Re: [Xenomai] Hilscher driver for cifX boards

["Stéphane LOS" <slos@hilscher.com>]

Le 08/02/2013 14:40, Jan Kiszka a écrit :
> [re-adding the list]
>
> On 2013-02-08 14:28, Stéphane LOS wrote:
>> Le 08/02/2013 12:28, Jan Kiszka a écrit :
>>> On 2013-02-08 10:18, Gilles Chanteperdrix wrote:
>>>> On 02/08/2013 10:07 AM, Stéphane LOS wrote:
>>>>
>>>>> Le 07/02/2013 17:11, Gilles Chanteperdrix a écrit :
>>>>>> On 02/07/2013 03:53 PM, Stéphane LOS wrote:
>>>>>>
>>>>>>> Hello Sirs,
>>>>>>>
>>>>>>> Hilscher is offering a Linux driver based on UIO for cifX boards.
>>>>>>>
>>>>>>> In my understanding, down to 1ms cycle time, a PREEMPT RT solution
>>>>>>> should be enough.
>>>>>>>
>>>>>>> The cifX boards can manage with bus cycle times down to 250µs like with
>>>>>>> EtherCAT or Sercos III firmwares.
>>>>>>>
>>>>>>> So it seems in that cases that using Xenomai would be the way to go.
>>>>>>> I suppose that it would be needed to modify or change the existing
>>>>>>> driver but I can't figure out how things (Xenomai / RTDM / UIO) fit
>>>>>>> together.
>>>>>>>
>>>>>>> UIO is the kernel module that allows the mapping of the board memory to
>>>>>>> user space.
>>>>>>>
>>>>>>> The cifX driver uses the libpciaccess to pick up the board and retrieve
>>>>>>> some board information from UIO before the mapping.
>>>>>>> Then it uses pthread and rt functions when accessing the board.
>>>>>>>
>>>>>>> Since UIO and libpciaccess are only used during the initialization, is
>>>>>>> it a problem for a Xenomai application ?
>>>>>>>
>>>>>>> We have setup a Xenomai system and tried to compile the user land
>>>>>>> library with Xenomai options and flags and it seems we have been successful.
>>>>>>> The driver should be using the POSIX skin of Xenomai if we have been lucky.
>>>>>>>
>>>>>>> I can't see why we would need RTDM. Any hint please ?
>>>>>>>
>>>>>>> I am an absolute beginner in the Xenomai arena, don't throw me to the
>>>>>>> lions...
>>>>>>>
>>>>>> If UIO is used to register an interrupt handler for instance, the
>>>>>> interrupt handler will not be called in real-time context when used with
>>>>>> Xenomai, so, you would have to use the (deprecated) native or posix skin
>>>>>> services to register a user-space interrupt handler, or more likely
>>>>>> write an RTDM driver. On the other hand, if what you need is simply
>>>>>> accessing the board registers through MMIO, then you do not need RTDM.
>>>>>>
>>>>>> While accessing registers from user-space may be tempting, there is a
>>>>>> risk of ending up with an application where the driver code is not
>>>>>> clearly separated. Writing a driver separated from the application is
>>>>>> preferable, as it provides a sane isolation between the two. If you
>>>>>> change the hardware, you just have to rewrite a driver which follows the
>>>>>> same profile, if you want to write another application using the same
>>>>>> driver, you can keep the driver.
>>>>>>
>>>>> Thank you for your kind support Gilles.
>>>>>
>>>>> The cifX Device Driver is Hilscher's library to deal with cifX boards
>>>>> and is available for the major OSes.
>>>>> Additionally it is available to anybody as source code, the cifX Driver
>>>>> Toolkit when one has to create a driver for his own OS.
>>>>>
>>>>> This driver library accesses the board interface which is a Dual Port
>>>>> Memory.
>>>>>
>>>>> So the user application shall use this layer and gets independence from
>>>>> the target OS.
>>>>>
>>>>> I understand that we should create an RTDM driver instead of a UIO
>>>>> driver and adapt the user library so that it uses the RTDM driver.
>>>>> Am I right ?
>>>> I tried to explain why it may be better to create an RTDM driver, but in
>>>> this case this may not be the best option. The answer to your question
>>>> depends on what you have to do to implement the driver. As I said, if
>>>> you simply have to access MMIO registers, user-space may be fine, if you
>>>> have to handle interrupts kernel-space (so, RTDM) is preferable.
>>> Are we talking about linux/drivers/uio/uio_cif.c here? That one
>>> obviously has interrupt support.
>>>
>>> If your customers may want to use Xenomai 3 with I-pipe instead of
>>> Preempt-RT underneath (both options will exist), RTDM will still be
>>> required for interrupt handling. If you like to, you could propose such
>>> a driver for Xenomai integration. That would ensure it will come with
>>> future releases.
>>>
>>> I also wonder if it didn't make sense for us to provide an UIO-like
>>> infrastructure for such use cases (single-user device drivers with IRQ
>>> event channel needs).
>>>
>>> Jan
>>>
>> I am talking about the new products based on the netX chip :
>> http://lxr.free-electrons.com/source/drivers/uio/uio_netx.c
> Ah, I see. Structurally similar, though.
>
>> I have been through :
>> http://www.xenomai.org/index.php/Xenomai:Roadmap#Toward_Xenomai_3
>>
>> Looks like we should create an RTDM driver and build our Xenomai
>> specific libcifx on top of it.
>>
>> Since the kernel now includes by default the UIO stuff, the board will
>> likely be detected twice, once by UIO and second by the RTDM driver.
>> Is it a problem ?
>> Should the user of the RTDM driver disable UIO / netX in the kernel ?
> It's not problem to have multiple drivers registered for the same IDs.
> You can always rebind them via sysfs or black-list one of them in the
> local modprobe configuration.
>
> Jan
>
Sorry for not posting to the list, wrong button pushed.

Thank you and Gilles for your answer.

I bet there will be more questions. Have a nice week end.

Best Regards,
Cordialement,

Stéphane LOS
slos@hilscher.com
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