DevGuide/Communications

This page describes the way the communications with the aircrafts are implemented in paparazzi

We'll start with high level stuff such as sending your own telemetry message or datalink (uplink) message. We'll then look at the lower layers

sending telemetry message

describe your message in the telemetry section in conf/messages.xml

this should looks like this

<message name="MARK" id="32">
  <field name="ac_id" type="uint8"/>
  <field name="lat" type="float" unit="deg"/>
  <field name="long" type="float" unit="deg"/>
</message>

the id has to be unique the fields can have type int8, int16, int32, uint8, uint16, uint32, float and arrays of those

they must be aligned in order to work on arm7 ( write more on that )

this enable all the ground system to deal with your message and generate sending code for the airborne system the generated code is in var/include/messages.h

from the airborne code you can send the message by using this code, for example

DOWNLINK_SEND_MARK(&ant_v2x_data.xraw, &ant_v2x_data.yraw, \
                   &ant_v2x_data.xcal, &ant_v2x_data.ycal, \
                   &ant_v2x_data.heading, &ant_v2x_data.magnitude, \
                   &ant_v2x_data.temp, &ant_v2x_data.distor, \
                   &ant_v2x_data.cal_status);

you can also have the autopilot send the message periodically For doing that, in your telemetry file ( for example conf/telemetry/default.xml you can make your own it is referenced in the airframe file) you can add a line like

<message name="CALIB_START"    period="1"/> 

meaning that CALIB_START will be sent every second you then need to specify the arguments to your message in the sw/airborne/ap_downlink.h header by providing a macro

PERIODIC_SEND_DEBUG_CALIB_START()

you can have different telemetry modes having different rates for each message. FOr example you might want a verbose mode and a stealth mode

when sent by the aircraft the message will be available on the ground ivy bus

you can watch it using the messages program or with ivyprobe

the file sw/ground_segment/cockpit/ant_track.c shows how to receive a message in a C program for ocaml, we have a higher level library to receive messages

adding datalink (uplink) messages

This is similar to the above. Add your message in the datalink section of messages.xml This will generate parsing code for the airborne program (var/include/dl_protocol.h).

You then can add your handler in the sw/airborne/datalink.c code (a way should be fined to include external code in that) or you can just rewrite your own dl_parse_msg() function, for example in a test program where you want to receive only your own messages.

The "transport" layer

Paparazzi can use the built-in transport layer of different hardware (currently only wavecards and xbee/xtends) and also provides his own layer for hardware lacking it (showing as remote serial ports). Files xbee.[ch] and pprz_transport.[ch].