as I couldn't get dual display running on my CM3L hardware I've started some tests with my freshly arrived RPi 4 2GB.
Started with DSI display only which worked fine from the start.
With DSI still connected I've added a HDMI display which did not show any content. Don't know what I did exactly but suddenly the HDMI display came to life and I had dual display running. Tested the screen configuration tool and so far s good.
Anyhow, will try with a fresh SD card to see if I'm able to replicate it.
Now off to new horizons! With the HDMI configured as primary display I've tried to get my Adafruit 5in + Kippah running. Well, what should I say ... tried x configs ... checked wiring y times because the screen was not working. Then had the idea to check the status of my GPIO with 'raps-gpio get'.
Surprise surprise! GPIO were still at default!
Conclusion: from my testing I need to say that 'dtoverlay=dpi24' fails to initialize GPIO to ALT2 mode for DPI. Changing the method of how to initialize to 'gpio=0-27=a2' and the DPI display started to work.
Strange to see that the GPIO timing seems to have changed for Pi4 as the display image is incorrect. By the way: I know that jamesh has such a display in the office (or knows somebody who has one), so should be easy to replicate. I've used the timing from DPI page, but here is my full config.txt for your reference :
Code: Select all
# For more options and information see
# Some settings may impact device functionality. See link above for details
# uncomment if you get no picture on HDMI for a default "safe" mode
# uncomment this if your display has a black border of unused pixels visible
# and your display can output without overscan
# uncomment the following to adjust overscan. Use positive numbers if console
# goes off screen, and negative if there is too much border
# uncomment to force a console size. By default it will be display's size minus
# uncomment if hdmi display is not detected and composite is being output
# uncomment to force a specific HDMI mode (this will force VGA)
# uncomment to force a HDMI mode rather than DVI. This can make audio work in
# DMT (computer monitor) modes
# uncomment to increase signal to HDMI, if you have interference, blanking, or
# no display
# uncomment for composite PAL
#uncomment to overclock the arm. 700 MHz is the default.
# Uncomment some or all of these to enable the optional hardware interfaces
# Uncomment this to enable the lirc-rpi module
# Additional overlays and parameters are documented /boot/overlays/README
# Enable audio (loads snd_bcm2835)
# Enable DRM VC4 V3D driver on top of the dispmanx display stack
# Dustom DPI timing for Adafruit 5in + Kippah
dpi_timings=800 0 40 48 88 480 0 13 3 32 0 0 0 60 0 32000000 6
here's the original image: https://drive.google.com/file/d/1hBS80x ... nDjJe/view
Strange thing that happens with DPI display is where the driver places it. Both display were overlapping! Sure, one can use the screen configuration tool to arrange them, but why is it working correctly in case of DSI and not for DPI?
This is what it looks like:
https://drive.google.com/file/d/1uzcuKw ... G65Yu/view
https://drive.google.com/file/d/17k4kbG ... y8-eY/view
Also noted during boot that DSI or DPI always will show console/boot screen up to the point where the new driver kicks in. Might only be a minor problem but can cause some issues, so would like to understand why this is happening.
Note: The Pi get's really hot ... so hot that one can burn his fingers when touching the board for longer time. That's why I did not dare to put it into the new official case.