Path: utzoo!attcan!uunet!cbmvax!valentin
From: valentin@cbmvax.commodore.com (Valentin Pepelea)
Newsgroups: comp.sys.amiga.tech
Subject: Re: AmigaOS/UNIX - A Suggestion
Message-ID: <15151@cbmvax.commodore.com>
Date: 15 Oct 90 09:06:04 GMT
References: <606@macuni.mqcc.mq.oz> <298@pdxgate.UUCP> <6782@sugar.hackercorp.com> <8081@gollum.twg.com> <6789@sugar.hackercorp.com> <90287.120957DXB132@psuvm.psu.edu>
Reply-To: valentin@cbmvax.commodore.com (Valentin Pepelea)
Organization: Commodore, West Chester, PA
Lines: 38

In article <90287.120957DXB132@psuvm.psu.edu> DXB132@psuvm.psu.edu writes:
>
> I don't understand why people keep referring to the Amiga OS as "real time".
> What's real time about it? I don't see timing specifications in the Rom
> Kernal Manual.  In theory, any task or interrupt may be held off for an
> infinitely long time (I guess you could call that a timing specification...
> :-))

Write a program that disables all interrupts, counts up to 10000, re-enables
all interrupts, and waits for 0.1 secs. All in a loop. Now start typing on the
keyboard. Neat feedback eh? Or better yet, start performing disk I/O. Most
impressive, eh?

So the true answer is no, an interrupt may not be held off for a long time,
unless you are a masochist. There may be implementation errors which prevent
interrupts from being processed when they should be, and tasks from being
switched at the proper time, but that does not remove the real time
characteristics of the operating system.

If you look at the operating system description from the Exec manual, you will
notice features found uniquely in real time operating systems. Like task
exceptions, which are normally used in case a critical error occurrs to perform
some recovery actions.

An operating system may be referred to as real time if it guarantees that an
event will be processed within a specified amount of time, in case of 'hard'
constraints. In case of soft constraints, it merely implies that the
usefullness of the system degrades with the amount of time that passes by.
In this case, the fact that events are deterministic (they are guaranteed
to be executed - eventually) allows us to call this a real time operating
system. Strictly by the book.

Valentin
-- 
The Goddess of democracy? "The tyrants    Name:    Valentin Pepelea
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