[Ovmsdev] Fixed VIN from IncomingPollReply first frame data?

Michael Balzer dexter at expeedo.de
Sun May 6 16:02:58 HKT 2018


just a note: I've used this neat ISO-TP implementation for my Arduino projects: https://github.com/altelch/iso-tp

…specifically for https://github.com/dexterbg/Twizy-Cfg to provide the OBD2 commands.

The OVMS OBD polling framework is currently really just meant to provide periodical polling of basic registers. I will need a more flexible and complete ISO-TP
implementation for issue #95 as well, was thinking about a general service for this like I did with CANopen.

The Twizy has no standard OBD2 registers and does not follow the standard OBD2 addressing scheme, but of course also provides DTCs and device access via ISO-TP
if you know the device addresses.

The polling framework is necessary for the Renault Zoe implementation as well, and Wolfgang (Zoe developer) also had some troubles with it. So if you'd like to
implement a better ISO-TP framework, go ahead :)

As with CAN, a generalized OBD2 service could later also be configured with just a registers to metrics mapping scheme to provide a basic vehicle adaptation
without needing to code anything.


Am 06.05.2018 um 02:56 schrieb Robin O'Leary:
> 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
> 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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Michael Balzer * Helkenberger Weg 9 * D-58256 Ennepetal
Fon 02333 / 833 5735 * Handy 0176 / 206 989 26

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