Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!mips!apple!dlyons
From: dlyons@Apple.COM (David A. Lyons)
Newsgroups: comp.sys.apple2
Subject: Re: Appletalk memory locations
Message-ID: <52972@apple.Apple.COM>
Date: 16 May 91 21:29:30 GMT
References: <0.netnews.info.apple@pro-novapple> <1991May16.095217.5951@nntp-server.caltech.edu>
Organization: Apple Computer Inc., Cupertino, CA
Lines: 44

In article <1991May16.095217.5951@nntp-server.caltech.edu> toddpw@nntp-server.caltech.edu (Todd P. Whitesel) writes:
>[...]
>AppleTalk on the GS does not occupy any memory needed by 8 bit programs
>(except some patches to Prodos). What is probably killing you is the same
>thing that kills Tim Meekins' "Spinning Z" demo -- using //e methods to
>access the extra 64K without temporarily disabling interrupt services
>(mainly AppleTalk packet reception in this case) causes a system crash the
>instant a packet comes in, because the AppleTalk drivers can't handle it.
>The interrupt manager jerks around enough before it gets around to polling
>AppleTalk, I would have thought it'd take care of this, but apparently not.
>
>In short, if my guess is right, what the developer needs to hear is that
>the auxiliary memory routines need to set interrupts temporarily. I've had
>to do this with my own code; perhaps DTS can shed some light on the exact
>switches so you can tell the developer exactly what to look for.
>
>Todd Whitesel
>toddpw @ tybalt.caltech.edu

Disabling interrupts is overkill (but if it's only for short times and for
a small fraction of the time, it will work).

All you *need* to do is follow the main/aux stack pointer rules as documented
in the IIe Technical Reference Manual, the Apple IIgs Firmware Reference
Manual, and probably other places too.  In short, the main-memory stack
pointer is stored at $0100 in aux mem whenever the aux stack is in use, and
the aux-memory stack pointer is stored at $0101 in aux mem whenever the main
stack is in use.

If you use the AUXMOVE and XFER routines in the 80-column firmware, stack
switching is automatically taken care of for you.

The interrupt handler does all the appropriate "jerking around"--when it
has to switch to the main stack from the auxiliary stack, is sets the
stack pointer from the auxmem $0100 location.  If you have failed to set
this value, the interrupt handler winds up overwriting part of the stack
you were using, since it had no way to know which part you were using.
-- 
David A. Lyons, Apple Computer, Inc.      |   DAL Systems
Apple II System Software Engineer         |   P.O. Box 875
America Online: Dave Lyons                |   Cupertino, CA 95015-0875
GEnie:DAVE.LYONS  CompuServe:72177,3233 Internet:dlyons@apple.com

My opinions are my own, not Apple's.