[Xenomai-core] Re: [PATCH] Shared irqs v.5

[Dmitry Adamushko <dmitry.adamushko@domain.hid>]

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On 23/01/06, Jan Kiszka <jan.kiszka@domain.hid> wrote:
>
> Dmitry Adamushko wrote:
> > Hello Jan,
> >
> > as I promised earlier today, here is the patch.
>
> I finally had a look at your patch (not yet a try), and it looks really
> nice and light-weight.


I have another version here at hand. The only difference is that
xnintr_irq_handler() handles all interrupts and destinguished the timer
interrupt via "irq == XNARCH_TIMER_IRQ" to handle it appropriately. This
way, the i-cache is, hopefully, used a bit more effectively. But it doesn't
make a big difference in other parts of code so you may start testing with
the one I posted earlier.


Now I only have two topics on my wish list:
>
o Handling of edge-triggered IRQs (ISA-cards...). As I tried to explain,
>   in this case we have to run the IRQ handler list as long as the full
>   list completed without any handler reporting XN_ISR_ENABLE back. Then
>   and only then we are safe to not stall the IRQ line. See e.g.
>   serial8250_interrupt() in linux/drivers/serial/8250.c for a per-driver
>   solution and [1] for some discussion on sharing IRQs (be warned, it's
>   from the evil side ;) ).


Ok. e.g. we may introduce another flag to handle such a special case.
Something along XN_ISR_EDGETIRQ and maybe a separate
xnintr_etshirq_handler() (xnintr_attach() will set it up properly) so to
avoid interfering with another code. No big overhead I guess.
serial8250_interrupt() defines a maximum number of iterations so we should
do the same (?) to avoid brain-damaged cases.

  On our systems we already have two of those use-cases: the xeno_16550A
>   handling up to 4 devices on the same IRQ on an ISA card (I don't want
>   to know what worst-case latency can be caused here...) and our
>   SJA-1000 CAN driver for PC/104 ISA card with 2 controllers on the same
>   interrupt line. So a common solution would reduce the code size and
>   potential bug sources.
>
> o Store and display (/proc) the driver name(s) registered on an IRQ line
>   somewhere (ipipe?). This is just a nice-to-have. I introduced the RTDM
>   API with the required argument in place, would be great if we can use
>   this some day.


Yes, the proper /proc extension should be avalable. Actually, the "native"
skin can't be extended to support the shared interrupts only by adding a new
flag. The "problem" is the way the /proc/xenomai/registry/interrupts is
implemented there (and I assume any other skin follows the same way). The
rt_registry object is created per each RT_INTR structure and, hence, per
each xnintr_t.

I'd see the following scheme :

either

/proc/xenomai/interrupts lists all interrupts objects registered on the
nucleus layer (xnintr_t should have a "name" field).

IRQN      drivers

3              driver1
...
5              driver2, driver3

and the skin presents per-object information as

ll /proc/xenomai/registry/interrupts

driver1
driver2
driver3

each of those files contains the same information as now.

To achieve this,

1) xnintr_t should be extended with a "name" field;

2) rt_intr_create() should contain a "name" argument and not use
auto-generation (as "irqN") any more.

or

ll /proc/xenomai/registry/interrupts

3
5

Those are directories and e.g.

ll /proc/xenomai/registry/interrupts/5

driver2
driver3

Those are "files" and contain the same information as now.

This is harder to implement since the registry interface should be extended
(for each skin).


> ...

> Jan
>
>
> PS: Still at home?


Yes. This week I'm going to Belgium to attend a few meeting with some
customers of my potential employer. So my next step for the nearest future
will be finally determined there :)


How many degrees Centigrade? I guess our current -9°C
> here in Hannover must appear ridiculous, almost subtropical warm to you.
> ;)


Hey, I'm not from Syberia :o) This is a kind of common delusion I guess as
the whole former USSR is assotiated with cold winters, bears, eak.. KGB etc.
:o)

from wikipedia.com (about Belarus) :

"The climate <http://en.wikipedia.org/wiki/Climate> ranges from harsh
winters <http://en.wikipedia.org/wiki/Winter> (average January temperatures
are in the range −8 °C to −2 °C) to cool and moist
summers<http://en.wikipedia.org/wiki/Summer>(average temperature 15 °C
to 20 °C)."

Actually, last days it was very cooooold - even about -30C. This happens
from time to time but very rare (once in a few years or so) and it's not
considered as something normal here. e.g. schools were closed a few last
days when the temperature was below -25. Actually, the weather is getting
crazy last years and not only here :)

[1] http://www.microsoft.com/whdc/system/sysperf/apic.mspx
>
>
>

--
Best regards,
Dmitry Adamushko

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