Hi
I have an issue with a custom board I designed : basically, MIDI data is received on the Serial (RX) port when the USB is connected on the computer, but it doesn't work when USB is connected to a smartphone charger.
MIDI Out works fine in both cases.
If I add a debug line on SERIAL_MIDI.read(), I can see that the Serial port receives data when the USB is connected on the computer, but there is absolutely no sign of activity when plugged to an external power source.
This makes me think that it is a hardware problem. But then, I don't understand why changing the power source would kind of de-activate the RX pin.
I am using the RP2040 Earle Philhower core.
Here is a schematic for the RP2040 / Serial MIDI part of the circuit (the whole circuit can be found here)
The code can be found here (it's pretty big)