Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!usc!wuarchive!uunet!mcsun!ukc!stl!crosfield!djhr
From: djhr@crosfield.co.uk (dave redman)
Newsgroups: comp.sys.acorn
Subject: ARM3 upgrade
Keywords: 30Mhz ARM3
Message-ID: <9887@suns6.crosfield.co.uk>
Date: 7 May 91 11:03:55 GMT
Organization: Crosfield Electronics, Hemel Hempstead, United Kingdom.
Lines: 63

Hello all,

anyone know anything about ARM3's ?

I bought a 30MHz ARM3 and fitted it to an A340..

It worked fine until I switched the ARM3 cache on and then...

The machine would run VERY fast for about 3 mins ( from cold ) and then all
hell breaks loose with modules dying left right and centre.

It was quite amusing watching the OS modules die one at a time with an
Address Exception error...

Anyway I think I traced the problem..

  I bought the Atomwide 4Meg memory upgrade and it has the MEMC1a fitted
  but it also uses a PEEL18CV8 -35 ( fitted between the CPU and MEMC sockets )
  Now if my maths serves this device can only run at 28.5 MHz ( max ).

  I have since modded the ARM3 motherboard to run at 25Mhz and everything works
  fine, however I WOULD like to go back to 30MHz and I propose to do this by
  replacing the -35 device with a -15.

  If anyone at acorn ( or otherwise ) would like to comment about this solution
  I would appreciate it. Or if anyone would like to post me the ABEL source for
  the PAL I would be even happier. ( I tried to read the device but it has the
  security fuse blown. - must be a BIG market for ripped off MEMC1a control
  PALs. )

I am curious abut something else though.. In my VLSI data book it says the ARM3
runs at 20Mhz.. does this mean a 30Mhz device is just a 20Mhz device that
happens to run at 30Mhz or is my Nov. 1990 VLSI data book already out of date ?

So the moral of this story..

    IF you buy a Watford Electronics 30Mhz ARM3 it may not work..

to be fair.. Watford DID tell me that in SOME machines the 30Mhz beasty doesnt
work.

Here are some performance figs I just ran..

	Machine		Dhyrstones per sec
	ARM2		5289
	ARM3 @ 25Mhz	14883
	SUN3/60		2888
	SUN/Spark1	8000
	SUN/Spark2	16000

And the SUN times were ONLY counting the executing procedures times not the
whole process time.

dave.

##############################################################################
# David Redman,                      #  JANET      :                         #
# Software/Hardware Engineer,        #  EARN/BITNET:                         #
# Crosfield Electronics Ltd,         #  UKNET      : djhr@cel.uucp           #
# Three Cherry Trees Lane,           #  Phone: 0442 230000  ext 3378         #
# Hemel Hempstead, Herts.            #                                       #
# United Kingdom                     #                                       #
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