Running Xinu in User mode

[robinkrens]

Is it possible to run Xinu in User mode?
I checked the system and device calls, but this seems a bit problematic.
For example, code like this in UART write:

wait(uartptr->osema);

If it is a process running in kernel mode and then wait get called that's fine. But if a process is in user mode and this code is executed in supervisor/handler/kernel mode, how does that work?