🚀 go-pugleaf

In article <64@mit-prep.ARPA>, tmb@mit-prep.ARPA (Thomas M. Breuel) writes:
> The fact that it is difficult to restart an instruction that received
> a bus fault on the 68000 makes it difficult to implement paging.
> However, an MMU has other uses besides paging, e.g. to protect processes
> from one another, to help utilise memory more efficiently, and
> to allow swapping and process duplication (a la fork(1); you can't
> implement fork(1), in general, on the 68000 without an MMU).
> 
> I consider it a grave mistake not to have included even a rudimentary kind
> of address remapping on the Amiga; even just an adder on the address lines
> of the 68000 would have simplified the system software and allowed some
> kind of swapping to be hacked.
> 
> 						Thomas.

I understand your first paragraph completely.  But you lost me on the second.
I can see where a MMU that provides protection only would be useful but
address mapping is still of no use.  Not without a 68010, admittedly an
easy upgrade, but not provided.  If you mapped a some address block to
another would you not HAVE to ensure it was a legal RAM/ROM address?  One
faulty address and your back to GURU type crashes, yes?   I guess it be
nice to learn from you what type of paging you could implement with just an
adder, etc.  Enlighten me.  Mail if you must.  Post if it seems of general
interest to all 68000 based machines.


-- 
Jeff Gortatowsky       {allegra,seismo}!rochester!kodak!elmgate!jdg
Eastman Kodak Company  
<Kodak won't be responsible for the above comments, only those below>