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From: pstevens@pioneer.arpa (Paul Stevens RCE Sterling)
Newsgroups: comp.os.vms
Subject: PFN Mapping
Message-ID: <2362@ames.arpa>
Date: Wed, 15-Jul-87 14:20:34 EDT
Article-I.D.: ames.2362
Posted: Wed Jul 15 14:20:34 1987
Date-Received: Fri, 17-Jul-87 06:38:57 EDT
Sender: usenet@ames.arpa
Reply-To: pstevens@pioneer.UUCP (Paul Stevens RCE Sterling)
Distribution: world
Organization: NASA Ames Research Center, Moffett Field, Calif.
Lines: 18
Keywords: PFN, $CRMPSC
Summary: $CRMPSC question


	I have a question about mapping I/O space using $CRMPSC.  I am using
the SEC$M_PFNMAP qualifier to map the PFN's associated with some device
registers, and let me preface this by saying that I have gotten it to work.
One of the parameters that I pass to $CRMPSC seems to be sort of 'magic'
though.  I use the SEC$M_EXPREG to map the range into the first available
address in my process virtual address space and the system service manual 
says that in this case the array INADR will determine only if the mapping
will be to P0 or to P1 space, it does not say *how* it will determine this!
By looking at an example in SYS$EXAMPLES of a BLISS program which does PFN
mapping I learned that the magic number of 200 seems to do the trick.
My question is why? and how do you get it to map to P1 space, though I don't
see why you would ever want to do that.
	If you want to email to me I will post a final answer, however, I
am new to the net and can't really give a known path by which to reach me.
	Thanks for any info
		P. Stevens
	        (415)-694-4887