Motorola DSP Developer's Kit

xcorr-r.asm

C=mot###_xcorr(A,B, MAXLAG, 'flag')

Description

This function returns the length 2*M-1 cross-correlation sequence in a column vector where A and B are length N real vectors

Input/Output

Input: Vector A, vector B, int MAXLAG, and int 'flag'

Output: Vector C

Algorithm

N = LengthA;
//The following are algorithm of xcorr
    for (i = Max(1, (N - MAXLAG)); i <= N - 1; i ++) {
        for (j = 0; j < = i - 1; j ++) {
            C[i ] += B[j+1] * A[j + N - i + 1];
       }
        if (flag == "biased") C[i] /= N;
        else if (flag == "unbiased") C[i] /= i ;
    }
    for (i = N; i <= Min((2 * N - 1), (N + MAXLAG)); i ++) {
        for (j = 0; j <= 2 * N - i - 1; j ++) {
            C[i] += A[j+1] * B[j + i - N + 1];
       }
        if (flag == "biased") C[i] /= N;
        else if (flag == "unbiased") C[i] /= (2 * N - i);
    }
    if (flag == "coeff") {
        for (i = Max(1, (N - MAXLAG)); i <= Min((2 * N - 1), (N + 
MAXLAG)); i ++) {
            C[i] / = C[N];
       }
    }
    
    // Format vector C
    if (MAXLAG >= N) {
        LengthC = 2 * MAXLAG + 1;
        df = MAXLAG - N + 1;
        for (i = LengthC;  i >= 1 ; i --) {
            if ( i > df && i <= LengthC - df ) {
                C[i] = C[i - df];
           }

            else {
 C[i] = 0;
           }
       }
    } 
    else {
        C = C(N - MAXLAG : LengthC);
    }

Memory & Register

Memory allocation:

In X memory:

• Label X:INA is used for input data of vector A
• Label X:INA+ LENGTH(A) is used for output data of vector C

In Y memory:

• Label Y:INB is used for the input data of vector B

Register usage:

• R2 stores the address of the length of vector A
• R3 = MAXLAG
• R7 = 'flag'
• R7= 0 -- 'none'
• R7 = 1 -- 'biased'
• R7 = 4 -- 'coeff'
• N7 = 24 for dsp56300, or 16 for dsp56600
• R1 stores the address of the index of vector C
• R0 stores the address of the index of vector A
• R4 stores the address of the index of vector B
• N7 is used for temporary storage of R7
• R7 is used for temporary storage of the address of vector A or B
• R5 and R6 are used as loop control

Assumes M{0...7} = $ffffff

Status Register

The assembly function xcorr-r.asm does not explicitly set any status registers/bits during the function execution.

Data Size Limit

The total size of all vectors can't be larger than the continuous available data memory size.

Data Range Limit

The value of input vectors must be between -1.0 and +1.0.

Precision

In the case of DSP563, precision is 18 bits.

In the case of DSP566, precision is 10 bits.

Perfumes Limit

DSP563:

DSP566:

sum-c.asm

xcorr-c.asm