5.5.3 FIRDecimate

Description

FIRDecimate decimates the sequence of the source samples at a rate of R to 1, or equivalently, it downsamples the signal by a factor of R.

Effectively,

y[n] = x[Rn].

To diminish the effect of aliasing, the source samples are first filtered and then downsampled. The decimated results are stored in the sequence of destination samples, and the delay values are updated.

Prototype

fractional* FIRDecimate (int numSamps, fractional* dstSamps, fractional* srcSamps, FIRStruct* filter, int rate);

Arguments

Return

Pointer to the base address of the destination sample.

Remarks

Number of filter coefficients is M, with M being an integer multiple of R.

Coefficients, h[m], defined in 0 ≤ m < M, are not implemented as a circular modulo buffer.

Delay, d[m], defined in 0 ≤ m < M, are not implemented as a circular modulo buffer.

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

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

(See also FIRStruct, FIRStructInit and FIRDelayInit.)

Source File

• firdecim_aa.s

Cycle counts for PIC32A:

(*All values with numCoeffs = 32; rate = 2)

System resource usage

• W0…W7 - used, not restored
• W8…W11 - saved, used, restored
• ACCA - used, not restored
• CORCON - saved, used, restored
• REPEAT instruction(s) usage – 2