[Xenomai-help] events and domains

[Xenomai-help] events and domains

[Giuseppe Lipari]

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"??

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?

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

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

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?).


Giuseppe Lipari and Paolo Gai



-- 
------------------------------------------------------
| Prof. Giuseppe Lipari      |
| RETIS Lab                  |
| Scuola Superiore Sant'Anna | tel:   +39 050 882030
| via G. Moruzzi, 1          | fax:   +39 050 882003
| 56124 Pisa (PI)            | email: lipari@domain.hid
------------------------------------------------------

Re: [Xenomai-help] events and domains

[Philippe Gerum]

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.