sound, add ym2612 channel clipping, ladder effect

pico/pico.h

@@ -75,6 +75,7 @@ extern void *p32x_bios_g, *p32x_bios_m, *p32x_bios_s;
 #define POPT_EN_PWM         (1<<21)
 #define POPT_PWM_IRQ_OPT    (1<<22)
 #define POPT_DIS_FM_SSGEG   (1<<23)
+#define POPT_EN_FM_LADDER   (1<<24) //x00 0000
 
 #define PAHW_MCD  (1<<0)
 #define PAHW_32X  (1<<1)

pico/sound/sound.c

@@ -67,7 +67,9 @@ void PsndRerate(int preserve_state)
     ym2612_pack_state();
     memcpy(state, YM2612GetRegs(), 0x204);
   }
-  YM2612Init(Pico.m.pal ? OSC_PAL/7 : OSC_NTSC/7, PicoIn.sndRate, !(PicoIn.opt&POPT_DIS_FM_SSGEG));
+  YM2612Init(Pico.m.pal ? OSC_PAL/7 : OSC_NTSC/7, PicoIn.sndRate,
+        ((PicoIn.opt&POPT_DIS_FM_SSGEG) ? 0 : ST_SSG) |
+        ((PicoIn.opt&POPT_EN_FM_LADDER) ? ST_LADDER : 0));
   if (preserve_state) {
     // feed it back it's own registers, just like after loading state
     memcpy(YM2612GetRegs(), state, 0x204);

pico/sound/ym2612.c

@@ -918,6 +918,14 @@ typedef struct
 
 
 #if !defined(_ASM_YM2612_C) || defined(EXTERNAL_YM2612)
+#include <limits.h>
+static int clip(int n) 
+{
+    unsigned b = 14, s = n < 0;
+    if (s + (n>>(b-1))) n = (int)(s + INT_MAX) >> (8*sizeof(int)-b);
+    return n;
+}
+
 static void chan_render_loop(chan_rend_context *ct, int *buffer, int length)
 {
 	int scounter;					/* sample counter */
@@ -1226,6 +1234,7 @@ static void chan_render_loop(chan_rend_context *ct, int *buffer, int length)
 
 		/* mix sample to output buffer */
 		if (smp) {
+			smp = clip(smp);  /* saturate to 14 bit */
 			if (ct->pack & 1) { /* stereo */
 				if (ct->pack & 0x20) /* L */ /* TODO: check correctness */
 					buffer[scounter*2] += smp;
@@ -1256,12 +1265,21 @@ static void chan_render_prep(void)
 	crct.lfo_inc = ym2612.OPN.lfo_inc;
 }
 
-static void chan_render_finish(void)
+static void chan_render_finish(int *buffer, unsigned short length, int active_chans)
 {
 	ym2612.OPN.eg_cnt = crct.eg_cnt;
 	ym2612.OPN.eg_timer = crct.eg_timer;
 	g_lfo_ampm = crct.pack >> 16; // need_save
 	ym2612.OPN.lfo_cnt = crct.lfo_cnt;
+
+	/* apply ladder effect. NB only works if buffer was empty beforehand! */
+	if (active_chans && (ym2612.OPN.ST.flags & ST_LADDER)) {
+		length <<= crct.pack & 1;
+		while (length--) {
+			*buffer -= (*buffer < 0)*4 << 5;
+			buffer++;
+		}
+	}
 }
 
 static UINT32 update_lfo_phase(FM_SLOT *SLOT, UINT32 block_fnum)
@@ -1835,21 +1853,21 @@ int YM2612UpdateOne_(int *buffer, int length, int stereo, int is_buf_empty)
 	BIT_IF(flags, 1, (ym2612.ssg_mask & 0xf00000) && (ym2612.OPN.ST.flags & 1));
 	if (ym2612.slot_mask & 0xf00000) active_chs |= chan_render(buffer, length, 5, flags|((pan&0xc00)>>6)|(!!ym2612.dacen<<2)) << 5;
 #undef	BIT_IF
-	chan_render_finish();
+	chan_render_finish(buffer, length, active_chs);
 
 	return active_chs; // 1 if buffer updated
 }
 
 
 /* initialize YM2612 emulator */
-void YM2612Init_(int clock, int rate, int ssg)
+void YM2612Init_(int clock, int rate, int flags)
 {
 	memset(&ym2612, 0, sizeof(ym2612));
 	init_tables();
 
 	ym2612.OPN.ST.clock = clock;
 	ym2612.OPN.ST.rate = rate;
-	ym2612.OPN.ST.flags = (ssg ? 1:0);
+	ym2612.OPN.ST.flags = flags;
 
 	OPNSetPres( 6*24 );
 

pico/sound/ym2612.h

@@ -108,6 +108,9 @@ typedef struct
 	INT32	dt_tab[8][32];/* DeTune table       */
 } FM_ST;
 
+#define ST_SSG		1
+#define ST_LADDER	2
+
 /***********************************************************/
 /* OPN unit                                                */
 /***********************************************************/
@@ -162,7 +165,7 @@ typedef struct
 extern YM2612 ym2612;
 #endif
 
-void YM2612Init_(int baseclock, int rate, int ssg);
+void YM2612Init_(int baseclock, int rate, int flags);
 void YM2612ResetChip_(void);
 int  YM2612UpdateOne_(int *buffer, int length, int stereo, int is_buf_empty);
 
@@ -184,9 +187,9 @@ int  YM2612PicoStateLoad2(int *tat, int *tbt);
 #else
 /* GP2X specific */
 #include <platform/gp2x/940ctl.h>
-#define YM2612Init(baseclock,rate,ssg) do { \
+#define YM2612Init(baseclock,rate,flags) do { \
-	if (PicoIn.opt&POPT_EXT_FM) YM2612Init_940(baseclock, rate, ssg); \
+	if (PicoIn.opt&POPT_EXT_FM) YM2612Init_940(baseclock, rate, flags); \
-	else               YM2612Init_(baseclock, rate, ssg); \
+	else               YM2612Init_(baseclock, rate, flags); \
 } while (0)
 #define YM2612ResetChip() do { \
 	if (PicoIn.opt&POPT_EXT_FM) YM2612ResetChip_940(); \

pico/sound/ym2612_arm.S

@@ -924,6 +924,10 @@ crl_algo_done:
     tst     r0, r0
     beq     ctl_sample_skip
     orr     r4, r4, #8              @ have_output
+    lsr     r1, r0, #31             @ clip (saturate) sample to 14 bit
+    adds    r2, r1, r0, asr #13
+    subne   r0, r1, #0x80000001
+    asrne   r0, r0, #18
     tst     r12, #1
     beq     ctl_sample_mono
 

platform/common/menu_pico.c

@@ -561,6 +561,7 @@ static menu_entry e_menu_adv_options[] =
 	mee_onoff     ("Emulate Z80",              MA_OPT2_ENABLE_Z80,    PicoIn.opt, POPT_EN_Z80),
 	mee_onoff     ("Emulate YM2612 (FM)",      MA_OPT2_ENABLE_YM2612, PicoIn.opt, POPT_EN_FM),
 	mee_onoff     ("Disable YM2612 SSG-EG",    MA_OPT2_DISABLE_YM_SSG,PicoIn.opt, POPT_DIS_FM_SSGEG),
+	mee_onoff     ("Enable YM2612 ladder effect",MA_OPT2_DISABLE_YM_LAD,PicoIn.opt, POPT_EN_FM_LADDER),
 	mee_onoff     ("Emulate SN76496 (PSG)",    MA_OPT2_ENABLE_SN76496,PicoIn.opt, POPT_EN_PSG),
 	mee_onoff     ("Emulate Game Gear LCD",    MA_OPT2_ENABLE_GGLCD  ,PicoIn.opt, POPT_EN_GG_LCD),
 	mee_onoff     ("Disable idle loop patching",MA_OPT2_NO_IDLE_LOOPS,PicoIn.opt, POPT_DIS_IDLE_DET),

platform/common/menu_pico.h

@@ -50,6 +50,7 @@ typedef enum
 	MA_OPT2_ENABLE_Z80,
 	MA_OPT2_ENABLE_YM2612,
 	MA_OPT2_DISABLE_YM_SSG,
+	MA_OPT2_DISABLE_YM_LAD,
 	MA_OPT2_ENABLE_SN76496,
 	MA_OPT2_ENABLE_YM2413,
 	MA_OPT2_ENABLE_GGLCD,