[Ovmsdev] Fixed VIN from IncomingPollReply first frame data?

Robin O'Leary ovmsdev at caederus.org
Sun May 6 08:56:27 HKT 2018

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:


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:

		case 0x02:  // VIN (multi-line response)

                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?

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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