[rtai] RTEMS RTAI module

Joel Sherrill joel.sherrill at OARcorp.com
Tue Aug 28 18:41:25 UTC 2001

Bernhard Kuhn wrote:
> Erwin Rol schrieb:
> > Hi did anybody ever think about for example using
> > a other OSS RTOS as a module to run under RTAI ?
> Yes, me :-)

It sounds interesting to me as well. :)

I have dug through the RTAI page and don't seem to be able to
find the magic page to describe their HAL.  I understand the
basic structure but would like to see precisely what had to 
be glued together.
> > In principle it should be possible to have a BSP for
> > RTEMS that ends up being a linux kernel module under RTAI.
> You mean having RTEMS running as an application on top
> of RTAI similar to RTEMS for Linux in user space?
> Sounds interessting. 

And I suspect not terribly difficult once you knew precisely
what the mapping of a BSP to the RTAI was.

> My former thoughts were having
> RTEMS as an alternative to RTAI on top if the RTHAL,

I think this would be quite interesting to do and 
offer a neat environment.

> but i abandoned the idea, because RTEMS only offers
> a periodic mode scheduler.
> BTW: i recently had contacts with developers at
> OAR and it seems that they like to implement a
> oneshot mode scheduler ...

You and I had some private email about this and I don't 
think it is tough to implement once one works out
the details of not breaking compatability with the 
existing code base.  My first thought was that
the existing rtems_clock_tick() would indicate
the periodic amount and be a wrapper over something 
like rtems_clock_tick_variable( nanoseconds ).  
There would have to be some work in the Watchdog and
probably clock tick handling code to handle the difference
between counting ticks and counting nanoseconds.
And there would have to be a callback to the clock tick
driver to set the varying timer period.

I really don't think it would be that bad a task.
Probably outside my unpaid free time right now. :)

> With your idea, it realy means only to have to
> provide an RTAI-BSP for RTEMS and everything
> should work fine. This would certainly make
> RTAI more interessting to other ppl out there
> using RTEMS for quite a while.
> best regards
> Bernhard
> BTW: at the research institute i worked for a while,
> we started running RTEMS in parallel with Linux
> on an SMP box, means: one CPU is fully dedicated
> to RTEMS, (ab)using it's 512 KB Cache as RAM.
> No TLB invalidation and no Cache flushing :-)

This is cool. Is there info on the web?  published papers?

> --
> Bernhard Kuhn, Software Engineer, Lineo Inc. (Where Open Meets Smart)

Joel Sherrill, Ph.D.             Director of Research & Development
joel at OARcorp.com                 On-Line Applications Research
Ask me about RTEMS: a free RTOS  Huntsville AL 35805
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