[B.A.T.M.A.N.] Alfred GPS higher update rate

[B.A.T.M.A.N.] Alfred GPS higher update rate

[Keith Chew]

Hi

I am experimenting with using Alfred on a group of drones (initially
10 units) to send their GPS locations to each other.

The drones will be connected via batman-adv on WIFI, and each of them
read the GPS every 200ms (5Hz).

I would like to change alfred-gpsd from updating the GPS coordinates
every 10s to 200ms.

Does anyone see any issues with this change? ie it is even feasible/practical?

Regards
Keith

Re: [B.A.T.M.A.N.] Alfred GPS higher update rate

[Andrew Lunn]

On Thu, Oct 22, 2015 at 11:07:48AM +1300, Keith Chew wrote:
> Hi
> 
> I am experimenting with using Alfred on a group of drones (initially
> 10 units) to send their GPS locations to each other.
> 
> The drones will be connected via batman-adv on WIFI, and each of them
> read the GPS every 200ms (5Hz).
> 
> I would like to change alfred-gpsd from updating the GPS coordinates
> every 10s to 200ms.
> 
> Does anyone see any issues with this change? ie it is even feasible/practical?

You need to change more than alfred-gpsd. The core alfred server does
updates every 10 seconds. You need to change ALFRED_INTERVAL so that
it will propagate GPS data faster. If you want 200ms, i doubt such a
change would be accepted back to the core code. So you probably need
to add a command line option to allow setting this interval.

alfred-gpsd will also need some changes. It currently updated the
information in alfred every 2 seconds. You will need to modify this as
well.

When i wrote the alfred-gpsd code, i was not particularly interested
in fast updates. So you might need to change the architecture a
little. In particular, i knew gpsd was giving fixes much faster than
alfred would distribute them, so i didn't tell alfred about every
change. You might need this.

	Andrew

Re: [B.A.T.M.A.N.] Alfred GPS higher update rate

[Keith Chew]

Hi Andrew

> You need to change more than alfred-gpsd. The core alfred server does
> updates every 10 seconds. You need to change ALFRED_INTERVAL so that
> it will propagate GPS data faster. If you want 200ms, i doubt such a
> change would be accepted back to the core code. So you probably need
> to add a command line option to allow setting this interval.
>

Yes, I see the option and will have go at changing it for testing.

> alfred-gpsd will also need some changes. It currently updated the
> information in alfred every 2 seconds. You will need to modify this as
> well.
>

Ah, I did not know about this one, thank you very much for the
pointer, will also update this.

> When i wrote the alfred-gpsd code, i was not particularly interested
> in fast updates. So you might need to change the architecture a
> little. In particular, i knew gpsd was giving fixes much faster than
> alfred would distribute them, so i didn't tell alfred about every
> change. You might need this.

This is not a problem, I can look into this. I am worried about the
5Hz update rate, would the alfred/batman network layer be able to
handle the data. I was thinking of writing an app at a higher level on
the drone to broadcast the data to each other, but since alfred
conceptually already does what I want (except at a lower rate), my
plan was to first try it.

Thanks again for your help, much appreciated.

Regards
Keith

Re: [B.A.T.M.A.N.] Alfred GPS higher update rate

[Andrew Lunn]

> This is not a problem, I can look into this. I am worried about the
> 5Hz update rate, would the alfred/batman network layer be able to
> handle the data.

It probably can. But you need to watch out for other services using
alfred. You probably don't want to be updating VIS data at 5Hz.

Also, you probably don't want to be sending announce master packets at
that rate.

  Andrew