Openwrt machine is connected through the serial port to another machnie used as console. While this "console" machine operates, everything is fine. But when I shut it down and power it off, keeping it physically connected to openwrt machine, I have noticed the openwrt machine gets spare invalid false input and output from the console port - I can see it when after connecting console machine through console serial port and pressing enter key there's a garbage mostly consisting of @ character.
It would not be so a nuisance, but last time I was doing remote firmware upgrade with console machine off (but physically connected to openwrt machine), and as it later appeared, the upgrade hung just before repartitioning the internal eMMC of the openwrt machine (in the platform.sh script).
How did I know that? I turned on the console machine, connected through picocom to the console of the openwrt machine, enter key was just doing LF, but when I pressed ^C it started flashing the eMMC and completed the upgrade process.
When powering off the console machine, I explicitly performed log out of the openwrt machine from the console.
I have tried sysupgrading once more with console machine on - no problems.
I do not think we will be able to find the root cause of the problem after reimaging - what exactly have hung in the machine.
But do you have any idea - may something phantom be happening on the console wires causing such a behavior?