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From: michael@orcisi.UUCP
Newsgroups: comp.sys.ibm.pc
Subject: Re: MS Windows and Physical memory?
Message-ID: <897@orcisi.UUCP>
Date: Sun, 15-Feb-87 17:48:38 EST
Article-I.D.: orcisi.897
Posted: Sun Feb 15 17:48:38 1987
Date-Received: Sun, 15-Feb-87 22:35:17 EST
References: <105500001@datacube> <9965@cgl.ucsf.edu.ucsfcgl.UUCP> <232@netxcom.UUCP>
Organization: Optical Recording Corporation, Toronto, Ontario
Lines: 22

> >>Has anyone had experience using Microsoft Windows where they need
> >>to talk to hardware using pointers?  Does Windows allow explicet
> >>pointers to physical memory?
> 
> Well, I *have* done just this in Microsoft C.  The thing to remember is
> that "0xA0000" is a 20 bit value, so you must either:
> 
> 1)  Use the Large model, or
> 
> 2)  Declare a Far pointer, and enable 'NEAR' and 'FAR' during compile, ie:
> 
> 	static char far *p = 0xa0000;
> 
> (or, in deference to Don's suggestion)
> 
> 	static char far *p = FP_SEG(0xa000) + FP_OFF(0x0);

In general, this can be used to talk to hardware but won't work for
data that is not FIXED or locked.

In practice, you have to arbitrate task access to the hardware
device when more than one copy of the application is running under Windows.