#368 GBA sound mixing optimization

src/fixed/common.h

@@ -2839,7 +2839,7 @@ int32 doTutorial(ItemObj* lara, int32 track);
 void sndInit();
 void sndInitSamples();
 void sndFreeSamples();
-void sndFill(uint8* buffer, int32 count);
+void sndFill(int8* buffer, int32 count);
 void* sndPlaySample(int32 index, int32 volume, int32 pitch, int32 mode);
 void sndPlayTrack(int32 track);
 bool sndTrackIsPlaying();

src/platform/gba/asm/common_asm.inc

@@ -94,6 +94,9 @@
 .equ MIN_INT32,     0x80000000
 .equ MAX_INT32,     0x7FFFFFFF
 
+.equ SND_VOL_SHIFT,     6
+.equ SND_FIXED_SHIFT,   8
+
 // res = divTable[x] (uint16)
 .macro divLUT res, x
     add \res, \x, #DIVLUT_ADDR

src/platform/gba/asm/sndIMA.s

@@ -10,9 +10,8 @@ stepLUT .req r6
 step    .req r7
 n       .req r8
 index   .req r9
-outA    .req r12
-outB    .req lr
-tmp     .req outB
+out     .req r12
+tmp     .req out
 
 IMA_STEP_SIZE = 88
 
@@ -33,12 +32,12 @@ IMA_STEP_SIZE = 88
     cmpgt idx, #IMA_STEP_SIZE
     movgt idx, #IMA_STEP_SIZE
 
-    mov \out, smp, asr #2
+    mov \out, smp, asr #(2 + SND_VOL_SHIFT)
 .endm
 
 .global sndIMA_asm
 sndIMA_asm:
-    stmfd sp!, {r4-r9, lr}
+    stmfd sp!, {r4-r9}
 
     ldmia state, {smp, idx}
 
@@ -47,18 +46,18 @@ sndIMA_asm:
 .loop:
     ldrb n, [data], #1
 
-    decode4 n, outA
-
-    mov n, n, lsr #4
+    decode4 n, out
+    strb out, [buffer], #1
 
-    decode4 n, outB
+    mov n, n, lsr #4
 
-    stmia buffer!, {outA, outB}
+    decode4 n, out
+    strb out, [buffer], #1
 
     subs size, #1
     bne .loop
 
     stmia state, {smp, idx}
 
-    ldmfd sp!, {r4-r9, lr}
+    ldmfd sp!, {r4-r9}
     bx lr

src/platform/gba/asm/sndPCM.s

@@ -13,34 +13,53 @@ ampB    .req r8
 outA    .req r9
 outB    .req r12
 last    .req count
-tmp     .req outB
+tmpSP   .req outB
+tmp     .req ampA
+
+.macro clamp amp
+    // Vanadium's clamp trick (-128..127)
+    mov tmp, \amp, asr #31  // tmp <- 0xffffffff
+    cmp tmp, \amp, asr #7  // not equal
+    eorne \amp, tmp, #0x7F  // amp <- 0xffffff80
+.endm
 
 .global sndPCM_asm
 sndPCM_asm:
-    mov tmp, sp
+    mov tmpSP, sp
     stmfd sp!, {r4-r9}
 
-    ldmia tmp, {data, buffer, count}
+    ldmia tmpSP, {data, buffer, count}
 
     mla last, inc, count, pos
     cmp last, size
     movgt last, size
 
 .loop:
-    ldrb ampA, [data, pos, lsr #8]
+    ldrb ampA, [data, pos, lsr #SND_FIXED_SHIFT]
     add pos, pos, inc
-    ldrb ampB, [data, pos, lsr #8]
+    ldrb ampB, [data, pos, lsr #SND_FIXED_SHIFT]
     add pos, pos, inc
-    cmp pos, last
 
+    // can't use signed PCM because of LDRSB restrictions
     sub ampA, ampA, #128
     sub ampB, ampB, #128
 
-    ldmia buffer, {outA, outB}
-    mla outA, volume, ampA, outA
-    mla outB, volume, ampB, outB
-    stmia buffer!, {outA, outB}
+    mul ampA, volume
+    mul ampB, volume
+
+    ldrsb outA, [buffer, #0]
+    ldrsb outB, [buffer, #1]
+
+    add outA, ampA, asr #SND_VOL_SHIFT
+    add outB, ampB, asr #SND_VOL_SHIFT
 
+    clamp outA
+    clamp outB
+
+    strb outA, [buffer], #1
+    strb outB, [buffer], #1
+
+    cmp pos, last
     blt .loop
 
 .done:

src/platform/gba/main.cpp

@@ -95,7 +95,7 @@ bool osLoadGame()
 
 void osJoyVibrate(int32 index, int32 L, int32 R) {}
 
-extern uint8 soundBuffer[2 * SND_SAMPLES + 32]; // 32 bytes of silence for DMA overrun while interrupt
+extern int8 soundBuffer[2 * SND_SAMPLES + 32]; // 32 bytes of silence for DMA overrun while interrupt
 
 HWAVEOUT waveOut;
 WAVEFORMATEX waveFmt = { WAVE_FORMAT_PCM, 1, SND_OUTPUT_FREQ, SND_OUTPUT_FREQ, 1, 8, sizeof(waveFmt) };
@@ -123,7 +123,7 @@ void soundFill()
 {
     WAVEHDR *waveHdr = waveBuf + curSoundBuffer;
     waveOutUnprepareHeader(waveOut, waveHdr, sizeof(WAVEHDR));
-    sndFill((uint8*)waveHdr->lpData, SND_SAMPLES);
+    sndFill((int8*)waveHdr->lpData, SND_SAMPLES);
     waveOutPrepareHeader(waveOut, waveHdr, sizeof(WAVEHDR));
     waveOutWrite(waveOut, waveHdr, sizeof(WAVEHDR));
     curSoundBuffer ^= 1;
@@ -482,7 +482,7 @@ void updateInput()
     if (key_is_down(KEY_SELECT))  keys |= IK_SELECT;
 }
 
-extern uint8* soundBuffer;
+extern int8 soundBuffer[2 * SND_SAMPLES + 32];
 
 void soundInit()
 {

src/platform/gba/sound.cpp

@@ -17,30 +17,23 @@ int32 IMA_STEP[] = { // IWRAM !
 
 #if defined(__GBA__) && defined(USE_ASM)
     extern const uint8_t TRACKS_IMA[];
-    // the sound mixer works during VBlank, this is a great opportunity for exclusive access to VRAM without any perf penalties
-    // so we use part of offscreen VRAM as sound buffers (704 + 384 = 1088 bytes)
-    int32* mixerBuffer = (int32*)(MEM_VRAM + VRAM_PAGE_SIZE + FRAME_WIDTH * FRAME_HEIGHT);
-    uint8* soundBuffer = (uint8*)(MEM_VRAM + VRAM_PAGE_SIZE + FRAME_WIDTH * FRAME_HEIGHT + SND_SAMPLES * sizeof(int32)); // use 2k of VRAM after the first frame buffer as sound buffer
 #else
     extern const void* TRACKS_IMA;
-    int32 mixerBuffer[SND_SAMPLES];
-    uint8 soundBuffer[2 * SND_SAMPLES + 32]; // 32 bytes of silence for DMA overrun while interrupt
 #endif
 
+int8 soundBuffer[2 * SND_SAMPLES + 32]; // 32 bytes of silence for DMA overrun while interrupt
+
 #ifdef USE_ASM
     #define sndIMA      sndIMA_asm
     #define sndPCM      sndPCM_asm
-    #define sndWrite    sndWrite_asm
 
     extern "C" {
-        void sndIMA_asm(IMA_STATE &state, int32* buffer, const uint8* data, int32 size);
-        int32 sndPCM_asm(int32 pos, int32 inc, int32 size, int32 volume, const uint8* data, int32* buffer, int32 count);
-        void sndWrite_asm(uint8* buffer, int32 count, int32 *data);
+        void sndIMA_asm(IMA_STATE &state, int8* buffer, const uint8* data, int32 size);
+        int32 sndPCM_asm(int32 pos, int32 inc, int32 size, int32 volume, const uint8* data, int8* buffer, int32 count);
     }
 #else
     #define sndIMA      sndIMA_c
     #define sndPCM      sndPCM_c
-    #define sndWrite    sndWrite_c
 
 #define DECODE_IMA_4(n)\
     step = IMA_STEP[idx];\
@@ -56,14 +49,16 @@ int32 IMA_STEP[] = { // IWRAM !
     } else {\
         smp += step >> 3;\
     }\
-    *buffer++ = smp >> (16 - (8 + SND_VOL_SHIFT));
+    amp = smp >> 8;\
+    *buffer++ = SND_ENCODE(X_CLAMP(amp, SND_MIN, SND_MAX));
 
-void sndIMA_c(IMA_STATE &state, int32* buffer, const uint8* data, int32 size)
+void sndIMA_c(IMA_STATE &state, int8* buffer, const uint8* data, int32 size)
 {
     uint32 step, index;
 
     int32 smp = state.smp;
     int32 idx = state.idx;
+    int32 amp;
 
     for (int32 i = 0; i < size; i++)
     {
@@ -77,7 +72,7 @@ void sndIMA_c(IMA_STATE &state, int32* buffer, const uint8* data, int32 size)
     state.idx = idx;
 }
 
-int32 sndPCM_c(int32 pos, int32 inc, int32 size, int32 volume, const uint8* data, int32* buffer, int32 count)
+int32 sndPCM_c(int32 pos, int32 inc, int32 size, int32 volume, const uint8* data, int8* buffer, int32 count)
 {
     int32 last = pos + count * inc;
     if (last > size) {
@@ -86,32 +81,23 @@ int32 sndPCM_c(int32 pos, int32 inc, int32 size, int32 volume, const uint8* data
 
     while (pos < last)
     {
-        *buffer++ += SND_DECODE(data[pos >> SND_FIXED_SHIFT]) * volume;
+        int32 amp = SND_DECODE(*buffer) + ((SND_DECODE(data[pos >> SND_FIXED_SHIFT]) * volume) >> SND_VOL_SHIFT);
+        *buffer++ = SND_ENCODE(X_CLAMP(amp, SND_MIN, SND_MAX));
         pos += inc;
     }
 
     return pos;
 }
-
-void sndWrite_c(uint8* buffer, int32 count, int32 *data)
-{
-    for (int32 i = 0; i < count; i++)
-    {
-        int32 samp = X_CLAMP(data[i] >> SND_VOL_SHIFT, SND_MIN, SND_MAX);
-        buffer[i] = SND_ENCODE(samp);
-    }
-}
 #endif
 
-
 struct Music
 {
     const uint8*  data;
     int32         size;
     int32         pos;
     IMA_STATE     state;
 
-    void fill(int32* buffer, int32 count)
+    void fill(int8* buffer, int32 count)
     {
         int32 len = X_MIN(size - pos, count >> 1);
 
@@ -135,7 +121,7 @@ struct Sample
     int32        volume;
     const uint8* data;
 
-    void fill(int32* buffer, int32 count)
+    void fill(int8* buffer, int32 count)
     {
         pos = sndPCM(pos, inc, size, volume, data, buffer, count);
 
@@ -276,7 +262,7 @@ void sndStop()
     music.data = NULL;
 }
 
-void sndFill(uint8* buffer, int32 count)
+void sndFill(int8* buffer, int32 count)
 {
 #ifdef PROFILE_SOUNDTIME
     PROFILE_CLEAR();
@@ -290,22 +276,20 @@ void sndFill(uint8* buffer, int32 count)
     }
 
     if (music.data) {
-        music.fill(mixerBuffer, count);
+        music.fill(buffer, count);
     } else {
-        dmaFill(mixerBuffer, 0, SND_SAMPLES * sizeof(int32));
+        dmaFill(buffer, 0, SND_SAMPLES * sizeof(buffer[0]));
     }
 
     int32 ch = channelsCount;
     while (ch--)
     {
         Sample* sample = channels + ch;
 
-        sample->fill(mixerBuffer, count);
+        sample->fill(buffer, count);
 
         if (!sample->data) {
             channels[ch] = channels[--channelsCount];
         }
     }
-
-    sndWrite(buffer, count, mixerBuffer);
 }