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From: mks@cbmvax.commodore.com (Michael Sinz)
Newsgroups: comp.sys.amiga.programmer,comp.sys.amiga.hardware,adsp.sw,adsp.hw
Subject: Re: 68040 Compatibility Warning
Message-ID: <22100@cbmvax.commodore.com>
Date: 3 Jun 91 12:21:20 GMT
References: <22049@cbmvax.commodore.com> <1991Jun1.175626.3234@wintermute.north.de>
Reply-To: mks@cbmvax.commodore.com (Michael Sinz)
Organization: Commodore, West Chester, PA
Lines: 23

In article <1991Jun1.175626.3234@wintermute.north.de> kaba@wintermute.north.de (Kai Bartels) writes:
>mks@cbmvax.commodore.com (Michael Sinz) writes:
>>CopyBack. CopyBack means that when a program writes data to
>>memory, it goes into the cache but *not* into the physical RAM.
>>That means that if something was to read that RAM and it did not
>>go through the data cache on the 68040, it will see old data.
>>The two main examples of this are DMA devices and the instruction
>>reading of the CPU itself.  This means that even if the
>Another important case where that mode can be deadly is in a multi-processor
>machine. Has Motorola or C= taken any precautions in this direction. It'd be
>really nice to run ADos2.0 or SVR4 on two or three processors!

Yes, the 68040 has support for this.  It is called bus snooping.  The only
thing it does not do is snoop the bus between its own caches!  (That is
one of the bigger mistakes, along with the fact that you can only Push back
the data cache *and* clear it.  You can not just push it back)
/----------------------------------------------------------------------\
|      /// 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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