[Xenomai-help] is rt_task_shadow ok?

[Xenomai-help] is rt_task_shadow ok?

[Stolz, Stefan, PGR2]

Hello,

i have a little question about rt_task_shadow(). I'm not sure if it is
ok to use ist like i do in my application.
The basic conditions of my app are:
 - it is a embedded linux (Sysgo ELinOS) with Xenomai 2.0.4 
   (old but unfortunatly no newer version is available for ELinOS)
 - the app listens on a tcp-port for commands from a client app.
 - one command ist for starting a simulation of some signals on the
parallel-port; 
   this simulation have to be hard-real-time

at first the tcp-server-part was in a non-rt-app which startet the
simulation-task with the normal xenomai-functions.
While the simulation is running i have to exchange data between the
tcp-server and the rt-task. 
The Problem is, that things like semaphores and mutexes doesn't work
with nrt-tasks.
now i found the rt_task_shadow-function. So after starting my app i call
this funktion and switch the process into a xenomai task (with the lowes
priority). At the moment everything seems ok; but are there any known
problems with this approach?

Kind regards,

Stefan Stolz

Re: [Xenomai-help] is rt_task_shadow ok?

[Jan Kiszka]

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Stolz, Stefan, PGR2 wrote:
> Hello,
> 
> i have a little question about rt_task_shadow(). I'm not sure if it is
> ok to use ist like i do in my application.
> The basic conditions of my app are:
>  - it is a embedded linux (Sysgo ELinOS) with Xenomai 2.0.4 
>    (old but unfortunatly no newer version is available for ELinOS)

Role your own? For simple Xenomai applications it's ok to stick with
what Sysgo provides. But for more complex scenarios I would seriously
recommend to update Xenomai+kernel.

Using a recent version will enable you to gain better community support
and to exploit those nice enhancements and fixes we added in the meantime.

>  - the app listens on a tcp-port for commands from a client app.
>  - one command ist for starting a simulation of some signals on the
> parallel-port; 
>    this simulation have to be hard-real-time
> 
> at first the tcp-server-part was in a non-rt-app which startet the
> simulation-task with the normal xenomai-functions.
> While the simulation is running i have to exchange data between the
> tcp-server and the rt-task. 
> The Problem is, that things like semaphores and mutexes doesn't work
> with nrt-tasks.
> now i found the rt_task_shadow-function. So after starting my app i call
> this funktion and switch the process into a xenomai task (with the lowes
> priority). At the moment everything seems ok; but are there any known
> problems with this approach?

You already picked the recommended scheme: shadowed Linux task on the
borderline, mostly running under Linux control (SCHED_OTHER), but being
able to become RT for synchronisation with high-prio RT tasks.

Jan


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