TMS320F28379D: Adding CPU Timer1 Interrupt to Matlab Simulink Model

Hi, 

I have a working Matlab Simulink model for CAN & IPC communication, and using Embedded Code, I managed to compile and build C code for CCS environment. So far so good. Then, I added CPU Timer1 interrupt routine (copied from TI CCS code example). Already configured the CPU Timer1 parameter correctly (proven from another solely CCS project without any components from Matlab model). I noticed that in the CCS project integrated with Matlab Simulink model, the CPU Timer1 interrupt routine cannot be executed. Every time, the program runs the statement to enable CPU Timer1 interrupt as follow 

      IER |= M_INT13;  

the program went to :  Illegal Interrupt Handler, and did not execute the interrupt routine defined for CPU Timer1. 

Why was that happened ? 

Please advise a remedy. 

Thank you.