Re: linux-can ISOTP module

[Oliver Hartkopp <socketcan@hartkopp.net>]

Hello Maxime and Laurent,

On 05.06.2014 12:18, Maxime Jayat wrote:

>> Ok, with isotp.h api, i understand that we can parameter block size, stmin,
>> wftmax, transmission time (n_ax), padding.
>> But how can i specify the timing n_CS (time between flow control reception
>> and first consecutive frame) and the timing n_BS (time between first frame
>> reception and flow control emission)? In the same way, is it possible to
>> specify according timeout (n_BR for flow control timeout reception, and n_CR
>> for consecutive frame timeout reception)?

Hm - didn't know that n_CS is important at all ...
I'll take a look, if this can be integrated easily.

>>>>
>>>> For extended adressing method, it seems that both rx and tx frame must have
>>>> the same first byte in can frame (the one set by ext_address field of the
>>>> structure). This is correct for mixed addressing method (see Iso15765-2),
>>>> but for extended adressing method, we should be able to specify different
>>>> Target and source adress. I have not seen anything like this.
>>>
>>> One socket represents one virtual 1:1 connection (defined by two CAN
>>> identifiers and optional with one address extension) on the CAN bus.
>>>
>>> If you want to receive from different sources just create different sockets
>>> (and e.g. use select() to listen to many open socket file descriptors).
>>>
>>> The protocol engine has always to answer with the correct address information.
>>>
>> With this method, how can i have a segmented transfer like this:
>> 0x6a7  0x55 0x10 0x08 ........
>> 0x687  0xAA 0x30 0x00 0x00
>> 0x6a7  0x55 0x21 .....
>>
>> The connection i need is between two ECU, using IDs 0x6a7/687 and one has
>> adress extension 0x55, the other 0xAA (this adressing method is used on some
>> FIAT ECUs for example), but i don't see how it can work using two socket.
> I confirm.
> This is a problem that we also encountered on a BMW ECU with the current
> implementation of ISOTP.
> The use-case is real and not currently supported.

Ooops!

I've never read anything about an address extension used this way.
Despite the fact that this is used at FIAT and BMW - can this be found
somewhere in the protocol specification??

> I had to hack isotp.c, adding a socket option to be able to choose an
> address extension for the reception. Probably not the best solution but
> it worked.

I wonder if it would work to just add an rx address extension u8 element to
struct can_isotp_options:

struct can_isotp_options {

        __u32 flags;            /* set flags for isotp behaviour.       */
                                /* __u32 value : flags see below        */

        __u32 frame_txtime;     /* frame transmission time (N_As/N_Ar)  */
                                /* __u32 value : time in nano secs      */

        __u8  ext_address;      /* set address for extended addressing  */
                                /* __u8 value : extended address        */

        __u8  txpad_content;    /* set content of padding byte (tx)     */
                                /* __u8 value : content on tx path      */

        __u8  rxpad_content;    /* set content of padding byte (rx)     */
                                /* __u8 value : content on rx path      */

        __u8  rx_ext_address;   /* set address for extended addressing  */
                                /* __u8 value : extended address        */

};

/* flags for isotp behaviour */

#define CAN_ISOTP_LISTEN_MODE   0x001   /* listen only (do not send FC) */
#define CAN_ISOTP_EXTEND_ADDR   0x002   /* enable extended addressing */
#define CAN_ISOTP_TX_PADDING    0x004   /* enable CAN frame padding tx path */
#define CAN_ISOTP_RX_PADDING    0x008   /* enable CAN frame padding rx path */
#define CAN_ISOTP_CHK_PAD_LEN   0x010   /* check received CAN frame padding */
#define CAN_ISOTP_CHK_PAD_DATA  0x020   /* check received CAN frame padding */
#define CAN_ISOTP_HALF_DUPLEX   0x040   /* half duplex error state handling */
#define CAN_ISOTP_FORCE_TXSTMIN 0x080   /* ignore stmin from received FC */
#define CAN_ISOTP_FORCE_RXSTMIN 0x100   /* ignore CFs depending on rx stmin */
#define CAN_ISOTP_RX_EXT_ADDR   0x200   /* different rx extended addressing */


pahole can-isotp.ko says:

struct can_isotp_options {
        __u32                      flags;                /*     0     4 */
        __u32                      frame_txtime;         /*     4     4 */
        __u8                       ext_address;          /*     8     1 */
        __u8                       txpad_content;        /*     9     1 */
        __u8                       rxpad_content;        /*    10     1 */

        /* size: 12, cachelines: 1, members: 5 */
        /* padding: 1 */
        /* last cacheline: 12 bytes */
};

So this could be a working extension ...

Regards,
Oliver