Message-ID: <F554E1189472D21198D000805F654BFE59FFE3@ntxchangerend.engr.rendition.com>
From: yjtseng <yjtseng AT micron DOT com>
To: djgpp AT delorie DOT com, nate AT cartsys DOT com, dj AT delorie DOT com
Cc: yjtseng AT micron DOT com
Subject:  cwsdpr0.exe 4/15/99
Date: Thu, 15 Apr 1999 11:08:39 -0600
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Reply-To: djgpp AT delorie DOT com

So. May I make a bold conclusion that,  in cwsdpmi.exe, the linear address
will always equal  the physical address even after going through the page
directory and page table stuff (as you guys put it: it is the way set up by
the dpmi host)? And if so, I should be able to get the physical address of
any allocated memory through the linear base address in segment descriptor
selected by its segment selector  and then plus the offset, i.e.,

	Physical address = _addr + offset,  after
__dpmi_get_segment_base_address (int _selector,  unsigned long * _addr) is
called, right?

Should  I breathe better now?

Thanks

Jay Yichang Tseng



	-----Original Message-----
	From:	Nate Eldredge [SMTP:nate AT cartsys DOT com]
	Sent:	April 14, 1999 4:06 PM
	To:	djgpp AT delorie DOT com
	Subject:	Re: cwsdpr0.exe 4/14/99

	yjtseng wrote:
	> 
	> All right,
	> 
	> Now, fact:      CR0=0x80000019 which means paging is on. If I maps
physical
	> address 0xfb000000 to linear address using
	> __dpmi_physical_address_mapping(&mi) as shown in FAQ 18.7, the
returned
	> linear address is 0xfb00000000 which the same as physical address
	> 0xfb000000. How can this be? It does not make sense, right? Unless
the
	> paging mechanism is off, which is not true, as evidenced by
CR0=0x80000019.
	> Since paging is used, shouldn't the linear address be different
from the
	> physical address after Int 31H, function 0800H?

	Not necessarily.

	[(Over-)simplified explanation]

	Paging uses a scheme whereby each page in the linear address space
has a
	page table entry, which contains an address in physical memory where
the
	page actually resides.  This may (as in your case) or may not be the
	same as the linear address.

	Essentially all paging does is provide a level of indirection
between
	linear and physical memory.  How the mapping works out is up to the
DPMI
	server.

	-- 

	Nate Eldredge
	nate AT cartsys DOT com