Thank you for your response
So rootcb isn't the "scheduler task".
I was thinking it was this task which was determining what thread to run,
depending of its parameters (priority, periodicity, scheduling mode).
I go back to the code to understand how it work ...
> xnthread_init does part of the initialization. The low level part of
> rootcb (its xnarchtcb_t member) is initialized twice, first by the call
> to xnarch_init_tcb in xnthread_init, and then overriden by
> xnarch_init_root_tcb in xnpod_init.
> For any other thread than root, the thread would be given a stack and
> entry point by the call to xnarch_init_thread in xnpod_start_thread. But
> the root thread is Xenomai idle task, a placeholder for whatever task
> Linux is currenty running. At the time where xnpod_init is called, the
> root thread is the current context, so already has a stack and is
> already running.
> Gilles Chanteperdrix.