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

     TMS5220 simulator

     Written for MAME by Frank Palazzolo
     With help from Neill Corlett
     Additional tweaking by Aaron Giles
     TMS6100 Speech Rom support added by Raphael Nabet
     PRNG code by Jarek Burczynski backported from tms5110.c by Lord Nightmare
     Chirp/excitation table fixes by Lord Nightmare
     Various fixes by Lord Nightmare
     Modularization by Lord Nightmare

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

#include "sndintrf.h"
#include "tms5220.h"


/* Pull in the ROM tables */
#include "tms5220r.c"

/*
  Changes by R. Nabet
   * added Speech ROM support
   * modified code so that the beast only start speaking at the start of next frame, like the data
     sheet says
*/
#define USE_OBSOLETE_HACK 0


#ifndef TRUE
	#define TRUE 1
#endif
#ifndef FALSE
	#define FALSE 0
#endif


struct tms5220
{
	/* these contain data that describes the 128-bit data FIFO */
	#define FIFO_SIZE 16
	UINT8 fifo[FIFO_SIZE];
	UINT8 fifo_head;
	UINT8 fifo_tail;
	UINT8 fifo_count;
	UINT8 fifo_bits_taken;


	/* these contain global status bits */
	/*
        R Nabet : speak_external is only set when a speak external command is going on.
        tms5220_speaking is set whenever a speak or speak external command is going on.
        Note that we really need to do anything in tms5220_process and play samples only when
        tms5220_speaking is true.  Else, we can play nothing as well, which is a
        speed-up...
    */
	UINT8 tms5220_speaking;	/* Speak or Speak External command in progress */
	UINT8 speak_external;	/* Speak External command in progress */
	#if USE_OBSOLETE_HACK
	UINT8 speak_delay_frames;
	#endif
	UINT8 talk_status; 		/* tms5220 is really currently speaking */
	UINT8 first_frame;		/* we have just started speaking, and we are to parse the first frame */
	UINT8 last_frame;		/* we are doing the frame of sound */
	UINT8 buffer_low;		/* FIFO has less than 8 bytes in it */
	UINT8 buffer_empty;		/* FIFO is empty*/
	UINT8 irq_pin;			/* state of the IRQ pin (output) */

	void (*irq_func)(int state); /* called when the state of the IRQ pin changes */


	/* these contain data describing the current and previous voice frames */
	UINT16 old_energy;
	UINT16 old_pitch;
	INT32 old_k[10];

	UINT16 new_energy;
	UINT16 new_pitch;
	INT32 new_k[10];


	/* these are all used to contain the current state of the sound generation */
	UINT16 current_energy;
	UINT16 current_pitch;
	INT32 current_k[10];

	UINT16 target_energy;
	UINT16 target_pitch;
	INT32 target_k[10];

	UINT16 previous_energy;         /* needed for lattice filter to match patent */

	UINT8 interp_count;		/* number of interp periods (0-7) */
	UINT8 sample_count;		/* sample number within interp (0-24) */
	UINT16 pitch_count;

	INT32 u[11];
	INT32 x[10];

	INT32 RNG;      /* the random noise generator configuration is: 1 + x + x^3 + x^4 + x^13 */
	INT8 excitation_data;

	/* R Nabet : These have been added to emulate speech Roms */
	int (*read_callback)(int count);
	void (*load_address_callback)(int data);
	void (*read_and_branch_callback)(void);
	UINT8 schedule_dummy_read;			/* set after each load address, so that next read operation
                                              is preceded by a dummy read */

	UINT8 data_register;				/* data register, used by read command */
	UINT8 RDB_flag;					/* whether we should read data register or status register */

	/* flag for variant tms0285/tms5200 emulation */
	/* The TMC0285 AKA TMS5200 is an early variant of the TMS5220 used in
       the early releases of the Speech Module for the TI-99/4(a) computer,
       in Zaccaria's 'Money Money', and in a few other places.
       The TMS5200 has a bug in its state machine PLA which causes it to
       incorrectly use the LPC K3 parameter table for both K3 and K4.
       (the chip has the unused K4 parameter in its internal ROM, but it is
       never accessed due to the PLA bug)
       The bug was fixed in the quickly-released TMS5220.
       TI may have sold the remaining stocks of TMS5200s at a discount, and
       apparently provided a special encoder to work around the bug.
       Other than the bug, the two chips are identical.
       Another variant of the TMS5220 is the TMS5220C/TSP5220C, which adds
       an additional opcode (to select the data rate).
     */
	tms5220_variant variant;
    /* The TMS52xx has two different ways of providing output data: the
       analog speaker pin (which was usually used) and the Digital I/O pin.
       The internal DAC used to feed the analog pin is only 8 bits, while the
       digital pin gives full 12? bit resolution to the output data.
     */
    UINT8 digital_select;
};


/* Static function prototypes */
static void process_command(struct tms5220 *tms);
static int extract_bits(struct tms5220 *tms, int count);
static int parse_frame(struct tms5220 *tms, int the_first_frame);
static void check_buffer_low(struct tms5220 *tms);
static void set_interrupt_state(struct tms5220 *tms, int state);
static INT16 lattice_filter(void *chip);
static INT16 clip_and_wrap(INT16 cliptemp);


#define DEBUG_5220	0


void *tms5220_create(int index)
{
	struct tms5220 *tms;

	tms = malloc_or_die(sizeof(*tms));
	memset(tms, 0, sizeof(*tms));

	state_save_register_item_array("tms5220", index, tms->fifo);
	state_save_register_item("tms5220", index, tms->fifo_head);
	state_save_register_item("tms5220", index, tms->fifo_tail);
	state_save_register_item("tms5220", index, tms->fifo_count);
	state_save_register_item("tms5220", index, tms->fifo_bits_taken);

	state_save_register_item("tms5220", index, tms->tms5220_speaking);
	state_save_register_item("tms5220", index, tms->speak_external);
	state_save_register_item("tms5220", index, tms->talk_status);
	state_save_register_item("tms5220", index, tms->first_frame);
	state_save_register_item("tms5220", index, tms->last_frame);
	state_save_register_item("tms5220", index, tms->buffer_low);
	state_save_register_item("tms5220", index, tms->buffer_empty);
	state_save_register_item("tms5220", index, tms->irq_pin);

	state_save_register_item("tms5220", index, tms->old_energy);
	state_save_register_item("tms5220", index, tms->old_pitch);
	state_save_register_item_array("tms5220", index, tms->old_k);

	state_save_register_item("tms5220", index, tms->new_energy);
	state_save_register_item("tms5220", index, tms->new_pitch);
	state_save_register_item_array("tms5220", index, tms->new_k);

	state_save_register_item("tms5220", index, tms->current_energy);
	state_save_register_item("tms5220", index, tms->current_pitch);
	state_save_register_item_array("tms5220", index, tms->current_k);

	state_save_register_item("tms5220", index, tms->target_energy);
	state_save_register_item("tms5220", index, tms->target_pitch);
	state_save_register_item_array("tms5220", index, tms->target_k);

	state_save_register_item("tms5220", index, tms->previous_energy);

	state_save_register_item("tms5220", index, tms->interp_count);
	state_save_register_item("tms5220", index, tms->sample_count);
	state_save_register_item("tms5220", index, tms->pitch_count);

	state_save_register_item_array("tms5220", index, tms->u);
	state_save_register_item_array("tms5220", index, tms->x);

	state_save_register_item("tms5220", index, tms->RNG);
	state_save_register_item("tms5220", index, tms->excitation_data);

	state_save_register_item("tms5220", index, tms->schedule_dummy_read);
	state_save_register_item("tms5220", index, tms->data_register);
	state_save_register_item("tms5220", index, tms->RDB_flag);
	state_save_register_item("tms5220", index, tms->digital_select);

	return tms;
}


void tms5220_destroy(void *chip)
{
	free(chip);
}

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

     tms5220_reset -- resets the TMS5220

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

void tms5220_reset_chip(void *chip)
{
	struct tms5220 *tms = chip;

	/* initialize the FIFO */
	/*memset(tms->fifo, 0, sizeof(tms->fifo));*/
	tms->fifo_head = tms->fifo_tail = tms->fifo_count = tms->fifo_bits_taken = 0;

	/* initialize the chip state */
	/* Note that we do not actually clear IRQ on start-up : IRQ is even raised if tms->buffer_empty or tms->buffer_low are 0 */
	tms->tms5220_speaking = tms->speak_external = tms->talk_status = tms->first_frame = tms->last_frame = tms->irq_pin = 0;
#if USE_OBSOLETE_HACK
	tms->speak_delay_frames = 0;
#endif
	if (tms->irq_func) tms->irq_func(0);
	tms->buffer_empty = tms->buffer_low = 1;

	tms->RDB_flag = FALSE;

	/* initialize the energy/pitch/k states */
	tms->old_energy = tms->new_energy = tms->current_energy = tms->target_energy = 0;
	tms->old_pitch = tms->new_pitch = tms->current_pitch = tms->target_pitch = 0;
	memset(tms->old_k, 0, sizeof(tms->old_k));
	memset(tms->new_k, 0, sizeof(tms->new_k));
	memset(tms->current_k, 0, sizeof(tms->current_k));
	memset(tms->target_k, 0, sizeof(tms->target_k));

	/* initialize the sample generators */
	tms->interp_count = tms->sample_count = tms->pitch_count = 0;
        tms->RNG = 0x1FFF;
	memset(tms->u, 0, sizeof(tms->u));
	memset(tms->x, 0, sizeof(tms->x));

	if (tms->load_address_callback)
		(*tms->load_address_callback)(0);

	tms->schedule_dummy_read = TRUE;
}



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

     tms5220_set_irq -- sets the interrupt handler

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

void tms5220_set_irq(void *chip, void (*func)(int))
{
	struct tms5220 *tms = chip;
    tms->irq_func = func;
}


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

     tms5220_set_read -- sets the speech ROM read handler

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

void tms5220_set_read(void *chip, int (*func)(int))
{
	struct tms5220 *tms = chip;
	tms->read_callback = func;
}


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

     tms5220_set_load_address -- sets the speech ROM load address handler

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

void tms5220_set_load_address(void *chip, void (*func)(int))
{
	struct tms5220 *tms = chip;
	tms->load_address_callback = func;
}


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

     tms5220_set_read_and_branch -- sets the speech ROM read and branch handler

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

void tms5220_set_read_and_branch(void *chip, void (*func)(void))
{
	struct tms5220 *tms = chip;
	tms->read_and_branch_callback = func;
}


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

     tms5220_set_variant -- sets the tms5220 core to emulate its buggy forerunner, the tms0285

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

void tms5220_set_variant(void *chip, tms5220_variant new_variant)
{
	struct tms5220 *tms = chip;
	tms->variant = new_variant;
}


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

     tms5220_data_write -- handle a write to the TMS5220

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

void tms5220_data_write(void *chip, int data)
{
	struct tms5220 *tms = chip;

    /* add this byte to the FIFO */
    if (tms->fifo_count < FIFO_SIZE)
    {
        tms->fifo[tms->fifo_tail] = data;
        tms->fifo_tail = (tms->fifo_tail + 1) % FIFO_SIZE;
        tms->fifo_count++;

		/* if we were speaking, then we're no longer empty */
		if (tms->speak_external)
			tms->buffer_empty = 0;

        if (DEBUG_5220) logerror("Added byte to FIFO (size=%2d)\n", tms->fifo_count);
    }
    else
    {
        if (DEBUG_5220) logerror("Ran out of room in the FIFO!\n");
    }

    /* update the buffer low state */
    check_buffer_low(tms);

	if (! tms->speak_external)
		/* R Nabet : we parse commands at once.  It is necessary for such commands as read. */
		process_command (tms/*data*/);
}


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

     tms5220_status_read -- read status or data from the TMS5220

      From the data sheet:
        bit 0 = TS - Talk Status is active (high) when the VSP is processing speech data.
                Talk Status goes active at the initiation of a Speak command or after nine
                bytes of data are loaded into the FIFO following a Speak External command. It
                goes inactive (low) when the stop code (Energy=1111) is processed, or
                immediately by a buffer empty condition or a reset command.
        bit 1 = BL - Buffer Low is active (high) when the FIFO buffer is more than half empty.
                Buffer Low is set when the "Last-In" byte is shifted down past the half-full
                boundary of the stack. Buffer Low is cleared when data is loaded to the stack
                so that the "Last-In" byte lies above the half-full boundary and becomes the
                ninth data byte of the stack.
        bit 2 = BE - Buffer Empty is active (high) when the FIFO buffer has run out of data
                while executing a Speak External command. Buffer Empty is set when the last bit
                of the "Last-In" byte is shifted out to the Synthesis Section. This causes
                Talk Status to be cleared. Speed is terminated at some abnormal point and the
                Speak External command execution is terminated.

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

int tms5220_status_read(void *chip)
{
	struct tms5220 *tms = chip;

	if (tms->RDB_flag)
	{	/* if last command was read, return data register */
		tms->RDB_flag = FALSE;
		return(tms->data_register);
	}
	else
	{	/* read status */

		/* clear the interrupt pin */
		set_interrupt_state(tms, 0);

		if (DEBUG_5220) logerror("Status read: TS=%d BL=%d BE=%d\n", tms->talk_status, tms->buffer_low, tms->buffer_empty);

		return (tms->talk_status << 7) | (tms->buffer_low << 6) | (tms->buffer_empty << 5);
	}
}



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

     tms5220_ready_read -- returns the ready state of the TMS5220

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

int tms5220_ready_read(void *chip)
{
	struct tms5220 *tms = chip;
    return (tms->fifo_count < FIFO_SIZE-1);
}


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

     tms5220_ready_read -- returns the number of cycles until ready is asserted

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

int tms5220_cycles_to_ready(void *chip)
{
	struct tms5220 *tms = chip;
	int answer;


	if (tms5220_ready_read(tms))
		answer = 0;
	else
	{
		int val;

		answer = 200-tms->sample_count+8;

		/* total number of bits available in current byte is (8 - tms->fifo_bits_taken) */
		/* if more than 4 are available, we need to check the energy */
		if (tms->fifo_bits_taken < 4)
		{
			/* read energy */
			val = (tms->fifo[tms->fifo_head] >> tms->fifo_bits_taken) & 0xf;
			if (val == 0)
				/* 0 -> silence frame: we will only read 4 bits, and we will
                therefore need to read another frame before the FIFO is not
                full any more */
				answer += 200;
			/* 15 -> stop frame, we will only read 4 bits, but the FIFO will
            we cleared */
			/* otherwise, we need to parse the repeat flag (1 bit) and the
            pitch (6 bits), so everything will be OK. */
		}
	}

	return answer;
}


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

     tms5220_int_read -- returns the interrupt state of the TMS5220

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

int tms5220_int_read(void *chip)
{
	struct tms5220 *tms = chip;
    return tms->irq_pin;
}



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

     tms5220_process -- fill the buffer with a specific number of samples

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

void tms5220_process(void *chip, INT16 *buffer, unsigned int size)
{
	struct tms5220 *tms = chip;
    int buf_count=0;
    int i, interp_period, bitout;

tryagain:

    /* if we're not speaking, parse commands */
	/*while (!tms->speak_external && tms->fifo_count > 0)
        process_command(tms);*/

    /* if we're empty and still not speaking, fill with nothingness */
	if ((!tms->tms5220_speaking) && (!tms->last_frame))
        goto empty;

    /* if we're to speak, but haven't started, wait for the 9th byte */
	if (!tms->talk_status && tms->speak_external)
    {
        if (tms->fifo_count < 9)
           goto empty;

        tms->talk_status = 1;
		tms->first_frame = 1;	/* will cause the first frame to be parsed */
		tms->buffer_empty = 0;
	}

#if 0
	/* we are to speak, yet we fill with 0s until start of next frame */
	if (tms->first_frame)
	{
		while ((size > 0) && ((tms->sample_count != 0) || (tms->interp_count != 0)))
		{
			tms->sample_count = (tms->sample_count + 1) % 200;
			tms->interp_count = (tms->interp_count + 1) % 25;
			buffer[buf_count] = 0x00;	/* should be (-1 << 8) ??? (cf note in data sheet, p 10, table 4) */
			buf_count++;
			size--;
		}
	}
#endif

#if USE_OBSOLETE_HACK
    /* apply some delay before we actually consume data; Victory requires this */
    if (tms->speak_delay_frames)
    {
    	if (size <= tms->speak_delay_frames)
    	{
    		tms->speak_delay_frames -= size;
    		size = 0;
    	}
    	else
    	{
    		size -= tms->speak_delay_frames;
    		tms->speak_delay_frames = 0;
    	}
    }
#endif

    /* loop until the buffer is full or we've stopped speaking */
	while ((size > 0) && tms->talk_status)
    {

        /* if we're ready for a new frame */
        if ((tms->interp_count == 0) && (tms->sample_count == 0))
        {
            /* Parse a new frame */
			if (!parse_frame(tms, tms->first_frame))
				break;
			tms->first_frame = 0;

            /* Set old target as new start of frame */
            tms->current_energy = tms->old_energy;
            tms->current_pitch = tms->old_pitch;
            for (i = 0; i < 10; i++)
                tms->current_k[i] = tms->old_k[i];

            /* is this a zero energy frame? */
            if (tms->current_energy == 0)
            {
                /*mame_printf_debug("processing frame: zero energy\n");*/
                tms->target_energy = 0;
                tms->target_pitch = tms->current_pitch;
                for (i = 0; i < 10; i++)
                    tms->target_k[i] = tms->current_k[i];
            }

            /* is this a stop frame? */
            else if (tms->current_energy == (energytable[15] >> 6))
            {
                /*mame_printf_debug("processing frame: stop frame\n");*/
                tms->current_energy = energytable[0] >> 6;
                tms->target_energy = tms->current_energy;
				/*tms->interp_count = tms->sample_count =*/ tms->pitch_count = 0;
				tms->last_frame = 0;
				if (tms->tms5220_speaking)
					/* new speech command in progress */
					tms->first_frame = 1;
				else
				{
					/* really stop speaking */
					tms->talk_status = 0;

					/* generate an interrupt if necessary */
					set_interrupt_state(tms, 1);
				}

                /* try to fetch commands again */
                goto tryagain;
            }
            else
            {
                /* is this the ramp down frame? */
                if (tms->new_energy == (energytable[15] >> 6))
                {
                    /*mame_printf_debug("processing frame: ramp down\n");*/
                    tms->target_energy = 0;
                    tms->target_pitch = tms->current_pitch;
                    for (i = 0; i < 10; i++)
                        tms->target_k[i] = tms->current_k[i];
                }
                /* Reset the step size */
                else
                {
                    /*mame_printf_debug("processing frame: Normal\n");*/
                    /*mame_printf_debug("*** Energy = %d\n",tms->current_energy);*/
                    /*mame_printf_debug("proc: %d %d\n",last_fbuf_head,fbuf_head);*/

                    tms->target_energy = tms->new_energy;
                    tms->target_pitch = tms->new_pitch;

                    for (i = 0; i < 4; i++)
                        tms->target_k[i] = tms->new_k[i];
                    if (tms->current_pitch == 0)
                        for (i = 4; i < 10; i++)
                        {
                            tms->target_k[i] = tms->current_k[i] = 0;
                        }
                    else
                        for (i = 4; i < 10; i++)
                            tms->target_k[i] = tms->new_k[i];
                }
            }
        }
        else if (tms->interp_count == 0)
        {
            /* Update values based on step values */
            /*mame_printf_debug("\n");*/

            interp_period = tms->sample_count / 25;
            tms->current_energy += ((tms->target_energy - tms->current_energy) >> interp_coeff[interp_period]);
            if (tms->old_pitch != 0)
                tms->current_pitch += ((tms->target_pitch - tms->current_pitch) >> interp_coeff[interp_period]);

            /*mame_printf_debug("*** Energy = %d\n",tms->current_energy);*/

            for (i = 0; i < 10; i++)
            {
                tms->current_k[i] += ((tms->target_k[i] - tms->current_k[i]) >> interp_coeff[interp_period]);
            }
        }

        if (tms->old_energy == 0)
        {
            /* generate silent samples here */
			tms->excitation_data = 0x00; /* I'm not sure if this is actually RIGHT, the current_energy may be forced to zero when we've just passed a zero energy frame. However, this does work too. May be removed later. */
        }
        else if (tms->old_pitch == 0)
        {
            /* generate unvoiced samples here */
			if (tms->RNG & 1)
				tms->excitation_data = -0x40; /* according to the patent it is (either + or -) half of the maximum value in the chirp table, so +-64 */
			else
				tms->excitation_data = 0x40;
        }
        else
        {
            /* generate voiced samples here */
			tms->excitation_data = chirptable[tms->pitch_count%sizeof(chirptable)];
        }

        /* Update LFSR every clock, like patent shows */
        bitout = ((tms->RNG >> 12) & 1) ^
                 ((tms->RNG >> 10) & 1) ^
                 ((tms->RNG >>  9) & 1) ^
                 ((tms->RNG >>  0) & 1);
        tms->RNG >>= 1;
        tms->RNG |= bitout << 12;

		buffer[buf_count] = clip_and_wrap(lattice_filter(tms)); /* execute lattice filter and clipping/wrapping */

        if (tms->digital_select == 0) /* if digital is NOT selected... */
		  buffer[buf_count] &= 0xff00; /* mask out all but the 8 dac bits */

        /* Update all counts */

        size--;
        tms->sample_count = (tms->sample_count + 1) % 200;

        if (tms->current_pitch != 0)
            tms->pitch_count = (tms->pitch_count + 1) % tms->current_pitch;
        else
            tms->pitch_count = 0;

        tms->interp_count = (tms->interp_count + 1) % 25;
        buf_count++;
    }

empty:

    while (size > 0)
    {
		tms->sample_count = (tms->sample_count + 1) % 200;
		tms->interp_count = (tms->interp_count + 1) % 25;
		buffer[buf_count] = 0x00;	/* should be (-1 << 8) ??? (cf note in data sheet, p 10, table 4) */
        buf_count++;
        size--;
    }
}

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

     clip_and_wrap -- clips and wraps the 14 bit return value from the lattice filter to its final 10 bit value (-512 to 511), and upshifts this to 16 bits

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

static INT16 clip_and_wrap(INT16 cliptemp)
{
        /* clipping & wrapping, just like the patent shows */

	if (cliptemp > 2047) cliptemp = -2048 + (cliptemp-2047);
	else if (cliptemp < -2048) cliptemp = 2047 - (cliptemp+2048);

	if (cliptemp > 511) { mame_printf_debug ("cliptemp > 511\n");
	    return 127<<8; }
        else if (cliptemp < -512) { mame_printf_debug ("cliptemp < -512\n");
	    return -128<<8; }
        else
            return cliptemp << 6;
}


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

     lattice_filter -- executes one 'full run' of the lattice filter on a specific byte of
     excitation data, and specific values of all the current k constants,  and returns the
     resulting sample.
     Note: the current_k processing here by dividing the result by 32768 is necessary, as the stored
     parameters in the lookup table are the 10 bit coefficients but are pre-multiplied by 512 for
     ease of storage. This is undone on the real chip by a shifter here, after the multiply.

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

static INT16 lattice_filter(void *chip)
{
        struct tms5220 *tms = chip;
        /* Lattice filter here */
        /* Aug/05/07: redone as unrolled loop, for clarity - LN*/
        /* Copied verbatim from table I in US patent 4,209,804:
           notation equivalencies from table:
           Yn(i) == tms->u[n-1]
           Kn = tms->current_k[n-1]
           bn = tms->x[n-1]
    */
        tms->u[10] = (tms->excitation_data * tms->previous_energy) >> 8; /* Y(11) */
        tms->u[9] = tms->u[10] - ((tms->current_k[9] * tms->x[9]) / 32768);
        tms->u[8] = tms->u[9] - ((tms->current_k[8] * tms->x[8]) / 32768);
        tms->x[9] = tms->x[8] + ((tms->current_k[8] * tms->u[8]) / 32768);
        tms->u[7] = tms->u[8] - ((tms->current_k[7] * tms->x[7]) / 32768);
        tms->x[8] = tms->x[7] + ((tms->current_k[7] * tms->u[7]) / 32768);
        tms->u[6] = tms->u[7] - ((tms->current_k[6] * tms->x[6]) / 32768);
        tms->x[7] = tms->x[6] + ((tms->current_k[6] * tms->u[6]) / 32768);
        tms->u[5] = tms->u[6] - ((tms->current_k[5] * tms->x[5]) / 32768);
        tms->x[6] = tms->x[5] + ((tms->current_k[5] * tms->u[5]) / 32768);
        tms->u[4] = tms->u[5] - ((tms->current_k[4] * tms->x[4]) / 32768);
        tms->x[5] = tms->x[4] + ((tms->current_k[4] * tms->u[4]) / 32768);
        tms->u[3] = tms->u[4] - ((tms->current_k[3] * tms->x[3]) / 32768);
        tms->x[4] = tms->x[3] + ((tms->current_k[3] * tms->u[3]) / 32768);
        tms->u[2] = tms->u[3] - ((tms->current_k[2] * tms->x[2]) / 32768);
        tms->x[3] = tms->x[2] + ((tms->current_k[2] * tms->u[2]) / 32768);
        tms->u[1] = tms->u[2] - ((tms->current_k[1] * tms->x[1]) / 32768);
        tms->x[2] = tms->x[1] + ((tms->current_k[1] * tms->u[1]) / 32768);
        tms->u[0] = tms->u[1] - ((tms->current_k[0] * tms->x[0]) / 32768);
        tms->x[1] = tms->x[0] + ((tms->current_k[0] * tms->u[0]) / 32768);
        tms->x[0] = tms->u[0];
        tms->previous_energy = tms->current_energy;
        return tms->u[0];
}


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

     process_command -- extract a byte from the FIFO and interpret it as a command

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

static void process_command(struct tms5220 *tms)
{
    unsigned char cmd;

    /* if there are stray bits, ignore them */
	if (tms->fifo_bits_taken)
	{
		tms->fifo_bits_taken = 0;
        tms->fifo_count--;
        tms->fifo_head = (tms->fifo_head + 1) % FIFO_SIZE;
    }

    /* grab a full byte from the FIFO */
    if (tms->fifo_count > 0)
    {
		cmd = tms->fifo[tms->fifo_head];
		tms->fifo_count--;
		tms->fifo_head = (tms->fifo_head + 1) % FIFO_SIZE;

		/* parse the command */
		switch (cmd & 0x70)
		{
		case 0x10 : /* read byte */
			if (tms->schedule_dummy_read)
			{
				tms->schedule_dummy_read = FALSE;
				if (tms->read_callback)
					(*tms->read_callback)(1);
			}
			if (tms->read_callback)
				tms->data_register = (*tms->read_callback)(8);	/* read one byte from speech ROM... */
			tms->RDB_flag = TRUE;
			break;

		case 0x30 : /* read and branch */
			if (DEBUG_5220) logerror("read and branch command received\n");
			tms->RDB_flag = FALSE;
			if (tms->read_and_branch_callback)
				(*tms->read_and_branch_callback)();
			break;

		case 0x40 : /* load address */
			/* tms5220 data sheet says that if we load only one 4-bit nibble, it won't work.
              This code does not care about this. */
			if (tms->load_address_callback)
				(*tms->load_address_callback)(cmd & 0x0f);
			tms->schedule_dummy_read = TRUE;
			break;

		case 0x50 : /* speak */
			if (tms->schedule_dummy_read)
			{
				tms->schedule_dummy_read = FALSE;
				if (tms->read_callback)
					(*tms->read_callback)(1);
			}
			tms->tms5220_speaking = 1;
			tms->speak_external = 0;
			if (! tms->last_frame)
			{
				tms->first_frame = 1;
			}
			tms->talk_status = 1;  /* start immediately */
			break;

		case 0x60 : /* speak external */
			tms->tms5220_speaking = tms->speak_external = 1;
#if USE_OBSOLETE_HACK
            tms->speak_delay_frames = 10;
#endif

			tms->RDB_flag = FALSE;

            /* according to the datasheet, this will cause an interrupt due to a BE condition */
            if (!tms->buffer_empty)
            {
                tms->buffer_empty = 1;
                set_interrupt_state(tms, 1);
            }

			tms->talk_status = 0;	/* wait to have 8 bytes in buffer before starting */
			break;

		case 0x70 : /* reset */
			if (tms->schedule_dummy_read)
			{
				tms->schedule_dummy_read = FALSE;
				if (tms->read_callback)
					(*tms->read_callback)(1);
			}
			tms5220_reset_chip(tms);
			break;
        }
    }

    /* update the buffer low state */
    check_buffer_low(tms);
}



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

     extract_bits -- extract a specific number of bits from the FIFO

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

static int extract_bits(struct tms5220 *tms, int count)
{
    int val = 0;

	if (tms->speak_external)
	{
		/* extract from FIFO */
    	while (count--)
    	{
        	val = (val << 1) | ((tms->fifo[tms->fifo_head] >> tms->fifo_bits_taken) & 1);
        	tms->fifo_bits_taken++;
        	if (tms->fifo_bits_taken >= 8)
        	{
        	    tms->fifo_count--;
        	    tms->fifo_head = (tms->fifo_head + 1) % FIFO_SIZE;
        	    tms->fifo_bits_taken = 0;
        	}
    	}
    }
	else
	{
		/* extract from speech ROM */
		if (tms->read_callback)
			val = (* tms->read_callback)(count);
	}

    return val;
}



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

     parse_frame -- parse a new frame's worth of data; returns 0 if not enough bits in buffer

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

static int parse_frame(struct tms5220 *tms, int the_first_frame)
{
	int bits = 0;	/* number of bits in FIFO (speak external only) */
	int indx, i, rep_flag;

	if (! the_first_frame)
	{
    /* remember previous frame */
    tms->old_energy = tms->new_energy;
    tms->old_pitch = tms->new_pitch;
    for (i = 0; i < 10; i++)
        tms->old_k[i] = tms->new_k[i];
	}

    /* clear out the new frame */
    tms->new_energy = 0;
    tms->new_pitch = 0;
    for (i = 0; i < 10; i++)
        tms->new_k[i] = 0;

    /* if the previous frame was a stop frame, don't do anything */
	if ((! the_first_frame) && (tms->old_energy == (energytable[15] >> 6)))
		/*return 1;*/
	{
		tms->buffer_empty = 1;
		return 1;
	}

	if (tms->speak_external)
    	/* count the total number of bits available */
		bits = tms->fifo_count * 8 - tms->fifo_bits_taken;

    /* attempt to extract the energy index */
	if (tms->speak_external)
	{
    bits -= 4;
    if (bits < 0)
        goto ranout;
	}
    indx = extract_bits(tms, 4);
    tms->new_energy = energytable[indx] >> 6;

	/* if the index is 0 or 15, we're done */
	if (indx == 0 || indx == 15)
	{
		if (DEBUG_5220) logerror("  (4-bit energy=%d frame)\n",tms->new_energy);

		/* clear tms->fifo if stop frame encountered */
		if (indx == 15)
		{
			tms->fifo_head = tms->fifo_tail = tms->fifo_count = tms->fifo_bits_taken = 0;
			tms->speak_external = tms->tms5220_speaking = 0;
			tms->last_frame = 1;
		}
		goto done;
	}

    /* attempt to extract the repeat flag */
	if (tms->speak_external)
	{
    bits -= 1;
    if (bits < 0)
        goto ranout;
	}
    rep_flag = extract_bits(tms, 1);

    /* attempt to extract the pitch */
	if (tms->speak_external)
	{
    bits -= 6;
    if (bits < 0)
        goto ranout;
	}
    indx = extract_bits(tms, 6);
    tms->new_pitch = pitchtable[indx] / 256;

    /* if this is a repeat frame, just copy the k's */
    if (rep_flag)
    {
        for (i = 0; i < 10; i++)
            tms->new_k[i] = tms->old_k[i];

        if (DEBUG_5220) logerror("  (11-bit energy=%d pitch=%d rep=%d frame)\n", tms->new_energy, tms->new_pitch, rep_flag);
        goto done;
    }

    /* if the pitch index was zero, we need 4 k's */
    if (indx == 0)
    {
        /* attempt to extract 4 K's */
		if (tms->speak_external)
		{
        bits -= 18;
        if (bits < 0)
            goto ranout;
		}
        tms->new_k[0] = k1table[extract_bits(tms, 5)];
        tms->new_k[1] = k2table[extract_bits(tms, 5)];
        tms->new_k[2] = k3table[extract_bits(tms, 4)];
		if (tms->variant == variant_tms0285)
			tms->new_k[3] = k3table[extract_bits(tms, 4)];	/* ??? */
		else
			tms->new_k[3] = k4table[extract_bits(tms, 4)];

        if (DEBUG_5220) logerror("  (29-bit energy=%d pitch=%d rep=%d 4K frame)\n", tms->new_energy, tms->new_pitch, rep_flag);
        goto done;
    }

    /* else we need 10 K's */
	if (tms->speak_external)
	{
    bits -= 39;
    if (bits < 0)
        goto ranout;
	}

    tms->new_k[0] = k1table[extract_bits(tms, 5)];
    tms->new_k[1] = k2table[extract_bits(tms, 5)];
    tms->new_k[2] = k3table[extract_bits(tms, 4)];
	if (tms->variant == variant_tms0285)
		tms->new_k[3] = k3table[extract_bits(tms, 4)];	/* ??? */
	else
		tms->new_k[3] = k4table[extract_bits(tms, 4)];
    tms->new_k[4] = k5table[extract_bits(tms, 4)];
    tms->new_k[5] = k6table[extract_bits(tms, 4)];
    tms->new_k[6] = k7table[extract_bits(tms, 4)];
    tms->new_k[7] = k8table[extract_bits(tms, 3)];
    tms->new_k[8] = k9table[extract_bits(tms, 3)];
    tms->new_k[9] = k10table[extract_bits(tms, 3)];

    if (DEBUG_5220) logerror("  (50-bit energy=%d pitch=%d rep=%d 10K frame)\n", tms->new_energy, tms->new_pitch, rep_flag);

done:
	if (DEBUG_5220)
	{
		if (tms->speak_external)
			logerror("Parsed a frame successfully in FIFO - %d bits remaining\n", bits);
		else
			logerror("Parsed a frame successfully in ROM\n");
	}

	if (the_first_frame)
	{
		/* if this is the first frame, no previous frame to take as a starting point */
		tms->old_energy = tms->new_energy;
		tms->old_pitch = tms->new_pitch;
		for (i = 0; i < 10; i++)
			tms->old_k[i] = tms->new_k[i];
    }

    /* update the tms->buffer_low status */
    check_buffer_low(tms);
    return 1;

ranout:

    if (DEBUG_5220) logerror("Ran out of bits on a parse!\n");

    /* this is an error condition; mark the buffer empty and turn off speaking */
    tms->buffer_empty = 1;
	tms->talk_status = tms->speak_external = tms->tms5220_speaking = the_first_frame = tms->last_frame = 0;
    tms->fifo_count = tms->fifo_head = tms->fifo_tail = 0;

	tms->RDB_flag = FALSE;

    /* generate an interrupt if necessary */
    set_interrupt_state(tms, 1);
    return 0;
}



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

     check_buffer_low -- check to see if the buffer low flag should be on or off

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

static void check_buffer_low(struct tms5220 *tms)
{
    /* did we just become low? */
    if (tms->fifo_count <= 8)
    {
        /* generate an interrupt if necessary */
        if (!tms->buffer_low)
            set_interrupt_state(tms, 1);
        tms->buffer_low = 1;

        if (DEBUG_5220) logerror("Buffer low set\n");
    }

    /* did we just become full? */
    else
    {
        tms->buffer_low = 0;

        if (DEBUG_5220) logerror("Buffer low cleared\n");
    }
}



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

     set_interrupt_state -- generate an interrupt

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

static void set_interrupt_state(struct tms5220 *tms, int state)
{
    if (tms->irq_func && state != tms->irq_pin)
    	tms->irq_func(state);
    tms->irq_pin = state;
}
