[Ovmsdev] Java and questions

Mark Webb-Johnson mark at webb-johnson.net
Thu Mar 15 13:03:01 HKT 2012

Answers/Comments, below, in-line

On 15 Mar 2012, at 12:08 AM, Tom Saxton wrote:

> on 3/14/12 8:26 AM, Mark Webb-Johnson wrote:
>> It is possible for there to be more than 1 app connected, controlling the car,
>> but not so likely.
> Cathy and I are likely to be both monitoring the car from time to time. I
> expected we'd coordinate on any commands sent to the car, but I wouldn't
> want anything bad to happen if we both happen to send commands at the same
> time.

I don't think anything bad could happen, but it is possible for the commands to 'collide' and only one to be active. That said, both Apps would get updated as to the new status, so it would be fairly obvious what is going on.

>> The car tries to maintain a connection to the server always. There is no way
>> for the app or server to message or call the car without that connection
>> established.
> There's evidence to suggest that the way the Leaf handles this is by sending
> a text message to the car telling it to connect to the server to get
> commands. This way commands only go over the presumably secure and
> authenticated data connection, but the car only has to listen for text
> messages when idle.

Kind of messy, imho.

The way we do it seems to require a baseline GPRS network usage of about 30KB/day. That is about 1MB a month and well within most plans.

The advantage of the way it is done, is that you can always see the status as of worst-case 10 minutes since the car lost GSM/GPRS connection. Connection to the car is also very very fast (1 to 3 seconds, normally).

Regards, Mark.

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