Make better use of banked registers in FIQ mode to shrink the iPod FIQ

handler a bit.


git-svn-id: svn://svn.rockbox.org/rockbox/trunk@8920 a1c6a512-1295-4272-9138-f99709370657

2 files changed, 41 insertions, 37 deletions

diff --git a/firmware/crt0.S b/firmware/crt0.S
index 061ffebeab..e7210e6d78 100644
--- a/firmware/crt0.S
+++ b/firmware/crt0.S
@@ -285,6 +285,12 @@ boot_table:
     /* Set up stack for FIQ mode */ 
     msr    cpsr_c, #0xd1
     ldr    sp, =fiq_stack
+#if CONFIG_CPU == PP5020 || CONFIG_CPU == PP5002
+    /* We'll load the banked FIQ mode registers with useful values here.
+       These values will be used in the FIQ handler in pcm_playback.c */
+    ldr    r12, =0x70002800 /* IISCONFIG */
+    ldr    r11, =p
+#endif
     /* Let abort mode use IRQ stack */
     msr    cpsr_c, #0xd7
     ldr    sp, =irq_stack
diff --git a/firmware/pcm_playback.c b/firmware/pcm_playback.c
index 6d60c40fdb..75b3de4f90 100644
--- a/firmware/pcm_playback.c
+++ b/firmware/pcm_playback.c
@@ -330,6 +330,8 @@ static bool pcm_playing;
 static bool pcm_paused;
 static int pcm_freq = 0x6; /* 44.1 is default */
 
+/* NOTE: The order of these two variables is important if you use the iPod
+   assembler optimised fiq handler, so don't change it. */
 unsigned short* p IBSS_ATTR;
 long p_size IBSS_ATTR;
 
@@ -552,36 +554,38 @@ bool pcm_is_playing(void)
 void fiq(void) ICODE_ATTR __attribute__((naked));
 void fiq(void)
 {
+    /* r12 contains IISCONFIG address (set in crt0.S to minimise code in actual
+     * FIQ handler. r11 contains address of p (also set in crt0.S). Most other
+     * addresses we need are generated by using offsets with these two.
+     * r12 + 0x40 is IISFIFO_WR, and r12 + 0x0c is IISFIFO_CFG.
+     * r8 and r9 contains local copies of p_size and p respectively.
+     * r10 is a working register.
+     */
     asm volatile (
-        "ldr r12, =0x70002800 \n\t" /* r12 = IISCONFIG */
-        "ldr r11, [r12]       \n\t"
-        "bic r11, r11, #0x2   \n\t" /* clear interrupt */
-        "str r11, [r12]       \n\t"
-        "ldr r8, =p_size      \n\t"
-        "ldr r9, =p           \n\t"
-        "ldr r8, [r8]         \n\t" /* r8 = p_size */
-        "ldr r9, [r9]         \n\t" /* r9 = p */
-        "ldr r10, =0x70002840 \n\t" /* r10 = IISFIFO_WR */
-        "ldr r11, =0x7000280c \n\t" /* r11 = IISFIFO_CFG */
+        "ldr r10, [r12]       \n\t"
+        "bic r10, r10, #0x2   \n\t" /* clear interrupt */
+        "str r10, [r12]       \n\t"
+        "ldr r8, [r11, #4]    \n\t" /* r8 = p_size */
+        "ldr r9, [r11]        \n\t" /* r9 = p */
     ".loop:                   \n\t"
         "cmp r8, #0           \n\t" /* is p_size 0? */
         "beq .more_data       \n\t" /* if so, ask pcmbuf for more data */
     ".fifo_loop:              \n\t"    
-        "ldr r12, [r11]       \n\t" /* read IISFIFO_CFG to check FIFO status */
-        "and r12, r12, #0x3f0000\n\t"
-        "cmp r12, #0x10000    \n\t" 
+        "ldr r10, [r12, #0x0c]\n\t" /* read IISFIFO_CFG to check FIFO status */
+        "and r10, r10, #0x3f0000\n\t"
+        "cmp r10, #0x10000    \n\t" 
         "bls .fifo_full       \n\t" /* FIFO full, exit */
-        "ldr r12, [r9], #4    \n\t" /* load two samples to r12 */
-        "mov r12, r12, ror #16\n\t" /* put left sample at the top bits */
-        "str r12, [r10]       \n\t" /* write top sample, lower sample ignored */
-        "mov r12, r12, lsl #16\n\t" /* shift lower sample up */
-        "str r12, [r10]       \n\t" /* then write it */
+        "ldr r10, [r9], #4    \n\t" /* load two samples */
+        "mov r10, r10, ror #16\n\t" /* put left sample at the top bits */
+        "str r10, [r12, #0x40]\n\t" /* write top sample, lower sample ignored */
+        "mov r10, r10, lsl #16\n\t" /* shift lower sample up */
+        "str r10, [r12, #0x40]\n\t" /* then write it */
         "subs r8, r8, #4      \n\t" /* check if we have more samples */
         "bne .fifo_loop       \n\t" /* yes, continue */
     ".more_data:              \n\t"
-        "stmdb sp!, { r0-r3, lr}\n\t" /* stack scratch regs and lr */
-        "ldr r0, =p           \n\t" /* load parameters to callback_for_more */
-        "ldr r1, =p_size      \n\t"
+        "stmdb sp!, { r0-r3, r12, lr}\n\t" /* stack scratch regs and lr */
+        "mov r0, r11          \n\t" /* r0 = &p */
+        "add r1, r11, #4      \n\t" /* r1 = &p_size */
         "str r9, [r0]         \n\t" /* save internal copies of variables back */
         "str r8, [r1]         \n\t"
         "ldr r2, =callback_for_more\n\t"
@@ -589,36 +593,30 @@ void fiq(void)
         "cmp r2, #0           \n\t" /* check for null pointer */
         "movne lr, pc         \n\t" /* call callback_for_more */
         "bxne r2              \n\t"
-        "ldmia sp!, { r0-r3, lr}\n\t"
-        "ldr r8, =p_size      \n\t" /* reload p_size and p */
-        "ldr r9, =p           \n\t"
-        "ldr r8, [r8]         \n\t" 
-        "ldr r9, [r9]         \n\t"
+        "ldmia sp!, { r0-r3, r12, lr}\n\t"
+        "ldr r8, [r11, #4]    \n\t" /* reload p_size and p */
+        "ldr r9, [r11]        \n\t"
         "cmp r8, #0           \n\t" /* did we actually get more data? */
         "bne .loop            \n\t" /* yes, continue to try feeding FIFO */
     ".dma_stop:               \n\t" /* no more data, do dma_stop() and exit */
         "ldr r10, =pcm_playing\n\t"
         "strb r8, [r10]       \n\t" /* pcm_playing = false (r8=0, look above) */
-        "ldr r10, =0x70002800 \n\t" /* r10 = IISCONFIG */
-        "ldr r11, [r10]       \n\t" 
-        "bic r11, r11, #0x20000002\n\t" /* disable playback FIFO and IRQ */
-        "str r11, [r10]       \n\t"
+        "ldr r10, [r12]       \n\t" 
+        "bic r10, r10, #0x20000002\n\t" /* disable playback FIFO and IRQ */
+        "str r10, [r12]       \n\t"
         "mrs r10, cpsr        \n\t"
         "orr r10, r10, #0x40  \n\t" /* disable FIQ */
         "msr cpsr_c, r10      \n\t"
         "ldr r10, =pcm_paused \n\t"
         "strb r8, [r10]       \n\t" /* pcm_paused = false */
     ".exit:                   \n\t"
-        "ldr r10, =p_size     \n\t" /* save back p_size and p, then exit */
-        "ldr r11, =p          \n\t"
-        "str r8, [r10]        \n\t"
+        "str r8, [r11, #4]    \n\t"
         "str r9, [r11]        \n\t"
         "subs pc, lr, #4      \n\t" /* FIQ specific return sequence */
     ".fifo_full:              \n\t" /* enable IRQ and exit */
-        "ldr r12, =0x70002800 \n\t" /* r12 = IISCONFIG */
-        "ldr r11, [r12]       \n\t"
-        "orr r11, r11, #0x2   \n\t" /* set interrupt */
-        "str r11, [r12]       \n\t"
+        "ldr r10, [r12]       \n\t"
+        "orr r10, r10, #0x2   \n\t" /* set interrupt */
+        "str r10, [r12]       \n\t"
         "b .exit              \n\t"
     );
 }