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From: jhf@lanl.ARPA (Joseph Fasel)
Newsgroups: net.arch
Subject: Re: Cray "A" processor
Message-ID: <3351@lanl.ARPA>
Date: Thu, 22-May-86 13:18:09 EDT
Article-I.D.: lanl.3351
Posted: Thu May 22 13:18:09 1986
Date-Received: Sat, 24-May-86 05:26:41 EDT
References: <310@cernvax.UUCP> <3106@lanl.ARPA>
Organization: Los Alamos National Laboratory
Lines: 28

Allen Baum was apparently unable to post news from host "apple", and
asked me to post the following for him:
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The CRAY A-machine that is used in the I/O processor of the Cray-X/MP
is a 16-bit machine with 128 instructions. There is an accumulator, an
index register, 512 operand registers, and 64K words of local memory.

More than a quarter of the opcodes are unconditional and conditional
branches/calls(returns?) of various flavors. The only branch
conditions are Carry=0, Acc.=0, and their inverses.  There appears to
be a 16 deep return stack, but I'm not sure how its used.

Another quarter of the opcodes are I/O channel functions of the form:
Do function N on channel C (C can be the contents of a reg or a literal).

There are a few control instructions, and the remaining instructions
are the arithmetic/logical class.

The operations are simple: +,-, inc, dec, and, move, and shifts.
The addressing modes are simple: immediate, operand reg. direct,
operand reg. indirect (thru index reg), and local memory indirect
(thru operand regs.)

Instructions are mostly 16 bit, with a few 32 bit (includes 16bit
immediate field).


	Allen Baum, Apple Computer