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From: stever@videovax.UUCP
Newsgroups: comp.sys.amiga
Subject: Re: The LIVE Digitizer from A-Squared and the 68020
Message-ID: <4419@videovax.Tek.COM>
Date: Tue, 2-Jun-87 11:09:33 EDT
Article-I.D.: videovax.4419
Posted: Tue Jun  2 11:09:33 1987
Date-Received: Fri, 5-Jun-87 01:27:16 EDT
References: <8705290639.AA04316@ingres.Berkeley.EDU>
Reply-To: stever@videovax.Tek.COM (Steven E. Rice, P.E.)
Organization: Tektronix Television Systems, Beaverton, Oregon
Lines: 26

In article <8705290639.AA04316@ingres.Berkeley.EDU>, Doug Merritt
(hatcher@INGRES.BERKELEY.EDU) writes:

> . . . The thing [LIVE]
> has to use self-modifying code just to implement *menus*...that's about
> as bandwidth limited as you get! (Note that this prevents its use on a
> 68020, since the cache on a 68020 prevents self-modifying code.)
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

Nope!  If you want to do such things on a 68020, just clear the Enable
bit in the Cache Control Register.  To quote the book,

   Clearing this bit will disable the cache (force continuous misses,
   and suppress fills) and force the processor to always access external
   memory.  The cache will remain disabled as long as this bit is
   cleared.  The user must set this bit, which is automatically
   cleared whenever the processor is reset, to enable the cache.

                        MC68020 32-Bit Microprocessor User's Manual
                        (page 7-3, paragraph 7.1.2.2)

					Steve Rice

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