[Ovmsdev] Fixed VIN from IncomingPollReply first frame data?

Mark Webb-Johnson mark at webb-johnson.net
Sun May 6 10:25:00 HKT 2018

I seem to remember that the leaf has a module that bridges the two CAN buses. The issue was that if you poll on the wrong bus when the car is asleep, it wakes up the car 12V (clicking relay), does the poll, then goes back to sleep (clicking relay).

Better to use passively transmitted traffic. Perhaps a flag is set to ignore incoming messages until the buses are identified, then when the trigger can message is seen, the arrangement of buses can be determined and the flag cleared.

Regards, Mark.

> On 6 May 2018, at 10:12 AM, Greg D. <gregd2350 at gmail.com> wrote:
> Hi Robin,
> I'm guessing that the VIN might only be accessible on one of the two CAN interfaces.  Would that be sufficient to determine which bus is which?
> Greg
> Robin O'Leary wrote:
>> On Tue, May 01, 2018 at 09:59:04PM +0800, Mark Webb-Johnson wrote:
>>> Suggestion: Can the model year of the car be determined from the VIN?
>>> We do that for a few other of the models.
>> So in order to read the Leaf VIN and battery data, I had some fun getting
>> to know the ins and outs of ISO-TP and UDS so I could write my own packet
>> reassembler.  Of course, it was only when I had it all working nicely that
>> it dawned on me that Mark's comment above meant that there was probably
>> already code for that somewhere that would have saved me the effort,
>> which there is, in OvmsVehicle::PollerReceive and IncomingPollReply.  Duh!
>> But when I swapped over to using those methods, I got different
>> results---the first byte of the VIN was missing, and IncomingPollReply
>> never got called with ml_remain==0 for the much longer battery data.
>> So now I was glad that I had my own version for comparison, as it made
>> me more sure than I might otherwise have been that PollerReceive was
>> processing the first frame incorrectly.  Indeed, I think it is doing
>> two things wrong: it starts reading data from byte 5 not byte 4, and it
>> gets the overall length wrong by 2 (this confusion is likely because the
>> length given in the ISO-TP layer includes the two UDS header bytes, but
>> the rest of the UDS processing expects those bytes not to be counted in
>> the data passed to IncomingPollReply).  Fixing both of those made both
>> the Leaf VIN and battery data come out correctly.  My changes are here:
>> https://github.com/caederus-ovms/Open-Vehicle-Monitoring-System-3/tree/leaf-poll <https://github.com/caederus-ovms/Open-Vehicle-Monitoring-System-3/tree/leaf-poll>
>> That leads me to wonder how existing uses of this code haven't run in
>> to the same problems.  It is used in at least two places that seem like
>> they should have been affected:
>> 	OvmsVehicleOBDII::IncomingPollReply
>> 		case 0x02:  // VIN (multi-line response)
>> 	OvmsVehicleKiaSoulEv::IncomingVMCU
>>                 case 0x02: // VIN (multi-line response):
>> So could it be that the PollerReceive code is correct after all and that
>> I am misunderstanding how it works, maybe because there is something
>> odd about the Leaf?  Could any developers knowledgable about the OBDII
>> interface and the Kia Soul see if my changes make things better or worse?
>> Thanks.
>> btw, I still don't know the answer to the original question of whether
>> the model year of the car can be determined from the VIN, but at least
>> we can now easily see what it is!
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