Reference Implementation of a PSD estimator We provide for you in Appendix D and E a complete C implementation of a PSD estimator. The input is an IIR-filtered pseudo-noise (PN) sequence generator and the PSD estimate is based on windowing the autocorrelation with a rectangular window. The code consists of the files lab4b.c, lab4b.h, intrinsics.h, pn.c, iirfilt.c, autocorr.c, c_fft_given_iirc.asm, and the previously-given TI FFT routine. The assembly file c_fft_given_iirc.asm differs from c_fft_given.asm in that the window array has been removed and variables and arrays associated with IIR filtering have been added. Note that the multiply functions in the functions are actually compiler directives contained in intrinsics.h. Make sure you know which ones are used and why; note that VPO is not defined by the TI compiler, therefore the corresponding section of the #ifdef statement is not used. Open up the lab4b.pjt project and Rebuild All. Load lab4b.out onto the DSP and run the code. Make sure that an IIR-filtered PN sequence appears on channel 1 and its PSD estimate appears on channel 2. Does the output match your expectations based on the theory? Does this application illustrate any limitations of the FFT implementation? (Hint: note that most of the values in the FFT input are zero.) The previously-given C implementation uses a similar algorithm as the TI FFT; take a look at the C code for help. What are the limitation(s) of the FFT that show up in this application? In lab4b.h M sets the number of autocorrelation points that are calculated. What is the maximum value of M that allows the reference routines to run in real time? In determining this value you may find it useful to connect a wave-function generator to the input and copy input on that channel into channel 1 of output. You may limit M to powers of 2 minus 1.

Appendix A: Main routine, header files for PSD estimator lab4b.h intrinsics.h lab4b.c lab4bmain.c

> 15)

/* fractional multiply with fractional mode already on (int result) */
#define _i_mul_fract_fb1_ii(w0,w1) \
         (vpo_l_mul_ii(w0,w1) >> 16)

#define _set_fract_bit() vpo_set_fract()
#define _reset_fract_bit() vpo_reset_fract()
#define _set_ovm_bit() vpo_set_ovm()
#define _reset_ovm_bit() vpo_reset_ovm()

#define _l_add_shiftl_li(w0,w1) (((int32)(w0))+(((int32)(int16)(w1))<<16) )
#define _l_sub_shiftl_li(w0,w1) (((int32)(w0))-(((int32)(int16)(w1))<<16) )

#else

/* fractional multiply without fractional mode (long result) */
#define _l_mul_fract_fb0_ii(w0,w1) \
         (((long int)w0 * (long int)w1) << 1)

/* fractional multiply with fractional mode already on (long result) */
#define _l_mul_fract_fb1_ii(w0,w1) \
         (((long int)w0 * (long int)w1))

/* fractional multiply without fractional mode (int result) */
#define _i_mul_fract_fb0_ii(w0,w1) \
         (((long int)w0 * (long int)w1) >> 15)

/* fractional multiply with fractional mode already on (int result) */
#define _i_mul_fract_fb1_ii(w0,w1) \
         (((long int)w0 * (long int)w1) >> 16)

#define _set_fract_bit() asm("	ssbx frct")
#define _reset_fract_bit() asm("	rsbx frct")
#define _set_ovm_bit() asm("	ssbx ovm")
#define _reset_ovm_bit() asm("	rsbx ovm")

#endif /* VPO */

#endif /* INTRINSICS_H */

        ]]>


#include "lab4b.h"
#define IIR_order 4

extern int iirptr;
unsigned int *iseed;
extern int autocorr_out[N];
extern int state[IIR_order];

void init_DMA();

void main()
{
    int i;
 
	
    DSK5510_init();						// init BSL
    
    DSK5510_rset(DSK5510_MISC, 0x03);	// route McBSP0/1 to J3


	// Initialize autocorr_out to zero since some values will remain zero
	for (i = 0; i < N; ++i)
	{
		autocorr_out[i] = 0;
	}

	for ( i = 0; i < IIR_order; ++i)
		state[i] = 0;
    
    // Start McBSP0 I2S slave
    MCBSP_start(hMcbsp0, MCBSP_XMIT_START | MCBSP_RCV_START |
	MCBSP_SRGR_START | MCBSP_SRGR_FRAMESYNC, 220);
    
    // Start McBSP1 I2S master
    MCBSP_start(hMcbsp1, MCBSP_XMIT_START | MCBSP_RCV_START |
	MCBSP_SRGR_START | MCBSP_SRGR_FRAMESYNC, 220);
   
	init_DMA();							// configure DMA and interrupts

	*iseed = 1;	
	iirptr = 0;
   
    return;								// let DSP/BIOS scheduler take over
}

]]>

Appendix E: Additional routines for PSD estimator pn.c iirfilt.c autocorr.c c_fft_given_iirc.asm

> 15) & 1 ^ (*iseed >> 1) & 1 ^ *iseed & 1;
   /* Leftshift the seed and put the result of the XOR's in bit 1. */
   *iseed=(*iseed << 1) | newbit;  
   return(newbit);
}

void rand_fillbuffer(void)
{
   int i;

   for (i = 0; i < N; ++i)
   {
      if (randbit()) autocorr_in[i] =  32767;
      else           autocorr_in[i] = -32767;
   }
}

        ]]>

= 2*M+1                        */
/*               assumed to be full of zeros at start      */
/*               output in zero-phase form                 */
/***********************************************************/
/* Works for TMS320C55X series 							   */

#include "lab4b.h"
#include "intrinsics.h"

extern int autocorr_in[L];
extern int autocorr_out[N];

void autocorr(void)
{
   int i,j,temp;

   _set_fract_bit();
   for(i=0;i<=M;++i)
   {
      long int sum=0;
      for(j=0;j<(L-i);++j)
      {
         temp = _i_mul_fract_fb1_ii(autocorr_in[j],autocorr_in[j+i]);
         sum += temp;
      }
      autocorr_out[i]=(int)(sum >> logL);
   }
   _reset_fract_bit();

   /* Copy values for negative indeces at end of buffer */
   for(i=1,j=N-1;i<=M;++i,--j)
   {  autocorr_out[j]=autocorr_out[i]; }
}

        ]]>