Path: utzoo!utgpu!news-server.csri.toronto.edu!cs.utexas.edu!usc!elroy.jpl.nasa.gov!jarthur!nntp-server.caltech.edu!toddpw
From: toddpw@nntp-server.caltech.edu (Todd P. Whitesel)
Newsgroups: comp.sys.apple2
Subject: Re: Building a NEW computer
Message-ID: <1990Dec7.013152.7391@nntp-server.caltech.edu>
Date: 7 Dec 90 01:31:52 GMT
References: <10895.apple.net@pro-angmar> <14668@smoke.brl.mil>
Organization: California Institute of Technology, Pasadena
Lines: 20

WDC's microcontroller versions of the 65c02 and 65816 have true vectored
interrupts for EVERYTHING... they are extremely nice microcontrollers and
I can see why they are popular.

The problem with interrupts in the Apple II was that Woz's original IRQ handler
used a zero page location, and backwards compatibility issues became important
_before_ he had a chance to fix it. Add that to the fact that Apple didn't
settle on an interrupt handler protocol until Prodos -- there were memory
state issues to deal with by then and things were just messy.

The GS and GS/OS do a far better job, but the real solution is true vectored
interrupts. The 65816 provides support for externally vectored interrupts
(in fact, all you need is an SRAM and a PAL) but Apple hasn't done anything
about it.

It's tempting to do something like this as an add-on -- it wouldn't be pretty
but it could be done. It might be easier to add to the Zip or the TWGS.

Todd Whitesel
toddpw @ tybalt.caltech.edu