5.5.13 IIRLattice

Description

IIRLattice uses a lattice structure implementation to apply an IIR filter to the sequence of the source samples. It then places the results in the sequence of the destination samples and updates the delay values.

Prototype

 typedef struct { 
  int order; 
  fractional* kappaVals; 
  fractional* gammaVals; 
  fractional* delay; 
} IIRLatticeStruct;

fractional* IIRLattice (int numSamps, fractional* dstSamps, fractional* srcSamps, IIRLatticeStruct* filter);

Arguments

Filter Structure:


Parameters	Description
order	Filter order (also M, M ≤ N; see FIRLattice for N)
kappaVals	Base address for lattice coefficients (also k), either in X-Data or program memory
gammaVals	Base address for ladder coefficients (also g), either in X-Data or program memory. If NULL, the function will implement an all-pole filter.
delay	Base address for delay (also d), only in Y-Data

Filter Description:


Parameters	Description
numSamps	Number of input samples to filter (also N; with N being multiple of R)
dstSamps	Pointer to the destination samples (also y)
srcSamps	Pointer to the source samples (also x)
filter	Pointer to the IIRLatticeStruct filter structure

Return

Pointer to the base address of the destination sample.

Remarks

Lattice coefficients, k[m], defined in 0 ≤ m ≤ M.

Ladder coefficients, g[m], defined in 0 ≤ m ≤ M (unless if implementing an all-pole filter).

Delay, d[m], defined in 0 ≤ m ≤ M.

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

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

Note: The fractional implementation provided with this library is prone to saturation.

Appropriately scaling the input signal, prior to applying the filter, should prevent the fractional implementation from saturating.

Source File

iirlatt_aa.s

Cycle counts for PIC32A:


Source Vector Size	Cycles if coefficients in X-mem	Cycles if coefficients in P-mem
32	9586	15290
64	19122	30522
128	38194	60986
256	76338	121914
512	152626	243770
1024	305202	487482
2048	610254	774906

(*All values with M = 32)

System resource usage

W0…W7 - used, not restored
W8…W14 - saved, used, restored
ACCA - used, not restored
CORCON - saved, used, restored
REPEAT instruction(s) usage – None