I use Raspberry Pi 4 CM in bound with CM4-to-Pi4-Adapter. I've flashed a custom Yocto-image in that, using rpiBoot and RPi Imager for. Now I'm trying check my Raspberry's features, but when I try to connect it to Waveshark HDMI LCD (H) display (1024 X 600) there is nothing. The display once it powered on ligths grey then shows a some weird screen for a half of the second and finally stays black. The green light on the board glows brightly at the same time, but at some point it blinks very quickly and dims. I can see faint periodic blinks, like a pulsation, but I find it difficult to say which ones, short or long, as in the documentation.
I don't literally have any idea where should I find an error. The Yocto image I use just simple core-image-minimal with ssh and some Qt and GPIO's libraries included. The flashing was succesful as Imager says.
The screen output, sorry for blurry and overexposed photo
I've searched a lot of forums with same problems and done some steps from, like change a config.txt file, especially hdmi fields, but with some values of them I don't see even the screen I've uploaded.
The answer was hidden at https://www.waveshare.com/wiki/7inch_HDMI_LCD_(H)_(with_case)
Just add this at the end of the config.txt:
config_hdmi_boost=10
hdmi_group=2
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0
And change in # Enable VC4 Graphics:
dtoverlay=vc4-kms-v3d to dtoverlay=vc4-fkms-v3d