Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Path: utzoo!mnetor!seismo!husc6!bloom-beacon!wpd From: wpd@athena.mit.edu (William P Doyle) Newsgroups: comp.sys.m68k Subject: How does one implement VM in a 68000? Message-ID: <1029@bloom-beacon.MIT.EDU> Date: Sun, 28-Jun-87 18:28:41 EDT Article-I.D.: bloom-be.1029 Posted: Sun Jun 28 18:28:41 1987 Date-Received: Sun, 28-Jun-87 20:39:40 EDT Sender: daemon@bloom-beacon.MIT.EDU Reply-To: wpd@athena.mit.edu (William P Doyle) Distribution: world Organization: MIT Project Athena Lines: 24 I was recently speaking with a gentleman who informed me that it was possible to implement virtual memory with a 68000 (not a 68010, 20, etc...), providing, of course, that one has an appropriate MMU. I was under the impression that, because the 68000 could not restart instructions, VM wasn't possible. His argument went something like, "You know that you will never page fault while in the supervisor mode, so you just insert probes in the user mode." Now, I could have misunderstood him, or perhaps, mis-remembered what he said, but I just don't understand. Does this mean that, before each instruction, there must be a TST instruction to see if the page is in memory? I could beleive that, the buserr handler would then just check to see if this "probe" instruction was at fault and be able to restart the program, (after loading the appropriate page into memory), at the following instruction. These seems a bit inefficient though :-). Could someone please enlighten me? ______________________________________________ | | | Patrick Doyle wpd@ATHENA.MIT.EDU | | ...{decvax,ihnp4}!mit-eddie!mit-athena!wpd | |____________________________________________|