Why do the block ports disconnect when I update a model with a Level 2 MATLAB S-Function in it?

I wrote a Level 2 MATLAB S-Function, and whenever I update my model (ctrl + d), the input ports disconnect from the block. See the screenshots below and the attached files. Why does this happen? Are there any workarounds?

Before updating the model:

After updating the model:

Answer 1

[MathWorks Support Team]

This issue is related to the "NumInputPorts" property of the "Simulink.RunTimeBlock" class:

https://www.mathworks.com/help/simulink/slref/simulink.runtimeblock.html#f29-86418

This occurs when the NumInputPorts is initially set to zero in the "setup" method of the S-Function, and then is later set to a nonzero value:

The ports on the block are dynamically updated, so when the following line is executed,

>> block.NumInputPorts = 0;

All of the input ports from the block are removed. Then, when

>> block.NumInputPorts = 1;

is executed, an input port is added to the block, but there is no memory of previous connections, so the input signal is disconnected.

If you need to write logic in your S-Function to determine the number of ports the block will have, use an intermediate variable as follows: