I use a RPi3 with the Recalbox OS for some retrogaming. And I want to use the official 7" DPI monitor when it's portable, and the HDMI when I connect it to the TV. I tried plugging the HDMI cable in, and it registers and switches channel, but the picture is just black on the tv and the 7" display is still working.
Can I somehow make this work automatically, without changing the config.txt file every time I want to change output? Or is it possible to mirror the DPI output to the HDMI output?