How to store object(like udp object) in level-2 s-function?

Hello all,

I want to send control input from Matlab to FlightGear and receive aircraft data from FlightGear to Matlab with UDP communication.

So I made a code below:

function FG_Simulink(block)

% Level-2 MATLAB file S-Function for UDP communication with FlightGear

setup(block)

function setup(block)

% Register number of dialog parameters

block.NumDialogPrms = 0; % UDP send and receive ports

% Register number of input and output ports

block.NumInputPorts = 4; % aileron, elevator, rudder, throttle

block.NumOutputPorts = 11; % u, v, w, alpha, beta, p, q, r, phi, theta, psi

% Setup functional port dimensions

block.SetPreCompInpPortInfoToDynamic;

block.SetPreCompOutPortInfoToDynamic;

% Register sample times

% Specify discrete sample time with a period of 0.01 seconds and an offset of 0

block.SampleTimes = [0, 0]; % Correct format for discrete sample time

% Specify the block simStateCompliance.

block.SimStateCompliance = 'DefaultSimState';

% Register methods

block.RegBlockMethod('Start', @Start);

block.RegBlockMethod('Outputs', @Outputs);

block.RegBlockMethod('Terminate', @Terminate);

block.RegBlockMethod('SetInputPortSamplingMode', @SetInputPortSamplingMode);

block.RegBlockMethod('PostPropagationSetup', @DoPostPropSetup);

function SetInputPortSamplingMode(block, port, mode)

% Set the input port sampling mode

block.InputPort(port).SamplingMode = mode;

% Set the same sampling mode for all output ports

for i = 1:block.NumOutputPorts

block.OutputPort(i).SamplingMode = mode;

end

function DoPostPropSetup(block)

% Setup Dwork

block.NumDworks = 0;

% Setup Pwork (Pointer Work Vector) for storing UDP object

block.NumPworks = 2; % We need to store two UDP objects

function Start(block)

% Declare persistent variables to store UDP sender and receiver

persistent UdpSender UdpReceiver

% Initialize UDP sender and receiver

% Retrieve ports from dialog parameters

if isempty(UdpSender)

try

UdpSender = udpport("IPV4",'LocalPort',55001, 'Timeout', 1);

block.Pwork(1).Data = UdpSender;

catch e

error('Failed to bind sender UDP port: %s', e.message);

end

end

if isempty(UdpReceiver)

try

UdpReceiver = udpport("IPV4",'LocalPort',55002, 'Timeout', 1);

block.Pwork(2).Data = UdpReceiver;

catch e

error('Failed to bind receiver UDP port: %s', e.message);

end

end

function Outputs(block)

% Retrieve UDP objects from UserData

% Create input data vector

inputVector = zeros(1, 4);

inputVector(1) = block.InputPort(1).Data; % aileron

inputVector(2) = block.InputPort(2).Data; % elevator

inputVector(3) = block.InputPort(3).Data; % rudder

inputVector(4) = block.InputPort(4).Data; % throttle

Udpsender = block.Pwork(1).Data;

Udpreceiver = block.Pwork(2).Data;

% Send input data to FlightGear

try

write(Udpsender, inputVector, 'double', "LocalPort",55002); % Send to FlightGear receive port

catch e

warning('Failed to send data to FlightGear: %s', '%s', e.message);

end

% Receive flight data from FlightGear

try

data = read(Udpreceiver, 88, "double"); % 11 floats * 4 bytes each

if ~isempty(data)

outputVector = typecast(data, 'double');

for i = 1:block.NumOutputPorts

block.OutputPort(i).Data = outputVector(i);

end

end

catch e

% Handle timeout or any read errors

warning('Failed to receive data from FlightGear: %s', '%s', e.message);

end

function Terminate(block)

But when I launch a simulink file, the error was occured : "Cause: The property 'NumPworks' is not recognized for the class 'Simulink.MSFcnRunTimeBlock'."

I know that Dwork can not store the object type data, so if you have any idea to solve this problem, please let me know.

Thank you.

Answer 1

[Divyam]

Hi @준호,

To store the UDP packets associated with a specific Simulink block, the "UserData" parameter of the Simulink block can be utilized to store data across callbacks. For your reference, I have made the edits to the "Start" function which incorporates the desired functionality.

function Start(block)
    % Declare persistent variables to store UDP sender and receiver
    persistent UdpSender UdpReceiver
    
    %-- Get the block path --%
    blockPath = gcb(block);
    
    %-- Comment the below line if you don't wish to store the UserData persistently --%
    set_param(gcb, 'UserDataPersistent', 'on');
    
    % Initialize UDP sender and receiver
    % Retrieve ports from dialog parameters
    if isempty(UdpSender)
        try
            UdpSender = udpport("IPV4",'LocalPort',55001, 'Timeout', 1);
            %-- Setting the UserData property to store UDP object --%
            set_param(blockPath, 'UserData', UdpSender); 
        catch e
            error('Failed to bind sender UDP port: %s', e.message);
        end
    end
    if isempty(UdpReceiver)
        try
            UdpReceiver = udpport("IPV4",'LocalPort',55002, 'Timeout', 1);
            %-- Setting the UserData property to store UDP object --%
            set_param(blockPath, 'UserData', UdpReceiver);
        catch e
            error('Failed to bind receiver UDP port: %s', e.message);
        end
    end

For more information regarding the 'UserData' parameter, you can refer to this documentation: https://www.mathworks.com/help/simulink/ug/associating-user-data-with-blocks.html

[준호]

Hi Divyam,

I followed your advice, but the following issues have occurred:

1. In the line blockPath = gcb(block);, an error message saying 'Invalid Simulink object handle.' appears. However, if I remove the block parameter from gcb, it works.
2. In the Output method, when I call get_param to obtain the udpport object, I get a warning message stating, 'Loading udpport objects from a MAT-file is not supported.'

Here is a code.

function Start(block)
%   Declare persistent variables to store UDP sender and receiver
    persistent UdpSender UdpReceiver
%   Initialize UDP sender and receiver

%   Get the block path
    blockPath = gcb();

%  Comment the below line if you don't wish to store the UserData persistently
    set_param(blockPath, 'UserDataPersistent', 'on');

    if isempty(UdpSender)
        try
            UdpSender = udpport("IPV4",LocalHost="127.0.0.1",LocalPort=55002);
        catch e
            error('Failed to bind sender UDP port: %s', e.message);
        end
    end

    if isempty(UdpReceiver)
        try
            UdpReceiver = udpport("IPV4",LocalHost="127.0.0.1",LocalPort=55001);
        catch e
            error('Failed to bind receiver UDP port: %s', e.message);
        end
    end

    % Check the information about udp objects
    disp(UdpSender);
    disp(UdpReceiver);

    try
    %  Setting the UserData property to store UDP object
        Objects = [UdpSender, UdpReceiver];
        set_param(blockPath, 'UserData', Objects);
    catch e
        error('Failed to store UDP objects: %s', e.message);
    end
    
function Outputs(block)
    % Retrieve UDP objects from UserData
    % Create input data vector
    inputVector = zeros(1, 4);
    inputVector(1) = block.InputPort(1).Data; % aileron
    inputVector(2) = block.InputPort(2).Data; % elevator
    inputVector(3) = block.InputPort(3).Data; % rudder
    inputVector(4) = block.InputPort(4).Data; % throttle

    % Get the persistant UDP object
    try
        [Sender, Receiver] = get_param(gcb, 'UserData');
    catch e
        warning('Failed to get object: %s', '%s', e.message);
    end

    % Send input data to FlightGear
    try
        write(Sender, inputVector, 'double', "LocalPort",55002); % Send to FlightGear receive port
    catch e
        warning('Failed to send data to FlightGear: %s', '%s', e.message);
    end

    % Receive flight data from FlightGear
    try
        data = read(Receiver, 88, "double"); % 11 floats * 4 bytes each
        if ~isempty(data)
            outputVector = typecast(data, 'double');
            for i = 1:block.NumOutputPorts
                block.OutputPort(i).Data = outputVector(i);
            end
        end
    catch e
        % Handle timeout or any read errors
        warning('Failed to receive data from FlightGear: %s', '%s', e.message);
    end

How can I troubleshoot it?

[Divyam]

Hi @준호, to use the 'gcb' command effectively in order to get the path of the block, you first need to select the block for which you are performing the operation. In your use case it would indeed make sense to omit the 'block' parameter from the 'gcb' command.

As an alternative, remove the 'gcb' command from your code and add 'blockPath' as a function input parameter itself, that should resolve your error.

To avoid writing data to the MAT file you can write data to the UDP port itself via this method.

u1 = udpport;
% Writing the data to the UDP socket itself
write(u1,<data>,<destination address>,<destination port>)
% Reading the data from a UDP socket
dataRead = read(u1,u1.NumBytesAvailable,'uint8')

https://www.mathworks.com/help/instrument/udpport.write.html