[Ovmsdev] VDS calculated state vs. data available via CAN

[Mark Webb-Johnson]

Tom,

Answers, inline, below.

Regards, Mark.

On 24 Apr, 2012, at 1:42 AM, Tom Saxton wrote:

> When the VDS on a v1.5 Roadster gets reset, it loses the following
> information:
> 
>    Charge History
>    Energy History
>    Trip Meter Drive Time
>    Wh/mile history graph
> 
> I take this to mean that these things are calculated from info on the CAN
> bus and stored in the VDS.

Yes, that makes sense.

> In v1.5 Roadsters, the energy history got screwed up by a firmware update
> more than a year ago. The regen energy numbers shown are often ludicrous. In
> extreme examples, the day and month regen numbers can be larger than the net
> energy numbers. No doubt related to that, I see the regen number going up
> when the car is parked. (That's a nice trick!) I take this to mean that
> something on the CAN bus changed but the VDS firmware hasn't been updated.
> 
> Things that are preserved over a VDS reset:
> 
> Charge time, mode and current limit. (Current limit is stored by location,
> presumably by the VMS.)
> Trip distance and net energy used.
> 
> So, presumably all of the values in this group can be queried from the CAN
> bus.

We have discovered charge mode and current limit. It is periodically sent from the VMS. Charge kW is also on the bus.

I recently worked on charge time and mechanism (on-demand/delayed) and found the command/response codes for these, but haven't found any periodic transmission for this on the bus, yet. Are you 100% certain charge time is maintained across VMS power failure?

We (Michael, or me?) have also discovered trip distance and odometer. I haven't found net energy used, yet, (not really gone looking) but it is presumably there somewhere. Trip is on id#100, B1=0x9c, and is in 1/10th of a mile - that is fully decoded. There is also an odometer message with this in id#402 - that how some not-yet-decoded bytes at the start, but they don't appear to be incremental are are more likely bit states for something. If energy use is there, it is on one of the undiscovered messages.

Instantaneous amps is available on the dashboard message id#400 B1=0x02 (we use it to spoof the digital speedo).

> Trip efficiency also persists. It may be calculated by the VDS or available
> on the CAN bus.
> 
> My most recent trip meter showed 46.7 miles, 11.32 kWh, and 243 Wh/mile. If
> you do the math, 11.32 kWh / 46.7 miles = 242.398 Wh/mi, which should round
> to 242. Since the trip distance has been found on the bus at 0.1 mi
> resolution, it seems like that's the best data the VDS has. If there are
> higher resolution numbers somewhere (VMS?), then maybe the real values are
> 46.65 miles and 11.324 kWh -> 242.74 Wh/mi which rounds up to 243. So,
> perhaps the efficiency number is calculated elsewhere and broadcast on the
> CAN bus. Alternatively, the VDS either may have a higher resolution energy
> number than what it's showing or perhaps it just does math badly.

I wouldn't rule out a bad rounding in the VDS. Rounding is done in so many places in the Tesla systems, and often different. For example - reset the trip and look at it on the car speedo vs VDS. We found similar things with the miles/kilometer conversion.

>    Tom
> 
> 
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