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Troubleshooting • Re: Raspberry Pi 3a/Bookworm + Lo-tech VGA HAT woes

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So RE: Issue 1

I'm running Raspberry Pi OS (Bookworm) 32-bit Lite.

With these commented out it works:

#dtoverlay=vc4-kms-v3d
#max_framebuffers=2

As it falls back to fbdev "legacy" mode and works fine even on Bookworm. Sadly, without any 3d acceleration and slower graphics.

So, from what you've said this isn't possible without a vc4-kms-vga666. However, I don't think this will work as dpi24 uses extra pins and it doesn't appear vga666 is a perfect subset (due to lower color depth). Unfortunately vc4-kms-dpi-generic doesn't support dpi24 either and vc4-kms-dpi-dpi24 doesn't exist.

I think to use an accelerated driver I would need a different VGA hat or to patch generic to work. I might shelve this for now as its not the main issue. Thanks for pointing me in the right direction!

Issue 2 & 3 I am still unsure about.

2) Can anyone else with other hats change resolution AFTER reboot using xrandr after adding the custom resolutions, or are we stuck on what is specific in config.txt?

3) Do resolutions 640x480 and under work?

Thanks!
bookworm uses wlr-randr

where do you get that Info from that 'vc4-kms-dpi-generic‘ doesn't support 24bit?
from the README

Code:

rgb565                  Change to RGB565 output on GPIOs 0-19        rgb565-padhi            Change to RGB565 output on GPIOs 0-8, 12-17, and                                20-24        bgr666                  Change to BGR666 output on GPIOs 0-21.        bgr666-padhi            Change to BGR666 output on GPIOs 0-9, 12-17, and                                20-25        rgb666-padhi            Change to RGB666 output on GPIOs 0-9, 12-17, and                                20-25        bgr888                  Change to BGR888 output on GPIOs 0-27        rgb888                  Change to RGB888 output on GPIOs 0-27
sorry, don't know the HAT you're using but from their wiki they don't seem to be aware what exists
https://www.lo-tech.co.uk/wiki/Lo-tech_RPi_VGA_Adapter so would consider it as 'low-tech' *lol*

what does below give you?

Code:

dtoverlay=vc4-kms-dpi-genericdtparam=clock-frequency=29500000dtparam=rgb888=1dtparam=bus-format=0x100adtparam=width-mm=154,height-mm=83dtparam=hactive=800,hfp=24,hsync=72,hbp=96dtparam=vactive=480,vfp=3,vsync=10,vbp=7dtparam=hsync-invert,vsync-invert
lowest resolution I've used on DPI was 480x272
Image

Statistics: Posted by aBUGSworstnightmare — Sat Jun 21, 2025 10:26 am



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