Virtual T

Goal: Use Virtual T together with Desklink on the same machine.

Setup: I've connected Virtual T to a port provided by com0com. It is paired
to another port connected to DeskLink (or a terminal emulator for
testing).

Problem: The TX empty status in the UART never gets set after a character
is transmitted (port D8 returns 80, not 90). I can transmit exactly one
character and thereafter, the application hangs.