Path: utzoo!attcan!utgpu!jarvis.csri.toronto.edu!rutgers!apple!motcsd!xdos!doug
From: doug@xdos.UUCP (Doug "It's A Feature" Merritt)
Newsgroups: comp.sys.amiga
Subject: Re: AmigaOS is real-time?
Message-ID: <350@xdos.UUCP>
Date: 28 May 89 17:31:53 GMT
References: <16284@louie.udel.EDU>
Reply-To: doug@xdos.UUCP (Doug "It's A Feature" Merritt)
Organization: Hunter Systems, Mountain View CA (Silicon Valley)
Lines: 57

In article <16284@louie.udel.EDU> 451061%UOTTAWA.BITNET@cornellc.cit.cornell.edu (Valentin Pepelea) writes:
>Furthermore these manipulations are only a few instructions long. On the Amiga,
>any task is allowed to disable interrupts for no more than 250 nanoseconds.

Wow! Now that's what I call *responsive*. I knew the Amiga was fast,
but that's really amazing.

>The EXEC itself abides by this defined limitation, and very loosely.

Very loosely indeed, I would say. At about a 125 nanosecond clock,
that's two cycles. As I recall the fastest instructions take *three*
clocks. So either the EXEC accomplishes everything it needs to do
in 2/3rds of an instruction, or else it violates this guideline
(at least to the extent of executing one whole instruction). I
wonder which it is? :-)

>1. EXEC reference manual, CBM, Addison-Wesley 1986.
>   Be sure to read all of it. Disregard the part where they tell you to use
>   Forbid() all over the place. Carl was really sick when he instructed that.

Yes indeed. I, too, am very fond of gurus.

>3. Guru's Guide #1: Interrupts, Carl Sassenrath, Sassenrath Research, 1987.
>   Even with the EXEC disassembly, you will still learn a lot from the designer
>   of the EXEC him-self. Includes nice diagrams and examples in C.

Truly a great book. The book is actually copyright 1988 and only just
hit the streets recently. I hope Carl does many more books in the series.

>4. 68000 User's Guide 6th edition, Motorola, Motorola Inc. 1989.
>   Look at the timing tables. Even at a mere 7.16 MHz, the 68000 can still
>   manipulate those lists within the requires 250 ns.

Hmmm. Apparently you really believe this. Must be that newfangled
new math.

>Whoa! You are very confused.

Ah, er, um, no comment. :-)

>Virtual memory has *nothing* to do with real-time systems.

I'll buy that.

>[ comments about what real time systems are good for deleted ]
>...Or a cumputer with a graphical user interface controlling a multi-tasking
>   environment...

Excellent point.

Sorry I poked a little fun there, it was hard to resist. No offense intended.
	Doug
-- 
Doug Merritt		{pyramid,apple}!xdos!doug
Member, Crusaders for a Better Tomorrow		Professional Wildeyed Visionary

"Welcome to Mars; now go home!" (Seen on a bumper sticker off Phobos)