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/***************************************************************************
* __________ __ ___.
* Open \______ \ ____ ____ | | _\_ |__ _______ ___
* Source | _// _ \_/ ___\| |/ /| __ \ / _ \ \/ /
* Jukebox | | ( <_> ) \___| < | \_\ ( <_> > < <
* Firmware |____|_ /\____/ \___ >__|_ \|___ /\____/__/\_ \
* \/ \/ \/ \/ \/
* $Id$
*
* Copyright (C) 2006 Thom Johansen
*
* All files in this archive are subject to the GNU General Public License.
* See the file COPYING in the source tree root for full license agreement.
*
* This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
* KIND, either express or implied.
*
****************************************************************************/
.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
movem.l (11*4+16, %sp), %d6-%d7 | load num. channels and shift count
subq.l #1, %d7 | EMAC gives us one free shift
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
.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
movclr.l %acc0, %d2 | fetch and write result
asl.l %d7, %d2 | restore fixed point format
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, %d6 | 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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