Assembler optimised crossfeed routine for ARM. Performance improvement is more than double. Should work fine, but watch your ears nevertheless.

git-svn-id: svn://svn.rockbox.org/rockbox/trunk@10608 a1c6a512-1295-4272-9138-f99709370657

apps/SOURCES

@@ -76,6 +76,7 @@ eq.c
 dsp_cf.S
 eq_cf.S	 	
 #elif defined(CPU_ARM) && !defined(SIMULATOR)
+dsp_arm.S
 eq_arm.S
 #endif
 eq_menu.c

apps/dsp_arm.S

@@ -0,0 +1,79 @@
+/***************************************************************************
+ *             __________               __   ___.
+ *   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 }
+

apps/dsp_asm.h

@@ -22,7 +22,7 @@
 #ifndef _DSP_ASM_H
 #define _DSP_ASM_H
 
-#ifdef CPU_COLDFIRE
+#if defined(CPU_COLDFIRE) || defined(CPU_ARM)
 #define DSP_HAVE_ASM_CROSSFEED
 void apply_crossfeed(int32_t* src[], int count);
 #endif