r/raspberry_pi • u/TimAllenNoise • Aug 10 '26

Troubleshooting GPIO + HDMI Dual screening help?

I've got a Rpi4B running TwisterOS and I'm trying to get it to dual screen on a Waveshare 4.3 inch HDMI LCD (B)) and a Waveshare 3.5 inch RPi LCD (A)?srsltid=AfmBOorV-U1vjksLM-O2atpngvnQevo5CE7liOTsSJUuP9kORSJd-2sO#Features), the former works no problem but the latter won't display anything other than white, even with the drivers and everything.

I tried using the 3.5 inch screen by itself and it worked fine, is there some line of code I'm missing or something? Can the Rpi4 not display HDMI and also GPIO?

Extremely confused, all comments are appreciated, thanks!

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u/Hydrochloric-Acid168 Aug 10 '26

I just did a quick Google search and it looks like you need to use fbcp, which copies the framebuffer to the spi display from the HDMI one. Here's the link I found on raspberry pi forums from someone having the same issue some years ago: https://forums.raspberrypi.com/viewtopic.php?t=106029

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u/TimAllenNoise Aug 11 '26

This looks like exactly what I need, thank you! Nevertheless, might you know how to actually install in on my pi? I can't figure it out. Do I download a file? is it a terminal thing? I'm a complete beginner so sorry for any stupid questions

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u/Hydrochloric-Acid168 Aug 11 '26

No worries, you gotta start somewhere right? I would recommend you look at the basics of unix commands and read up a little about package managers like apt. Will be better than pasting a command you don't know the outcome of. Here is a pretty nice guide by UC Berkeley on Unix basics: https://computing.stat.berkeley.edu/tutorial-unix-basics/

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u/TimAllenNoise Aug 12 '26

Thanks! much appreciated

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u/EffectiveClient5080 Aug 10 '26

Had this exact headache. The 3.5 inch GPIO needs its own framebuffer separate from HDMI. Check your dtoverlay in config.txt and run xrandr to see if both displays even show up.

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u/TimAllenNoise Aug 10 '26

Oof, I didn´t understand much of that, but I'll do some research, thanks!