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Path: utzoo!utcs!wagner
From: wagner@utcs.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: 68010 W/1.5MEG INTERNAL - WILL IT WORK?
Message-ID: <1986Dec23.114239.27932@utcs.uucp>
Date: Tue, 23-Dec-86 11:42:39 EST
Article-I.D.: utcs.1986Dec23.114239.27932
Posted: Tue Dec 23 11:42:39 1986
Date-Received: Tue, 23-Dec-86 19:07:03 EST
References: <877@ulowell.UUCP> <1154@cbmvax.cbmvax.cbm.UUCP>
Reply-To: wagner@utcs.UUCP (Michael Wagner)
Organization: University of Toronto Computing Services, general purpose UNIX
Lines: 34
Checksum: 12631

In article <1154@cbmvax.cbmvax.cbm.UUCP> grr@cbmvax.UUCP (George Robbins) writes:
>A) The 68010 is not completly compatible with the 68000, but a little
>help from the trap routines in the OS can smooth things over.
>Unfortunatly, the added features don't help much in an Amiga - it runs
>a few percent faster, but that's it.  Most of the features that were
>added to the 68010 were to make it easy to do virtual memory systems
>with a some kind of mmu.

I thought the speedup was on the order of 10%.  Did I mis-remember?

Two features in the 68010 make for a faster chip.  Loop mode, and a
general stream-lining of the multiply and divide algorithms.  According
to the upgrate notes on fish disk 18, one can expect a speedup of from
4-50% (8-50% claimed in Motorola Documentation).  Multiply/divide performance
can be expected to be 10% better (without recoding).  Loop mode performance
(needs recoding, I expect) can be from 20-80% better.

Loop mode, for those who haven't dived into the hardware manuals yet, 
is this (amazing) scheme for keeping a few instructions in an on-chip
'cache'.  When the loop runs 'in' the cache, the only storage fetches are
for operands.  Tight loops such as looking for blanks could potentially
use such a feature and speed up considerably.

So, question:  Did anyone go to the trouble of trying to exploit loop mode
in the Amiga EXEC?  Does BCPL try to exploit it?  Does the Lattice C code
generator?  How about the Lattice library?  How about MANX?

In any case, if the cost of a 68010 was low enough, it might be worth it
for the 4-8% worst case speedup.  After all, it does buy back some of the
17-20% of the CPU that seems to be leaking away all the time.  And who knows,
maybe the little loops that it's running when it's leaking are the sort that
can be speeded up by loop mode! :-)

Michael