What did you see from “ls -l /dev/ttyTHS1 /dev/ttyS1”? Also, if worried about voltages, is your USB serial UART running at the correct 3.3V level?
What did you see from “ls -l /dev/ttyTHS1 /dev/ttyS1”? Also, if worried about voltages, is your USB serial UART running at the correct 3.3V level?