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Re: [Paparazzi-devel] telemetry doesn't work

From: Felix Ruess
Subject: Re: [Paparazzi-devel] telemetry doesn't work
Date: Tue, 3 May 2011 14:17:46 +0200

Hi Arnaud,

> I have the GSC blank problem with the following materials
> tiny 2.11
> XBEE pro ZB 24
> Lucid (10.04)
> The modems are configured at Baudrate 9600. I have checked the Pan id (1 for
> both) and Node identifier (PPRZ_GROUND and PPRZ_AIRBORNE)
> I'm sure the modems are working because I tested them with X-CTU terminals
> on two laptops and what I wrote in one terminal appeared the the other one
> in both ways.

Did you test the direct communication under Linux as well? Just make
sure that you have the udev rules copied and the modem (well, the
USB-serial converter) is recognized.

> I have tested with the default tinyFw.xml airframe (in Reorg code) which
> matches the modems configuration (pprz transparent, B9600). There are no
> problems in building and uploading.
> But when I execute, I don't see any blinking of the LED on Ground Modem and
> testing with X-CTU after execution, I don't receive anything from airborne
> modem. And the GCS is blank.

The GCS stays blank until you receive messages...
If you configured both modems to 9600 baud (you should really set a
higher baud rate, 57600 is recommended), did you make sure that the
link agent on the ground station laptop was also running with 9600
baud? Just add "-s 9600" to the line of the link in the paparazzi
center and restart the link.

> I suppose the telemetry (ie messages emitted by the airborne module) doesn't
> work, but I have no idea why.
> I have several questions which may help to understand where the pb lies.
> 1/ What happens exactly in first after execution? (I believe there is
> exchange procedure between the two modems)

Do you mean what happens between the modems themselves to establish a
connection or what paparazzi does?

> 2/ What contain telemetry messages?

Information about your aircraft like status, position, speed, etc..
payload, etc..

> 3/ Is it necessary to have a complete matching between airframe and hardware
> in the sense of : if a servo is not connected, or the engine, (for tests)
> could it raise a blank pb?

No, that is not necessary. If you get a blank GCS, you are not
receiving any messages at all. If you don't have some
sensors/actuators connected that does not matter at this point.

> 4/ Where are used the names PPRZ_GROUND and PPRZ_AIRBORNE that I entered
> during modems flashing?

These are node identifiers that the ZigBee stack of the modems can use
to directly address modems, what identifiers you set is not really
The important part is that you set the same PAN (zigbee Personal Area
Network) id on both sides, so the airborne modem will join the network
of the one one the ground.
So this is nothing Paparazzi specific, just general modem setup.
Paparazzi just treats it like a normal serial connection.
But as you can communicate this seems to be all fine...

Cheers, Felix

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