Subject: accessing ttyS0 or ttyUSB0

From: Iulian Tocu <[email-masked]>
Date: Tue, 4 Jun 2024 14:42:36 +0200

Hi all,

I'm trying to access a serial console of a different system. Let's
call it the target system. This target system has the boot handled
by u-boot and I need to stop it at its countdown and enter some
boot options. The target system has the u-boot console over
the serial line and it's connected to my host machine with
an old serial cable to the COM0 port.
In the past, I had a live Linux that I was using to start host
machine and I remember I was happy with "screen /dev/ttyS0 115200".
Today, I've installed Alpine Linux v3.20 32-bit to my host machine
(install mode: sys) and I see strange output from my target system
no matter if I'm using mincom ("minicom -D /dev/ttyS0 -b 115200")
or screen.
It looks like the line feed or some settings are not correct on
this serial line. So I've started to play with some stty commands
but I didn't find a proper configuration for my ttyS0.
Also I'm not able to enter any commands (or stop the u-boot).
Next, I've brought in my host system an USB-to-serial dongle and
switch my attempts to /dev/ttyUSB0 but again without success. Same
output problem, same ignored-input problem.
I noticed that my settings set by stty are also changing back somehow.
So beside the usual 115200/8/N/1, I think I'm missing something.
Do you have any hints for me to find the proper way?

Thanks!
Iulian