Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uwm.edu!ogicse!unicorn!n8840371
From: n8840371@unicorn.wwu.edu (Todd Crowe)
Newsgroups: comp.os.os2.programmer
Subject: Re: IOPL in 2.0
Message-ID: <1990Sep20.181913.3348@unicorn.wwu.edu>
Date: 20 Sep 90 18:19:13 GMT
References: <57504@microsoft.UUCP>
Organization: Western Washington University, Bellingham WA.
Lines: 32

ericsa@microsoft.UUCP (Eric Sassaman) writes:
>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.

I won't deny that any of this is true, but I *think* it omits an important
point.  About 6(?) monthes ago in either Computer Language or DR Dobbs there
was an article on using IOPL segments to read/write the I/O ports.  It
mentioned that there was a function that enabled/disabled port access (even
to IOPL segments).  In OS/2 1.x this function didn't do anything, since the
286 is not able to offer individual I/O ports (and disallow others).  But
according to the article there were supposed to be required in OS/2 2.0.

I think the name of the function was DosEnablePortAccess (or something
similar).  If this isn't enough information let me know and I can look
up the article.

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+++++ +++Western+++++  |                   Todd Crowe                        |
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      +++++++++++++++        "Dont get your hair in an uproar!!!"
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+++++ +++Western+++++  |                   Todd Crowe                        |
 +++++++Washington+++  |  n8840371@unicorn.wwu.edu or TODDC@nessie.wwu.edu   |