Enter command. Try 'help' for a list of builtin commands
-> speed 38400
-> exit

----------------------
????????pb_fkt(): starting power-down sequence...
systemd[1]: Stopping Mark kernel activated network interfaces as up...
         Stopping Mark kernel activated network interfaces as up...
[  OK  ] Stopped Mark kernel activated network interfaces as up.
[  OK  ] Stopped target Application Mode.
[  OK  ] Stopped target Graphical Interface.
[  OK  ] Stopped target Multi-User System.
[  OK  ] Stopped target Remote File Systems.
[  OK  ] Stopped target Login Prompts.
   
<HANGS-HERE>

The line which normally comes after "Stopped target Login Prompts." is the "Stopping Serial Getty on ttymxc4...".