Re: CAN libpcap capture endianess

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

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On 09/12/2013 08:52 AM, Ico Doornekamp wrote:
> * On 2013-09-11 22:11:04 +0200, Marc Kleine-Budde wrote:
>  
>> I'm not familiar with the tcpdump capture format, but the
>> "(little-endian)" above suggests that the format supports both little
>> and big endianes.
> 
> As far as I know wireshark should be able to handle both formats.
> 
> Maybe I can change the question so it's not directly related to capture formats
> and wireshark:
> 
> I have can packets of SDO transfers (not the same objects, though). Can anyone
> tell me which one has the data in proper byte order as it passed on the CAN
> bus?

I don't speak CANopen...

> 1: 8a 05 00 00 08 00 00 00 43 18 10 03 2f 01 00 00  
> 2: 00 00 06 02 08 5f db f6 2f 00 18 02 01 00 00 00   
> 
> 1. packet #10 from capture-10. Node ID 10, SDO 0x1018sub3
> 2. packet #39 from capture-yegor. Node ID SDO 0x0018sub2

...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)));
> };

Marc

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