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

[Wolfgang Grandegger <wg@domain.hid>]

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?

> 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.

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

Thanks for clarifying things.

Wolfgang.