interpolate.c

CHP 4 - Real-Time Digital Signal Processing: Implementations and Applications, Second Edition by Sen

// 
//  Project: Experiment 4.5.7 Sample Rate Convertor using FIR filter - Chapter 4
//  File name: interpolate.c   
//
//  Description: This is the implementation of a fixed-point interpolaiton filter
//
//  For the book "Real Time Digital Signal Processing: 
//                Implementation and Application, 2nd Ed"
//                By Sen M. Kuo, Bob H. Lee, and Wenshun Tian
//                Publisher: John Wiley and Sons, Ltd
//
//  Tools used: CCS v.2.12.07
//              TMS320VC5510 DSK Rev-C
//

#include "interpolation.h"

// Define DSP system memory map
#pragma CODE_SECTION(interpolate, ".text:fir");

void interpolate(short *x, short blkSize, 
                 short *h, short order, 
                 short *y, 
                 short *w, short *index,
                 short intp)
{
  short i,j,k,n,m;
  long sum;
  short *c;

  k = *index;
  for (j=0; j<blkSize; j++)               // Block processing
  {
    c = h;
    w[k] = *x++;                          // Get the current data to delay line
    m = k;
    for (n=0; n<intp; n++)
    {
      for (sum=0, i=0; i<order; i++)      // FIR filter processing
      {
        sum += c[i*intp] * (long)w[k++];
        if (k == order)                   // Simulate circular buffer
        {
          k = 0;
        }
      }   		
      *y++ = (short)(sum>>14);            // Save filter output
      c++;
      k = m;
    }

    k--;
    if (k<0)                              // Update index for next time
    {
      k += order;
    }
  }
  *index = k;                            // Update circular buffer index
}