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From: jbuck@galileo.berkeley.edu (Joe Buck)
Newsgroups: comp.arch
Subject: Re: bizarre instructions
Keywords: instructions  bizarre  symmetry
Message-ID: <11459@pasteur.Berkeley.EDU>
Date: 26 Feb 91 19:28:04 GMT
References: <14710@sunquest.UUCP>
Sender: news@pasteur.Berkeley.EDU
Reply-To: jbuck@galileo.berkeley.edu (Joe Buck)
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Lines: 16

|> Donald Lindsay writes:
|> >- addressing modes which studies could not find a single use of.
|> >  (PDP-11 autodecrement deferred - omitted from the VAX.)

Way back in 1979 I had a job writing code for an LSI-11 board with
4K words of core memory and no O/S (it was basically an interrupt-driven
controller for interfacing a couple of array processors together),
and I found use for several of the weird autodecrement-deferred
instructions: including a "program" with one instruction word and
one data word that would zero all of memory and then halt, returning
control to the built-in ODT debugger.  Can any PDP-11 programmers
figure out what it was?

--
Joe Buck
jbuck@galileo.berkeley.edu	 {uunet,ucbvax}!galileo.berkeley.edu!jbuck	


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