LinuxSA Mailing list archives

  From: Andrew Pullin <drewp@bigpond.com>
  To  : Alan Kennington <akenning@dog.topology.org>
  Date: Wed, 31 Mar 1999 14:46:10 +0930

Re: Linux in real time (was More Meeting Information)

Hi Guys,
	I am just interested in this bit Alan has brought up about Linux as a real
time operating system. Before I start, I must admit that I am NOT an expert
here, and that I am trying to learn about it, and so I may previously been
led up the garden path, so if I say something wrong, I won't get upset if
you correct me. I have been talking to a few people at Flinders Uni about
this a bit, but they all have told me that standard Unix (or Linux or BSD
etc), while it _can_ run processes as a real time application, it was not
designed to do this, and that dedicated real time operating systems should
be used (like RT Unix I think it is called that is a Real Time version of
Unix). The reason for this is that apparently under load, ie many processes
running, you can't synchronise the processes properly because unless you
run some under the nice flag, they all have the same priority. Also you run
into problems when you use the fork() command, in that you have no control
over the order in which the newly created processes run either.

	As a little background, I have studied a University Operating systems
course that ran for 1 Semester. I am aware of only basic OS communications,
however I am familiar with using Semaphores, and I have written code to
demonstrate these. Most of my knowledge has come from enquiring about
extending our programming project, which was simulating manufacturing
machines that made items at different speeds. I wanted to fully synchronise
the machines, but was told it wasn't possible under Unix, we were using
Solaris at the time, but could have used Linux just as easily.

	O.K. guys (& girls if we want to be picky) I admit I have little knowledge
in the subject, but I am interested in learning about it. So try not to
turn the heat up too much.

	Cheers!
		Andrew.

> My favourite examples are in the area of certain kinds of
> communications systems, which require real-time software
> and also GUIs, and must run on minimal hardware.
> Linux is good at all three:
> 
> 1.
> Linux has an excellent real-time environment, provided by
> the kernel module functionality, which is excellently supported,
> because the _OS_ is open source, and therefore you can
> really understand what is ont he other side of the device-kernel
> interface. With other unixes, not to mention MS software etc.,
> the device-kernel interface is a cause of real fear and anxiety
> to programmers, because they don't know what's on the other side.
> 
 
> 3.
> Linux can run on the minimal sort of hardware that is often found
> in real-time projects involving communications, and similar
> projects requiring microcontrollers etc.
> The linux web server in a matchbox is a good example.

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