Re: [Socketcan-users] [Xenomai-help] Re: send error: permission denied

[Jan Kiszka <jan.kiszka@domain.hid>]

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Wolfgang Grandegger wrote:
> Jan Kiszka wrote:
>> Wolfgang Grandegger wrote:
>>> Hi Daniel,
>>>
>>> Daniel Schnell wrote:
>>>> Hi,
>>>>
>>>>  
>>>>
>>>> I am new to socket can.
>>>>
>>>>  
>>>>
>>>> I wanted to test the rtcan driver in combination with Linux and
>>>> Xenomai and made a little program according to the rtcansend program
>>>> but with some response time measurements.
>>>>
>>>>  
>>>>
>>>> However after setting up the socket I get –EPERM when trying to send a
>>>> packet to the can device. As the documentation doesn’t state anything
>>>> about this error when calling rt_dev_send() I wonder why the error if
>>>> at all doesn’t appear earlier if I try to setup the socket. The test
>>>> program already ran nicely when I tested the peak can drivers for
>>>> linux. I just changed the driver specific calls.
>>>>
>>>>  
>>>>
>>>> Attached you find the complete test file, the function task() is the
>>>> one to blame.
>>>>
>>>>  
>>>>
>>>> I am a bit stuck with this, so maybe someone can give me a slight hint
>>>> in what i am doing wrong.
>>> I tried your program on my system and got the same error. The problem
>>> is, that rt_dev_send() is called from non-RT context, which is illegal.
>>
>> ...but should not matter if the caller is a Xenomai thread in "Linux"
>> mode.
>>
>>> At a first glance, it's not obvious to me why. Therefore I added the
>>> Xenomai Help ML to the CCs.
>>
>> How did you all compile the program [1]? Using xeno-config
>> --posix-cflags / --posix-ldflags?
> 
> No, ah, oh. It works using the above flags, indeed. I see, that it calls
> _rtdm_sendmsg in secondary execution mode (none-RT) first, which
> returned -ENOSYS (-38). Then I guess, the context is switch to primary
> mode and _rtdm_sendmsg is called again, correct?
> 

Exactly, that's how it works.

>> Jan
>>
>>
>> PS: Daniel, if you go the POSIX way, you don't have to use rt_dev_, you
>> can use the normal POSIX API directly. That services will be wrapped on
>> the Xenomai core just like pthread&friends.
> 
> Cool. I was not yet aware of that.

Yes, and one should try to keep the sources clean (though mixing is
technically fine): either go native and pick real-time related services
from this API (would include task creation here) or go POSIX and use
only that API. If unsure about the status of some particular function,
see the docs or <xeno-installation>/lib/posix.wrappers for the list of
available bindings. (*)

> 
>> [1]https://lists.berlios.de/pipermail/socketcan-users/attachments/20060821/ff454f48/cantest_rt.obj
>>
> 
> Thanks for clarifying things.
> 
> Wolfgang.
> 

Jan


(*) Native has the charm of being more explicit ("This is hard-RT, any
    other service not.") and sometimes more handy to use. POSIX is
    standard, thus far easier portable. And it may already be well known
    to the programmer.


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