rx_src.c

TI的DSP C55X的应用程序

/***********************************************************************************/
/*                      IS54 Baseband Simulation Software                          */
/*                                                                                 */
/*  File Description : IS54 Receive Filtering and Decimation                       */
/*  File Name        : rx_src.c                                                    */
/*  Date             : 12/30/93                                                    */
/*                   : July, 20001 - Modified for TMS320C55x project               */
/*                                                                                 */
/*    This subroutine takes a PI/4 DQPSK encoded square-root raised cosine         */
/*    sequence of data at 4X symbol rate and produces raised cosine filtered       */
/*    I & Q streams at 1X symbol rate. The filtering is controlled by a            */
/*    synchronization process which passes an input parameter to this subroutine   */
/*    telling it the offset to use in the filtering process.                       */
/*                                                                                 */
/*    This subroutine assumes it will generate 163 I,Q output pairs. Therefore,    */
/*    at least (samp_offset + 163*4) input I,Q pairs must be present at input      */
/*    buffer pointers I_SRC and Q_SRC.                                             */
/*                                                                                 */
/*    INPUTS                                                                       */
/*        I_SRC       : Vector of in-phase components of PI/4 DQPSK encoded        */
/*                      data at 4X symbol rate (basically the output               */
/*                      of a differential encoder). Note that this array must      */
/*                      contains at least (samp_offset + 163*4) samples.           */
/*                                                                                 */
/*        Q_SRC       : Vector of quadrature components of PI/4 DQPSK encoded      */
/*                      data at 4X symbol rate (again the output of                */
/*                      a differential encoder). Note that this array must         */
/*                      contains at least (samp_offset + 163*4) samples.           */
/*                                                                                 */
/*        samp_offset : An offset obtained from synchronization telling the        */
/*                      subroutine which sample of the input array to begin        */
/*                      filtering with.                                            */
/*                                                                                 */
/*        filt        : A vector containing a 48 tap square-root raised            */
/*                      cosine filter (12 symbols * 4 samples/symbol)              */
/*                                                                                 */
/*  OUTPUTS                                                                        */
/*        I           : A vector of in-phase components of square-root raised      */
/*                      cosine filtered PI/4 DQPSK data. Note that 163 samples     */
/*                      will be written to this buffer.                            */
/*                                                                                 */
/*        Q           : A vector of quadrature components of square-root raised    */
/*                      cosine filtered PI/4 DQPSK data. Note that 163 samples     */
/*                      will be written to this buffer.                            */
/*                                                                                 */
/***********************************************************************************/

/* Include Files */

#include <intrindefs.h>

/* Defines */

/* Function Prototypes */

void rx_src( int*, int*, int, int*, int*, int* );

/* External Function Prototypes */

/* Data */

/* External Data */

/* Code */

void rx_src( int *I_SRC, int *Q_SRC, int samp_offset, int *filt, int *I, int *Q )
{
    int     i, j, *filt_ptr,*isrc_ptr, *qsrc_ptr;
    long    I_ltemp, Q_ltemp;
    

/* Update pointers to SRC data to start at sync point */
    
    I_SRC += samp_offset;
    Q_SRC += samp_offset;

/********************/
/* Filter Data Loop */
/********************/
    
    for (i = 163 ; i > 0 ; i--)
    {
       /* Initialize pointers to input data */
        isrc_ptr = I_SRC;
        qsrc_ptr = Q_SRC; 
        
       /* Set filter pointer to filter */
        filt_ptr = filt; 
        
       /* Perform 48-tap filter */  
        I_ltemp = _lsmpy( (*(isrc_ptr++)), (*filt_ptr) );
        Q_ltemp = _lsmpy( (*(qsrc_ptr++)), (*(filt_ptr++)) );
        for (j = 46 ; j > 0 ; j--)
        {
            I_ltemp = _smac(I_ltemp, (*(isrc_ptr++)), (*filt_ptr) );
            Q_ltemp = _smac(Q_ltemp, (*(qsrc_ptr++)), (*(filt_ptr++)) );
        }
        I_ltemp = _smacr(I_ltemp, (*isrc_ptr), (*filt_ptr) );
        Q_ltemp = _smacr(Q_ltemp, (*qsrc_ptr), (*filt_ptr) );
        
       /* Store output samples */
        *(I++) = (I_ltemp>>16);
        *(Q++) = (Q_ltemp>>16);
       
       /* Update start sample pointers */    
        I_SRC += 4;
        Q_SRC += 4;
    }      
    
    return;
}