Path: utzoo!utgpu!utstat!jarvis.csri.toronto.edu!mailrus!eecae!tank!mimsy!chris
From: chris@mimsy.UUCP (Chris Torek)
Newsgroups: comp.arch
Subject: Re: Interrupts
Message-ID: <16554@mimsy.UUCP>
Date: 27 Mar 89 14:55:45 GMT
References: <28200294@mcdurb>
Organization: U of Maryland, Dept. of Computer Science, Coll. Pk., MD 20742
Lines: 26

In article <28200294@mcdurb> aglew@mcdurb.Urbana.Gould.COM writes,
as a side point:
>Am I correct in saying that this is a dead issue - that
>the "use a single entry point, since all UNIX does is
>move everybody together" idea has won out?  Or, is it just
>that UNIX has never been written to take advantage of
>vectored interrupts?

4BSD Unix on the VAX uses all the vectors.  The only `peculiarity' is
that, e.g., all DH/DM receive interrupts wind up calling the same C
routine, with the device index number as an argument.  (Of course, on
the SBI (780 and 8600), the hardware does not actually do the
vectoring; the support code in locore.s makes these look like the other
VAXen.)

If the `vector' number is in a memory location, the difference between
true vectored interrupts and software vectors is the instruction sequence

	move	@actual_vector,reg
	add	base,reg
	jump	@reg

which does not seem very expensive....
-- 
In-Real-Life: Chris Torek, Univ of MD Comp Sci Dept (+1 301 454 7163)
Domain:	chris@mimsy.umd.edu	Path:	uunet!mimsy!chris