Path: utzoo!utgpu!jarvis.csri.toronto.edu!mailrus!csd4.milw.wisc.edu!bionet!ames!elroy!gryphon!richard
From: richard@gryphon.COM (Richard Sexton)
Newsgroups: comp.sys.amiga.tech
Subject: 80860 as a math processor
Keywords: Nothing to do with Portal
Message-ID: <14716@gryphon.COM>
Date: 15 Apr 89 03:08:10 GMT
Reply-To: richard@gryphon.COM (Richard Sexton)
Organization: Trailing Edge Technology, Redondo Beach, CA
Lines: 59

In article <865@savax.UUCP> thompson@savax.UUCP (thompson mark) writes:
>In article <1619@dretor.dciem.dnd.ca> king@dretor.dciem.dnd.ca (Stephen King) writes:
>
>Not foolish at all. Actually, the 120 MOPS is achieved on the 40MHz part
>by simultaneously executing a floating point add, floating point multiply,
>and an integer ALU operation in a single clock cycle. This doesn't even
>include whatever operation the graphics block is performing. Consequently,
>the 50 MHz part can attain 150 MOPS.

Yes, the 80860 looks like the only decent piece of silicon to come
out of intel since the 8051.

However, I believe it would be impossible to sustain that FLOP rate
as a math coprocessor in an Amiga.

Consider the 68881/2 or the Weitek chip: when a floating point
instruction is hit, BINGO, the hardware executes it.

Bit since the 80860 is not a 680x0 coprocessor, some hardware/software
interface will need to be worked out. This is a simplified version;
it coulkd take a dozen instructions each for the 680x0 and 80860
to completely pass the operands and resukt back and forth.

	68000: Hmm, I need to take the square root of 6.6

					80860: dum de dum dd dum

        68000: hey 80860, ar you busy ?

					80860: nope

	68000: here, 80860, heres a number

					80860: ok, got it

	68000: hey 80860, are you busy ?

					80860: nope ?

	68000: Ok, do a square root will ya ?

	68000: 80860 are you done

					80860: of course!



Whereas a true 680x0 math coprocessor has none of this nonsense, it
just executes inline floating point instructions.

So it will take some calculations to determine if the 80860
is actually a superior math processor. Where it would really
shine though, would be where you could unbundle a monolithic
process, such as a matrix inversion or the like. Clearly this
is something a pure math coprocessor could not do.

-- 
       ``Parents who have children, have children who have children''
richard@gryphon.COM  decwrl!gryphon!richard   gryphon!richard@elroy.jpl.NASA.GOV