Relay-Version: version B 2.10 5/3/83; site utzoo.UUCP
Path: utzoo!mnetor!seismo!rutgers!sri-unix!hplabs!cae780!amdcad!neptune!brian
From: brian@neptune.AMD.COM (Brian McMinn)
Newsgroups: comp.arch
Subject: Am29000 & register windows
Message-ID: <118@neptune.AMD.COM>
Date: Thu, 19-Mar-87 11:34:24 EST
Article-I.D.: neptune.118
Posted: Thu Mar 19 11:34:24 1987
Date-Received: Sat, 21-Mar-87 06:13:25 EST
Organization: Advanced Micro Devices, Inc., Austin, Texas
Lines: 23
Keywords: Am29000,register windows

There was some vigorous (done with much arm waving) discussion in
this news group a few weeks ago about the "optimum" size granularity
for a register window.  I couldn't say much then, but the Am29000 was
announced Monday, so I can add my comments now.

Contrary to what seemed to be a general consensus in that discussion,
the Am29000 has no major speed problems with performing a full 7-bit
add in the register access path.  This allows us to address ALL 128
local registers without moving the stack pointer and gives us a
minimum allocatable unit of ONE register (ie., the stack pointer can
point ANYWHERE in the 128 local registers).

How did we do it?  1) a well balanced pipeline, and 2) good circuit
design.  The 7-bit add did require some speed related circuit design,
but the pipeline is balanced such there is no single speed limiting
pathway.  The whole chip hits its speed limit at about the same clock
frequency.

	The Am29000 design team (based in Austin).
-- 
	Brian McMinn		1-(512)-462-5389
	Advanced Micro Devices	domainLand:  brian@neptune.AMD.COM
	Austin, Texas		bangLand:   ...!amdcad!neptune!brian