[Ovmsdev] OBD2ECU use with latest Roadster cable?

Mark Webb-Johnson mark at webb-johnson.net
Tue Aug 4 09:06:28 HKT 2020


I updated the TMC thread as follows:

Here are the Tesla Roadster CAN bus details:
Instrumentation: OVMS CAN1 (on OVT1): 1MHz, on DIAG pins 6/1. Contains VDS, TPMS, Instrumentation Display.
Powertrain: OVMS CAN2 (on OVT1): 500Kbps, on DIAG pins 7/2. Contains PEM, Switchpack, etc.
ESS: OVMS CAN3 (on OVT1): 125Kbps, on DIAG pins 11/4. Contains ESS and HVAC.
The problem you had is the cable you have between OVMS and the car wires all three CAN buses. Then when you start up the obd2ecu on CAN3 at 500kbps that conflicts with the vehicle's own ESS CAN bus at 125Kbps you are running this on top of. You mess up the vehicle comms between the VMS, HVAC, and ESS. It would make no difference if the HUD cable was plugged in, or not.

Switching to CAN2 solved the problem because that is the powertrain CAN bus also at 500Kbps. However, this is still possibly dangerous, because the message IDs on the bus may conflict. But probably ok.

Given the limitations, and work we are doing with OVMS, it is probably best to keep CAN1 and CAN3 for OVMS-car comms (as those are the two most useful CAN buses and I plan to release some functionality on CAN3 ESS bus to show battery brick voltages and temperatures). If you are concerned with possible ID conflict, you can disconnect CAN2 at the DIAG connector (pins #4 and #11) to make sure you don't conflict.

This is always going to be vehicle specific, and probably best addressed by adding Tesla Roadster specific documentation. It would be useful to be able to confiture the baud rate of the bus in the obd2ecu code (but we are limited by what baud rates the HUDs will support during their negotiation).

Regards, Mark.

> On 4 Aug 2020, at 1:29 AM, Greg D. <gregd2350 at gmail.com> wrote:
> Hi Mark,
> So, following the "OVMS issue: obdii on can3 crashes VMS" thread on TMC
> led me to an "oops!", I think...  Did I miss something?
> With the updated OVMS cable to the Diag port on the Roadster, the report
> is that all 3 CAN busses are connected to the car.  If so, doesn't that
> make the obd2ecu process impossible to run, since there's no CAN bus
> available on the 26 pin port to connect a HUD to?  And, if one were to
> hook up a HUD to the 26 pin port, wouldn't its polls be sent on (at 500
> kb/s) through the OVMS wiring to the car, confusing the car?
> Is the older (single CAN bus) cable still available?  That, I would
> think, would fix the problem.  I have the original cable, so haven't
> noticed anything wrong.  The OP on that thread also claimed the original
> cable, which doesn't make sense.
> Where is the Oops?
> Greg
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