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Article #2358Re: Bus contention
From: Landon Dyer
Date: Sun, 02 Feb 1986 23:46
Date: Sun, 02 Feb 1986 23:46
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1528 bytes
Don't bother "poke-blasting" the memory controller ("MMU") address
space. There's nothing interesting there. If you don't believe me,
then go ahead.
The 68000 makes a bus request every 4 cycles. This means that there are
3 other cycles available for doing stuff. 2 of these cycles are used for
video DMA. 1 more is used for disk DMA.
Now, it is NOT true that the 68000 makes a memory access every 4
cycles (I lied.) The processor is given a window every 4 cycles,
and it is stopped if it makes a request that is out of line. It
quickly falls back into step. This means that the processor loses
cycles occasionally, but very occasionally.
(If you don't beleive me, go ahead: write some assembly language
benchmarks and count cycles. THEN you can start talking numbers
about "occasionally".)
Multiport RAM on a consumer machine? Yick. How much does that COST?
-landon
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Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP Posting-Version: version B 2.10.3 4.3bsd-beta 6/6/85; site ucbvax.BERKELEY.EDU Path: arc1-ca.pugleaf.net!utzoo!watmath!clyde!burl!ulysses!ucbvax!info-atari From: G.DYER@SU-SCORE.ARPA (Landon Dyer) Newsgroups: net.micro.atari Subject: Re: Bus contention Message-ID: <12180256423.9.G.DYER@SU-SCORE.ARPA> Date: Sun, 2-Feb-86 18:46:51 EST Article-I.D.: SU-SCORE.12180256423.9.G.DYER Posted: Sun Feb 2 18:46:51 1986 Date-Received: Tue, 4-Feb-86 03:15:59 EST References: <360@ccivax.UUCP> Sender: daemon@ucbvax.BERKELEY.EDU Organization: The ARPA Internet Lines: 24