Problem with serial port Jetson nano B01

I have a problem with the serial port as follows:
I use the serial ttyTHS1 to communicate Jetson B01 kit with an MCU, normally if I don’t plug in the usb cable to connect the Jetson B01 to the computer, and then Jetson KIT boots successfully, the data transmission between Jetson and the MCU via ttyTHS1 is good, but when I plug in the usb cable to connect the Jetson and the computer then reboot the jetson board the MCU can’t communicate with the Jetson via ttyTHS1 anymore. Only when I eject USB that the computer recognizes Jetson as a usb device and remove usb cable and then reboot Jeson KIT, the transmission is back to normal. I want to know why is that? Is there any way to fix this problem?

Hi thuantran.tdh,

Are you using the devkit or custom board for Jetson Nano?

Could you help to try the following command after connect the USB to host PC?

$sudo systemctl stop nvgetty.service
$sudo systemctl disable nvgetty.service

If the issue still exists, please help to provide the serial console log of both situation.

I will add that after you’ve disabled the serial console the way @KevinFFF mentions, you should see if it outputs any debug content during boot by connecting it to a serial console program. Use setting 115200 8N1. If there is no output, then you are good to go; if there is boot content from early boot stages, then it is still enabled in the bootloader as a serial terminal and would need to be disabled further. Serial console is able to interrupt boot, and if there is any activity on the line during boot, then it think someone hit a key on the keyboard and wants to halt and drop into a shell.

thanks for your supports, i realized that, when jetson is connected to the MCU via ttyTHS1, if the jetson hasn’t started yet and the MCU sends data, it will cause the above problem. So I rewrote the MCU firmware to wait for jetson to successfully start up before the MCU starts sending data.

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