ROSSIER Daniel wrote:
We finally succeeded in the port of Xenomai on our Freescale i.MX21 board
(The board used is the CSB535FS issued from Cogent with the BSP from Microcross)
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
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
but of course we are willing to make any adaptations to fulfill the
requirements for that.
I don't know to what extent this (1 or 2) patch(es) can be integrated in the
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.
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.
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