5.5.11 IIRCanonic

Description

IIRCanonic applies an IIR filter, using a cascade of canonic (direct form II) biquadratic sections, to the sequence of the source samples. It places the results in the sequence of the destination samples and updates the delay values.

Prototype

 typedef struct { 
  int numSectionsLess1; 
  fractional* coeffsBase; 
  fractional* delayBase; 
  int initialGain; 
  int finalShift; 
} IIRCanonicStruct; 

fractional* IIRCanonic (int numSamps, fractional* dstSamps, fractional* srcSamps, IIRCanonicStruct* filter);

Arguments

Filter Structure:

Filter Description:

Return

Pointer to the base address of the destination sample.

Remarks

There are five coefficients per second order (biquadratic) sections (generated externally) arranged in the ordered set - {a₂[s], a₁[s], a₀[s], b₁[s], b₀[s]}, 0 ≤ s < S.

The delay is made up of two words of filter state per section {d₁[s], d₂[s]}, 0 ≤ s < S.

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

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

The initial gain value is applied to each input sample prior to entering the filter structure.

The output scale is applied as a shift to the output of the filter structure prior to storing the result in the output sequence. It is used to restore the filter gain to 0 dB. Shift count may be zero; if not zero, it represents the number of bits to shift: negative indicates shift left, positive is shift right. 

Source File

• iircan_aa.s

Function Profile

Cycle counts for PIC32A:

(*All values with S = 5)

System resource usage

• W0…W7 - used, not restored
• W8…W9 - saved, used, restored
• ACCA - used, not restored
• CORCON - saved, used, restored
• REPEAT instruction(s) usage – None