Matlab UDP Recieve Error

Hi,

I'm running FlightGear simulation software and output some variable data through UDP on the loopback address 127.0.0.1, port 1234. Using the SocketTest application I can see the data being received however I would like to do this through Matlab which is running on the same PC.

I've read through the following example: https://uk.mathworks.com/matlabcentral/answers/10234-recieving-udp-from-iphone

I try to run the following:

    while(1)
         u = udp('localhost',1234,'localport',1234);
         u.InputBufferSize = 1000;
         u.DatagramReceivedFcn = @localReadDatagram;
         fopen(u);
    end

My issue is that I always get the error: "Unsuccessful open: Address already in use: Cannot bind ", can anyone help?

Thanks, Joe

Answer 1

[Walter Roberson]

You should probably use a different localport unless the receiving software insists that the transmitting port be 1234 . localport is the port number that data is transmitted from.

[Joe Fleming]

Ok so changing the Flightgear port to 5000 and then changing my Matlab code to:

while(1)
   u = udp('localhost',5001,'localport',5000);
   u.InputBufferSize = 1000;
   u.DatagramReceivedFcn = @localReadDatagram;
   fopen(u);
end

I now get the following error:

 Error using icinterface/fopen (line 83)
Unsuccessful open: Address already in use: Cannot bind

Error in UDP_Connection (line 6)
fopen(u);

Undefined function or variable 'localReadDatagram'.

Error in instrcb (line 36)
        feval(val{1}, obj, eventStruct, val{2:end});

Warning: The DatagramReceivedFcn is being disabled. To enable the callback property
either connect to the hardware with FOPEN or set the DatagramReceivedFcn property.

[Walter Roberson]

Ah, the problem is that you are doing the open in a loop. You should only open once, and then make sure that u does not go out of scope while you use it. Remember to close it after you are done.

[Joe Fleming]

Ok so I've removed the code from a while loop and I'll just close it through the command window manually for now. Socket test shows the address as 127.0.0.1:52867, so I've set the the ports to the following, is that correct?

u = udp('localhost',52867,'localport',5000);
u.InputBufferSize = 1000;
u.DatagramReceivedFcn = @localReadDatagram;
fopen(u);

I now get the error:

Undefined function or variable 'localReadDatagram'.

Error in instrcb (line 36)
        feval(val{1}, obj, eventStruct, val{2:end});

[Joe Fleming]

All sorted - Thanks for your help