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I'm running the Qt5 application on my raspberry pi and I would like to introduce some kind of a power-saving feature.

I don't use x11 or wayland, because I don't need it, but I use gles2 (OpenGL for Embedded Systems).

I want to use tvservice --off and tvservice --preferred to toggle between turned off / turned on screen.

My problem is that when I call tvservice --preferred the display turns on but the screen is black (no application output is shown).

Question:
How can I turn it on and see the application that was running previously?

Tested:
When I restart the Qt5 application - it's being displayed correctly.

Changing foreground virtual terminal with chvt (as suggested here) does not help.

Changing framebuffer depth to different and back again with fbset -depth 16 ; fbset -depth 32 (I've seen it on some forum, cannot find which) also does not help.

Any ideas?

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1 Answer 1

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30

tvservice is not the best to turn off and on the screen.

Much better way to do this (found after a day of searching) is using vcgencmd command (more on this here).

vcgencmd display_power 0 turns off the screen

vcgencmd display_power 1 turns on the screen

This allows the Qt application to be visible on the screen after turning it off and back on.

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5
  • This is perfect! I was looking for something like this for a Pi3..
    – WreckeR
    Mar 8, 2018 at 18:27
  • 2
    Thanks, @lewiatan - I had been using tvservice with Raspian Stretch but it had the problems described in the original question when I switched to Buster. vcgencmd works as hoped.
    – Eric Smith
    Dec 20, 2019 at 16:16
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    I searched for ages with this problem, thanks for posting this. Like @EricSmith, I'm also using Raspian Buster and found that tvservice just wouldn't work. Thanks again!
    – dariom
    Mar 4, 2020 at 17:40
  • On my model 1 type B vcgencmd does nothing but tvservice works with buster. Pls. refer to forums.raspberrypi.com/viewtopic.php?t=257631
    – user333869
    Dec 4, 2022 at 14:37
  • Works on Raspian Buster 32 bit on a Pi4 with a single monitor.
    – Earl Ruby
    Apr 15 at 1:42

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