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@***********************************************************
@ Function: WT_VoiceFilter
@ Processor: ARM
@ Description:
@ Implements a 2-pole low-pass filter with resonanance
@
@ Usage:
@ void WT_VoiceFilter(
@ S_FILTER CONTROL *pFilter,
@ S_WT_FRAME *pWTFrame);
@
@ Copyright 2005 Sonic Network, Inc.
@****************************************************************
@ Revision Control:
@ $Revision: 496 $
@ $Date: 2006-12-11 14:33:26 -0800 (Mon, 11 Dec 2006) $
@****************************************************************
@
@ where:
@ S_FILTER_CONTROL *pFilter
@ PASSED IN: r0
@
@ S_WT_FRAME *pWTFrame
@ PASSED IN: r1
@****************************************************************
.include "ARM_synth_constants_gnu.inc"
.arm
.text
.global WT_VoiceFilter
@ Register usage
@ --------------
pFilter .req r0
pWTFrame .req r1
pBuffer .req r2
numSamples .req r3
z1 .req r4
z2 .req r5
b1 .req r6
b2 .req r7
K .req r8
tmp0 .req r1 @ reuse register
tmp1 .req r9
tmp2 .req r10
@SaveRegs RLIST {r4-r10, lr}
@RestoreRegs RLIST {r4-r10, pc}
.func WT_VoiceFilter
WT_VoiceFilter:
STMFD sp!, {r4-r10, lr}
@
@ Setup passed parameters in their destination registers
@----------------------------------------------------------------
LDR pBuffer, [pWTFrame, #m_pAudioBuffer]
LDR numSamples, [pWTFrame, #m_numSamples]
@load state variables from pFilter structure
LDRSH z1, [pFilter, #m_z1]
LDRSH z2, [pFilter, #m_z2]
@load coefficients from pWTFrame structure
LDR K, [pWTFrame, #m_k]
LDR b1, [pWTFrame, #m_b1]
LDR b2, [pWTFrame, #m_b2]
RSB b1, b1, #0 @ b1 = -b1
RSB b2, b2, #0 @ b2 = -b2
MOV b2, b2, ASR #1 @ b2 = b2 >> 1
MOV K, K, ASR #1 @ K = K >> 1
@
@ Start processing
@----------------------------------------------------------------
LDRSH tmp0, [pBuffer] @ fetch sample
FilterLoop:
SMULBB tmp2, z1, b1 @ tmp2 = z1 * -b1
SMLABB tmp2, z2, b2, tmp2 @ tmp2 = (-b1 * z1) + (-b2 * z2)
MOV z2, z1 @ delay line
SMLABB tmp0, tmp0, K, tmp2 @ tmp1 = (K * x[n]) + (-b1 * z1) + (-b2 * z2)
LDRSH tmp1, [pBuffer, #NEXT_OUTPUT_PCM] @ fetch next sample
MOV z1, tmp0, ASR #14 @ shift result to low word
STRH z1, [pBuffer], #NEXT_OUTPUT_PCM @ write back to buffer
SMULBB tmp2, z1, b1 @ tmp2 = z1 * -b1
SUBS numSamples, numSamples, #2 @ unroll loop once
SMLABB tmp2, z2, b2, tmp2 @ tmp2 = (-b1 * z1) + (-b2 * z2)
SMLABB tmp1, tmp1, K, tmp2 @ tmp1 = (K * x[n]) + (-b1 * z1) + (-b2 * z2)
MOV z2, z1 @ delay line
MOV z1, tmp1, ASR #14 @ shift result to low word
LDRGTSH tmp0, [pBuffer, #NEXT_OUTPUT_PCM] @ fetch next sample
STRH z1, [pBuffer], #NEXT_OUTPUT_PCM @ write back to buffer
BGT FilterLoop
@ save z terms
@----------------------------------------------------------------
STRH z1, [pFilter, #m_z1]
STRH z2, [pFilter, #m_z2]
@ Return to calling function
@----------------------------------------------------------------
LDMFD sp!,{r4-r10, lr}
BX lr
.endfunc
.end
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