jbm@uncle.UUCP (John B. Milton) (03/14/89)
In article <1429@mtunb.ATT.COM> jcm@mtunb.UUCP (John McMillan) writes: >In article <296@carroll1.UUCP> dnewton@carroll1.UUCP (Dave Newton) writes: >>The 68010 has a built-in MMU (Memory Management Unit) which is vital to >>the UNIXpc's multi-tasking operation. >Please so inform Motorola: They've yet to realize this! ya ba dee yub >Their documentation is stupid enough to suggest they SUPPORT virtual > memory (page faults, etc.) with improved restarts in the 68010. > (I'm not sure one couldn't do the same with a 68000 -- given > the ungodsly effort I've seen for Z8000 instruction-restart -- > but it wouldn't be pretty!-) They did a very good job, considering. >I'd recommend using the OFF-chip MMU that the 3B1 comes with, and which, > alas, limits the 3B1 to 4MB VM. And which EXISTS, if that's of concern. Yes, for THIS machine I would. Although having to copy the portion of the mapping memory for a given process in and out with every context switch is time consuming, it was more than worth the alternative when this machine was designed. Now that big, high speed static RAMs are becoming available, I could see this method taken even further. >> Switching it for a 68000 would indeed >>be very bad. > ^^^ Not really fatal, if you have TWO 68000s. This was actually suggest by Motorola in an app. note, and IMPLEMENTED in the SUN-2 (or was it the SUN-1?). What you do is, when a page fault occures, hold off DTACK to the CPU that just did this nasty thing, then run on the SECOND 68000 to do the paging. When everything is okydoky, release DTACK and let the first 68000 continue. The first one doesn't know that there was a many ms delay between two CYCLES of one instruction. Of course, you have to be able to disable any watch-dog BERR timers while all this is going on. >"Fatal", yes. Bad? Thats a moral or ethical decision. (Unless you're a > politician where such things are NOPs.) Hmm, ok. >Everyone is CAPABLE of submitting answers or statements: > 1) Recognize your limits and > 2) try to exercise more courtesy -- like reading to the end of the > news listings to see if others have posted replies. The only way people LEARN is by asking questions. At first stupid maybe, questions anyway. Many wonderful things have come from some "uninformed" person asking what appears to be a stupid question. **** D O N ' T F L A M E , I N F O R M **** I think I just found a new .signature John -- John Bly Milton IV, jbm@uncle.UUCP, n8emr!uncle!jbm@osu-cis.cis.ohio-state.edu (614) h:294-4823, w:764-2933; AMPR: 44.70.0.52; Don't FLAME, inform!
jcm@mtunb.ATT.COM (was-John McMillan) (03/15/89)
In article <494@uncle.UUCP> jbm@uncle.UUCP (John B. Milton) writes: >In article <1429@mtunb.ATT.COM> jcm@mtunb.UUCP (John McMillan) writes: >>In article <296@carroll1.UUCP> dnewton@carroll1.UUCP (Dave Newton) writes: >>>The 68010 has a built-in MMU (Memory Management Unit) which is vital to >>>the UNIXpc's multi-tasking operation. >>Please so inform Motorola: They've yet to realize this! >ya ba dee yub ^^^^^^^^^^^^^ -- ? Since my statement was and IS correct -- Motorola has never claimed to have a built-in MMU in the 68010 -- I remain curious as to the precise translation of your wit ?-) >>Their documentation is stupid enough to suggest they SUPPORT virtual >> memory (page faults, etc.) with improved restarts in the 68010. >> (I'm not sure one couldn't do the same with a 68000 -- given >> the ungodsly effort I've seen for Z8000 instruction-restart -- >> but it wouldn't be pretty!-) >They did a very good job, considering. I agree: I was saying WHAT MOTOROLA PUBLISHES & DOES -- as opposed to the previous submitter's MISINFORMING people about what they do! "SUPPORT" is a capital idea; "built-in" is an overstated case. More Sloowwwllllyyyyy: The first point I was making was that Motorola documents their 68010 processor as one which S U P P O R T S V i r t u a l M e m o r y. {Thanks for the spacing clues %-} >>I'd recommend using the OFF-chip MMU that the 3B1 comes with, and which, >> alas, limits the 3B1 to 4MB VM. And which EXISTS, if that's of concern. >Yes, for THIS machine I would. Although having to copy the portion of the ^^^^-Uh... THIS machine was the THE CONTEXT of the original Q&A. Floating Point assistance for the 3B1.... >mapping memory for a given process in and out with every context switch is >time consuming, it was more than worth the alternative when this machine >was designed. Now that big, high speed static RAMs are becoming available, I >could see this method taken even further. (I'd recommend, say, Pittsburgh.) >>> Switching it for a 68000 would indeed >>>be very bad. >> ^^^ >Not really fatal, if you have TWO 68000s. Maybe there's room on your disk expansion board;-} If not, it's probably irrelevant to the discussion of FPA on the 3B1. But it IS interesting! (Not that THIS mortal grasps the instruction re-start mechanism therein... but it might be unnecessary?) But, back to CONTEXT -- it would be FATAL to any extent 3B1 software ============================================ to replace the 3B1's 68010 with a 68000! Period! >>"Fatal", yes. Bad? Thats a moral or ethical decision. (Unless you're a >> politician where such things are NOPs.) >Hmm, ok. Ooo ooohhhhh! An agreement?????? (Naw.... just a typo, fur shur!) >>Everyone is CAPABLE of submitting answers or statements: ^^^^^^^^^^^^^^^^^^^^^ >> 1) Recognize your limits and >> 2) try to exercise more courtesy -- like reading to the end of the >> news listings to see if others have posted replies. >The only way people LEARN is by asking questions. At first stupid maybe, >questions anyway. Many wonderful things have come from some "uninformed" >person asking what appears to be a stupid question. > > **** D O N ' T F L A M E , I N F O R M **** An admirable motto. (But, I'd feel hurt if I thought JBM was referring to ME!) I didn't flame a QUESTION -- I flamed an ANSWER that was posted NOT by anyone who has familiarity with the subject, but by someone who was smitten by an urge to help -- regardless (1) of their limited familiarity with the subject and (2) the answers that had been submitted well before their posting. There is ample reason to believe some people LEARN by mis-answering questions. Indeed, many wonderful things have come from some "un-informed" Bozo answering an honest question with a honestly half-wit reply -- I do it regularly! (But I'd recommend practicing this in the closet for awhile before coming-out....) (dnewton: I'm calling ME not YOU a Bozo! You'll have to work on it awhile to get past being just over-enthusiastic.) I don't believe in these windy, broadly posted, negligibly informative drivelings! Had JBM sent a memo to me, or had he appeared better focussed on my general insanity I'd have dropped it. Which I do now, with no more follow-ups on it from here! j mcmillan -- att!dev!null
guy@auspex.UUCP (Guy Harris) (03/16/89)
>Not really fatal, if you have TWO 68000s. This was actually suggest by Motorola >in an app. note, and IMPLEMENTED in the SUN-2 (or was it the SUN-1?). Neither. The original Sun-1s (not all caps, please; when used as the name of the company or in product names, it's not an acronym) had a 68000, as I remember, and didn't run an OS that supported VM. A Sun-1 could be upgraded to an '010 machine; the Sun-2's were all '010 machines. The '010 machines didn't need that trick. As I remember, Apollo and Masscomp *did* use the "two 68000s" trick.