Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!rochester!kodak!elmgate!jdg From: jdg@elmgate.UUCP (Jeff Gortatowsky) Newsgroups: net.micro.atari16,net.micro.amiga,net.micro.68k Subject: Re: 68000 Memory Managment Message-ID: <510@elmgate.UUCP> Date: Mon, 18-Aug-86 12:36:19 EDT Article-I.D.: elmgate.510 Posted: Mon Aug 18 12:36:19 1986 Date-Received: Tue, 19-Aug-86 21:03:24 EDT References: <508@elmgate.UUCP> <64@mit-prep.ARPA> Organization: Eastman Kodak Co., Rochester, NY Lines: 30 Keywords: 68000 atari amiga 68k mmu Summary: If paging with a 68000 is impossible? Why worry address REMAPPING on the Amiga or any other 68000 based machine? Xref: mnetor net.micro.atari16:1635 net.micro.amiga:4305 net.micro.68k:1140 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