Re: unsure - socketCAN blocking

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

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On 10/08/2012 12:16 PM, Steffen Rose wrote:
> Hello, 
> I'm unsure, what I see.
> 
> I use:
> Virtual box - Host Win 7/Guest kubuntu 
> Linux lisa 3.2.0-30-generic #48-Ubuntu SMP Fri Aug 24 16:52:48 UTC 2012 x86_64 
> x86_64 x86_64 GNU/Linux
> 
> SocketCAN connector is a EMS CPC-USB.
> 
> On startup, the network works fine.
> In different situation one or both directions (RX/TX) stop it's work.
> My Linux program say:
> 
> 	write: No buffer space available
> 
> It's the write to the socketcan device can0.

Your program probably produces CAN frames faster than they could be
delivered by your CAN hardware. Your choices are:
1) If the write/sendto system call returns with -ENOBUFS,
   add the filedesciptor to poll/select and wait for it to be writeable
   again. For some known, but not yet resolved reasons (a.k.a. bug),
   the poll/select will return immediately, but the write will fail
   again. To workaround this usleep for some milliseconds between
   the write/sendto and the poll/select system call.

2) Increase txqueue length to 10000 or so.
   (ifconfig can0 txqueuelen 10000)
   This avoids to trigger the above bug and your write/sendto will
   block until the queues are free again and your CAN frame will added
   to the send queue. With this workaround poll/select work as expected,
   i.e. when they return the socket is writeable without problems.

Hope that helps,
Marc
-- 
Pengutronix e.K.                  | Marc Kleine-Budde           |
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