Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!microsoft!ericsa
From: ericsa@microsoft.UUCP (Eric Sassaman)
Newsgroups: comp.os.os2.programmer
Subject: IOPL in 2.0
Message-ID: <57504@microsoft.UUCP>
Date: 18 Sep 90 02:43:57 GMT
Organization: Microsoft Corp., Redmond WA
Lines: 20


> I recently tried to experience the IOPL segment in OS/2 2.0. By
> setting IOPL=YES in the config.sys file. By declairing SEGMENTS
> IO_TEXT IOPL in the definition file. Writting an IO_TEXT segment with
> priviledge instruction in assembly routine. Made a dummy c file which
> essencially calls the assembly routine. Generated an EXE file to run.
> The executable always give me a page fault error. Does anybody knows
> if the IOPL segment exist and runs reliablly in the OS/2 2.0
> environment(386 CPU). It will be appreciated that if you can tell me
> how to write such program.

The problem is that port I/O from an OS/2 2.0 32-bit application is
only allowed in a ring zero code segment. An IOPL segment runs at ring
2; at this level port I/O is not allowed in a 32-bit application. In
order for you to do direct port I/O under OS/2 2.0, you will need to
either write your application as 16-bit or write a device driver that
runs at ring 0. This device driver can be either 16 bit or 32 bit.

Eric Sassaman
Microsoft OS/2 Systems Support