5.5.8 FIRLMS

Description

FIRLMS applies an adaptive FIR filter to the sequence of source samples, stores the results in the sequence of destination samples and updates the delay values.

The filter coefficients are also updated, at a sample-per-sample basis, using a Least Mean Square algorithm applied according to the values of the reference samples.

Prototype

fractional* FIRLMS (int numSamps, fractional* dstSamps, fractional* srcSamps, FIRStruct* filter, fractional* refSamps, fractional muVal);

Arguments

Return

Pointer to the base address of the destination sample.

Remarks

Number of the filter coefficients is M.

Coefficients, h[m], defined in 0 ≤ m < M, are implemented as a circular modulo buffer.

Delay, d[m], defined in 0 ≤ m < M, is implemented as a circular modulo buffer, placed in Y-data space.

Source samples, x[n], defined in 0 ≤ n < N.

Reference samples, r[n], defined in 0 ≤ n < N.

Destination samples, y[n], defined in 0 ≤ n < N.

Adaptation:

h_m[n] = h_m[n - 1] + mu * (r[n] - y[n]) * x[n - m] for 0 ≤ n < N, 0 ≤ m < M.

The operation could result in saturation if the absolute value of (r[n] - y[n]) is greater than or equal to 1.

Filter coefficients must not be allocated in the program memory, because in that case, their values could not be adapted. If filter coefficients are detected as allocated in program memory, the function returns NULL.

(See also FIRStruct, FIRStructInit and FIRInterpDelayInit.)

Source File

• firlms_aa.s

Cycle counts for PIC32A:

(*All values with numCoeffs = 32)

System resource usage

• W0…W7 - used, not restored
• W8…W12 - saved, used, restored
• ACCA - used, not restored
• CORCON - saved, used, restored
• MODCON - saved, used, restored
• XMODSTRT - saved, used, restored
• XMODEND - saved, used, restored
• YMODSTRT - saved, used, restored
• YMODEND - saved, used, restored
• REPEAT instruction(s) usage – 1