the kind of problems you see, which are non-issues on gpu’s with open-source driver like AMD for high-performance/functionality needs and Intel for more modest performance/functionality needs.

Discrete graphics cards like yours are easily swappable, and finding a suitable replacement from AMD would likely cost less than 200 Euros. In the end it is a question of how much your time and productivity is worth to you or your employer/lab leader. By using a card with proprietary driver, you are depriving yourself of half the advantage of switching to Linux in the first place. At least you will still get better diagnostics even with NVidia on Linux, so you can’t as easily fool yourself into corrupted data collection as on Windows, or even worse on Apples macOS trainwreck.

best,
-mario