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From: wsr@lmi-angel.UUCP (Wolfgang Rupprecht)
Newsgroups: net.micro.68k
Subject: Re: The Motorola 68030 (mem access time)
Message-ID: <83@lmi-angel.UUCP>
Date: Thu, 2-Oct-86 00:32:15 EDT
Article-I.D.: lmi-ange.83
Posted: Thu Oct  2 00:32:15 1986
Date-Received: Sat, 4-Oct-86 05:39:03 EDT
References: <8609262336.AA01693@cory.Berkeley.EDU>
Reply-To: wsr@lmi-angel.UUCP (Wolfgang Rupprecht)
Organization: LISP Machine, Inc (Cambridge Engineering HQ)
Lines: 16

>  For the 68030,  the utility is this : you present a paragraph address
>(bottom 7 bits zero).  Then you clock four times, loading four thirty-two
>bit words into cache.  You have just saved most of the work involved in
>your next three memory cycles.  As far as memory access time goes, lots of
>ripple mode devices can clock out ripple bits at better than 62.5 ns/bit.
>  Somebody who has a real live data sheet, is this right?

The 'nibble' mode devices (thats the buzz-word for the above type of
transfer) that I've seen *don't* need the bottom n-bits zero-ed. They
will accept any address as the first, and give you the next 3
addresses (modulo-4) next. This is even better, as it allows you to
read the address that you are really interested in first, and do the
prefetches last. 

-- 
Wolfgang Rupprecht	{harvard|decvax!cca|mit-eddie}!lmi-angel!wsr