How are COM ports handled?

[Paul1]

Dear VirtualBox community,
Recently I installed Windows XP inside of a host XP in order to run some old software that refused to work with SP3.

The software uses a COM port, which attaches to an IR tower, to program a small external computer (called an RCX). This setup seemed to send and receive fine, however the small computer did not seem to understand what the IR tower was transmitting. I used another piece of software in the guest, which is compatible with SP3, and found again that the IR tower didn't transmit properly. When I tried said program on the host, it transmitted fine and the RCX understood.

I was wondering, how exactly does VirtualBox handle COM communication? Is there a way to hand complete control of a COM port to the guest?

Best Regards,
Paul

[Perryg]

My experience with Com ports is they can not handle more than 9600 baud using VBox. Any more and it appears to garble the data.
As far as a direct connection to the hardware from the guest it can not be done, at least as far as I know with any virtualizer.

[Paul1]

Ah interesting. I've looked up the specs and it transmits at a 2400 baud rate, definitely quite old. However, it handles the COM port in quite a custom way. However in both the host and guest, the device settings are set to 9600. I wonder if it might be that the host is transmitting at the wrong rate? I will experiment later.

Are there any developers about to answer how virtualbox handles COM ports?