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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2006-2007 Thom Johansen
*
* This program is free software; you can redistribute it and/or
* modify it under the terms of the GNU General Public License
* as published by the Free Software Foundation; either version 2
* of the License, or (at your option) any later version.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
/* uncomment this to make filtering calculate lower bits after shifting.
* without this, "shift" - 1 of the lower bits will be lost here.
*/
/* #define HIGH_PRECISION */
/*
* void eq_filter(int32_t **x, struct eqfilter *f, unsigned num,
* unsigned channels, unsigned shift)
*/
.text
.global eq_filter
eq_filter:
lea.l (-11*4, %sp), %sp
movem.l %d2-%d7/%a2-%a6, (%sp) | save clobbered regs
move.l (11*4+8, %sp), %a5 | fetch filter structure address
move.l (11*4+20, %sp), %d7 | load shift count
subq.l #1, %d7 | EMAC gives us one free shift
#ifdef HIGH_PRECISION
moveq.l #8, %d6
sub.l %d7, %d6 | shift for lower part of accumulator
#endif
movem.l (%a5), %a0-%a4 | load coefs
lea.l (5*4, %a5), %a5 | point to filter history
.filterloop:
move.l (11*4+4, %sp), %a6 | load input channel pointer
addq.l #4, (11*4+4, %sp) | point x to next channel
move.l (%a6), %a6
move.l (11*4+12, %sp), %d5 | number of samples
movem.l (%a5), %d0-%d3 | load filter history
/* d0-d3 = history, d4 = temp, d5 = sample count, d6 = lower shift amount,
* d7 = upper shift amount, a0-a4 = coefs, a5 = history pointer, a6 = x[]
*/
.loop:
/* Direct form 1 filtering code. We assume DSP has put EMAC in frac mode.
* y[n] = b0*x[i] + b1*x[i - 1] + b2*x[i - 2] + a1*y[i - 1] + a2*y[i - 2],
* where y[] is output and x[] is input. This is performed out of order
* to do parallel load of input value.
*/
mac.l %a2, %d1, %acc0 | acc = b2*x[i - 2]
move.l %d0, %d1 | fix input history
mac.l %a1, %d0, (%a6), %d0, %acc0 | acc += b1*x[i - 1], x[i] -> d0
mac.l %a0, %d0, %acc0 | acc += b0*x[i]
mac.l %a3, %d2, %acc0 | acc += a1*y[i - 1]
mac.l %a4, %d3, %acc0 | acc += a2*y[i - 2]
move.l %d2, %d3 | fix output history
#ifdef HIGH_PRECISION
move.l %accext01, %d2 | fetch lower part of accumulator
move.b %d2, %d4 | clear upper three bytes
lsr.l %d6, %d4 | shift lower bits
#endif
movclr.l %acc0, %d2 | fetch upper part of result
asl.l %d7, %d2 | restore fixed point format
#ifdef HIGH_PRECISION
or.l %d2, %d4 | combine lower and upper parts
#endif
move.l %d2, (%a6)+ | save result
subq.l #1, %d5 | are we done with this channel?
jne .loop
movem.l %d0-%d3, (%a5) | save history back to struct
lea.l (4*4, %a5), %a5 | point to next channel's history
subq.l #1, (11*4+16, %sp) | have we processed both channels?
jne .filterloop
movem.l (%sp), %d2-%d7/%a2-%a6
lea.l (11*4, %sp), %sp
rts
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