1

I am trying to set up the teacher's computer in a university room, having two identical displays on the table. One of these displays should be duplicated on the e-Blackboard connected via HDMI. Obviously, the computer has two graphical cards (the internal card does not support more than two outputs at one, despite having four ports: VGA, DVI, DP and HDMI. Another card has DVI and VGA. We managed to successfully connect two desktop monitors via two DVI ports. We also can connect the e-Blackboard via the HDMI port and make an extended display, not using anythyng more than the standard MATE Display configuration GUI tool. In xrandr output, this looks like:

profesors@ZK10-431-P:~$ xrandr --listmonitors
Monitors: 3
 0: +*HDMI-1-1 1920/521x1080/293+0+0  HDMI-1-1
 1: +DVI-0 1920/521x1080/293+1920+0  DVI-0
 2: +HDMI-1-2 3840/1660x2160/934+3840+0  HDMI-1-2

However, if I try to make the monitor 2 duplicated on the e-Blackboard 3 AND scale the image twice to stretch it over the whole blackboard, I am having issues.

xrandr --output HDMI-1-1 --mode 1920x1080 --primary --pos 0x0 --output DVI-0 --mode 1920x1080 --pos 1920x0 --output HDMI-1-2 --scale-from 1920x1080 --same-as DVI-0

causes the e-Blackboard to only show the 2nd display in the upper left quarter, with the same resolution as on the desktop monitor.

Same is with:

xrandr --output HDMI-1-1 --mode 1920x1080 --primary --pos 0x0 --output DVI-0 --mode 1920x1080 --pos 1920x0 --output HDMI-1-2 --mode 3840x2160 --scale 0.5x0.5 --scale-from 1920x1080 --same-as DVI-0

and also

xrandr --output HDMI-1-1 --mode 1920x1080 --primary --pos 0x0 --output DVI-0 --mode 1920x1080 --pos 1920x0 --output HDMI-1-2 --same-as DVI-0 --mode 3840x2160 --scale 0.5x0.5

EDIT: Interestingly, whenever I call xrandr again with any combination of options, even same options in different order, it causes a crash after which it becomes impossible to apply any xrandr command (same error message will be printed after this and any subsequent xrandr command):

X Error of failed request:  BadValue (integer parameter out of range for operation)
  Major opcode of failed request:  140 (RANDR)
  Minor opcode of failed request:  7 (RRSetScreenSize)
  Value in failed request:  0x0
  Serial number of failed request:  50
  Current serial number in output stream:  51

Also, if I put the e-Blackboard (HDMI-1-2) in front of DVI-0 and added --same-as HDMI-1-2 to DVI-0, the MATE (or should I say lightdm?) crashed altogether, throwing me out to the login screen, often with black desktop monitors and picture only on the e-Blackboard (which was super convenient), and the only way to resolve was to restart the PC.

Finally:

xrandr --output HDMI-1-1 --mode 1920x1080 --primary --pos 0x0 --rotate normal --output DVI-0 --mode 3840x2160 --scale 2x2 --pos 1920x0 --rotate normal --output HDMI-1-2 --same-as DVI-0

causes:

xrandr: cannot find mode 3840x2160

for obvious reasons...

Can anyone suggest anything please?

2
  • I edited because the reasons for the crash are more likely to be just calling xrandr another time, not a specific combination...
    – Esmu Igors
    Aug 30, 2022 at 16:14
  • Note, there is a GUI arandr that might help when trying out new configurations.
    – meuh
    Aug 30, 2022 at 16:43

1 Answer 1

1

My colleague came in and suggested the obvious: I just changed the e-Blackboard's resolution to 1920x1060 instead of 3840x2160. This solution was so plainly obvious that it completely escaped me before... <:-D

You must log in to answer this question.

Not the answer you're looking for? Browse other questions tagged .