Article View: comp.arch
Article #1975Re: more Observability
From: Roy Smith
Date: Fri, 25 Aug 1989 01:33
Date: Fri, 25 Aug 1989 01:33
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In article <1063@cernvax.UUCP> hjm@cernvax.UUCP (Hubert Matthews) writes:
> So, please, no more write-only registers or similar gate saving tricks.
My impression of Unibus read-only and write-only registers sharing
the same address was that it wans't meant to save gates, but address space.
On a Unibus, you only have (if I remember correctly) 4K of I/O space and
that space was sparsely used, in an effort to make auto-configure possible
(i.e. if there is something at address 77XXXX, it must be a YY-11). With
32-bit address spaces common today, this is probably not necessary.
In a sense, DEC did the same with their pdp-11 opcodes; "add byte"
was really "subtract word". Given the confines of a 16 bit word, I suspect
they did the right thing, but again, it's probably not necessary today.
--
Roy Smith, Public Health Research Institute
455 First Avenue, New York, NY 10016
{att,philabs,cmcl2,rutgers,hombre}!phri!roy -or- roy@alanine.phri.nyu.edu
"The connector is the network"
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Path: arc1-ca.pugleaf.net!utzoo!attcan!uunet!cs.utexas.edu!tut.cis.ohio-state.edu!rutgers!phri!roy From: roy@phri.UUCP (Roy Smith) Newsgroups: comp.arch Subject: Re: more Observability Message-ID: <3954@phri.UUCP> Date: 25 Aug 89 01:33:13 GMT References: <5945@pt.cs.cmu.edu> <21547@cup.portal.com> <1063@cernvax.UUCP> Reply-To: roy@phri.UUCP (Roy Smith) Organization: Public Health Research Inst. (NY, NY) Lines: 18