C code generation - dataStack datatype

I have this Matlab function (mfile):

function [NPIfilt offNPIfilt predNPIfilt stateOut stateOutVar RR] = NPI(pv,sp,op,status,par,stateIn,stateInVar)

I need to call this function from Simulink simulation (run for whole simulation time), and I would prefer to have it as C code (in a S-function). So I created the C code via Matlab coder: codegen -report NPI.m -args {pv,sp,op,status,par,stateIn,stateInVar} , but in the C code there is one additional parameter of the function: NPIStackData *SD (the signature of function is:

void NPI(NPIStackData *SD, real_T pv, real_T sp, real_T op, real_T status, const real_T par[18], const real_T stateIn[16], const real_T stateInVar[1984], real_T *NPIfilt, real_T *offNPIfilt, real_T *predNPIfilt, real_T stateOut[16], real_T *stateOutVar, real_T RR[3])).

The datatype NPIStackData is defined in :

   14   typedef struct
   15   {
   16       struct
   17       {
   18           creal_T alpha1_data[1983];
   19           creal_T beta1_data[1983];
   20       } f0;
   21       struct
   22       {
   23           creal_T eiga_data[1983];
   24       } f1;
   25       struct
   26       {
   27           creal_T x_data[1983];
   28       } f2;
   29       struct
   30       {
   31           real_T stateInVar[1984];
   32       } f3;
   33   } NPIStackData;

What is the reason for this new datatype, and how should I deal with it (how to initialize it in order to be able to call the function? Thank you very much.