Re: read() question from newbie

[Oliver Hartkopp <socketcan@hartkopp.net>]

On 05.03.2012 18:49, Michael Economides wrote:

> On Sat, Mar 3, 2012 at 1:05 AM, Oliver Hartkopp <socketcan@hartkopp.net> wrote:
>> On 02.03.2012 23:09, Michael Economides wrote:
>>
>>> I am trying to use the cantest program to read.  It just blocks on the
>>> read, and stays there forever.
>>>
>>>  I can see on my scope there are can messages coming across the bus (from a
>>> different microcontroller attached to the bus).
>>>
>>> I have already verified I can write using cantest.
>>>
>>> In other words, this works:  ./cantest can0 1F334455#1122334455667788
>>>
>>> But this doesn't:  ./cantest can0
>>>
>>
>>
>> Hello Mike,
>>
>> where is this tool 'cantest' from?
>>
>> I don't know it either from the SocketCAN utils
>>
>> https://gitorious.org/linux-can/can-utils
>>
>> nor from the Pengutronix canutils
>>
>> http://git.pengutronix.de/?p=tools/canutils.git;a=summary
>>
>> Maybe you can alternatively try the SocketCAN utils to test.
>>
>> Regards,
>> Oliver
> 
> Hi Oliver,
> 
> Thanks for your reply.
> 
> "cantest" is a slightly modified version of cansend.c from the link
> above.  it does a read() as well as a write().
> 
>   basically what i'm seeing is CAN frames (standard format) coming
> across the bus, but read() call just blocks as if nothing is there.
> 
> A coworker of mine reports that the read() is responding only to
> extended frame format.
> 
> Can you provide any insight into this?  Specifically, how do we
> configure our CAN socket to respond to extended vs. standard frames?
> We would like to use standard, not extended.


Please just type

	candump any

to check whether you really get anything in your system.

Using 'candump any' without any additional provided filter definitions
displays anything (EFF&SFF) which is received on the host.

Don't know what you've 'slightly modified' :-)

Therefore check with a unmodified candump first.

Regards,
Oliver