Naked Science Forum

Non Life Sciences => Geek Speak => Topic started by: syhprum on 13/07/2011 10:55:44

Title: Does COM1 work under Virtual XP?
Post by: syhprum on 13/07/2011 10:55:44

I have two programs that require the use of COM1 which is available no problem when using windows 7, but when I use virtual XP on windows 7 which runs the programs perfectly the COM1 connection which is needed for the PCR1000 communications receiver or the FAX Modem is no longer available.

Title: Re: Does COM1 work under Virtual XP?
Post by: Geezer on 13/07/2011 19:52:41

Perhaps that would have required them to implement a "virtual UART" in virtual XP?

Virtual systems tend to get a bit tricky when it comes to physical interfaces. I don't know anything about Virtual XP, but I suspect the issue revolves around the ownership of the physical hardware. Ultimately, that has to be under the control of the host OS (they can't both own it at the same time) so, they would have had to implement some sort of proxy for the low level COM1 port, and that means precisely emulating all the characteristics of the physical hardware in software, in real time, which, though it may not be impossible, darn near is, so they ducked it  [:D]

Title: Does COM1 work under Virtual XP?
Post by: syhprum on 13/07/2011 21:42:34

Thanks for the reassurance that it is a failure on the part of the writers of the virtual software and not something I have left undone.

Title: Does COM1 work under Virtual XP?
Post by: Geezer on 13/07/2011 22:02:45

I suspect it's a problem for any legacy software that accesses the hardware without going through some sort of driver. I'm slightly surprised they are still supporting COM1 etc., even in the native OS, but it only goes to show how long it takes for a standard to die off once it's been adopted.

The goofy thing about this is that there were operating systems around long before MS-Dos that prohibited this sort of behaviour precisely to prevent the problem you are now running into!

Title: Does COM1 work under Virtual XP?
Post by: CliffordK on 14/07/2011 08:04:57

Is it possible that you would have IRQ conflicts?  Most of the problems with IRQs disappeared with Windows XP, but perhaps they are still there, just hidden.

If you have an unused COM1, make sure it is completely disabled?

Did you say either program will work, as long as the other hasn't been used?

Title: Does COM1 work under Virtual XP?
Post by: Geezer on 14/07/2011 18:04:20

Good point. Could be an interrupt problem.

When they say "virtual XP", do they really mean it's a virtual OS, or do they mean they are running in a mode that emulates XP?

If it's the latter, it ought to work.

Title: Does COM1 work under Virtual XP?
Post by: syhprum on 15/07/2011 09:31:07

It runs like having XP32 on a separate drive or partition within the computer, USB works fine I can operate my HP Laser jet printer via a USB converter.
When I come back from holiday I will purchase a USB to RS-232 converter and see how that behaves.