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

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

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On 09/18/2012 02:14 PM, Wolfgang Grandegger wrote:
> On 09/17/2012 09:19 PM, Oliver Hartkopp wrote:
>> Hello Heinz,
>>
>> On 17.09.2012 15:58, Heinz-Jürgen Oertel wrote:
>>
>>>
>>> is there a way to empty the tx buffer ?
>>
>>
>> Usually the buffer does not get empty due to a problem of the CAN controller
>> and/or the CAN network.
>>
>> So even if you could flush the queue the CAN controller is probably still
>> stuck with his processed frame.
>>
>> Setting the interface to DOWN and UP again re-initializes the CAN controller
>> and flushes all the queues.
>>
>> This would work - but all open sockets would get a notification of the
>> interface went down.
>>
>> Btw. IIRC there's a IFLA_CAN_RESTART functionality to kick the CAN controller
>> if it got stuck. It can by triggered by a netlink message. This is the same
>> configuration interface that's used to set the bittiming:
>>
>> http://lxr.linux.no/#linux+v3.5.4/include/linux/can/netlink.h#L103
>>
>> But i have currently no source code example as i always use the 'ip' tool from
>> the iproute2 package to configure my CAN interfaces:
>>
>> http://lxr.linux.no/#linux+v3.5.4/Documentation/networking/can.txt#L646
>>
>> Following that documentation
>>
>> 	ip link set can0 type can restart
>>
>> should do it for 'can0'.
> 
> No, this does only works if a bus-off is pending. See:
> 
> http://lxr.linux.no/#linux+v3.5.4/drivers/net/can/dev.c#L413
> 
> Well, the name IFLA_CAN_RESTART is not really well chosen.

Hmmm, it corresponds somewhat to the restart-ms property.

We have several customers who asked how to abort pending TX messages,
too. Which involves:
a) clear the TX-queue in Linux
b) clear queue in hardware
c) abort currently transmitting CAN frame

I think c) would be a usecase of its own, too.

Marc

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