Path: utzoo!censor!geac!torsqnt!news-server.csri.toronto.edu!cs.utexas.edu!uunet!motcid!wilner
From: wilner@motcid.UUCP (Corey S. Wilner)
Newsgroups: comp.sys.apple2
Subject: Re: Multitasking on a II
Message-ID: <5833@mint17.UUCP>
Date: 18 Dec 90 14:28:58 GMT
References: <11297.apple.net@pro-angmar> <1990Dec16.073531.1483@nntp-server.caltech.edu>
Organization: Motorola Inc., Cellular Infrastructure Div., Arlington Heights, IL
Lines: 33

toddpw@nntp-server.caltech.edu (Todd P. Whitesel) writes:

> Stuff omitted

>By the way, atomic instructions are NOT required for process communication,
>as Randy said (BTW Randy, Using 6502 Assembly Language was my
>first ML textbook) -- lack of them just makes it tougher. However, the 6502
>has always had INC/DEC, which are atomic

I don't see how the INC/DEC are going to do any good.  You cannot detect the
resource and sieze it with INC or DEC which is what is truly necessary for
a preemptive environment.  

It is interesting to note that the operating system we are using on a 
project here at work is VRTX32/68000 and they use one special rule:
	There is a parameter called the component disable level which
	sets the interrupt mask level whenever an indivisible check must
	be done.  An ISR at a level above the CDL must not make any calls to
	VRTX.  This prevents breakup of an indivisible operation.

The major problem I have seen was during the debugging stage where I read
the manual wrong and did not allocate enough stack space per task.  Needless
to say, we are not using an MMU and this led to one task's stack overwriting
another's!  Thank heaven for emulators!

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