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From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: MC68881/2 Support (hello, Dave Haynie)
Message-ID: <12014@cbmvax.commodore.com>
Date: 31 May 90 16:10:34 GMT
References: <1181@metaphor.Metaphor.COM> <1990May31.025529.28370@watdragon.waterloo.edu>
Reply-To: daveh@cbmvax (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 29

In article <1990May31.025529.28370@watdragon.waterloo.edu> gpsteffler@tiger.uwaterloo.ca (Glenn Steffler) writes:
>In article <1181@metaphor.Metaphor.COM> djh@dragon.metaphor.com (Dallas J. Hodgson) writes:

>Attention Hazy:

>Does the Amiga handle faults, and other hardware interrupts faster than
>a generic PC?  I know the 80386 is very slow when interrupts start
>wailing away in protect mode.

As in hardware interrupts, I assume you're getting at exceptions here, such
as F-line and A-line execptions.  In other words, traps for unimplemented
instructions.  Exceptions don't take a great deal of overhead on their
own; they basically store enough context on the stack to get back to where
they occurred, then call a routine at their assigned vector.  But they're
certainly more expensive than a JSR/RTS, or even the JSR/JMP/RTS you get
with Amiga libraries.  And you the expense of the exception is just the
beginning.  Once you're in the exception handler, the nature of the emulated
instruction must be determined: instruction type, operands, addressing modes.
With all this computed, and effective addresses calculated and all, the actual
routine for the instruction emulation must be called.  That last part it just
about all that's required for a library call.  So, while I have no idea how
bad '386 exceptions are, you can rest safe in the knowledge that in most cases,
instruction emulation via traps is not the best way to go on a 680x0 if you're
interested in speed.

-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
   {uunet|pyramid|rutgers}!cbmvax!daveh      PLINK: hazy     BIX: hazy
	"I have been given the freedom to do as I see fit" -REM