How to enable J44 serial /dev/ttyS0 in Jetson Nano

Robotics & Edge Computing Jetson & Embedded Systems Jetson Nano
1

HI,

I need to read serial data from J44 as I am already using J41 for other serial communication.
It is used as serial console login and I can’t change permissions to enable read/write.

Current permissions:
crw–w---- 1 root tty 4, 64 jan 28 14:23 /dev/ttyS0

I change it:

sudo chmod 666 /dev/ttyS0

Add other user to tty group or to group:

sudo usermod -a -G tty user1
sudo chmod g+r /dev/ttyS0

When I make these changes, it works, but only for some seconds (it is a GPS receiver), then returns to default behavior.

I looked in udev rules for some tty which relates to S0:

/etc/udev/rules.d$ grep tty *
55-tegraserial.rules:KERNEL==“ttyTHS*”, MODE=“0666”

But it only handles the THS*.
Is there some ADD rule to make it work?

lsof output (mainly last 3 lines):

sudo lsof | grep tty
systemd-l 4076 root 7r REG 0,17 4096 16299 /sys/devices/virtual/tty/tty0/active
systemd-l 4076 root 14u CHR 4,6 0t0 3149 /dev/tty6
systemd-l 4076 root 19u CHR 4,1 0t0 3146 /dev/tty1
agetty 4940 root cwd DIR 179,1 4096 2 /
agetty 4940 root rtd DIR 179,1 4096 2 /
agetty 4940 root txt REG 179,1 52296 393835 /sbin/agetty
agetty 4940 root mem REG 179,1 43336 525768 /lib/aarch64-linux-gnu/libnss_files-2.27.so
agetty 4940 root mem REG 179,1 76592 525705 /lib/aarch64-linux-gnu/libnsl-2.27.so
agetty 4940 root mem REG 179,1 43344 525642 /lib/aarch64-linux-gnu/libnss_nis-2.27.so
agetty 4940 root mem REG 179,1 31344 525712 /lib/aarch64-linux-gnu/libnss_compat-2.27.so
agetty 4940 root mem REG 179,1 3008640 399917 /usr/lib/locale/locale-archive
agetty 4940 root mem REG 179,1 1341080 525589 /lib/aarch64-linux-gnu/libc-2.27.so
agetty 4940 root mem REG 179,1 125896 525586 /lib/aarch64-linux-gnu/ld-2.27.so
agetty 4940 root 0u CHR 510,0 0t0 18720 /dev/ttyGS0
agetty 4940 root 1u CHR 510,0 0t0 18720 /dev/ttyGS0
agetty 4940 root 2u CHR 510,0 0t0 18720 /dev/ttyGS0
gdm-x-ses 5368 gdm 0u CHR 4,1 0t0 3146 /dev/tty1
gmain 5368 5370 gdm 0u CHR 4,1 0t0 3146 /dev/tty1
gdbus 5368 5425 gdm 0u CHR 4,1 0t0 3146 /dev/tty1
Xorg 5371 root 0u CHR 4,1 0t0 3146 /dev/tty1
Xorg 5371 root 11u CHR 4,1 0t0 3146 /dev/tty1
InputThre 5371 5424 root 0u CHR 4,1 0t0 3146 /dev/tty1
InputThre 5371 5424 root 11u CHR 4,1 0t0 3146 /dev/tty1
login 9395 root mem REG 179,1 10152 525805 /lib/aarch64-linux-gnu/security/pam_securetty.so
login 9395 root 0u CHR 4,64 0t0 200 /dev/ttyS0
login 9395 root 1u CHR 4,64 0t0 200 /dev/ttyS0
login 9395 root 2u CHR 4,64 0t0 200 /dev/ttyS0

I also tried usb-serial in this case but I am using camera and wi-fi in USB inputs and is conflicting with usb-serial (DMA kernel error) so my only option is UART.

I have seen many other answers like modify nvgetty behavior, etc but I none is working. I also think that Nano has different behavior than other NVidia embedded boards, as I saw some answers with ttyS0 that works.

Has anyone knows how to change this behavior and enable J44 from Jetson Nano for normal serial operation?

Thank you,

3

hello d.pensator,

could you please refer to post #3 by using the THS2 and the J44 pin.
please also check similar discussion thread, Topic 121038.
thanks

4

Ok, you suggest other workarounds. In case of usb-serial I can not use because my adaptor is conflicting with Usb camera and Usb wifi already in use.
Thanks anyway

5

After research the best solution I found is from post post which renames /dev/ttyS) to /dev/ttyS1 or any other name.
It works for my needs as it is ok to rename and change permission each boot.

But for production will be needed another solution.

I will leave this topic open, if someone finds better solution please answer.