Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!swrinde!elroy.jpl.nasa.gov!lll-winken!uunet!cbmvax!mks
From: mks@cbmvax.commodore.com (Michael Sinz)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Fusion-40, the 68040 Card for A2000 avail...
Message-ID: <22645@cbmvax.commodore.com>
Date: 24 Jun 91 12:34:31 GMT
References: <1991Jun20.114837.22962@unibi.uni-bielefeld.de> <1991Jun21.183207.27427@CAM.ORG>
Reply-To: mks@cbmvax.commodore.com (Michael Sinz)
Organization: Commodore, West Chester, PA
Lines: 57


 [Much stuff deleted]

In article <1991Jun21.183207.27427@CAM.ORG> menzies@CAM.ORG (Stephen Menzies) writes:
>markus@techfak.uni-bielefeld.de (Markus Illenseer) writes:
>>The Processor is working internally with a Tact-Rate of 50 Mhz, though the
>>external Rate will be 25 MHz.

Hold on...  Just because the CPU wants a 50MHz input clock does not mean
that you can call it 50MHz tact-rate.  The reason you place a 50MHz clock
into the chip is such that it can have a stable. 25MHz clock to play with.
In fact, some designs have 100MHz clocks going through a divider to bring
the 50MHz clock into the CPU.  This is again to provide a stable clock.
The 68040 (chip) currently is only available at 25MHz.  Anything trying to
imply 50MHz is pulling someone's chain.  Also, any attempt to go beyond
that clock rate is *VERY* dangerous and should be looked at as suspect.
(The 68040 is built to a rather tight spec and that includes the clock)

>The RCS board fits into the A2000 processor slot. The board runs at 1750
>Drystones/mip using Amiga Bench Drystone Rating. This translates to
?^^^^^^^^^^^^^?
>31650 Drystones/sec. Users can expect a much better rating once popular
>softwares are optimized for the 040. The board has been running under the
>2.0 OS and I might add, the present software runs even more reliably than
>under 1.3. For one, the Copyback caches can remain on ALL the time. The 2.0
>OS seems to have been developed with the 040 in mind.

Ok, so what is that?  A MIP is already rather silly measurement and then
adding a Drystones/mip?  Where did that come from?  Current testing shows
that a standard Drystones compiled by standard C with no special 68040
optimizations comes out to 23,000 to 25,000 rating if the 68040 caches
are full on and CopyBack mode is enabled.  A smarter compiler (68040 smart)
would be able to make this number higher, but there are very few compilers
out there that can do this and even fewer products compiled with them.

CopyBack mode, and in general the 68040, is not supported in AmigaDOS 1.3
or earlier.  There are many issues concerning caching that had not been
resolved back when 1.3 was made.  (The 68030 had just about been introduced
and the 68040 was just a "name")

AmigaDOS 2.0 supports all of the 68040 modes.  CopyBack mode is somewhat
supported in that if it is turned on, the ROM will correctly deal with it.
A simple SetFunction() to CacheControl() would let the system also use
the CACRF_CopyBack bit to turn on/off CopyBack.  However, some applications
may not be ready for 68040 and CopyBack.  CopyBack tends to make programs
that write code to RAM not work too well since even if the instruction cache
is flushed, the new code may not have been copied to physical RAM from
the cache.  2.0's CacheClearU() and CacheClearE() functions deal with that
issue correctly.

/----------------------------------------------------------------------\
|      /// Michael Sinz  -  Amiga Software Engineer                    |
|     ///                   Operating System Development Group         |
|    ///   BIX:  msinz      UUNET:  rutgers!cbmvax!mks                 |
|\\\///                                                                |
| \XX/     Quantum Physics:  The Dreams that Stuff is made of.         |
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