Re: What are you doing if the TX buffer overflows?

[Wolfgang Grandegger <wg@grandegger.com>]

On 09/18/2012 03:36 PM, Andrew Bell wrote:
> On Mon, Sep 17, 2012 at 2:33 PM, Oliver Hartkopp <socketcan@hartkopp.net> wrote:
>> On 17.09.2012 21:26, Andrew Bell wrote:
>>
>> The TX timeout functionality has been removed a long time ago. There was a
>> discussion about that topic that days.
>>
>> So what kind of driver do you have there? A PEAK PCAN driver?
> 
> We're using an old mscan driver.
> 
> So, what's supposed to happen?  Does the hardware just attempt to send
> once and then drop the packet if no acknowledgement is received?  Is
> an error frame generated?  Is the issue being discussed just one where
> the application writes faster than the frames can be put onto the bus,
> rather than the condition of the bus being bad?

The CAN hardware usually *retries* to send to message until you abort it
or stop the device (going bus-off). If the message does not go out,
first the hardware and then the software queues will fill up and finally
the send() fails with errno=ENOBUFS. The send can also end up returning
ENOBUFS if the CPU is sending faster than the packets go out. Hope this
answers your question.

Wolfgang.