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From: szs@inmet.UUCP
Newsgroups: net.arch
Subject: Q's about RISC and HLLs - (nf)
Message-ID: <580@inmet.UUCP>
Date: Fri, 9-Dec-83 22:32:40 EST
Article-I.D.: inmet.580
Posted: Fri Dec  9 22:32:40 1983
Date-Received: Sun, 11-Dec-83 01:11:43 EST
Lines: 42

#N:inmet:2500007:000:1842
inmet!szs    Dec  1 16:54:00 1983

I'm trying to do an evaluation of ISA technology to find ISAs
which will support Ada, for the next generation of Navy processors.
This discussion group has thus been a source of great interest to me.

There seem to be three basic choices in the field now: ISAs with great
complexity (Nebula, iAPX432), "run of the mill" ISAs (PDP-11, MIL-STD-1750A,
AN/AYK-43,44, etc.), and RISCy things.

There are ample results for Ada implementations for the middle category.
Code generation is sometimes a pain in the butt but doable.  Results
are often less than satisfactory.  I've first-hand experience with Ada
432, with much less than satisfactory performance.  FIRST QUESTION:
Is it the "memory management" access descriptor BS that slows it down
or the complexity of the 432's ISA in general???

Nebula seems to have the same instruction complexity (approximately)
as the 432, but with more "conventional" memory management. SECOND
QUESTION: Does anybody know how well Nebula works??  It seems that
writing an Ada code generator for Nebula will be a piece of cake
(compared to, say, MIL-STD-1750). 3RD QUESTION: (for SofTechers)
Is this true??

The dearth of real performance info for RISC is frustrating.
Details in Radin's and Patterson's stuff are too sketchy.  4th Q:
Does anyone have some size/time comparisons along with the
RISC "assembly" code for some common algorithms?? (turner?? and
what's this simulator you've got??)

(Side comment: It seems that at least some of the remaining
94% of the computer design job has been thrown in the compiler
writer's lap for RISC.)

5th Q: Given that Ada compilers are already almost too complicated
to get right until the 4th or 5th try, is it wise to give the
compiler writers the job of creating a meta-ISA also???

-Steve Stein (decvax!harpo!inmet.szs)
p.s. hi gary at ncsu and jerry at yalecom