> -----Message d'origine-----
> De : Philippe Gerum [mailto:[EMAIL PROTECTED]
> Envoyé : jeudi, 20. avril 2006 15:43
> À : ROSSIER Daniel
> Cc : firstname.lastname@example.org
> Objet : Re: [Xenomai-core] Xenomai on Freescale i.MX21 (ARM926J)
> ROSSIER Daniel wrote:
> > Dear all,
> > We finally succeeded in the port of Xenomai on our Freescale i.MX21
> board (ARM-926J);
> > (The board used is the CSB535FS issued from Cogent with the BSP from
> > To have further technical references, please see there:
> > So, you will find two patches: the first one (patch-linux-
> 2.6.14.imx21_1.0.0) is used to patch the Linux 2.6.14 for supporting the
> board. Then, the second one (adeos-ipipe-2.6.14-arm-imx21-0.1.00.patch)
> can be used against the imx21-enabled kernel for Xenomai, simply using the
> prepare-kernel.sh script. The patch was originally inspired from the
> Integrator/ARM11 patch; thanks to its author :-)
> > We will publish soon some results regarding the different latencies, but
> so far we measured about 2us between the IRQ and the timer reprogramming
> (at the ipipe level). The problem now is the jitter which is pretty high:
> about 1-2us, with some occasional peaks up to 5us.
> > Having quite a few experience with this kind of board, we don't know if
> it comes from the code itself, or purely from the hardware. Any
> idea/suggestions would be welcome. For periodic tasks around 20us,
> everything works perfecly.
> Those results are pretty impressive actually. Assuming that you compare
> those figures with those obtained from traditional standalone RTOS e.g.
> VxWorks on the same board, the critical difference with Xenomai is that
> Linux is competing for the hw resources, and for instance, happily
> trashes the cache under Xenomai's feet when scheduling its own tasks
> during Xeno's idle time. Additionally, Adeos adds a small overhead due
> to the interrupt virtualization, in exchange of real-time predictability
> for their delivery. Therefore, in this respect, 5 us does not look that
> bad already.
> Are 20 us a measure of the worst-case interrupt latency (i.e. running
> latency -t2), or scheduling latency in user-space (i.e. running latency
No, I think we can go lower; the measure we actually got between the IRQ and
the timer reprogramming is about 2 us with some jitters up to 5 us; we could
normally guarantee not to exceed 5 us between the IRQ and timer reprogramming.
Now, considering the ISR itself, we could get some time under 10us provided
that the ISR remains short.
So far, we measured the reaction time with the oscillo; we are now about to
check the latencies with the latency utility from Xenomai.
> > I don't know to what extent this (1 or 2) patch(es) can be integrated in
> the official distribution;
> but of course we are willing to make any adaptations to fulfill the
> requirements for that.
> For the technical part, I guess that anyone interested in the ARM
> support for Adeos/Xenomai will review this code; I'll be one of these
> people, for sure. The usefulness of such contribution looks obvious to me.
> For the non-technical part, a pre-requisite for adding code to the Adeos
> or Xenomai codebases is to properly identify it as coming from a
> legitimate source, so if you, as a submitter, can confirm that you may
> freely contribute it on behalf of the HEIG-VD (I guess?) or yourself,
> that's fine with us. Btw, at first glance, I did not find any additional
> GPL copyrights coming with your changes in the patches, it would be
> better to have them, so that we always know who contributed to what, as
> much as possible.
Yes, it's ok. HEIG-VD is the University of Applied Sciences of Western
Switzerland in Yverdon (http://www.heig-vd.ch) and I'm working at
the REDS Institute (http://reds.eivd.ch, unfortunately in French only at the
moment). We are granted to publish our work, at least
all part which are not directly bound to some industrial projects (I'm
trying to keep the stuff as open and public as possible ;-).
> > It's a first step; I hope it will help some other ARM9 developers and
> look forward to reading some feedbacks.
> > I profit to thank a lot the Xenomai team (Philippe, Jan, Gilles and the
> others) for their excellent work and support).
> Xenomai exists because people participate in the Sisyphean task of
> making it better, like you just did. In other words, welcome to the
> band. Let's roll the rock.
> > Kind regards
> > Daniel
> > ------------------------------------------------------------------------
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