TMDSLCDK6748: How to include previous samples for FIR filter DSPF_sp_fir_gen()

Hi all,

Can you help me figure out how to include previous samples in FIR filter. According to the TMS320C67x DSP Library Programmers Ref. Guide SPRU657C, the input array starts at x(-nh+1) and ends at x(nr-1).

To test the filter, I'm using the mcaspPlayBk.c from the StarterWare C6748_StarterWare_1_20_04_01. 

To construct the input array for the FIR filter, I'm increasing the buffer size from its default of 2000 samples to 2015 for a 16-tap filter. The problem I have (I think) is that I don't know how to insert (nh-1) previous samples to the head of buffer. Since the data comes in frames, I'm trying to save the last (nh-1) sample from the previous frame then using them in the "current" frame. But this isn't working.

Here is my code, which is modified version of mcaspPlayBk.c:

    while(1)
    {
        if(lastFullRxBuf != lastSentTxBuf)
        {
            /*
            ** Start the transmission from the link paramset. The param set
            ** 1 will be linked to param set at PAR_TX_START. So do not
            ** update paRAM set1.
            */
            parToSend =  PAR_TX_START + (parOffTxToSend % NUM_PAR);
            parOffTxToSend = (parOffTxToSend + 1) % NUM_PAR;
            parToLink  = PAR_TX_START + parOffTxToSend;

            lastSentTxBuf = (lastSentTxBuf + 1) % NUM_BUF;

            // is this necessary?
            memcpy(tempCharBuf, (void *)rxBufPtr[lastFullRxBuf], AUDIO_BUF_SIZE);
            /*
            **convert char array to short signed int array starting at NH
            */
            unpackMcASPBuf(tempCharBuf, NUM_SAMPLES_PER_AUDIO_BUF, NH, singleChannelInt);
            counter++; //for debugging
            /*
            ** insert previous samples to front of rx frame buffer for FIR filter
            */
            insertPrevSamples(singleChannelInt, previousSamples, NH);
            /*
            ** save trailing NH samples for next frame
            */
            saveTrailingSamples(singleChannelInt, NUM_SAMPLES_PER_AUDIO_BUF, previousSamples, NH);
            /*
            ** convert to sp float for FIR filter
            */
            intToFloat(singleChannelInt, NUM_SAMPLES_PER_AUDIO_BUF + NH, DSPInputSignal);
            /*
            **FIR filter
            */
            DSPF_sp_fir_gen(DSPInputSignal, filterCoefs, DSPOutputSignal, NH, NUM_SAMPLES_PER_AUDIO_BUF );
            /*
            ** convert back to int for txBuf
            */
            floatToInt(DSPOutputSignal, NUM_SAMPLES_PER_AUDIO_BUF, tempIntBuf);
            /*
            ** interleave back into txBuf short int to char conversion
            */
            packMcASPBuf(tempIntBuf, NUM_SAMPLES_PER_AUDIO_BUF, tempCharBuf);
            memcpy((void *)txBufPtr[lastSentTxBuf], tempCharBuf, AUDIO_BUF_SIZE);
            /*
            ** Send the buffer by setting the DMA params accordingly.
            ** Here the buffer to send and number of samples are passed as
            ** parameters. This is important, if only transmit section
            ** is to be used.
            */
            BufferTxDMAActivate(lastSentTxBuf, NUM_SAMPLES_PER_AUDIO_BUF,
      }
}

The functions are:

void insertPrevSamples(short signed int* x, short signed int* p, int np){ //p = previous
        int i=0;
        for(i= 0; i < np - 1 ; ++i)
                x[i] = p[i];
}

void saveTrailingSamples(short signed int* x, int nx, short signed int* p, int np){ //p = previous
        int i=0;
        for(i= 0; i < np - 1; i++)
                p[i] = x[nx + i];
}

void unpackMcASPBuf(unsigned char* x, int nx, int nh, short signed int* y){
    int i=0;
    int indx=0;
    for(i = nh; i < nx + nh; i++){
        y[i]  = x[indx+1] << 8;
        y[i] |= x[indx+0] << 0;
        indx += 8;
    }
}
void packMcASPBuf(short int* in, int size, unsigned char* out){
    int i=0;
    int indx=0;
    int byte0;
    int byte1;
    int byte4;
    int byte5;

    for(i=0; i< size/2; i++){
        out[indx+2] = 0;
        out[indx+3] = 0;
        out[indx+6] = 0;
        out[indx+7] = 0;

        byte0 = ( in[i] >> 0 );
        byte1 = ( in[i] >> 8 );
        byte4 = ( in[i] >> 16 );
        byte5 = ( in[i] >> 24 );

        out[indx+0] = (char)byte0;
        out[indx+1] = (char)byte1;

        out[indx+4] = (char)byte4;
        out[indx+5] = (char)byte5;
        indx += 8;
    }
}

Also included is a waveform showing the corrupted nh-1 samples at the head of the buffer. 

I hope this makes sense and sorry for the lengthy explanation and code.

thank you,

Scott