Path: utzoo!attcan!uunet!unsvax!uns-helios!alfter
From: alfter@uns-helios.nevada.edu (SCOTT ALFTER)
Newsgroups: comp.sys.apple2
Subject: Re: Multitasking on a II
Message-ID: <2451@unsvax.NEVADA.EDU>
Date: 10 Dec 90 23:31:18 GMT
References: <10395@ucrmath.ucr.edu> <2433@unsvax.NEVADA.EDU> <10425@ucrmath.ucr.edu>
Sender: news@unsvax.NEVADA.EDU
Organization: University of Nevada System Computing Services
Lines: 26

In article <10425@ucrmath.ucr.edu> rhyde@ucrmath.ucr.edu (randy hyde) writes:
>All you need to do multitasking on a II is a timer interrupt.
>I used an old 6840 timer chip on a board from some (now history)
>peripheral manufacturer.  I managed to get four processes running
>at once (at $800, $2000, $4000, and $6000).  Needless to say, these
>processes were highly aware of one another.  I did not attempt to
>take the project any farther than that....

Sounds like there might be a use for the Thunderclock's interrupt
generator after all--it'll make interrupts at any of 3 rates from 60
to 2400 Hz.  Set aside some memory to maintain information on each
process, and write an interrupt daemon to switch processes, and it
ought to work.  It also ought to run at a reasonable speed since the
processor is giving all its attention to one process until the
interrupt comes along to give it something else to work on.  It might
even be possible to get this thing to work under ProDOS.

Considering how slow some programs (such as some of pbmplus's
image-manipulation tools) run on even a 68030, I don't think I'd want
to try writing UNIX to run on an unaccelerated II. :-|

-----------------------------------------------------------------------------
Scott Alfter                             _/_
                                        / v \ Apple II:
Internet: alfter@uns-helios.nevada.edu (    ( the power to be your best!
   GEnie: S.ALFTER                      \_^_/