I’m continuing here my previous topic PD Power supply on Rock 4B+ with some problem when trying to debug over the UART.
We have UART-USB convertor with FTDI FT232RL chip (the same as in the tutorial on Rockpi4 wiki). When using for the debug console, we get only a lot of garbage and the board does not boot up at all (only green light on). Could be wrong baudrate? I recompiled u-boot/dts with lower baudrate but it does not help - no output at all.
However, we are able to use for normal serial communication on UART4 (/dev/ttyS4) but only in one direction (regardless the rate, works even with 1500000). I can send data from PC to Rock but not from Rock to PC. Nothing received.
So we bought different UART-USB convertor - Waveshare based on CH343G. And the problem is exactly opposite - we can send from Rock to PC but not from PC to Rock. It could be fine for the debug console as I need output only. But there is something strange:
When the converter is connected to PC and I connect RX, TX and GND to Rock pins, the Rock’s green power lights on although the power is not connected yet. Why? Now when I connect PD PSU, the board does not start at all. Nothing happens. When I use a standard RPi 5V/3A PSU, the board starts correctly and I receive output on serial console.