That's very cool, but just to point out: that's not JTAG, it's serial (UART).
JTAG is a much lower level protocol, typically used for hardware or low-level software debugging. Serial/UART gives you a command-line interface to the software that's running.
Using a JTAG interface is a lot more complicated. If you're interested in playing with it, check out OpenOCD.
There's a bunch of train video channels on YouTube (because, of course there are). I love throwing on something like [1] just as background while I'm working.
JTAG is a much lower level protocol, typically used for hardware or low-level software debugging. Serial/UART gives you a command-line interface to the software that's running.
Using a JTAG interface is a lot more complicated. If you're interested in playing with it, check out OpenOCD.