Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!uunet!cbmvax!daveh
From: daveh@cbmvax.commodore.com (Dave Haynie)
Newsgroups: comp.sys.amiga.tech
Subject: Re: [-] CHIP RAM Speed Problems
Message-ID: <15164@cbmvax.commodore.com>
Date: 15 Oct 90 17:40:29 GMT
References: <1990Oct9.042900.8479@IRO.UMontreal.CA> <28741@pasteur.Berkeley.EDU>
Reply-To: daveh@cbmvax.commodore.com (Dave Haynie)
Organization: Commodore, West Chester, PA
Lines: 39

In article <28741@pasteur.Berkeley.EDU> navas@cory.Berkeley.EDU writes:
>
>In article <1990Oct9.042900.8479@IRO.UMontreal.CA> martin@IRO.UMontreal.CA (Daniel Martin) writes:
>>
>>   I tested the speed of an A3000/25 MHz + Aztec v3.6 with the dhrystone v2.1 

>>   Why is there such a speed decrease (more than 3x)?

>Correct me if I'm wrong, but I thought that you had to synchronize with the
>CHIP memory for every access request....  That might explain it.
>[CHIP RAM accessed by chip memory at 7Mhz, and while the A3000 looks at that
> memory as 32 bit, I thought it could only look at it at that speed?]

Well, basically.  It doesn't make sense to speak of memory in terms of MHZ, 
since it isn't really clocked, per se.  The Chip memory in the 3000, like in
any Amiga, runs 560ns memory cycles.  Since the clocks that define the Chip
memory cycle aren't related to the 68030 clock in the 3000, there may also
be a synchronization delay, where some additional time must be added to get
the CPU and the memory into the proper state to communicate with one another.
Then there's the fact that, while the Chip memory cycle is 560ns, you have to
pick the right half of the cycle to start with it, otherwise there's an
additional wait during the Chip half of the cycle.  This resynchronization
which the Chip bus also happens on 68000 based Amigas, but it's more likely
to occur.

Fast RAM, on the other hand, runs a 200ns cycle on a 25MHz Amiga.  With burst
mode, the effective time turns out to be 110ns per 32 bit fetch, and there are
no synchronization delays of either kind found on the chip bus.  So after a
fashion, the Fast memory is between 5 and 8 times faster than Chip memory.  And
that's even before you start any heavy Denise or blitter/copper activity.

>David Navas                                   navas@sim.berkeley.edu



-- 
Dave Haynie Commodore-Amiga (Amiga 3000) "The Crew That Never Rests"
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	Standing on the shoulders of giants leaves me cold	-REM