ymz280b.c

十七种模拟器源代码 非常有用的作课程设计不可缺少的

/**********************************************************************************************
 *
 *   Yamaha YMZ280B driver
 *   by Aaron Giles
 *
 **********************************************************************************************/


#include <stdio.h>
#include <stdlib.h>
#include <math.h>

#include "driver.h"
#include "sasound.h"
#include "savegame.h"
#include "loadroms.h"

#define MAX_SAMPLE_CHUNK	10000

#define FRAC_BITS			14
#define FRAC_ONE			(1 << FRAC_BITS)
#define FRAC_MASK			(FRAC_ONE - 1)


/* struct describing a single playing ADPCM voice */
struct YMZ280BVoice
{
	UINT8 playing;			/* 1 if we are actively playing */

	UINT8 keyon;			/* 1 if the key is on */
	UINT8 looping;			/* 1 if looping is enabled */
	UINT8 mode;				/* current playback mode */
	UINT16 fnum;			/* frequency */
	UINT8 level;			/* output level */
	UINT8 pan;				/* panning */

	UINT32 start;			/* start address, in nibbles */
	UINT32 stop;			/* stop address, in nibbles */
	UINT32 loop_start;		/* loop start address, in nibbles */
	UINT32 loop_end;		/* loop end address, in nibbles */
	UINT32 position;		/* current position, in nibbles */

	INT32 signal;			/* current ADPCM signal */
	INT32 step;				/* current ADPCM step */

	INT32 loop_signal;		/* signal at loop start */
	INT32 loop_step;		/* step at loop start */
	UINT32 loop_count;		/* number of loops so far */

	INT32 output_left;		/* output volume (left) */
	INT32 output_right;		/* output volume (right) */
	INT32 output_step;		/* step value for frequency conversion */
	INT32 output_pos;		/* current fractional position */
	INT16 last_sample;		/* last sample output */
	INT16 curr_sample;		/* current sample target */
};

struct YMZ280BChip
{
	int stream;						/* which stream are we using */
	UINT8 *region_base;				/* pointer to the base of the region */
	UINT8 current_register;			/* currently accessible register */
	UINT8 status_register;			/* current status register */
	UINT8 irq_state;				/* current IRQ state */
	UINT8 irq_mask;					/* current IRQ mask */
	UINT8 irq_enable;				/* current IRQ enable */
	UINT8 keyon_enable;				/* key on enable */
	double master_clock;			/* master clock frequency */
	void (*irq_callback)(int);		/* IRQ callback */
	struct YMZ280BVoice	voice[8];	/* the 8 voices */
};

static struct YMZ280BChip ymz280b[MAX_YMZ280B];
static INT32 *accumulator;
static INT16 *scratch;

/* step size index shift table */
static int index_scale[8] = { 0x0e6, 0x0e6, 0x0e6, 0x0e6, 0x133, 0x199, 0x200, 0x266 };

/* lookup table for the precomputed difference */
static int diff_lookup[16];



INLINE void update_irq_state(struct YMZ280BChip *chip)
{
	int irq_bits = chip->status_register & chip->irq_mask;

	/* always off if the enable is off */
	if (!chip->irq_enable)
		irq_bits = 0;

	/* update the state if changed */
	if (irq_bits && !chip->irq_state)
	{
		chip->irq_state = 1;
		if (chip->irq_callback)
			(*chip->irq_callback)(1);
	}
	else if (!irq_bits && chip->irq_state)
	{
		chip->irq_state = 0;
		if (chip->irq_callback)
			(*chip->irq_callback)(0);
	}
}


INLINE void update_step(struct YMZ280BChip *chip, struct YMZ280BVoice *voice)
{
	double frequency;

	/* handle the sound-off case */
	if (audio_sample_rate == 0)
	{
		voice->output_step = 0;
		return;
	}

	/* compute the frequency */
	if (voice->mode == 1)
		frequency = chip->master_clock * (double)((voice->fnum & 0x0ff) + 1) * (1.0 / 256.0);
	else
		frequency = chip->master_clock * (double)((voice->fnum & 0x1ff) + 1) * (1.0 / 256.0);
	voice->output_step = (UINT32)(frequency * (double)FRAC_ONE / (double)audio_sample_rate);
}


INLINE void update_volumes(struct YMZ280BVoice *voice)
{
  if (voice->pan == 8)
	{
		voice->output_left = voice->level;
		voice->output_right = voice->level;
	}
	else if (voice->pan < 8)
	{
		voice->output_left = voice->level;
		voice->output_right = voice->level * voice->pan / 8;
	}
	else
	{
		voice->output_left = voice->level * (15 - voice->pan) / 8;
		voice->output_right = voice->level;
	}
}


/**********************************************************************************************

     compute_tables -- compute the difference tables

***********************************************************************************************/

static void compute_tables(void)
{
	int nib;

	/* loop over all nibbles and compute the difference */
	for (nib = 0; nib < 16; nib++)
	{
		int value = (nib & 0x07) * 2 + 1;
		diff_lookup[nib] = (nib & 0x08) ? -value : value;
	}
}



/**********************************************************************************************

     generate_adpcm -- general ADPCM decoding routine

***********************************************************************************************/

static int generate_adpcm(struct YMZ280BVoice *voice, UINT8 *base, INT16 *buffer, int samples)
{
	int position = voice->position;
	int signal = voice->signal;
	int step = voice->step;
	int val;

	/* two cases: first cases is non-looping */
	if (!voice->looping)
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* compute the new amplitude and update the current step */
		  val = base[position / 2] >> ((~position & 1) << 2);
			signal += (step * diff_lookup[val & 15]) / 8;

			/* clamp to the maximum */
			if (signal > 32767)
				signal = 32767;
			else if (signal < -32768)
				signal = -32768;

			/* adjust the step size and clamp */
			step = (step * index_scale[val & 7]) >> 8;
			if (step > 0x6000)
				step = 0x6000;
			else if (step < 0x7f)
				step = 0x7f;

			/* output to the buffer, scaling by the volume */
			*buffer++ = signal;
			samples--;

			/* next! */
			position++;
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* second case: looping */
	else
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* compute the new amplitude and update the current step */
		  val = base[position / 2] >> ((~position & 1) << 2);
		  signal += (step * diff_lookup[val & 15]) / 8;

			/* clamp to the maximum */
			if (signal > 32767)
				signal = 32767;
			else if (signal < -32768)
				signal = -32768;

			/* adjust the step size and clamp */
			step = (step * index_scale[val & 7]) >> 8;
			if (step > 0x6000)
				step = 0x6000;
			else if (step < 0x7f)
				step = 0x7f;

			/* output to the buffer, scaling by the volume */
			*buffer++ = signal;
			samples--;

			/* next! */
			position++;
			if ((UINT32)position == voice->loop_start && voice->loop_count == 0)
			{
				voice->loop_signal = signal;
				voice->loop_step = step;
			}
			if ((UINT32)position >= voice->loop_end)
			{
				if (voice->keyon)
				{
					position = voice->loop_start;
					signal = voice->loop_signal;
					step = voice->loop_step;
					voice->loop_count++;
				}
			}
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* update the parameters */
	voice->position = position;
	voice->signal = signal;
	voice->step = step;

	return samples;
}



/**********************************************************************************************

     generate_pcm8 -- general 8-bit PCM decoding routine

***********************************************************************************************/

static int generate_pcm8(struct YMZ280BVoice *voice, UINT8 *base, INT16 *buffer, int samples)
{
	int position = voice->position;
	int val;

	/* two cases: first cases is non-looping */
	if (!voice->looping)
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* fetch the current value */
			val = base[position / 2];

			/* output to the buffer, scaling by the volume */
			*buffer++ = (INT8)val * 256;
			samples--;

			/* next! */
			position += 2;
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* second case: looping */
	else
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* fetch the current value */
			val = base[position / 2];

			/* output to the buffer, scaling by the volume */
			*buffer++ = (INT8)val * 256;
			samples--;

			/* next! */
			position += 2;
			if ((UINT32)position >= voice->loop_end)
			{
				if (voice->keyon)
					position = voice->loop_start;
			}
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* update the parameters */
	voice->position = position;

	return samples;
}



/**********************************************************************************************

     generate_pcm16 -- general 16-bit PCM decoding routine

***********************************************************************************************/

static int generate_pcm16(struct YMZ280BVoice *voice, UINT8 *base, INT16 *buffer, int samples)
{
	int position = voice->position;
	int val;

	/* two cases: first cases is non-looping */
	if (!voice->looping)
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* fetch the current value */
			val = (INT16)((base[position / 2 + 1] << 8) + base[position / 2]);

			/* output to the buffer, scaling by the volume */
			*buffer++ = val;
			samples--;

			/* next! */
			position += 4;
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* second case: looping */
	else
	{
		/* loop while we still have samples to generate */
		while (samples)
		{
			/* fetch the current value */
			val = (INT16)((base[position / 2 + 1] << 8) + base[position / 2]);

			/* output to the buffer, scaling by the volume */
			*buffer++ = val;
			samples--;

			/* next! */
			position += 4;
			if ((UINT32)position >= voice->loop_end)
			{
				if (voice->keyon)
					position = voice->loop_start;
			}
			if ((UINT32)position >= voice->stop)
				break;
		}
	}

	/* update the parameters */
	voice->position = position;

	return samples;
}



/**********************************************************************************************

     ymz280b_update -- update the sound chip so that it is in sync with CPU execution

***********************************************************************************************/

static void ymz280b_update(int num, INT16 **buffer, int length)
{
	struct YMZ280BChip *chip = &ymz280b[num];
	INT32 *lacc = accumulator;
	INT32 *racc = accumulator + length;
	int v;

	/* clear out the accumulator */
	memset(accumulator, 0, 2 * length * sizeof(accumulator[0]));

	/* loop over voices */
	for (v = 0; v < 8; v++)
	{
		struct YMZ280BVoice *voice = &chip->voice[v];
		INT16 prev = voice->last_sample;
		INT16 curr = voice->curr_sample;
		INT16 *curr_data = scratch;
		INT32 *ldest = lacc;
		INT32 *rdest = racc;