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From: collins@encore.UUCP (Jeff Collins)
Newsgroups: comp.sys.nsc.32k
Subject: Re: cxp/rxp instructions
Message-ID: <1751@encore.UUCP>
Date: Mon, 13-Jul-87 09:54:06 EDT
Article-I.D.: encore.1751
Posted: Mon Jul 13 09:54:06 1987
Date-Received: Tue, 14-Jul-87 06:09:58 EDT
References: <10742@hi.UUCP>
Organization: Encore Computer Corp., Marlboro, MA
Lines: 20
Keywords: rxp/cxp instructions
Summary: cxp/rxp instructions

In article <10742@hi.UUCP>, cyrus@hi.UUCP (Tait Cyrus) writes:
> Here at the University of New Mexico, we will be starting to port
> GENIX 4.2 to a 32016/32032 board.  I have some questions.
> 
> 1) What good are the cxp/rxp instructions?
> 2) Why can't the "standard" jsr/ret instructions be used?
> 3) What advantages are there for going through a jump table instead
>    of jumping directly?
> 


	In normal operation these instructions should NOT be used.  They are 
much slower than jsr/ret.  We changed our compiler to not generate these 
instruction do to thier execution times.  In fact we modified the OS to 
use the MOD register as infrequently as possible (only on interrupts, where
we have no control over the CPU using it).

	The next National chip (32532) has a direct interrupt mode that does 
not go through the MOD table to find its vector.  We will be using that when
we upgrade...