From: russell DOT thamm AT dsto DOT defence DOT gov DOT au
Newsgroups: comp.os.msdos.djgpp
Subject: Re: Realtime & DJGPP
Date: Wed, 19 Aug 1998 03:49:53 GMT
Organization: Deja News - The Leader in Internet Discussion
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In article <Pine DOT A32 DOT 3 DOT 91 DOT 980818124113 DOT 73468A-100000 AT ieva05 DOT lanet DOT lv>,
  Andris Pavenis <pavenis AT lanet DOT lv> wrote:
> (Even if this maybe not nice to say this in DJGPP mailing list) I can
> suggest to try out Linux (more exactly modification of Linux for hard real
> time tasks: rt-linux)
>
> http://rtlinux.cs.nmt.edu/~rtlinux/
>
> You will not lose any service provided by normal Linux kernel and at the
> same time You'll additionally get support for real time tasks that
> are scheduled usually with only some (or some tenths) of microseconds
> latency even under rather heavy system load.

rtlinux apparently suffers the same fatal flaw as all other
real-time extensions to non-realtime OSs. You can't do real-time
I/O using the OS drivers. You have to write all your own drivers.
This is hardly surprising since the original OS was never designed
for real-time. Since real-time I/O is a vital component of every
hard RT application I've ever seen, this limitation is severe.

>
> DOS as I think is not the best environment for such tasks.
>

In actual fact, DOS is quite a good RT/OS. Disable the timer interrupt
and you have a totally deterministic system. Its main limitations are its
failure to utilize the full power of modern processors. Its lack of
a decent GUI is also a problem. DJGPP overcomes many of these limitations.
Its main weakness (real mode) is also a strength because it gives you
access to DOS device drivers. The extensive set of tools available for DJGPP
are a huge bonus. Most of the source code is available so the tools can be
customised and the price is unbeatable.

Russell


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