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From: "Dmitry A. Kazakov" <mailbox@dmitry-kazakov.de>
Newsgroups: comp.lang.ada
Subject: Re: Ada and linux real time
Date: Tue, 20 Mar 2012 09:04:51 +0100
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Date: 2012-03-20T09:04:51+01:00
List-Id: <comp.lang.ada>

On Mon, 19 Mar 2012 15:20:20 -0700 (PDT), slos wrote:

> But I am looking for a free alternative.

It would be rather difficult to find. Hardware protocols are very, if not
to say extremely, complex. The documentation is not free in most cases. So
free implementations are either non existent or do not go beyond simple
exercises.

> I am experimenting with Ada and Real Time on Linux and there are at
> least three alternatives : PREEMPT_RT for general control, Xenomai and
> RTAI for higher performance needs.

The only reason to have it preemptive is because of hardware communication
requiring asynchronous handling, e.g. a network stack. Unless you have
something very, very complex running in multiple cycles...

On the other hand something complex like that is quite difficult to ensure
meeting time constraints without doing a lot of additional work. So, if I
were you, I would not care. Just do your PLC and see if it works.

> - I am targeting simple process control for beginners but I want to be
> sure it can scale to motion control applications as well, and in this
> case I want to know the feasibility and experiment with it,

We did some scalability tests for our Ada software. In short, you should
not worry. If it does not scale, then not because of Ada.

> --  This package encapsulates all direct interfaces to OS services
> --  that are needed by the tasking run-time (libgnarl).

I don't think a PLC would need anything like that; maybe, but rather
unlikely.

-- 
Regards,
Dmitry A. Kazakov
http://www.dmitry-kazakov.de