Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!sdd.hp.com!zaphod.mps.ohio-state.edu!sol.ctr.columbia.edu!ucselx!crash!pnet01!lkoop
From: lkoop@pnet01.cts.com (Lamonte Koop)
Newsgroups: comp.sys.amiga.hardware
Subject: Re: Hurricane 2800 doesn't like 16 bit fast ram?
Message-ID: <4825@crash.cts.com>
Date: 5 Oct 90 09:16:01 GMT
Sender: root@crash.cts.com
Organization: People-Net [pnet01], El Cajon CA
Lines: 41

koren@hpfelg.HP.COM (Steve Koren) writes:
[stuff deleted]
>
>However, it doesn't work.  More specifically, the MicroBotics memory
>autoconfigures OK, but when accessed, it returns seemingly random values
>(or at least, not the values which were written there).  With the '030
>disconnected, the MicroBotics memory works fine.
>
>Someplace in the Hurricane 2800 docs, they mention a "bug in AmigaDos"
>which they claim prevents '030 data and instruction caches from working
>correctly with normal fast ram.  So far I haven't tested this (as their
>configuration program turns on caches by itself, and since the ram has
>already autoconfigured itself, its too late - system crash).  Is there
>any way I can use my other 2 meg with the '030 card?  Do any other
>'030 cards exhibit the same problems?
>
>Thanks to anyone who can offer some insight...
>
>    - steve (koren@hpfela.HP.COM)
I don't know about that.  I have a CSA Mega-Midget Racer 030 board with 32-bit
RAM, and 16-bit RAM on the system and it works fine.  The data cache is not
enabled on the 16-bit RAM, but there is a PAL to do this if I want it (never
saw the need...16-bit RAM cacheing probably won't add much perfomance).  I'm
not sure about this (someone correct me if I'm wrong), but I believe the
instruction cache should work fine in the 16-bit environment...the OS itself
will enable the ICache, and there are boards out there which have no 32-bit
RAM, but run 020s and 030s with the ICache on.  In fact, I've done some
testing about, and found that in a 16-bit RAM environment, it's possible to
make a 25MHz 030 run SLOWER than a 7.14MHz 68000, IF the Instruction cache is
off, and no 32-bit RAM is used.  The 020, 030, etc... are all very reliant on
the ICache as in integral part of their architecture, and to not use them in a
16-bit environment really exposes the processor to the bottleneck of said
environment.  In short, I'd be just a bit suspicious about the claim that a
bug in AmigaDOS prevents the ICache from woring properly in a 16-bit
environment.  But I COULD be wrong....



UUCP: {hplabs!hp-sdd ucsd nosc}!crash!pnet01!lkoop
ARPA: crash!pnet01!lkoop@nosc.mil
INET: lkoop@pnet01.cts.com