From: Lars Erdmann <lars DOT erdmann AT arcor DOT de>
Newsgroups: comp.os.msdos.djgpp
Subject: Windows NT: Writing to I/O port does nothing
Date: Mon, 03 Jun 2002 21:35:12 +0200
Organization: Arcor
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To: djgpp AT delorie DOT com
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Reply-To: djgpp AT delorie DOT com

Hi,

I have written a small app that (in order to do its stuff) writes to the
parallel port I/O ports.
Unfortunately, it's not a printing app or so, so I have to access the
ports directly.
Using outp() does not give me an error or trap but under Windows NT it
appears to do nothing.
When I use the same app under Windows95, it works ok.

Does WindowsNT allow direct access to I/O ports for DOS apps (as OS/2
does for example) ?
If not, how does it virtualize the I/O ports ? To me it looks like it is
doing nothing at all.
Looking at the deassimbling window of the RHIDE debugger it appeared to
me that the code segment is running at IOPL 3 so I would hope that I am
able to access I/O ports directly even if WindowsNT normally catches the
I/O port accesses or am I wrong ?

Lars