RPi4 2 X-Screens does not work

Using RPi4 OS11 bullseye (version of PTB3 is - all pageflipping, sync tests work well. Latency of visual stimulation verified with a photodiode ~4ms).

I am trying to set up 2 X-screens with the device, so that I can use 1 screen for visual stimulation, and the 2nd screen for looking at octave outputs. I did the XOrgConfCreator and XOrgConfSelector steps, assigned 2 screens accordingly.

However, when I log out after running XOrgConfSelector and selecting the config file for 2 x-screens, the screen goes blank and I get no hdmi output from the RPi4. Only thing I see is the black screen with a white bar(?) on the top left corner. I could reset the screens back to normal by deleting the config files or by editing the driver information in the /boot/config.txt file but cannot seem to get this working.

Any ideas? Thanks

Visual onset timestamping was verified by myself with a Datapixx on the older RPi 2B at some time before the pandemic to be accurate to <= 1 msec, and if I remember correctly also by myself with a VideoSwitcher+RtBox on the RPi 400 sometime early last year on RPi OS 10, so a measured latency of 4 ms with photodiode sounds about right, as most of it will be pixel switching latency of your display monitor, or of photo-diode response itself. Good!

I’m a bit surprised the sync tests and pageflipping would work on the latest and most up to date RPi OS 11 under PTB, as I just recently had to release PTB to work around changes in RPi OS 11 which broke pageflipping. That was just 10 days ago.

RPi was not ever tested by myself in a dual-X-Screen or dual-display configuration, only single-display, as I don’t have suitable 2nd microHDMI->HDMI adapter cable for RPi 4/400. Therefore there could be issues or (unknown to myself) bugs in the OS for dual-x-screen in theory, or even bugs with XOrgConfCreator, if the Pi needed special treatment.

If your lab did the right, rational and sane thing in time and bought a paid support membership in time, please post the authentication token generated via PsychPaidSupportAndServices, together with the xorg.conf file generated by XOrgConfCreator, and the Xorg.0.log file from a failed attempt, likely to be found in /var/log/Xorg.0.log, maybe also the output of the sudo dmesg command.

If you don’t possess a paid valid support membership already, I won’t be able to help you until late September. Our license management person started his summer vacation today and will be out of office until early September, so while labs can still buy paid memberships in our online shop, the bought license keys likely won’t get activated and become usable until he is back from vacation. But then my summer vacation will likely start, so no paid support will happen until I’m back and caught up late September.


Thanks for the response Mario. I’ll talk to the lab to purchase a support membership and then bother you again in late September. Thanks for supporting the pi and PTB3!