Re: [Xenomai] Hilscher driver for cifX boards

[Gilles Chanteperdrix <gilles.chanteperdrix@xenomai.org>]

On 02/08/2013 12:28 PM, Jan Kiszka wrote:

> 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).


The native and posix skin provide support for interrupts in user-space...


-- 
                                                                Gilles.