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Debug Generated Code During SIL Execution

If a SIL execution fails or you notice differences between the outputs of your original functions and the generated code, you can rerun the SIL execution with a debugger enabled. By inserting breakpoints, you can observe the behavior of code sections, which might help you to understand the cause of the problem.

For a SIL execution failure, you can also view information from the standard output and standard error streams in the MATLAB® Command Window. For example:

  • Output from printf statements in your code.

  • If you enable run-time error detection, messages sent to stderr.

  • Some low-level system messages.


During a SIL execution, the SIL application redirects the stdout and stderr streams. When the application terminates, the MATLAB Command Window displays the information from the redirected streams. The SIL application also provides a basic signal handler, which captures the POSIX® signals SIGFPE, SIGILL, SIGABRT, and SIGSEV. For this signal handler, the SIL application includes the file signal.h.

A SIL execution supports the following debuggers:

  • On Windows®, Microsoft® Visual Studio® debugger.

  • On macOS, LLDB Debugger (LLDB).

  • On Linux®, GNU® Data Display Debugger (DDD).


You can perform SIL debugging only if the MATLAB product family supports your Microsoft Visual C++®, Xcode, or GNU GCC compiler. For more information, see supported compilers.

To run a SIL execution with debugging enabled:

  1. On the Generate Code page, click Verify Code.

  2. Select the Enable source-level debugging for SIL check box.

  3. Click Run Generated Code.

On a Windows computer, your user_fn.c or user_fn.cpp file opens in the Microsoft Visual Studio IDE with debugger breakpoints at the start of the user_fn_initialize and user_fn functions.

You can now use the debugger features to observe code behavior. For example, you can step through code and examine variables.

To end the debugging session:

  1. Remove all breakpoints.

  2. Click the Continue button (F5).

    The SIL execution runs to completion.

  3. To terminate the SIL execution process, on the Test Output tab, click the link that follows To terminate execution, for example, clear kalman01_sil.

    The Microsoft Visual Studio IDE closes automatically.


If you select Debug > Stop Debugging, the SIL execution times out with the following error message:

Communications error: failed to send data to the target. There might be 
multiple reasons for this failure.


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