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Path: utzoo!utgpu!water!watmath!clyde!rutgers!seismo!mnetor!spectrix!John_M
From: John_M@spectrix.UUCP
Newsgroups: comp.arch
Subject: Re: Interrupt vectors.
Message-ID: <291@spectrix.UUCP>
Date: Sun, 7-Jun-87 15:48:20 EDT
Article-I.D.: spectrix.291
Posted: Sun Jun  7 15:48:20 1987
Date-Received: Sun, 7-Jun-87 23:42:46 EDT
References: <7408@boring.cwi.nl>
Reply-To: jmm@spectrix.UUCP (John Macdonald)
Organization: Spectrix Microsystems Inc., Toronto, Ontario, Canada
Lines: 43
Summary: M68020 provides what you want

In article <7408@boring.cwi.nl> jack@cwi.nl (Jack Jansen) writes:
> ...  you want all interrupts to jump to the same routine, and
>have the interrupt number handy somewhere. Operating Systems I'm
>familiar with all simulate this by either stealing a couple of bits
>in the PSR and go through pains to extract them again in the common
>interrupt routine, or, even worse, provide lots and lots of twisty little
>routines, all slightly different (like
>intvec128:	push	#128.
>		jmp	int_common	).
>
>Now, the sensible thing for the hardware to do seems to be to
>provide one vector, and push the interrupt number along with the
>PC, PSW and what have you.
>
>Is this scheme implemented on any machine?
>-- 
>	Jack Jansen, jack@cwi.nl (or jack@mcvax.uucp)
>	The shell is my oyster.

The Motorola 68020 provides almost what you ask for.  The exception
vector pushed onto the stack contains the exception index that caused
the trap.  Thus you can use a common routine that does all of the
shared code and then uses its "argument" in the exception vector to
determine which interrupt (or other trap) actually occurred.

It does not do one thing that you ask for - it does have separate
vectors for each exception.  You have to make them contain the same
address to have a shared handler.  It would have been a mistake for
Motorola to do things exactly as you ask - not every operating system/
hardware design would be set up in such a way that ALL of the interrupts
would be handled by a common routine.  It would be as much a mistake
for the hardware to insist that the software uses a common routine (which
you ask for) as it is to ensure that a common routine couldn't be used
(which you complain about).

This is a case where the hardware should provide mechanisms which are
capable of supporting any policy that the software designer chooses
to use.
-- 
---------  .signature eater food ---------
John Macdonald   UUCP:    {mnetor,utzoo} !spectrix!jmm
                 internet:Sorry. We're in range, but we're in no domain.
Disc-claimer: (noun) any hack's source directory