joel@gould9.UUCP (Joel West) (12/03/86)
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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