I have tried to use a host device, /dev/cuau0, in a Windows VM as COM1 but with no luck. Probably the bug is “It is almost like the CTS pin is permanently active but the actual device is not really ready for data.” as mentioned by Anthony Takata in this mail: https://lists.freebsd.org/pipermail/freebsd-emulation/2014-October/011927.html .
I have solved the problem via network as explayned here: https://lists.freebsd.org/pipermail/freebsd-emulation/2014-December/012066.html .
This approach has a main disadvantage: the VM can not be suspended because when resumed lost the connection with the host TCP socket.
Auto-assigned to maintainer vbox@FreeBSD.org
Is this still relevant? No maintainer feedback till now!