Re: [Xenomai-core] Some questions about the ARM port (Integrator vs. PXA)

[Jan Kiszka <jan.kiszka@domain.hid>]

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Detlef Vollmann wrote:
> ...
> And I think you're correct, for Xenomai it will work.
> Unfortunately I'm trying to do a general ipipe port for PXA.
> I'm doing this for a polytech who wants to use this with their
> students, and so they probably want to use it with other domain
> on top of ipipe (rtai 3.3, Siemens' implementation of the Posix
> RT interface, and maybe even an own domain for experimenting).

I think the problem is not that some interface is "public". The point is
rather that inherent characteristics like "always called with interrupts
off" or "has to be protected with ipipe_critical" are not yet
documented. Adding such comments to your work might be a start. The same
applies to how a domain can expect soon-to-expire timer events are handled.

Creating a generic patch without basing it on Xenomai-specific
assumption is a reasonable approach, for sure. Nevertheless, the first
non-Xenomai user you mentioned requires more patching and far more
cleanup/update of its core to work over ARM again. And the second one is
unfortunately still unpublished.

The third scenario is quite real. Example: I have an experimental patch
for the new irqbench pending that demonstrates how to lift simple IRQ
jobs over Xenomai in its own domain. Gives nice worst-case IRQ latencies
even on low-end, even under heavy Linux *and* Xenomai load (the latter
ATM only with a small patch against ipipe to enable preemptible IRQ
handlers for all non-heading domains, not only the root one).

Jan


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