So I'm trying to connect with a UART cable from my PC to the board (OPI3LTS). Here's what I did so far:
 

In desperation, I double checked every connection, to no avail. My devices are powered separately, so only the RX and TX cable are connected, and they are crossed as they should.

 

Set up permissions:

sudo chmod 666 /dev/ttyUSB0

 

Add user to dialout:

sudo adduser <user> dialout

 

Install minicom:

Set up minicom with the correct address: /dev/ttyUSB0
Set up the correct baud rate (115200 in this case)
Turn off flow control

 

Tried connecting via "screen", minicom and putty, all of them just show me a black CLI I can't write in.

 

Help? 🥲

Edited March 16, 20251 yr by devmichelcastilho

Still no clue what's happening...

Hi,

 

are you using a usb to serial converter or the real serial com port?

I did not see any ttyUSB0 listed in your boot log.

In case of the real serial com port you should not be using /dev/ttyUSB0, but /dev/ttyS0.

 

Using screen is sufficient. No settings besides baud rate (115200 for any Allwinner) need adjustments.

As mentioned above make sure your serial device is correct. If you are unsure, simply

- unplug

- run sudo dmesg -ew

- plug in and check output in the terminal with the command above.

 

Also make sure wiring is correct. Ground to ground and rx/tx crossed.

Thank you so much for the responses, IBV and Werner!

I'm connecting from the PC USB to the SBC serial com port, then attempting to run Screen from the PC.

Did you also start screen or minicom on the SBC ?

For example:
 

screen /dev/ttyS0 115200

 

And on PC:

screen /dev/ttyUSB0 115200

Make sure you use the same speed on both sides.

 

 

 

run dmesg, after you plug that uart into the port

it should show the usb dongle connected and the port

 

then a few more thiings,

• bad wires ensure that no matter what you do no data pass over the wires (I've seen this, especially those dupont pin connections)
• wrong connections ensure that no matter what you do no data pass over the wires. Are you sure you are talking to the correct *pins* and *port* on the host side?
• lousy dongles ensure that no matter what you do no data pass over the wires, get 'better' ones. oh well, this depends a little on luck, but I used ch340 usb-uart bridges, and they worked just well
  https://www.aliexpress.com/w/wholesale-ch340-uart.html
  searching usb uart normally returns a lot of entries
  https://www.aliexpress.com/w/wholesale-usb-uart.html
  if one doesn't work, try another
• oh then there is DTS overlay etc, sometimes that fix is needed
• bad / no drivers etc (dmesg should show it, on windows your mileage may vary)
• etc etc

 

the rationale is, if you did it once successfully, either remember how you did it or document it

 

sometimes, alternatives include, connect hdmi to monitor, usb keyboard and mouse and use as alternative console, mileage may vary.

 

 

I'll try those ag123, thanks!