Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.2 9/18/84; site puff.UUCP Path: utzoo!watmath!clyde!burl!ulysses!allegra!mit-eddie!think!harvard!cmcl2!seismo!uwvax!puff!sarwono From: sarwono@puff.UUCP Newsgroups: net.micro.68k,net.micro.16k Subject: Re: Re: Bus Error Effluvia Message-ID: <440@puff.UUCP> Date: Fri, 27-Sep-85 12:18:43 EDT Article-I.D.: puff.440 Posted: Fri Sep 27 12:18:43 1985 Date-Received: Mon, 30-Sep-85 00:55:03 EDT Organization: U of Wisconsin CS Dept Lines: 38 Xref: watmath net.micro.68k:1163 net.micro.16k:392 > My initial thought about this was "who cares if the processor doesn't backtrack > and redo the instructions after returning from the bus error," but after > thinking about it for a little while, I can think of at least two problems > that this might cause. > > 1) Since the processor can't get out onto the bus if it is busy either waiting > for ready or a bus error, one wouldn't think that it could corrupt > anything that is not recoverable. However, it can fiddle around > with its internal state all it wants to. Now, if one of the things > that it does internally is muck with some registers (a completely > valid thing to do) that would get changed as a result of the trap > handler, we have a problem, I would think. This seems real special > case, though I do remember that at least some early versions of > 4BSD paid attention to how register variables were allocated by the > c compiler, and used this information when mixing assembly with > c code... > > 2) In the same tack, I think that if Mot ever includes a data cache on their > chip, they will have to pay special attention to the amount of > concurrency they allow for data accesses on both the external bus > and the internal cache bus. > > So what do y'all think? Does anyone know exactly what the thing tosses on the > bus, and whether it is possible for the trap handler to modify the return > state such as to change the results of half-executed instructions > (or whole executed instructions after the bus-error write)? > -- > ...and I'm sure it wouldn't interest anybody outside of a small circle > of friends... > > Ken Shoemaker, Microprocessor Design for a large, Silicon Valley firm > > {pur-ee,hplabs,amd,scgvaxd,dual,qantel}!intelca!kds > > ---the above views are personal. They may not represent those of the > employer of its submitter. *** REPLACE THIS LINE WITH YOUR MESSAGE ***