Use PWM on the 32X for YM2612 DAC samples playback

viciious · Jun 12, 2024 · 85ddf8b · 85ddf8b
1 parent 749cd7c
commit 85ddf8b
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Showing 2 changed files with 91 additions and 2 deletions.
diff --git a/src-md/crt0.s b/src-md/crt0.s
@@ -67,6 +67,9 @@
         .equ STRM_LENLL,  0xFFFF
 
         .equ MARS_FRAMEBUFFER, 0x840200 /* 32X frame buffer */
+        .equ MARS_PWM_CTRL,    0xA15130
+        .equ MARS_PWM_CYCLE,   0xA15132
+        .equ MARS_PWM_MONO,    0xA15138
 
         .equ COL_STORE, 0x600800    /* WORD RAM + 2K */
 
@@ -403,6 +406,32 @@ main_loop_start:
         move.l  #0,0xA15120         /* let Master SH2 run */
 
 main_loop:
+        tst.w   dac_len
+        beq.b   main_loop_chk_ctrl  /* done/none, silence */
+
+        move.l  dac_samples,a0
+        move.w  dac_center,d1
+        move.w  dac_len,d2
+0:
+        tst.w   MARS_PWM_MONO       /* check mono reg status */
+        bmi.b   01f                 /* full */
+
+        move.b  (a0)+,d0            /* fetch dac sample */
+        eori.b  #0x80,d0            /* unsigned to signed */
+        ext.w   d0                  /* sign extend to word */
+        add.w   d0,d0               /* *2 */
+|       add.w   d0,d0               /* *4 */
+        add.w   d1,d0
+        move.w  d0,MARS_PWM_MONO
+
+        subq.w  #1,d2
+        bne.b   0b                  /* not done */
+        move.w  dac_center,MARS_PWM_MONO /* silence */
+01:
+        move.w  d2,dac_len
+        move.l  a0,dac_samples
+
+main_loop_chk_ctrl:
         tst.b   need_ctrl_int
         beq.b   main_loop_bump_fm
         move.b  #0,need_ctrl_int
@@ -3082,6 +3111,9 @@ vgm_ptr:
 vgm_size:
         dc.l    0
         .global    fm_rep
+dac_samples:
+        .global    dac_samples
+        dc.l    0
 fm_rep:
         dc.w    0
         .global    fm_idx
@@ -3092,6 +3124,16 @@ fm_stream:
 fm_stream_freq:
         dc.w    0
 
+dac_freq:
+        .global    dac_freq
+        dc.w    0
+dac_len:
+        .global    dac_len
+        dc.w    0
+dac_center:
+        .global    dac_center
+        dc.w    0
+
 rf5c68_start:
         dc.w    0
 rf5c68_freq_incr:

diff --git a/src-md/vgm.c b/src-md/vgm.c
@@ -11,12 +11,18 @@
 #define VGM_LZSS_BUF_SIZE   0x8000
 #define VGM_MAX_SIZE        0x18000
 
+#define VGM_USE_PWM_FOR_DAC
+
 #define MD_WORDRAM          (void*)0x600000
 #define MCD_WORDRAM         (void*)0x0C0000
 
 #define MD_WORDRAM_VGM_PTR  (MD_WORDRAM+VGM_WORDRAM_OFS)
 #define MCD_WORDRAM_VGM_PTR (MCD_WORDRAM+VGM_WORDRAM_OFS)
 
+#define MARS_PWM_CTRL       (*(volatile unsigned short *)0xA15130)
+#define MARS_PWM_CYCLE      (*(volatile unsigned short *)0xA15132)
+#define MARS_PWM_MONO       (*(volatile unsigned short *)0xA15138)
+
 static lzss_state_t vgm_lzss = { 0 };
 static int rf5c68_dataofs;
 static int rf5c68_datalen;
@@ -90,9 +96,9 @@ int vgm_setup(void* fm_ptr)
     if ((fm_ptr >= MD_WORDRAM_VGM_PTR && fm_ptr < MD_WORDRAM+0x20000) && pcm_baseoffs) {
         pcm_baseoffs += (fm_ptr - MD_WORDRAM_VGM_PTR);
     }
-    if (rf5c68_dataofs)
+    if (rf5c68_dataofs) {
         rf5c68_dataofs += pcm_baseoffs;
-
+    }
 
     // convert RF5C68's signed PCM samples to uchar because that's what the driver expects
     if ((fm_ptr >= MD_WORDRAM_VGM_PTR && fm_ptr < MD_WORDRAM+0x20000) && rf5c68_dataofs) {
@@ -170,24 +176,65 @@ void *vgm_cache_scd(const char *name, int offset, int length)
     return ptr;
 }
 
+#ifndef VGM_USE_PWM_FOR_DAC
 void vgm_play_scd_samples(int offset, int length, int freq)
 {
     void *ptr = (char *)MCD_WORDRAM_VGM_PTR + pcm_baseoffs + offset;
 
     scd_queue_setptr_buf(VGM_MCD_BUFFER_ID, ptr, length);
     scd_queue_play_src(VGM_MCD_SOURCE_ID, VGM_MCD_BUFFER_ID, freq, 128, 255, 0);
 }
+#endif
 
 void vgm_play_samples(int offset, int length, int freq)
 {
+#ifdef VGM_USE_PWM_FOR_DAC
+    extern uint16_t dac_freq, dac_len, dac_center;
+    extern void *dac_samples;
+
+    if (!cd_ok)
+        return;
+
+    if (dac_freq != freq)
+    {
+        int cycle;
+        int ntsc = 1;
+
+        dac_freq = freq;
+        if (ntsc)
+            cycle = (((23011361 << 1)/dac_freq + 1) >> 1) + 1; // for NTSC clock
+        else
+            cycle = (((22801467 << 1)/dac_freq + 1) >> 1) + 1; // for PAL clock
+        dac_center = cycle >> 1;
+
+        MARS_PWM_CTRL = 0x05; // left and right
+        MARS_PWM_CYCLE = cycle;
+        MARS_PWM_MONO = dac_center;
+        MARS_PWM_MONO = dac_center;
+        MARS_PWM_MONO = dac_center;
+    }
+
+    dac_samples = (char *)MD_WORDRAM_VGM_PTR + pcm_baseoffs + offset;
+    dac_len = length;
+#else
     if (cd_ok)
         vgm_play_scd_samples(offset, length, freq);
+#endif
 }
 
 void vgm_stop_samples(void)
 {
+#ifdef VGM_USE_PWM_FOR_DAC
+    extern uint16_t dac_len, dac_center;
+
+    dac_len = 0;
+    MARS_PWM_MONO = dac_center;
+    MARS_PWM_MONO = dac_center;
+    MARS_PWM_MONO = dac_center;
+#else
     if (cd_ok)
         scd_queue_stop_src(VGM_MCD_SOURCE_ID);
+#endif
 }
 
 void vgm_play_rf5c68_samples(int offset, int loopstart, int incr, int vol)