ESP32C3: Serial output garbage characters ( but firmware flashing is okay)

[zjustin]

I am loading basic test sketch into ESP32C3, wifiscan code from the sample sketches.

the board is a customised board with esp32c3.
firmware flashing via serial is working fine, so the serial communication hardware aspect part should be okay.

but when I load the sample wifi scan sketch into the board, I got just garbage output in serial port.

strange thing is if I do the same with the official ESp32C3 Dev board, it is working fine.

Any idea where it could have gone wrong?