//IIR.c  IIR filter using cascaded Direct Form II
//Coefficients a's and b's correspond to b's and a's from MATLAB

#include "bs1750.cof"       	 //BS @ 1750 Hz coefficient file
short dly[stages][2] = {0};    //delay samples per stage

interrupt void c_int11()	 //ISR
{
 int i, input;
 int un, yn;

 input = input_sample();	 //input to 1st stage
 for (i = 0; i < stages; i++)  //repeat for each stage
  {
   un=input-((b[i][0]*dly[i][0])>>15) - ((b[i][1]*dly[i][1])>>15);

   yn=((a[i][0]*un)>>15)+((a[i][1]*dly[i][0])>>15)+((a[i][2]*dly[i][1])>>15);

   dly[i][1] = dly[i][0]; 	 //update delays
   dly[i][0] = un;             //update delays
   input = yn;  			 //intermediate output->input to next stage
  }
   output_sample(yn);          //output final result for time n
   return;				 //return from ISR
}

void main()
{
  comm_intr();                 //init DSK, codec, McBSP
  while(1);				 //infinite loop
}