How are we to accurately interface with the Pi board if we do not know where things get connected to the processor? A simple example are the two signals leading into U5 of the A/V portion of the Pi 4. What exactly are they, what are they connected to and how do they work? Because I doubt they are PW...

New user here and not sure this is the correct board for this, but I am looking for full schematics to the Pi 4B. All I am finding is the 4B reduced schematics and then Compute Module full schematics that are Revision 3 and thus use a different processor.

Thanks in advance!

Scott