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

[Tom Saxton]

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.

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.

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.

    Tom