/*************************************************************************** * __________ __ ___. * 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. * ****************************************************************************/ .section .text .global apply_crossfeed apply_crossfeed: @ unfortunately, we ended up in a bit of a register squeeze here, and need @ to keep both the count and the delay line index on the stack :/ stmdb sp!, { r4-r11, lr } @ stack modified regs ldmia r0, { r2-r3 } @ r2 = src[0], r3 = src[1] ldr r0, =crossfeed_data ldmia r0!, { r4-r11 } @ load direct gain and filter data ldr r12, [r0, #13*4*2] @ fetch delay line index add r0, r0, r12, lsl #3 @ r0 = &delay[index][0] stmdb sp!, { r1, r12 } @ stack count and delay line index /* Register usage in loop: * r0 = &delay[index][0], r1 = accumulator high, r2 = src[0], r3 = src[1], * r4 = direct gain, r5-r7 = b0, b1, a1 (filter coefs), * r8-r11 = filter history, r12 = temp, r14 = accumulator low */ .cfloop: smull r14, r1, r6, r8 @ acc = b1*dr[n - 1] smlal r14, r1, r7, r9 @ acc += a1*y_l[n - 1] ldr r8, [r0, #4] @ r8 = dr[n] smlal r14, r1, r5, r8 @ acc += b0*dr[n] mov r9, r1, lsl #1 @ fix format for filter history ldr r12, [r2] @ load left input smlal r14, r1, r4, r12 @ acc += gain*x_l[n] mov r1, r1, lsl #1 @ fix format str r1, [r2], #4 @ save result smull r14, r1, r6, r10 @ acc = b1*dl[n - 1] smlal r14, r1, r7, r11 @ acc += a1*y_r[n - 1] ldr r10, [r0] @ r10 = dl[n] str r12, [r0], #4 @ save left input to delay line smlal r14, r1, r5, r10 @ acc += b0*dl[n] mov r11, r1, lsl #1 @ fix format for filter history ldr r12, [r3] @ load right input smlal r14, r1, r4, r12 @ acc += gain*x_r[n] str r12, [r0], #4 @ save right input to delay line mov r1, r1, lsl #1 @ fix format str r1, [r3], #4 @ save result ldr r12, [sp, #4] @ fetch delay line index from stack add r12, r12, #1 @ increment index cmp r12, #13 @ do we need to wrap to start of delay? moveq r12, #0 @ yes, wrap index to 0 subeq r0, r0, #13*4*2 @ also wrap back delay line ptr to start str r12, [sp, #4] @ stack delay line index again ldr r1, [sp] @ fetch count from stack subs r1, r1, #1 @ are we finished? strne r1, [sp] @ nope, save count back to stack bne .cfloop @ save data back to struct ldr r0, =crossfeed_data + 4*4 stmia r0, { r8-r11 } @ save filter history str r12, [r0, #30*4] @ save delay line index add sp, sp, #8 @ remove temp variables from stack ldmia sp!, { r4-r11, pc }