Negative consequences of jumper UART2_RXD and UART2_TXD pins?

Hi there,

are there any bad consequences possible, if you jumper the ART2 RXD and UART2 TXD pins?
I got a nvidia jetson nano with B01 board, i wanted to jumper pins 9 and 10 of the button header to start in force recovery mode. I accidentally connected pin 3 and 4, ART2 RXD and UART2 TXD, because i counted the pins from the wrong side, then i plugged in the micro USB power supply.
For some reason i takes eternities now for the system to boot, sometimes it doesn’t even boot at all.
I also detached die sd card before to copy some files and plugged it in later, so i’m not sure, if maybe the sd card is problematic (even though i just copied files without changing anything).

Can you assure me, that i didn’t damage the hardware by connecting the wrong pins?

Electrically there is no harm in this. In fact, jumper of TX to RX (and possibly also CTS to RTS) is considered “loopback”, and is useful for testing purposes. The issue you would run into is if there is an application listening to the UART. For example, serial console.

Imagine if this is serial console, and everything output during a boot gets fed to the console’s input just as if you were sitting there typing nonsense in on the keyboard. The console could get rather confused.

Every once in awhile some nonsense might actually be a command. There might be some side effect of that command, and the side effect might be harmless, or it might be fatal (very unlikely). Just as an example, what happens if the nonsense is “rm -Rf”? That’d be a problem. What if the command was “ls”? Technically that would not be a problem, but perhaps the name of a file is also a command, e.g., if the “ls” were in “/bin”.

Was the UART being used as serial console? Was the UART associated with anything else?

If you look at the output of this:
ls -l /dev/ttyS* /dev/ttyTHS*
…then you will see permissions of all serial UARTs.

If the group of that UART is “tty”, then this is a console. If the group of the UART is “dialout”, then this is a general purpose UART and not being used as a console.

NOTE: In the naming convention ttyS# and ttyTHS#, if the “#” is the same, then it is the same UART. There are often legacy driver (the ttyS# notation) and also “Tegra High Speed” (ttyTHS#) drivers available for the UART…you just wouldn’t want to use both drivers at the same time.

Great, thank you for your detailed answer, i get the point now.