Re: CAN libpcap capture endianess

[Ico Doornekamp <can@zevv.nl>]

* On 2013-09-12 10:52:34 +0200, Marc Kleine-Budde wrote:
 
> On 09/12/2013 10:47 AM, Ico Doornekamp wrote:
> > * On 2013-09-12 10:00:10 +0200, Marc Kleine-Budde wrote:
> >  
> >> ...but your CAN frames don't look correct in wireshark. I suggest you
> >> bring up the command line tools and use candump to display the raw CAN
> >> frames. Raw CAN frames, as they enter the application, are in host
> >> order. To be precise the can_id is in host order, as all other members
> >> are u8. "data" is an array of 8 x u8, which is in fact big endian
> >> ordered, if you want to access it with 2x32 or 64 bit.
> >>
> >>> struct can_frame {
> >>>         canid_t can_id;  /* 32 bit CAN_ID + EFF/RTR/ERR flags */
> >>>         __u8    can_dlc; /* frame payload length in byte (0 .. CAN_MAX_DLEN) */
> >>>         __u8    data[CAN_MAX_DLEN] __attribute__((aligned(8)));
> >>> };
> > 
> > I just did this. candump shows this:
> > 
> >   slcan0  58A   [8]  4B 12 20 04 D6 00 00 00
> > 
> > The raw data is shown in wireshark as
> > 
> >   8a 05 00 00 08 00 00 00  4b 12 20 04 d6 00 00 00
 
> "8a 05 00 00" in little endian is 0x0000058a, "08 00 00 00" is the dlc
> of 8. Looks correct.
> 
> > The CAN dissector parses this as identifier 0x0a050000 with the
> > 'extended' flag set , which seems to have the wrong endianess.
> > 
> > The CANopen dissector also interprets the identifier with wrong endian
> > order, and is thus not able to decode the rest of the packet.
> > 
> > If I'm not mistaking, both the CAN and CANopen dissector in wireshark
> > are thus assuming wrong endianess. I'll check the source and see if I
> > can come up with a proper patch for the wireshark team.
> 
> They are assuming the wrong endianes for your capture file. Yegor's
> capture file, which comes in another format, is interpreted correctly.

Sorry, I was not completely clear on this: I did the capturing on the
slcan0 interface from wireshark, so I did not make a capture file first.

-- 
:wq
^X^Cy^K^X^C^C^C^C