UDP and Variable-Size Signals

The Simulink^® Real-Time™ UDP sublibrary does not directly support variable-size signals. The UDP Send block input port accepts only fixed-size signals.

To send variable-size signals though UDP, determine the maximum number of elements of a fixed-size input signal that you expect to connect to the block. Use the second input, Length, to specify the number of elements of this input signal to send through UDP.

This example configures the MATLAB Function block to accept a variable-size signal and maps that signal to a fixed-size output signal. It outputs the number of relevant elements. You can output the fixed-size output signal and number of elements to the inputs of the UDP Send block.

1. To accept a variable-size input signal, create a MATLAB Function block.

2. In the MATLAB Function block, enter code like the following code. In this code, the maximum size of the variable-size input signal is 9.

   function [y,y_length] = fcn(u)
   %#codegen
   y = uint8(zeros(9,1));
   y_length = length(u);
   for a = 1:y_length
       y(a) = u(a);
   end

3. In the MATLAB^® Function Editor, click the Edit Data button. In Ports and Data Manager, select the data u, and then select the corresponding Variable size check box.

4. Select the data y and enter the size of the variable-size data input signal in the corresponding Size parameter. For this example, the size value is 9.

5. Provide a variable-size signal source for the MATLAB Function block.