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From: gnu@hoptoad.uucp (John Gilmore)
Newsgroups: net.micro.amiga
Subject: Re: LIFE on a 68020 (Re: Tom)
Message-ID: <1137@hoptoad.uucp>
Date: Fri, 26-Sep-86 04:24:16 EDT
Article-I.D.: hoptoad.1137
Posted: Fri Sep 26 04:24:16 1986
Date-Received: Fri, 26-Sep-86 20:57:15 EDT
References: <8609221813.AA04648@cory.Berkeley.EDU>
Organization: Nebula Consultants in San Francisco
Lines: 22

In article <8609221813.AA04648@cory.Berkeley.EDU>, dillon@CORY.BERKELEY.EDU (Matt Dillon) writes:
> 	With its cache, a 68020 doing simple blits would use most of bandwidth
> (100% for simple copies).  Since a 68020 usually has a faster clock than a
> 68000, it would easily beat out the Amiga's blitter.   Additionaly, you
> wouldn't need multiple blitter passes.
> 	Of course, the disadvantage is that it uses the processor... the system
> would basically stop while you're doing the blit.  But hell, you only live
> once.

It doesn't really matter whether the CPU is doing it or the blitter is
doing it -- if ANYBODY is burning up 100% of the memory bandwidth, the
system will "basically stop" -- or stop doing anything but the blit.

I think the Amiga blitter can be configured to steal basically all the
memory cycles (preempt the processor).  The CPU could also do a "wait"
instruction to pause until the next interrupt, test if the blitter
is done, and jump back to the wait if not.  While in a WAIT, the CPU
does not use any bus bandwidth.  I don't know if the memory arbitration
on the Amiga is smart enough to notice, though.
-- 
John Gilmore  {sun,ptsfa,lll-crg,ihnp4}!hoptoad!gnu   jgilmore@lll-crg.arpa
		     May the Source be with you!