[picodrive.git] / pico / sound / sn76496.c

/***************************************************************************\r
\r
  sn76496.c\r
\r
  Routines to emulate the Texas Instruments SN76489 / SN76496 programmable\r
  tone /noise generator. Also known as (or at least compatible with) TMS9919.\r
\r
  Noise emulation is not accurate due to lack of documentation. The noise\r
  generator uses a shift register with a XOR-feedback network, but the exact\r
  layout is unknown. It can be set for either period or white noise; again,\r
  the details are unknown.\r
\r
  28/03/2005 : Sebastien Chevalier\r
  Update th SN76496Write func, according to SN76489 doc found on SMSPower.\r
   - On write with 0x80 set to 0, when LastRegister is other then TONE,\r
   the function is similar than update with 0x80 set to 1\r
***************************************************************************/\r
\r
#ifndef __GNUC__\r
#pragma warning (disable:4244)\r
#endif\r
\r
#include "sn76496.h"\r
\r
#define MAX_OUTPUT 0x4800 // was 0x7fff\r
\r
#define STEP 0x10000\r
\r
\r
/* Formulas for noise generator */\r
/* bit0 = output */\r
\r
/* noise feedback for white noise mode (verified on real SN76489 by John Kortink) */\r
#define FB_WNOISE_T 0x3000	/* (15bits) bit15 = bit1 ^ bit2, TI */\r
#define FB_WNOISE_S 0x9000	/* (16bits) bit16 = bit0 ^ bit3, Sega PSG */\r
\r
/* noise feedback for periodic noise mode */\r
#define FB_PNOISE_T 0x4000	/* 15bit rotate for TI */\r
#define FB_PNOISE_S 0x8000	/* 16bit rotate for Sega PSG */\r
\r
#define FB_WNOISE FB_WNOISE_S	/* Sega */\r
#define FB_PNOISE FB_PNOISE_S\r
\r
\r
struct SN76496\r
{\r
	//sound_stream * Channel;\r
	int SampleRate;\r
	unsigned int UpdateStep;\r
	int VolTable[16];	/* volume table         */\r
	int Register[8];	/* registers */\r
	int LastRegister;	/* last register written */\r
	int Volume[4];		/* volume of voice 0-2 and noise */\r
	unsigned int RNG;	/* noise generator      */\r
	int NoiseFB;		/* noise feedback mask */\r
	int Period[4];\r
	int Count[4];\r
	int Output[4];\r
	int Panning;\r
};\r
\r
static struct SN76496 ono_sn; // one and only SN76496\r
int *sn76496_regs = ono_sn.Register;\r
\r
//static\r
void SN76496Write(int data)\r
{\r
	struct SN76496 *R = &ono_sn;\r
	int n, r, c;\r
\r
	/* update the output buffer before changing the registers */\r
	//stream_update(R->Channel,0);\r
\r
	r = R->LastRegister;\r
	if (data & 0x80)\r
		r = R->LastRegister = (data & 0x70) >> 4;\r
	c = r / 2;\r
\r
	if (!(data & 0x80) && (r == 0 || r == 2 || r == 4))\r
		// data byte (tone only)\r
		R->Register[r] = (R->Register[r] & 0x0f) | ((data & 0x3f) << 4);\r
	else\r
		R->Register[r] = (R->Register[r] & 0x3f0) | (data & 0x0f);\r
\r
	data = R->Register[r];\r
	switch (r)\r
	{\r
		case 0:	/* tone 0 : frequency */\r
		case 2:	/* tone 1 : frequency */\r
		case 4:	/* tone 2 : frequency */\r
			R->Period[c] = R->UpdateStep * data;\r
			if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;\r
			if (R->Count[c] > R->Period[c]) R->Count[c] = R->Period[c];\r
			if (r == 4)\r
			{\r
				/* update noise shift frequency */\r
				if ((R->Register[6] & 0x03) == 0x03)\r
					R->Period[3] = 2 * R->Period[2];\r
			}\r
			break;\r
		case 1:	/* tone 0 : volume */\r
		case 3:	/* tone 1 : volume */\r
		case 5:	/* tone 2 : volume */\r
		case 7:	/* noise  : volume */\r
			R->Volume[c] = R->VolTable[data & 0x0f];\r
			break;\r
		case 6:	/* noise  : frequency, mode */\r
			n = data;\r
			R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;\r
			n &= 3;\r
			/* N/512,N/1024,N/2048,Tone #3 output */\r
			R->Period[3] = 2 * (n == 3 ? R->Period[2] : R->UpdateStep << (4 + n));\r
\r
			/* reset noise shifter */\r
			R->RNG = FB_PNOISE;\r
			R->Output[3] = R->RNG & 1;\r
			break;\r
	}\r
}\r
\r
/*\r
WRITE8_HANDLER( SN76496_0_w ) {	SN76496Write(0,data); }\r
WRITE8_HANDLER( SN76496_1_w ) {	SN76496Write(1,data); }\r
WRITE8_HANDLER( SN76496_2_w ) {	SN76496Write(2,data); }\r
WRITE8_HANDLER( SN76496_3_w ) {	SN76496Write(3,data); }\r
WRITE8_HANDLER( SN76496_4_w ) {	SN76496Write(4,data); }\r
*/\r
\r
//static\r
void SN76496Update(short *buffer, int length, int stereo)\r
{\r
	int i;\r
	struct SN76496 *R = &ono_sn;\r
\r
	while (length > 0)\r
	{\r
		int vol[4];\r
		int left;\r
\r
\r
		/* vol[] keeps track of how long each square wave stays */\r
		/* in the 1 position during the sample period. */\r
		vol[0] = vol[1] = vol[2] = vol[3] = 0;\r
\r
		for (i = 0;i < 3;i++)\r
		{\r
			if (R->Output[i]) vol[i] += R->Count[i];\r
			R->Count[i] -= STEP;\r
			/* Period[i] is the half period of the square wave. Here, in each */\r
			/* loop I add Period[i] twice, so that at the end of the loop the */\r
			/* square wave is in the same status (0 or 1) it was at the start. */\r
			/* vol[i] is also incremented by Period[i], since the wave has been 1 */\r
			/* exactly half of the time, regardless of the initial position. */\r
			/* If we exit the loop in the middle, Output[i] has to be inverted */\r
			/* and vol[i] incremented only if the exit status of the square */\r
			/* wave is 1. */\r
			if (R->Count[i] < -2*R->Period[i] || R->Volume[i] == 0) {\r
				/* Cut off anything above the Nyquist frequency. */\r
				/* It will only create aliasing anyway. This is actually an */\r
				/* ideal lowpass filter with Nyquist corner frequency. */\r
				vol[i] += STEP/2; // mean value\r
				R->Count[i] = R->Output[i] = 0;\r
			}\r
			while (R->Count[i] < 0)\r
			{\r
				R->Count[i] += R->Period[i];\r
				if (R->Count[i] >= 0)\r
				{\r
					R->Output[i] ^= 1;\r
					if (R->Output[i]) vol[i] += R->Period[i];\r
					break;\r
				}\r
				R->Count[i] += R->Period[i];\r
				vol[i] += R->Period[i];\r
			}\r
			if (R->Output[i]) vol[i] -= R->Count[i];\r
		}\r
\r
		left = STEP;\r
		if (R->Output[3]) vol[3] += R->Count[3];\r
		do\r
		{\r
			int nextevent;\r
\r
			if (R->Count[3] < left) nextevent = R->Count[3];\r
			else nextevent = left;\r
\r
			R->Count[3] -= nextevent;\r
			if (R->Count[3] <= 0)\r
			{\r
				R->Output[3] = R->RNG & 1;\r
				R->RNG >>= 1;\r
				if (R->Output[3])\r
				{\r
					R->RNG ^= R->NoiseFB;\r
					vol[3] += R->Period[3];\r
				}\r
				R->Count[3] += R->Period[3];\r
			}\r
\r
			left -= nextevent;\r
		} while (left > 0 && R->Volume[3]);\r
		if (R->Output[3]) vol[3] -= R->Count[3];\r
\r
		length--;\r
		if (R->Panning == 0xff || !stereo) {\r
			unsigned int out =\r
				vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +\r
				vol[2] * R->Volume[2] + vol[3] * R->Volume[3];\r
\r
			if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;\r
\r
			out /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
			*buffer++ += out;\r
			if (stereo) *buffer++ += out;\r
		} else {\r
#define P(n) !!(R->Panning & (1<<(n)))\r
			unsigned int outl =\r
				vol[0] * R->Volume[0] * P(4) + vol[1] * R->Volume[1] * P(5) +\r
				vol[2] * R->Volume[2] * P(6) + vol[3] * R->Volume[3] * P(7);\r
			unsigned int outr =\r
				vol[0] * R->Volume[0] * P(0) + vol[1] * R->Volume[1] * P(1) +\r
				vol[2] * R->Volume[2] * P(2) + vol[3] * R->Volume[3] * P(3);\r
#undef P\r
			if (outl > MAX_OUTPUT * STEP) outl = MAX_OUTPUT * STEP;\r
			if (outr > MAX_OUTPUT * STEP) outr = MAX_OUTPUT * STEP;\r
\r
			outl /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
			outr /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
			*buffer++ += outl;\r
			*buffer++ += outr;\r
		}\r
	}\r
}\r
\r
void SN76496Config(int panning)\r
{\r
	struct SN76496 *R = &ono_sn;\r
	R->Panning = panning & 0xff;\r
}\r
\r
\r
static void SN76496_set_clock(struct SN76496 *R,int clock)\r
{\r
\r
	/* the base clock for the tone generators is the chip clock divided by 16; */\r
	/* for the noise generator, it is clock / 256. */\r
	/* Here we calculate the number of steps which happen during one sample */\r
	/* at the given sample rate. No. of events = sample rate / (clock/16). */\r
	/* STEP is a multiplier used to turn the fraction into a fixed point */\r
	/* number. */\r
	R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;\r
}\r
\r
\r
static void SN76496_set_gain(struct SN76496 *R,int gain)\r
{\r
	int i;\r
	double out;\r
\r
\r
	gain &= 0xff;\r
\r
	/* increase max output basing on gain (0.2 dB per step) */\r
	out = MAX_OUTPUT / 4.0;\r
	while (gain-- > 0)\r
		out *= 1.023292992;	/* = (10 ^ (0.2/20)) */\r
\r
	/* build volume table (2dB per step) */\r
	for (i = 0;i < 15;i++)\r
	{\r
		/* limit volume to avoid clipping */\r
		if (out > MAX_OUTPUT / 4) R->VolTable[i] = MAX_OUTPUT / 4;\r
		else R->VolTable[i] = out;\r
\r
		out /= 1.258925412;	/* = 10 ^ (2/20) = 2dB */\r
	}\r
	R->VolTable[15] = 0;\r
}\r
\r
\r
//static\r
void SN76496_set_clockrate(int clock,int sample_rate)\r
{\r
	struct SN76496 *R = &ono_sn;\r
\r
	R->SampleRate = sample_rate;\r
	SN76496_set_clock(R,clock);\r
}\r
\r
//static\r
int SN76496_init(int clock,int sample_rate)\r
{\r
	struct SN76496 *R = &ono_sn;\r
	int i;\r
\r
	//R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);\r
\r
	SN76496_set_clockrate(clock,sample_rate);\r
\r
	for (i = 0;i < 4;i++) R->Volume[i] = 0;\r
\r
	R->LastRegister = 0;\r
	for (i = 0;i < 8;i+=2)\r
	{\r
		R->Register[i] = 0;\r
		R->Register[i + 1] = 0x0f;	/* volume = 0 */\r
	}\r
\r
	for (i = 0;i < 4;i++)\r
	{\r
		R->Volume[i] = R->Output[i] = R->Count[i] = 0;\r
		R->Period[i] = R->UpdateStep;\r
	}\r
	R->RNG = FB_PNOISE;\r
	R->Output[3] = R->RNG & 1;\r
\r
	// added\r
	SN76496_set_gain(R, 0);\r
	R->Panning = 0xff;\r
\r
	return 0;\r
}\r
\r
Commit	Line	Data
cc68a136	1	/***************************************************************************\r
	2	\r
	3	sn76496.c\r
	4	\r
	5	Routines to emulate the Texas Instruments SN76489 / SN76496 programmable\r
	6	tone /noise generator. Also known as (or at least compatible with) TMS9919.\r
	7	\r
	8	Noise emulation is not accurate due to lack of documentation. The noise\r
	9	generator uses a shift register with a XOR-feedback network, but the exact\r
	10	layout is unknown. It can be set for either period or white noise; again,\r
	11	the details are unknown.\r
	12	\r
	13	28/03/2005 : Sebastien Chevalier\r
	14	Update th SN76496Write func, according to SN76489 doc found on SMSPower.\r
	15	- On write with 0x80 set to 0, when LastRegister is other then TONE,\r
	16	the function is similar than update with 0x80 set to 1\r
	17	***************************************************************************/\r
	18	\r
	19	#ifndef __GNUC__\r
	20	#pragma warning (disable:4244)\r
	21	#endif\r
	22	\r
	23	#include "sn76496.h"\r
	24	\r
af01b1b1	25	#define MAX_OUTPUT 0x4800 // was 0x7fff\r
cc68a136	26	\r
	27	#define STEP 0x10000\r
	28	\r
	29	\r
	30	/* Formulas for noise generator */\r
	31	/* bit0 = output */\r
	32	\r
	33	/* noise feedback for white noise mode (verified on real SN76489 by John Kortink) */\r
af01b1b1	34	#define FB_WNOISE_T 0x3000 /* (15bits) bit15 = bit1 ^ bit2, TI */\r
af01b1b1	35	#define FB_WNOISE_S 0x9000 /* (16bits) bit16 = bit0 ^ bit3, Sega PSG */\r
cc68a136	36	\r
cc68a136	37	/* noise feedback for periodic noise mode */\r
af01b1b1	38	#define FB_PNOISE_T 0x4000 /* 15bit rotate for TI */\r
af01b1b1	39	#define FB_PNOISE_S 0x8000 /* 16bit rotate for Sega PSG */\r
cc68a136	40	\r
af01b1b1	41	#define FB_WNOISE FB_WNOISE_S /* Sega */\r
af01b1b1	42	#define FB_PNOISE FB_PNOISE_S\r
cc68a136	43	\r
	44	\r
	45	struct SN76496\r
	46	{\r
	47	//sound_stream * Channel;\r
	48	int SampleRate;\r
	49	unsigned int UpdateStep;\r
	50	int VolTable[16]; /* volume table */\r
	51	int Register[8]; /* registers */\r
	52	int LastRegister; /* last register written */\r
	53	int Volume[4]; /* volume of voice 0-2 and noise */\r
af01b1b1	54	unsigned int RNG; /* noise generator */\r
cc68a136	55	int NoiseFB; /* noise feedback mask */\r
	56	int Period[4];\r
	57	int Count[4];\r
	58	int Output[4];\r
70efc52d	59	int Panning;\r
cc68a136	60	};\r
	61	\r
	62	static struct SN76496 ono_sn; // one and only SN76496\r
6396f461	63	int *sn76496_regs = ono_sn.Register;\r
cc68a136	64	\r
	65	//static\r
	66	void SN76496Write(int data)\r
	67	{\r
	68	struct SN76496 *R = &ono_sn;\r
5103774f	69	int n, r, c;\r
cc68a136	70	\r
	71	/* update the output buffer before changing the registers */\r
	72	//stream_update(R->Channel,0);\r
	73	\r
5103774f	74	r = R->LastRegister;\r
cc68a136	75	if (data & 0x80)\r
5103774f	76	r = R->LastRegister = (data & 0x70) >> 4;\r
5103774f	77	c = r / 2;\r
cc68a136	78	\r
5103774f	79	if (!(data & 0x80) && (r == 0 \|\| r == 2 \|\| r == 4))\r
	80	// data byte (tone only)\r
	81	R->Register[r] = (R->Register[r] & 0x0f) \| ((data & 0x3f) << 4);\r
cc68a136	82	else\r
5103774f	83	R->Register[r] = (R->Register[r] & 0x3f0) \| (data & 0x0f);\r
cc68a136	84	\r
5103774f	85	data = R->Register[r];\r
	86	switch (r)\r
	87	{\r
	88	case 0: /* tone 0 : frequency */\r
	89	case 2: /* tone 1 : frequency */\r
	90	case 4: /* tone 2 : frequency */\r
	91	R->Period[c] = R->UpdateStep * data;\r
	92	if (R->Period[c] == 0) R->Period[c] = R->UpdateStep;\r
6985cdd8	93	if (R->Count[c] > R->Period[c]) R->Count[c] = R->Period[c];\r
5103774f	94	if (r == 4)\r
	95	{\r
	96	/* update noise shift frequency */\r
	97	if ((R->Register[6] & 0x03) == 0x03)\r
	98	R->Period[3] = 2 * R->Period[2];\r
	99	}\r
	100	break;\r
	101	case 1: /* tone 0 : volume */\r
	102	case 3: /* tone 1 : volume */\r
	103	case 5: /* tone 2 : volume */\r
	104	case 7: /* noise : volume */\r
	105	R->Volume[c] = R->VolTable[data & 0x0f];\r
	106	break;\r
	107	case 6: /* noise : frequency, mode */\r
	108	n = data;\r
	109	R->NoiseFB = (n & 4) ? FB_WNOISE : FB_PNOISE;\r
	110	n &= 3;\r
	111	/* N/512,N/1024,N/2048,Tone #3 output */\r
fa0c5b45	112	R->Period[3] = 2 * (n == 3 ? R->Period[2] : R->UpdateStep << (4 + n));\r
5103774f	113	\r
5103774f	114	/* reset noise shifter */\r
af01b1b1	115	R->RNG = FB_PNOISE;\r
5103774f	116	R->Output[3] = R->RNG & 1;\r
5103774f	117	break;\r
cc68a136	118	}\r
	119	}\r
	120	\r
	121	/*\r
	122	WRITE8_HANDLER( SN76496_0_w ) { SN76496Write(0,data); }\r
	123	WRITE8_HANDLER( SN76496_1_w ) { SN76496Write(1,data); }\r
	124	WRITE8_HANDLER( SN76496_2_w ) { SN76496Write(2,data); }\r
	125	WRITE8_HANDLER( SN76496_3_w ) { SN76496Write(3,data); }\r
	126	WRITE8_HANDLER( SN76496_4_w ) { SN76496Write(4,data); }\r
	127	*/\r
	128	\r
	129	//static\r
4f265db7	130	void SN76496Update(short *buffer, int length, int stereo)\r
cc68a136	131	{\r
	132	int i;\r
	133	struct SN76496 *R = &ono_sn;\r
	134	\r
cc68a136	135	while (length > 0)\r
	136	{\r
	137	int vol[4];\r
cc68a136	138	int left;\r
	139	\r
	140	\r
	141	/* vol[] keeps track of how long each square wave stays */\r
	142	/* in the 1 position during the sample period. */\r
	143	vol[0] = vol[1] = vol[2] = vol[3] = 0;\r
	144	\r
	145	for (i = 0;i < 3;i++)\r
	146	{\r
	147	if (R->Output[i]) vol[i] += R->Count[i];\r
	148	R->Count[i] -= STEP;\r
	149	/* Period[i] is the half period of the square wave. Here, in each */\r
	150	/* loop I add Period[i] twice, so that at the end of the loop the */\r
	151	/* square wave is in the same status (0 or 1) it was at the start. */\r
	152	/* vol[i] is also incremented by Period[i], since the wave has been 1 */\r
	153	/* exactly half of the time, regardless of the initial position. */\r
	154	/* If we exit the loop in the middle, Output[i] has to be inverted */\r
	155	/* and vol[i] incremented only if the exit status of the square */\r
	156	/* wave is 1. */\r
fa0c5b45	157	if (R->Count[i] < -2*R->Period[i] \|\| R->Volume[i] == 0) {\r
6985cdd8	158	/* Cut off anything above the Nyquist frequency. */\r
	159	/* It will only create aliasing anyway. This is actually an */\r
	160	/* ideal lowpass filter with Nyquist corner frequency. */\r
af01b1b1	161	vol[i] += STEP/2; // mean value\r
	162	R->Count[i] = R->Output[i] = 0;\r
	163	}\r
	164	while (R->Count[i] < 0)\r
cc68a136	165	{\r
af01b1b1	166	R->Count[i] += R->Period[i];\r
af01b1b1	167	if (R->Count[i] >= 0)\r
cc68a136	168	{\r
	169	R->Output[i] ^= 1;\r
	170	if (R->Output[i]) vol[i] += R->Period[i];\r
	171	break;\r
	172	}\r
	173	R->Count[i] += R->Period[i];\r
	174	vol[i] += R->Period[i];\r
	175	}\r
	176	if (R->Output[i]) vol[i] -= R->Count[i];\r
	177	}\r
	178	\r
	179	left = STEP;\r
af01b1b1	180	if (R->Output[3]) vol[3] += R->Count[3];\r
cc68a136	181	do\r
	182	{\r
	183	int nextevent;\r
	184	\r
	185	if (R->Count[3] < left) nextevent = R->Count[3];\r
	186	else nextevent = left;\r
	187	\r
cc68a136	188	R->Count[3] -= nextevent;\r
	189	if (R->Count[3] <= 0)\r
	190	{\r
cc68a136	191	R->Output[3] = R->RNG & 1;\r
af01b1b1	192	R->RNG >>= 1;\r
	193	if (R->Output[3])\r
	194	{\r
	195	R->RNG ^= R->NoiseFB;\r
	196	vol[3] += R->Period[3];\r
	197	}\r
cc68a136	198	R->Count[3] += R->Period[3];\r
cc68a136	199	}\r
cc68a136	200	\r
cc68a136	201	left -= nextevent;\r
fa0c5b45	202	} while (left > 0 && R->Volume[3]);\r
af01b1b1	203	if (R->Output[3]) vol[3] -= R->Count[3];\r
cc68a136	204	\r
70efc52d	205	length--;\r
	206	if (R->Panning == 0xff \|\| !stereo) {\r
	207	unsigned int out =\r
	208	vol[0] * R->Volume[0] + vol[1] * R->Volume[1] +\r
cc68a136	209	vol[2] * R->Volume[2] + vol[3] * R->Volume[3];\r
cc68a136	210	\r
70efc52d	211	if (out > MAX_OUTPUT * STEP) out = MAX_OUTPUT * STEP;\r
	212	\r
	213	out /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
	214	*buffer++ += out;\r
	215	if (stereo) *buffer++ += out;\r
	216	} else {\r
	217	#define P(n) !!(R->Panning & (1<<(n)))\r
	218	unsigned int outl =\r
	219	vol[0] * R->Volume[0] * P(4) + vol[1] * R->Volume[1] * P(5) +\r
	220	vol[2] * R->Volume[2] * P(6) + vol[3] * R->Volume[3] * P(7);\r
	221	unsigned int outr =\r
	222	vol[0] * R->Volume[0] * P(0) + vol[1] * R->Volume[1] * P(1) +\r
	223	vol[2] * R->Volume[2] * P(2) + vol[3] * R->Volume[3] * P(3);\r
	224	#undef P\r
	225	if (outl > MAX_OUTPUT * STEP) outl = MAX_OUTPUT * STEP;\r
	226	if (outr > MAX_OUTPUT * STEP) outr = MAX_OUTPUT * STEP;\r
	227	\r
	228	outl /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
	229	outr /= STEP; // will be optimized to shift; max 0x4800 = 18432\r
	230	*buffer++ += outl;\r
	231	*buffer++ += outr;\r
	232	}\r
cc68a136	233	}\r
	234	}\r
	235	\r
70efc52d	236	void SN76496Config(int panning)\r
	237	{\r
	238	struct SN76496 *R = &ono_sn;\r
	239	R->Panning = panning & 0xff;\r
	240	}\r
	241	\r
cc68a136	242	\r
	243	static void SN76496_set_clock(struct SN76496 *R,int clock)\r
	244	{\r
	245	\r
	246	/* the base clock for the tone generators is the chip clock divided by 16; */\r
	247	/* for the noise generator, it is clock / 256. */\r
	248	/* Here we calculate the number of steps which happen during one sample */\r
	249	/* at the given sample rate. No. of events = sample rate / (clock/16). */\r
	250	/* STEP is a multiplier used to turn the fraction into a fixed point */\r
	251	/* number. */\r
	252	R->UpdateStep = ((double)STEP * R->SampleRate * 16) / clock;\r
	253	}\r
	254	\r
	255	\r
	256	static void SN76496_set_gain(struct SN76496 *R,int gain)\r
	257	{\r
	258	int i;\r
	259	double out;\r
	260	\r
	261	\r
	262	gain &= 0xff;\r
	263	\r
	264	/* increase max output basing on gain (0.2 dB per step) */\r
af01b1b1	265	out = MAX_OUTPUT / 4.0;\r
cc68a136	266	while (gain-- > 0)\r
	267	out = 1.023292992; / = (10 ^ (0.2/20)) */\r
	268	\r
	269	/* build volume table (2dB per step) */\r
	270	for (i = 0;i < 15;i++)\r
	271	{\r
	272	/* limit volume to avoid clipping */\r
af01b1b1	273	if (out > MAX_OUTPUT / 4) R->VolTable[i] = MAX_OUTPUT / 4;\r
cc68a136	274	else R->VolTable[i] = out;\r
	275	\r
	276	out /= 1.258925412; /* = 10 ^ (2/20) = 2dB */\r
	277	}\r
	278	R->VolTable[15] = 0;\r
	279	}\r
	280	\r
	281	\r
864ac1d6	282	//static\r
	283	void SN76496_set_clockrate(int clock,int sample_rate)\r
	284	{\r
	285	struct SN76496 *R = &ono_sn;\r
	286	\r
	287	R->SampleRate = sample_rate;\r
	288	SN76496_set_clock(R,clock);\r
	289	}\r
	290	\r
cc68a136	291	//static\r
	292	int SN76496_init(int clock,int sample_rate)\r
	293	{\r
	294	struct SN76496 *R = &ono_sn;\r
	295	int i;\r
	296	\r
	297	//R->Channel = stream_create(0,1, sample_rate,R,SN76496Update);\r
cc68a136	298	\r
864ac1d6	299	SN76496_set_clockrate(clock,sample_rate);\r
cc68a136	300	\r
	301	for (i = 0;i < 4;i++) R->Volume[i] = 0;\r
	302	\r
	303	R->LastRegister = 0;\r
	304	for (i = 0;i < 8;i+=2)\r
	305	{\r
	306	R->Register[i] = 0;\r
	307	R->Register[i + 1] = 0x0f; /* volume = 0 */\r
	308	}\r
	309	\r
	310	for (i = 0;i < 4;i++)\r
	311	{\r
af01b1b1	312	R->Volume[i] = R->Output[i] = R->Count[i] = 0;\r
af01b1b1	313	R->Period[i] = R->UpdateStep;\r
cc68a136	314	}\r
af01b1b1	315	R->RNG = FB_PNOISE;\r
cc68a136	316	R->Output[3] = R->RNG & 1;\r
	317	\r
	318	// added\r
	319	SN76496_set_gain(R, 0);\r
70efc52d	320	R->Panning = 0xff;\r
cc68a136	321	\r
	322	return 0;\r
	323	}\r
	324	\r