Mavlink from a server socket / How to encode a mavlink message without active transport?

[Gerard Toonstra]

Hi all,

In my case I use a bound socket / server connection to listen for GCS connections and then stream mavlink messages over that as soon as a client connects.

I'd like to send a couple of extra messages in the message flow, but I'm having some problems figuring out how I can successfully pack them up and send them over
the wire. So, if I receive an AP mavlink message and send the get_msgbuf() content over the wire directly, it works. When I construct my own packets, the
GCS complains about incorrect CRC's and header ID's.

The mavutil mavlink_connection function has no methods to allow a listening socket to be constructed and used for this use case.


What I use now is a fake inactive connection, which gives problems for the GCS based on incorrect CRC's and headers, python code:

        self.master = mavutil.mavlink_connection( "udp:127.0.0.1:12345" )
        msg = self.master.mav.heartbeat_encode( find_uav_type( hb.uavtype ), find_ap_type( hb.autopilot ), hb.base_mode, hb.custom_mode, hb.system_status )
        self.conn.send( msg.get_msgbuf() )

So, what is the procedure to only construct a correct message and hold it in a buffer somewhere, where custom code manages the transport?
( i.e. no code ending in *send, but which uses the *encode type of functions and then grabs the buffer? )

Or would it just be easier to add a tcplisten: kind of transport device to the mavutil code, write a small wrapper class similar to "mavtcp" and use that
instead?

Rgds,

Gerard

[Gerard Toonstra]

My real problem was that non-mavlink messages were received and could not be decoded.

What I eventually ended up doing is something like this (to simulate a vehicle):

        self.master = mavutil.mavlink_connection( "udp:127.0.0.1:12345", source_system=1 )
        self.master.mav = mavutil.mavlink.MAVLink(self.master, srcSystem=self.master.source_system, srcComponent=1)
        update_seq( self.master.mav.seq )
        msg = self.master.mav.heartbeat_encode( uavtype, autopilot_type, base_mode, custom_mode, system_status )
        conn.send( msg.get_msgbuf() )

[Ligia Frangello]

Hi Gerald, 

I am trying to simulate a vehicle on GCS over UDP/TCP, and send Mavlink messages, and it sounds like you are working on the same problem. 

Would you mind sharing what you have learned with me?

Thank you.