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From: guy@gorodish.UUCP
Newsgroups: comp.arch
Subject: Re: Interrupt vectors.
Message-ID: <20461@sun.uucp>
Date: Fri, 5-Jun-87 14:53:30 EDT
Article-I.D.: sun.20461
Posted: Fri Jun  5 14:53:30 1987
Date-Received: Sat, 6-Jun-87 20:02:54 EDT
References: <7408@boring.cwi.nl> <438@winchester.UUCP>
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In article <7408@boring.cwi.nl> jack@cwi.nl (Jack Jansen) writes:
> Now, given most modern operating systems, this is exactly what you
> *don't* want. If you want to handle interrupts in a high-level
> language, 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

In the OSes I'm familiar with, all interrupts *for a given type of
device* ultimately end up calling the same routine, providing a unit
number as an argument, but interrupts for two different devices end
up calling two different routines.  I presume you're talking about
the initial trap, though; the code invoked by that trap could figure
out both which interrupt routine to call (i.e., which type of device
is interrupting) and what unit number to pass as an argument (i.e.,
which of those devices is interrupting).

In article <438@winchester.UUCP>, mash@mips.UUCP (John Mashey) writes:
> Sure. The MIPS R2000 has 3 vectors: RESET, User TLBMISS (software handler
> for TLBmisses for the most frequent case, i.e., frequency makes it
> the only one worth a special case), and everything else.  It does
> what you say.

The diagram in "Operating System Support on a RISC" shows both the
Status and Cause registers.  The Cause register includes a 6-bit
ExtInt field, which I presume is a bitset indicating which of the 6
external interrupts are pending.  To what do these 6 interrupts
correspond?  Do they correspond to classes of devices?  I presume
you are not limited to 6 different devices attached to a system
containing an R2000, so you would "double up" on external interrupts
as necessary.

If so, how are the devices distinguished?  Is this done with polled
interrupts, or is some code provided in one of the other special
registers?
	Guy Harris
	{ihnp4, decvax, seismo, decwrl, ...}!sun!guy
	guy@sun.com