Visual synchronization error using an AMD Radeon RX 9070 XT card with Ubuntu 24.04 LTS

Hardware
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1

Dear PTB Team,

We have the latest licensed PTB Version (3.0.22.3) installed on Ubuntu 24.04.4 LTS with Matlab 2025b.

The CPU is a AMD Ryzen 9 9950X x 32 and the graphics card is a AMD Radeon RX 9070 XT.

Nevertheless, we are experiencing issues with the use of „pageflipping“ which may result in unreliable visual timing.

Using the DriftDemo for example -

the error messages are:

PTB-INFO: Psychtoolbox license is active on this machine for 358 more days until Sat Aug 14 16:40:55 2027

PTB-INFO: Up to 119 more days of offline use without internet connection, or offline reactivation, are possible until Sat Dec 19 12:36:34 2026

PTB-INFO: The support authentication token would be: 01a023f1-c27d-7f90-a69c-717da2d787c9

…

PTB-INFO: This is Psychtoolbox-3 for GNU/Linux X11, under Matlab 64-Bit Intel (Version 3.0.22 - Build date: Aug 10 2026).

PTB-INFO: OS support status: Linux 7.0.0-28-generic Supported.

…

PTB-INFO: OpenML OML_sync_control implementation with problematic glXGetSyncValuesOML() function detected. Enabling workaround for ok performance.

PTB-WARNING: Flip 3 for window 10 didn’t use pageflipping for flip. Visual presentation timing and timestamps are likely unreliable!

PTB-WARNING: Something is misconfigured on your system, otherwise pageflipping would have been used by the graphics driver for reliable timing.

PTB-WARNING: However, if you see this message only sporadically, this might be caused by onscreen popup messages a la “You have new mail!” or

PTB-WARNING: “New updates are ready to install” etc. Being low on free system memory can cause this as well, especially on integrated graphics chips.

PTB-WARNING: Read the Linux specific section of ‘help SyncTrouble’ for some other common causes and fixes for this problem.

… until Flip 12, then…

WARNING: VBL Calibration run No. 1 failed. Retrying…

PTB-WARNING: Flip 13 for window 10 didn’t use pageflipping for flip. Visual presentation timing and timestamps are likely unreliable!

PTB-WARNING: Something is misconfigured on your system, otherwise pageflipping would have been used by the graphics driver for reliable timing.

PTB-WARNING: However, if you see this message only sporadically, this might be caused by onscreen popup messages a la “You have new mail!” or

PTB-WARNING: “New updates are ready to install” etc. Being low on free system memory can cause this as well, especially on integrated graphics chips.

PTB-WARNING: Read the Linux specific section of ‘help SyncTrouble’ for some other common causes and fixes for this problem.

… until Flip 19, then…

WARNING: VBL Calibration run No. 2 failed. Retrying…

WARNING: Will enable VBL busywait-workaround before trying final VBL Calibration run No. 3.

WARNING: This will hopefully work-around graphics driver bugs of the GPU sync-to-retrace mechanism. Cross your fingers!

PTB-WARNING: Flip 20 for window 10 didn’t use pageflipping for flip. Visual presentation timing and timestamps are likely unreliable!

PTB-WARNING: Something is misconfigured on your system, otherwise pageflipping would have been used by the graphics driver for reliable timing.

PTB-WARNING: However, if you see this message only sporadically, this might be caused by onscreen popup messages a la “You have new mail!” or

PTB-WARNING: “New updates are ready to install” etc. Being low on free system memory can cause this as well, especially on integrated graphics chips.

PTB-WARNING: Read the Linux specific section of ‘help SyncTrouble’ for some other common causes and fixes for this problem.

… until Flip 26 …

PTB-WARNING: Flip 26 for window 10 didn’t use pageflipping for flip. Visual presentation timing and timestamps are likely unreliable!

PTB-WARNING: Something is misconfigured on your system, otherwise pageflipping would have been used by the graphics driver for reliable timing.

PTB-WARNING: However, if you see this message only sporadically, this might be caused by onscreen popup messages a la “You have new mail!” or

PTB-WARNING: “New updates are ready to install” etc. Being low on free system memory can cause this as well, especially on integrated graphics chips.

PTB-WARNING: Read the Linux specific section of ‘help SyncTrouble’ for some other common causes and fixes for this problem.

PTB-WARNING: Couldn’t even collect one single valid flip interval sample! Sanity range checks failed!

PTB-WARNING: Could be a system bug, or a temporary timing problem. Retrying the procedure might help if

PTB-WARNING: the latter is the culprit.

PTB-INFO: OpenGL-Renderer is AMD :: AMD Radeon RX 9070 XT (radeonsi, gfx1201, LLVM 20.1.2, DRM 3.64, 7.0.0-28-generic) :: 4.6 (Compatibility Profile) Mesa 25.2.8-0ubuntu0.24.04.2

PTB-INFO: Screen 1 : Window 10 : VBL startline = 768 : VBL Endline = -1

PTB-INFO: Will try to use OS-Builtin OpenML sync control support for accurate Flip timestamping.

PTB-INFO: Reported monitor refresh interval from operating system = 16.689197 ms [59.918999 Hz].

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

WARNING: Mismatch between measured monitor refresh interval and interval reported by operating system.

This indicates massive problems with VBL sync.

----- ! 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.

——————————————————————————————————————————————————————————————————

Do you have any ideas what to try next to solve the timing problems?

Best regards,

Till

2

Hi,

that’s the same issue as the thread referenced by the following post:

Cause:

Your AMD graphics card is more recent than the AMD driver shipping with the latest Ubuntu 24.04 LTS at the moment, as the graphics card was introduced after Ubuntu’s April 2024 release date. The included AMD X-Video driver can’t handle the card fully.

Solution: Run XOrgConfCreator(1) for expert mode, and answer “Use advanced settings?” with yes and “Use modesetting driver …?” with yes and select the created xorg.conf via XOrgConfSelector, then logout and login.

This switches from the outdated AMD specific X-Driver to the generic modesetting X-Driver, which can deal with your graphics card.

See the full referenced thread for thoughts about Ubuntu 26.04-LTS and further background info.

-mario

3

Dear Mario,

The solution with the modesetting driver for the AMD card worked for Ubuntu 24.04 LTS. Thank you for the support.

Meanwhile we found another solution with Kubuntu 26.04 LTS, which uses KDE and therefore has a smooth integration of X11. The AMD driver (amdgpu) is working with this system. It seems like an interesting option for those who want to use AMD cards in the future, as Kubuntu does not rely on Wayland, but uses X11 as a standard.

Best regards,

Till

4

Yes, KDE on (K)ubuntu 26.04-LTS would be the way forward, or any other desktop that still works with X11 native. Essentially, I think, any desktop environment except Ubuntu’s native Ubuntu desktop GUI or Gnome desktop.

One difference between Kubuntu and Ubuntu LTS is that the long-term support with regular Ubuntu 26.04-LTS is longer than with Kubuntu 26.04-LTS wrt. software and security updates, from what I understand. One can install KDE on regular Ubuntu - that’s how I do it, as I generally prefer KDE. It’s about one or two packages, whose exact name I always forget.

I did some light testing of the basics for Ubuntu 26.04-LTS a few months ago, and KDE seemed to behave just fine wrt. Psychtoolbox. I just haven’t had the time yet for the full extensive testing. That’s why my official recommendation on the website so far hasn’t changed from 24.04-LTS to 26.04-LTS. Also, “our” PTB mex files for Octave do not yet support 26.04-LTS, only the Matlab mex files should.