Costum c code is not working in Simulink 2008a?

I wrote a model in Matlab/Simulink 2011a and included a costum c function "MyFunction". The model compiles and simulates quite fine.

For compatibility reasons I must downgrade my model to Matlab/Simulink 2008a now. Compilation fails with the error: c2_myModel.obj .text undefined reference to 'MyFunction' I doubled check, that the settings in "Configuration Parameters -> Real-Time Workshop -> Custom Code" are equal to the working 2011a version.

I tracked the error further. In Matlab/Simulink 2011a the "Header File" entry is written to myModel_sfun.h below the comment "/* Custom Code from Simulation Target dialog*/". I can not find the "Header File" entry in 2008a.

What am I missing? Why is the custom code integration working in 2011a, but not in 2008a?

best regards, Raphael

[Kaustubha Govind]

How is the custom C-function being included? Are you using the S-function Builder or similar means?