Motorola DSP Developer's Kit

interp-r.asm

Y = mot###_interp(IDATA, R, LEN, B)

Description

This function resamples data at a higher rate using lowpass interpolation. The input data is real.

Y = INTERP (IDATA, R, LEN, B) resamples the sequence in vector IDATA at R times the original sample rate. The resulting resampled vector Y is R times longer, LENGTH(Y) = R*LENGTH(IDATA). A symmetric filter, B, allows the original data to pass through unchanged and interpolates between so that the mean square error between them and their ideal values is minimized. B is the interpolation filter.

Input/Output

Input: Real vector IDATA, int R, int LEN, and real vector B

Output: Real vector Y

Algorithm

int I;
for ( I = 0; I < lengthIDATA*R; I ++)
{
    Y[I] = 1;
}
for ( I = 0; I < lengthIDATA ; I = I ++)
{
    Y[I*R] = IDATA[I];
}
for( I = 0; I < 2*LEN*R; I ++)
{
    OD[I] = 0;
}

for (I = 0; I < 2 * LEN; I++)
{
    OD[I*R] = 2*IDATA[LEN-1] -IDATA[2*LEN - I];
}
/* Call filter  */
[OD, ZI] = filter(B, LEN, OD); 
[Y, ZF] = filter(B, LEN, Y, ZI]; 
for( I = 0, I < (lengthIDATA -LEN) * R; I++)
{
    Y[I] = Y[LEN*R+I];
}

for( I = 0; I < 2*LEN*R; I ++)
{
   OD[I] = 0;
}

for (I = 0; I < 2*LEN; I++)
{
   OD[I*R] = 2*IDATA[lengthIDATA] - IDATA[lengthIDATA -1 -I];
}
OD = filter (B, LEN, OD, ZF); 
for(I=0;I < LEN*R; I++)
{
   Y[lengthIDATA*R - LEN*R + I] = OD[I];
}

Memory & Register

Memory allocation

In X memory:

• X:(#INA) stores the start address of vector idata
• X:(INA+n) stores the start address of vector tb

In Y memory:

• X:(#INB) stores the start address of vector odata
• X:(INB+n*r) stores the start address of vector od

Register usage:

• N2 stores the location of n
• N3 stores the location of r
• N5 stores the location of l
• R2 stores the length of vector tb (2*r*l+1)
• N7 stores the location of n*r
• N0, N1, N4, and N6 are used for offset addressing

Status Register

The assembly function interp-r.asm does not set explicitly any status registers/bits.

Data Size Limit

The length of vector IDATA can't be larger than the continuous available data memory size.

Data Range Limit

The input data vector range is from -1.0 to +1.0, inclusive.

Precision

In the case of DSP563, precision is 21 bits.

In the case of DSP566, precision is 12 bits.

ifft-c.asm

interp-c.asm