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From: henry@utzoo.UUCP (Henry Spencer)
Newsgroups: net.micro.68k,net.micro.16k
Subject: Re: Re: PDP11s vs the micros
Message-ID: <5913@utzoo.UUCP>
Date: Tue, 27-Aug-85 12:15:11 EDT
Article-I.D.: utzoo.5913
Posted: Tue Aug 27 12:15:11 1985
Date-Received: Tue, 27-Aug-85 12:15:11 EDT
References: <2422@sun.uucp> <5883@utzoo.UUCP> <5890@utzoo.UUCP>, <124@desint.UUCP>
Organization: U of Toronto Zoology
Lines: 40

> Do I detect just a tiny rabid note here?

Who, me?  Just because I think dumping microstate onto the stack when you
get a page fault is a wretched botch to cover up the fact that Motorola
totally and utterly ignored virtual memory when they designed the 68000?
Nah.

> Henry, I think Dave's point was
> not that you only have to do 12 non-memory-referencing instructions to
> break even.

The way I read Dave's note (which is still the way I read it, looking back)
was "dumping microstate is a big win, because we can execute instructions
beyond the one that causes the fault, and not have to redo them, unlike
those cruddy architectures that have to stop dead when they hit a fault".
My point, somewhat overstated I admit, was that this is near-nonsense,
because the number of extra instructions is likely to be very small, not
large enough to make up for the greater volume of data that has to go
onto the stack at fault time.

> In any case, Henry, why bring up the red herring of the 68010?

Because Motorola trumpeted microstate dumping as a big win on the 68010 too.
"Look at us, we did it right, we don't have to restart the whole instruction
from scratch."  Feh.

> Or are you just in a flaming-at-Motorola mood?

I'm never out of flaming-at-the-680x0's-stupid-stack-puke-page-fault mode!

> Hmm, maybe you *are* in a mood.  In article <5883@utzoo.UUCP> you complain
> that some friends are all upset about the 300 bytes of state.  Now we
> find out that said friends maybe didn't even know about the f.p.-used
> flag?

No, we find out that *I* didn't know about it.  Said friends are disgusted
at the need to handle 300 bytes of state even *sometimes*, as it turns out.
-- 
				Henry Spencer @ U of Toronto Zoology
				{allegra,ihnp4,linus,decvax}!utzoo!henry