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From: alexande@drivax.UUCP (Mark Alexander)
Newsgroups: comp.sys.m68k,comp.sys.intel
Subject: Resumable String Instructions (was Re: Moto Ad etc.)
Message-ID: <1477@drivax.UUCP>
Date: Tue, 5-May-87 01:31:34 EDT
Article-I.D.: drivax.1477
Posted: Tue May  5 01:31:34 1987
Date-Received: Wed, 6-May-87 01:01:05 EDT
References: <930@intsc.UUCP> <1517@ncr-sd.SanDiego.NCR.COM>
Reply-To: alexande@drivax.UUCP (Mark Alexander)
Distribution: comp
Organization: Bob-ist Temple of Monterey
Lines: 16
Summary: How the V60 does it
Xref: mnetor comp.sys.m68k:445 comp.sys.intel:221

The V60 manages to achieve a neat compromise between the
two previously mentioned alternatives (generality but huge
stack frames, or dedicated registers and small stack frames).
The V60 allows complete generality in the source and destination
operands, but dedicates two registers for storing the temporary
values needed to resume the instruction after an interrupt.  The
loss of two registers is insignificant (the machine has 32 general
purpose registers); and only two extra words need to be saved on the
stack by interrupt handlers.

The V60 can get by with just two words because it does some
re-evaluation of the operands of the instruction when it's resumed
(this is where my understanding gets a little hazy).
-- 
Mark Alexander	...{hplabs,seismo,sun,ihnp4}amdahl!drivax!alexande
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