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From: jesup@pawl10.pawl.rpi.edu (Randell E. Jesup)
Newsgroups: comp.arch
Subject: Re: RPM-40 microprocessor @ 40 MHz; dat
Message-ID: <508@imagine.PAWL.RPI.EDU>
Date: 10 Mar 88 08:53:38 GMT
References: <9792@steinmetz.steinmetz.UUCP> <9852@steinmetz.steinmetz.UUCP> <7613@apple.Apple.Com>
Sender: news@imagine.PAWL.RPI.EDU
Reply-To: beowulf!lunge!jesup@steinmetz.UUCP
Organization: RPI Public Access Workstation Lab - Troy, NY
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In article <7613@apple.Apple.Com> bcase@apple.UUCP (Brian Case) writes:
>In article <9852@steinmetz.steinmetz.UUCP> sungoddess!oconnor@steinmetz.UUCP writes:
>No, I meant the Am29000 and the R2000, but let's not forget the SPARC
>(as in SUN 4s).  I really believe that the RPM40 is top dog in its
>world (MC680[012] family, 1750A processors, AN/YUK-14s).  Maybe the
>R2000 and the Am29000 wouldn't make it there, or maybe they would.  But
>don't say the RPM 40 doesn't need a TLB because its world is 1750As and
>AN/YUK-14s and then complain when John Mashey (for example) says that
>it won't make the best UNIX box.

	I think Dennis and I have been saying that can be used for Unix, not
that it's the fastest Unix processor around.  Whether or not it's the fastest
at Unix remains to be seen (if it ever will be at all), but it at least
stands a good chance.  It will not be, however, as fast at Unix as it would
be if that were the only design criteria.  Certain parts of it are optimized
for a different envirionment, but everything needed for unix is there.  For
example, it is optimized for a fair amount of FP stuff (in conjunction with
the not-formally-announced FP coprocessor), which is not the standard Unix
profile (except for things like Crays).
	No it doesn't have a TLB; yes, it can have an external one and has
been designed to work very well with such.

>benefit too.  You assume SRAMs.  You pay a cost, you get a benefit.  An
>Am29000 system can be built with VDRAMs (so could the RPM 40, I bet, but
>not at 40 MHz unless someone makes 40 MHz VDRAMs that I don't know of
>(the Am29000 will run into this wall soon too)): you pay a cost
>(performance loss compared with the max.) but you get a benefit (lower
>system cost when you want more memory than SRAMs will let you afford).

	Which is one of the reasons (along with bandwidth, etc) that we use
16-bit instructions, and fetch them 2 at a time at 20Mhz.  This means we
only need 50ns memory for the instruction side.
	When one designs a processor, one usually has to at least consider
system cost.  In some ways, we pay more attention to it than some others,
because one of our targets is embedded systems.  People building minis
usually have a lot more leeway on CPU and cache costs, and can throw hardware
(like custom multi-hundred Megabyte/sec busses, BIG SRAM caches, etc) at the
problems of max performance.
	The Am29000's ability to use VDRams is also a nice solution to the
problem of system cost.  As you said, I think the Rpm-40 is closer to the
Am29000 philosophically than the R2000.  It seems the R2000 is meant for 1
main purpose: running Unix REAL FAST.  It does a pretty good job at it.  The
Am29000 and Rpm-40 seem to have several purposes: classical micro applications,
embedded systems, running UNIX fast, etc.  So they might not beat the R2000
on a Unix-Mips (UIPS? :-) per Mhz, but they probably win in other applications.

>Now, as to who has better performance (which is the crux of this
>arguement, I think):  it can't be decided until we all agree on a system
>environment:  if you want to use your SRAMs, then let us use them too.
>If you want to talk about multi-tasking, then we should all have TLBs.

	To be most honest, it should be a system to do the application needed,
then measure performance/cost.  Exactly what goes into which system isn't
important, just overall system cost vs performance.  The parts exist, if you
pay for them, you use them.

	Folks, lets be careful to avoid the "my processor better than yours"
type of wars, and lets be careful to realize no 2 CPUs are designed for
the same constraints/applications/envirionments.  It also helps to try to
avoid defensiveness about one's 'baby', whatever that might be.  The
discussions here can be enlightening for all involved (witness the stuff on
Am29000 compare bytes, or RPM-40 leaving out Alu bypassing), so let's
stick to architecture.

     //	Randell Jesup			      Lunge Software Development
    //	Dedicated Amiga Programmer            13 Frear Ave, Troy, NY 12180
 \\//	beowulf!lunge!jesup@steinmetz.UUCP    (518) 272-2942
  \/    (uunet!steinmetz!beowulf!lunge!jesup) BIX: rjesup

(-: The Few, The Proud, The Architects of the RPM40 40MIPS CMOS Micro :-)