Path: utzoo!utgpu!jarvis.csri.toronto.edu!cs.utexas.edu!asuvax!noao!arizona!naucse!sbw
From: sbw@naucse.UUCP (Steve Wampler)
Newsgroups: comp.arch
Subject: Re: CISC Silent Spring
Message-ID: <1891@naucse.UUCP>
Date: 21 Feb 90 17:40:33 GMT
References: <9748@cbmvax.commodore.com>
Organization: Northern Arizona University, Flagstaff, AZ
Lines: 44

> This new "bat" machine is quite CISCy, and sounds pretty interesting,
> at least based on the tidbits from EE Times.  A 64 bit MPU with 
> instructions to support C-like things such as telling if one byte in
> a machine word is '\0' or '\n', or another which basically implements
> an 8-case switch statement.  Of course, like most new things, there
> are incredible MIPS claims for it but nothing like SpecMark or even
> Dhrystone out yet.
> 
> Dave Haynie Commodore-Amiga (Systems Engineering) "The Crew That Never Rests"

Well, I haven't seen the EE Times, but I know a little about the BAT.
The first model, the 6420, is, in my opinion, not a great implementation.
The 6430, however, is well implemented.  The BAT series does many of the
things that RISCS have been doing (large caches, lots of registers, etc.)
in a CISC environment (18 different addressing modes!)  Most of the
'common' instructions (i.e. RISC) are single cycle and typically one or
two bytes (so you can load 8 or 4 in one 64-bit bus access).  C-style
string functions and memory functions are encoded as single instructions
that operate 8-bytes at a time.  Function calls are 3(?) cycles, and
interupts are equally fast.  Also nice are the 256(?) data channels
for nice fast I/O.

The MIPS claim is misleading - that is for character processing
(where they should be *fast*, given the 8-byte parallelism), PEAK
performance.  The biggest win (aside from character processing)
is the small impact heavy I/O has on overall performance - it just
doesn't slow down much under heavy I/O.

Given the slow clocks on the 6420 and 6430, they do a pretty impressive
job.  I'm anxious to see what the faster clock versions do.

I'm supposed to be getting one next week - though the OS may follow
after that by another week or so - to play with.  If there's anything
really interesting in the real machine (I don't expect that much from
the 6420) I'll be happy to post it.

Oh, yes, it's a 48-bit address space.  One last interesting feature
is the ability to play with part of a register without affect the
other parts.  So you can put a 16-bit tag on a 48-bit address and
not have to unpack them into separate registers.  The machine *should*
be able to run Icon and Lisp like, well, a bat out of ....
-- 
	Steve Wampler
	{....!arizona!naucse!sbw}