Re: AppleTalk / Interrupts / ProDOS 8 / DOS 3.3 Launcher

[dempson@swell.actrix.gen.nz (David Empson)]

In article <1993Apr5.230256.29920@fawlty.towers.oz.au> johnmac@fawlty.towers.oz.au (John MacLean) writes:
> I have been trying for some time to get DOS 3.3 Launcher to work
> over an AppleShare network, but I'm having problems which I believe
> are caused by incorrect handling of Appletalk interrupts.
> I am therefore looking for help:
> 
> BACKGROUND QUESTIONS:

All three questions are answered by the "AppleShare Programmers' Guide
for the Apple II Family".  The basic rule is "don't disable interrupts".

In particular, interrupts must be enabled whenever you make a ProDOS-8
call that might access the network, or the IIgs will hang (it doesn't
say much about the IIe workstation card).

On the IIgs, if you disable interrupts for more than 90 microseconds
at a time, you may cause incoming characters to be lost.  If you are
connected to a server and have interrupts disabled for a long period
(several seconds) the server will drop your connection.  AppleTalk
timers will be disrupted if you lock out interrupts for more than 220
ms or thereabouts.

Basically, the less time you disable interrupts, the better.

> THE MAIN QUESTION:
> I have a rather unique situation in which I need to swap out the
> memory occupied by the ProDOS 8 MLI.
> Would it be possible to patch an interrupt vector (either in page 3
> of bank 0, or in bank E1/E0 on a GS) to handle the interrupts
> generated by Appletalk without having the MLI in memory?
> ProDOS is still in the language card, if this is any help.

ProDOS-8 itself isn't involved in handling AppleTalk interrupts on the
IIgs.  They are handled by the IIgs interrupt firmware.  Patching this
will achieve nothing except give you a headache trying to reinvent the
wheel.

I can't give you a definite answer on this one.

I suspect that you might be able to use the AppleTalk calls
"RamForbid" and "RamPermit" to temporarily disable dispatching for
received packets, but they are only supposed to be used for short
periods.  If you're switching out ProDOS-8 for an extended period,
you're probably out of luck.
-- 
David Empson                                                               
dempson@swell.actrix.gen.nz    <--- Note my new E-Mail address!            
Snail mail: P.O. Box 27-103, Wellington, New Zealand