Re: can4linux compilation for i.mx25 under 2.6.39

[Marc Kleine-Budde <mkl@pengutronix.de>]

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On 05/31/2012 03:29 PM, Martin Kozusky wrote:
> Dne 30.5.2012 16:18, Marc Kleine-Budde napsal(a):
>> On 05/30/2012 03:26 PM, Martin Kozusky wrote:
>>> Dne 30.5.2012 15:18, Marc Kleine-Budde napsal(a):
>>>> On 05/30/2012 02:50 PM, Martin Kozusky wrote:
>>>>>>> The best for me would be some kernel module which would just put
>>>>>>> the CAN
>>>>>>> frame into some big "from userspace available" buffer in the
>>>>>>> interrupt
>>>>>>> and nothing more. My app would check if there is anything new and
>>>>>>> read
>>>>>>> it out.
>>>>>>> There are around 1500/sec (at 250kbit) can frames on the bus when
>>>>>>> the
>>>>>>> problem arise, I think it's not that much.
>>>>>>
>>>>>> Are you writing the can frames to storage in the same thread as
>>>>>> receiving them?
>>>>>
>>>>>
>>>>> No, CAN has it's own thread, which is just making struct from can
>>>>> messages (reading via select() )  and writes them into another buffer.
>>>>> Then the main thread reads this buffer and writes to SD card. Now I
>>>>> changed it so that this buffer is 30MB big, so I first store all the
>>>>> messages into RAM, and when I don't need to record CAN frames
>>>>> anymore, I
>>>>> write all of them to card from this big buffer.
>>>>> But this is just limited workaround because I'm limited with the RAM
>>>>> size (so I had to make the buffer cyclic and just latest xxxx messages
>>>>> are stored, older are overwritten when the buffer is full).
>>>>
>>>> Have you setup realtime priorities for you CAN thread?
>>> No, I did't set up any special attributes. Do you mean I should use
>>> pthread_attr_setschedpolicy(ptr,SCHED_RR) or something else?
>>
>> or better SCHED_FIFO for your can thread.
> Hello Marc,
> I tried that and still when I write
> dd if=/dev/zero of=/mnt/mmcblk0p1/test bs=512 count=10000 (copy 5MB to
> SD card)  around 300 CAN frames (from 68500 frames) are lost :(

http://man7.org/linux/man-pages/man2/recvmmsg.2.html

Maybe you can use recvmmsg(). I don't know if it works already on can
sockets.

Marc

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Pengutronix e.K.                  | Marc Kleine-Budde           |
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