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Re: Second level cache?

To: riscy@pyramid.com
Subject: Re: Second level cache?
From: caret@pyramid.com (Neil Russell)
Date: Tue, 10 Aug 93 11:16:25 PDT
In-reply-to: <199308101106.AA17966@romeo.cs.Colorado.EDU>; from "Drew Eckhardt" at Aug 10, 93 5:06 am
Reply-to: riscy@pyramid.com
Sender: owner-riscy@pyramid.com
> Another alternative would be be having what passes as a memory
> controller in the talk to some other cache/memory controller
> instead of DRAM, again, you can't say that it will work until
> you see what the timing looks like.

What I understand is that the ARC chipset supports a secondary cache
similar to the way it does for the 486.  It is not necessary to use
the cache support signals from the R4k to have a secondary cache, although
it may mean that this cache will take two cycles to access data where
the R4000SC cache would take one.  This may not be great, but it is still
better than the cycles required to get data from DRAM.

Note that I am guessing about the timing issue; it may be that the ARC
chipset's cache logic can handle one cycle access.

With the ARC chipset's arangement, it is possible to add cache the same
as you would with a 486 MB; probably using the same cache chips.

BTW, Pyramid has a R4000MC machine, which uses the maximum 4Mbytes of
secondary cache.  I will ask if anyone has done some serious benchmarks
on how well this works.

> Waiting for an initial lead on these chips to drop out of thin air
> (as was the case with the 4200 with someone stumbling across a MIPS 
> press on the net, other people following up on NEC second sourcing
> them, and people on the list finally ending up with more solid data
> some time later) will take a random, potentially infinite amount
> of time :-)
> IMHO : We need to get parts and prices so their feasibility can be studied
> before a design is done, or we need to go ahead with a design so us
> software people have something to play with.

I, like quite a few others on this list, am hassling a distributor about
the NEC r4k.  I am having just as much joy as everyone else - none... ;-(
My personal opinion is that the R4k + ARC is the best solution that we
have.  Unfortunately, we cannot do anything without that information.
Stay tuned; when the manufacturers are forthcomming with the data,
we will be forthcomming with a board.

Neil Russell            (The wizard from OZ)
Pyramid Technology                      Email:  caret@pyramid.com
3860 N. First Street                    Voice:  (408) 428-7302
San Jose, CA 95134-1702                   FAX:  (408) 428-8845

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