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From: joel@gould9.UUCP (Joel West)
Newsgroups: comp.sys.m68k
Subject: 68851 access levels, future
Message-ID: <898@gould9.UUCP>
Date: Wed, 3-Dec-86 02:50:51 EST
Article-I.D.: gould9.898
Posted: Wed Dec  3 02:50:51 1986
Date-Received: Wed, 3-Dec-86 06:31:52 EST
Organization: Western Software Technology, Vista, CA
Lines: 25
Keywords: 68851, 68030, 68040

I was reading my 68851 technical summary tonight (incidentally, has
anyone seen the actual user's manual?  The local Motorola office doesn't
have it.) and came across a few questions when it began to make sense.

1. Isn't the ring numbering scheme (access levels) backwards?
   An unprivileged 68000 program would have address $00xxxxxx, but
   with the PMMU this becomes $E0xxxxxx.  On the VAX, with two
   address spaces (for four access levels), user-level space is
   $00xxxxxxx to $7Fxxxxxx, which seems more normal.
   
2. Is anyone actually using the PMMU with access levels? 2, 4 or 8?

3. I saw some preliminary documentation on the MC68030 that indicated
   restrictions on the CALLM/RTM usage, but I don't have anything
   more than the technical summary available now.  Is the CALLM
   the same, and does it support 1-8 access levels?  Or is the
   access level scheme being phased out?

4. Would it be safe to assume that processors after the MC68030
   will include an upward-compatible MMU?
-- 
	Joel West			     MCI Mail: 282-8879
	Western Software Technology, POB 2733, Vista, CA  92083
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