Matlab internal error before "mavlinkio" callback - how to catch?

I am using the UAV Toolbox for full-duplex communication multiple robots (indexed by {i} below) using a Matlab's mavlink support. Here is the setup code called from an appdesigner application:

            % Open mavlink connections
            app.dialect = mavlinkdialect(".\ares.xml");
            
            % Connect to a socket for receiving mavlink messages
            app.sendSock{i} = mavlinkio(app.dialect,"SystemID",254,"ComponentID",190);   % 'send' in the sense of the com2udp bridge
            connect(app.sendSock{i},"UDP",'LocalPort',app.NodeTable.Data.UDPport(i));  
            
            % Subscribe to whatever messages are sent from the nodes to the UDP port
            app.subscriber{i} = mavlinksub(app.sendSock{i}, BufferSize=50, NewMessageFcn=@avsCallback);
            
            % Set a different socket for sending mavlink commands
            app.recvSock{i} = mavlinkio(app.dialect,"SystemID",254,"ComponentID",190);   % 'recv' in the sense of the com2udp bridge
            recvPort = app.NodeTable.Data.UDPport(i)+20;
            connect(app.recvSock{i},"UDP",'LocalPort',recvPort);  

The callback function executes normally, but occasionally I get mavlink receive errors reported as unknown message IDs:

The Message ID is garbage. It was not sent by the robot, nor is it in any dialect. The reported ID appears to be random, and the error occurs repeatedly throughout a session. I suppose it is a communication error, and I would like to disregard it. The problem is that in order to toss it, I must first catch it. Since this is an internal error not in the direct call stack of any user Matlab code, I have been unable to do so. The exception occurs before the "avsCallback" function is executed and appears to be outside the scope of the main application. How can I catch this error?

This report seems similar to my goal:

AppDesigner global error handling

but unfortunately was not successful, particularly for a compiled application. Any help will be greatly appreciated.

[Jianxin Sun]

Hi Jim, what MAVLink version are you using on the robot and MATLAB?

[Jim]

version 2

Answer 1

[Jianxin Sun]

Hi Jim,

Since this error was thrown from the callback itself, there is no easy way for you to catch it.

One possible cause to this error is that your ares.xml was including some other message definition xmls that are newer than the one shipped with MATLAB. You can open your xml file and look for the files it included and put all the necessary file in the same folder where you run your code. For example the ardupilotmega.xml includes several other xmls.

<mavlink>
<include>common.xml</include>
<!-- Vendors -->
<include>uAvionix.xml</include>
<include>icarous.xml</include>
<include>loweheiser.xml</include>
<include>cubepilot.xml</include>
<include>csAirLink.xml</include>

If this didn't fix your issue, an alternative method could be to use MATLAB udpport object to read binary buffer directly and use mavlinkdialect.deserializemsg method to convert binary data to MATLAB data structure. And you can use try-catch to handle unrecognized packets. An example code might look like:

% Setup a receiver on localport 14550

dialect = mavlinkdialect(".\ares.xml");

udpReceive = udpport("datagram", "LocalPort", 14550);

% readdata callback is called when new data comes in,

configureCallback(udpReceive, "datagram", 1, @(src, ~)readdata(src, dialect))

% Setup a sender

udpsend = udpport("datagram", "LocalPort", 14580);

io = mavlinkio("common.xml", 2, "SystemID", 255, "ComponentID", 1);

msg = io.Dialect.createmsg("HEARTBEAT");

data = io.serializemsg(msg);

% Send heartbeat to 14550, should observe heartbeat msg print out in MATLAB command line

write(udpsend, data, "127.0.0.1", 14550);

function readdata(src, dialect)

data = read(src,1,"uint8");

% Use mavlinkdialect deserializemsg to convert binary data to MATLAB struct

try

msg = dialect.deserializemsg(uint8(data.Data));

disp(msg.Payload);

catch ME

% Catch issue when the binary data cannot be correctly parsed

% Print out the binary data packet that cannot be parsed

disp(uint8(data.Data));

disp(ME.message)

end

end

Also given the way the error was thrown from your code, it seems that the message with random message ID was recognized by MAVLink as a valid packet, I would be curious to see what corrupted binary are received on the receiver side to cause this.

Jianxin

[Jim]

This answers my question that there isn't a standard way to catch these internal errors. I did check that all the necessary included .xml files are in the home folder.

I have not yet implemented the suggested workaround to read the binary data directly, but will try to find some time to do so. I too am curious how the packet seems to have been accepted, except for the spurious message ID. I'll update this post once I add that instrumentation.