Re: [Xenomai-help] events and domains

[Philippe Gerum <rpm@xenomai.org>]

Giuseppe Lipari wrote:
> Dear all,
> 
> We are new to Xenomai and Adeos. We have some questions and I could not
> find answers to these in the documentation (but maybe we are not very
> good at finding things!). We hope someone can help!
> 
> 1) Adeos is able to handle events that are passed to domains.
> I understand that events are hw interrupts and "other things". In the
> docs, I see that an event can be a "soft interrupt". As soft interrupt
> can have different meanings in different contexts, what do you actually
> mean with "soft interrupt"??
>

Virtual interrupts (virq) actually. Pseudo-IRQ channels that are not 
mapped to real hardware but rather allocated by software to propagate 
software-generated events. For instance, Xeno uses a virq for carrying 
out asynchronous procedure calls from the primary to the secondary 
domain (see /proc/xenomai/apc).

> 2) Also, what exactly are hooks? In particular, when there is a
> context-switch between two non-Xenomai (Linux) threads running in user
> space, is any hook-event generated?
> 

Hooks == callbacks. Yes, Xeno uses this to track and monitor what the 
hell Linux is doing at any time wrt user-space tasks mapped to shadow 
Xeno threads. In nucleus/shadow.c, see do_schedule_event().

> 3) when a Xenomai thread starts executing, does it start in primary or
> in secondary mode?
> 

Primary, always. It's written in stone.

> 4) is the memory of a Xenomai thread allocated in user space? (I guess
> yes, but just to be sure!)
> 

No difference from regular Linux threads. Actually, a Xenomai thread 
running in user-space is a Linux thread on steroïd. To this end, what we 
call a shadow thread context is mapped to the initial Linux task 
context, so that the Xenomai scheduler can handle it too, in parallel to 
the regular Linux scheduler (in a mutally exclusive fashion though).

> 5) if  two UVMs are active at the same time, how they are scheduled with
> respect to each other? (I guess SCHED\_FIFO, but it looks somewhat
> strange to me: why not SCHED\_RR, at least for the application tasks?).
> 

It's explained in the "Introduction to UVMs" document.

> 
> Giuseppe Lipari and Paolo Gai
> 
> 
> 


-- 

Philippe.