Can an 030 need a PMMU?

[Michael Bodine]

Jeffrey Buchsbaum (63848e at eleazar.dartmouth.edu) writes:
> I called Dove Computer today to ask about an '030 board ugrade for the II. They
> ...
> from a marketing point of view. I thought the 030 had the PMMU in it.
> 
> One confused MacII hacker.
Somebody's confused alright, but it wouldn't appear to be you!  The 030 does 
have the mmu on-chip.  The only way an 030 upgrade would still require an 851
for external memory management is if 1) their software disabled the on-chip
mmu and 2) their (or somebody's) software required the full functionality of
the 851 -- the 030 mmu is a subset of the 68851;  not all instructions 
supported by an 020/851 pair are supported by the 030.  Even so, there would
have to be hardware modifications and code changes to support the fact that
the off-chip mmu by default only responds to a particular co-processor id
(i forget which, not relevant) so that any co-processor functions embedded
in object code would operate with the on-chip mmu.  To access an off-chip
mmu, you'd have to recode all mmu instructions to reference a different
co-processor id.  Seems like an awful lot of hassle to go thru when not
doing anything would most likely just make it work!

Anybody in Austin listening?  At Dove?
-- 
[ Michael Bodine, michael at mcdchg.UUCP,  (312) 576-7840                         ]
[ Opinions expressed are mine!  All mine!                                      ]
[ Motorola couldn't have them even if they wanted them!                        ]
[ No one else agrees with me;  why should my employer?                         ]