When an HDMI or DisplayPort monitor or TV is connected to a board, the board reads a small file called the EDID or Extended Display Identification Data from the display. The EDID provides information such as supported colors, resolutions, frequencies, and scan zones.
The board will check the list and try to find the first compatible mode based on this EDID data. This requires that the board be capable of generating a clock signal that it is able to use to synchronize with the display’s clock signal.
SBCs are more limited than full-blown GPUs in being able to generate arbitrary frequency clock signals so only certain major resolutions are well supported. Other resolutions are not well tested and may require some special clock generation strategy that varies depend on the specific implementation. Some clock frequencies might not be supported at all.
If you get no video and the board has booted, it is probably due to this issue. To help us improve our software, please report your monitor’s information to us so we can test these special modes and try to add support in the software.
To get the EDID file location of your monitor, run find /sys -iname edid. Copy the file to your home directory sudo cp EDID_FILE_PATH ~/edid and run xxd edid to dump the file as hex so you can post it.
To decode EDID, we recommend using edid-decode command, which will present a human readable breakdown. The parse-edid command also works but the EDID file needs to be piped into stdin and it has more limited parsing tables than edid-decode.
Since these are board/SoC specific, please use the following threads to report your monitor information.