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From: news@cl.cam.ac.uk (The news facility)
Newsgroups: comp.sys.acorn
Subject: Re: R140 & ARM3
Message-ID: <1991May11.102642.20136@cl.cam.ac.uk>
Date: 11 May 91 10:26:42 GMT
References: <3305@izar.dcs.exeter.ac.uk>
Reply-To: nbvs@cl.cam.ac.uk (Nicko van Someren)
Organization: U of Cambridge Comp Lab, UK
Lines: 35

In article <3305@izar.dcs.exeter.ac.uk> cca@dcs.exeter.ac.uk (Clive Carmock) writes:
>I gather that to use a SCSI interface on the R140, I have to use
>the Acorn interface, as this has extra circuitry for RISC iX.  
>
>DOes anyone know if any similar things apply to ARM3 upgrades for
>the R140.
>Has anyone added an ARM3 to an R140 - if so I'd be interested in any comments.
From: nbvs@cl.cam.ac.uk (Nicko van Someren)
Path: cl.cam.ac.uk!nbvs

ARM3s run fine in R140s since about RISCiX 1.14 or so.  The code in 1.2 that
we have in the lab here seems to work better as I think it is more careful
about when it flushes the cache.  However, the performence improvment on an
R140 is not as dramatic as under RISC OS, things tend to run about 70-100%
faster instead of the usual 200-300%.  Tests I have done seem to indicate
that adding another 4MB of RAM makes at least as much difference as an ARM3 if
you are running the X server software as the working set gets very large.
An ARM3 and 8MB together have almost additive gain in performance.  The other
problem with the R140 that has been fixed on the R260 is the disk speed.  The
st506 disk is far too slow for a swap device, especially since it does not
have DMA so the processor is tied up all the time the memory is being paged.
I think (I have not tried it) that the performance will improve you get rid of
the st506 drive and put if a SCSI one.  Giving it an ARM3, 8MB RAM and a SCSI
disk will make it go quite well, but then again you then almost have an R260.

On the subject of whos SCSI card you can use, I expect that you can only use
the ones from Acorn unless you have the kernel source.  If it is anything like
the ethernet code there is little or no modularity in it, and certainly no way
to add support for new hardware without a recompile.

Nicko

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| Nicko van Someren, nbvs@cl.cam.ac.uk, (44) 223 358707 or (44) 860 498903    |
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