devices/sound/zsg2.cpp

// license:BSD-3-Clause
// copyright-holders:Olivier Galibert, R. Belmont, hap, superctr
/*
    ZOOM ZSG-2 custom wavetable synthesizer

    Written by Olivier Galibert
    MAME conversion by R. Belmont
    Working emulation by The Talentuous Hands Of The Popularious hap
    Properly working emulation by superctr
    ---------------------------------------------------------

    Register map:
    000-5fe : Channel specific registers (48 channels)
              (high)   (low)
       +000 : xxxxxxxx -------- : Start address (low)
       +000 : -------- xxxxxxxx :   Unknown register (usually cleared)
       +002 : xxxxxxxx -------- : Address page
            : -------- xxxxxxxx : Start address (high)
       +004 : -------- -------- :   Unknown register (usually cleared)
       +006 : -----x-- -------- :   Unknown bit, always set
       +008 : xxxxxxxx xxxxxxxx : Frequency
       +00a : xxxxxxxx -------- : DSP ch 3 (right) output gain
            : -------- xxxxxxxx : Loop address (low)
       +00c : xxxxxxxx xxxxxxxx : End address
       +00e : xxxxxxxx -------- : DSP ch 2 (Left) output gain
            : -------- xxxxxxxx : Loop address (high)
       +010 : xxxxxxxx xxxxxxxx : Initial filter time constant
       +012 : xxxxxxxx xxxxxxxx : Current filter time constant
       +014 : xxxxxxxx xxxxxxxx : Initial volume
       +016 : xxxxxxxx xxxxxxxx : Current volume?
       +018 : xxxxxxxx xxxxxxxx : Target filter time constant
       +01a : xxxxxxxx -------- : DSP ch 1 (chorus) output gain
            : -------- xxxxxxxx : Filter ramping speed
       +01c : xxxxxxxx xxxxxxxx : Target volume
       +01e : xxxxxxxx -------- : DSP ch 0 (reverb) output gain
            : -------- xxxxxxxx : Filter ramping speed
    600-604 : Key on flags (each bit corresponds to a channel)
    608-60c : Key off flags (each bit corresponds to a channel)
    618     : Unknown register (usually 0x5cbc is written)
    61a     : Unknown register (usually 0x5cbc is written)
    620     : Unknown register (usually 0x0128 is written)
    628     : Unknown register (usually 0x0066 is written)
    630     : Unknown register (usually 0x0001 is written)
    638     : ROM readback address low
    63a     : ROM readback address high
    63c     : ROM readback word low
    63e     : ROM readback word high

    ---------------------------------------------------------

    Additional notes on the sample format, reverse-engineered
    by Olivier Galibert and David Haywood:

    The zoom sample rom is decomposed in 0x40000 bytes pages.  Each page
    starts by a header and is followed by compressed samples.

    The header is a vector of 16 bytes structures composed of 4 32bits
    little-endian values representing:
    - sample start position in bytes, always a multiple of 4
    - sample end position in bytes, minus 4, always...
    - loop position in bytes, always....
    - flags, probably

    It is interesting to note that this header is *not* parsed by the
    ZSG.  The main program reads the rom through appropriate ZSG
    commands, and use the results in subsequent register setups.  It's
    not even obvious that the ZSG cares about the pages, it may just
    see the address space as linear.  In the same line, the
    interpretation of the flags is obviously dependent on the main
    program, not the ZSG, but some of the bits are directly copied to
    some of the registers.

    The samples are compressed with a 2:1 ratio.  Each block of 4-bytes
    becomes 4 16-bits samples.  Reading the 4 bytes as a *little-endian*
    32bits values, the structure is:

    42222222 51111111 60000000 ssss3333

    's' is a 4-bit scale value.  '0000000', '1111111', '2222222' and
    '6543333' are signed 7-bits values corresponding to the 4 samples.
    To compute the final 16bits value, left-align and shift right by s.
    Yes, that simple.

    ---------------------------------------------------------

TODO:
- Filter and ramping behavior might not be perfect.
- clicking / popping noises in gdarius, raystorm: maybe the sample ROMs are bad dumps?
- memory reads out of range sometimes

*/

#include "emu.h"
#include "zsg2.h"

#include <algorithm>
#include <fstream>
#include <cmath>

#define EMPHASIS_INITIAL_BIAS 0
// Adjusts the cutoff constant of the filter by right-shifting the filter state.
// The current value gives a -6dB cutoff frequency at about 81.5 Hz, assuming
// sample playback at 32.552 kHz.
#define EMPHASIS_FILTER_SHIFT (16-10)
#define EMPHASIS_ROUNDING 0x20
// Adjusts the output amplitude by right-shifting the filtered output. Should be
// kept relative to the filter shift. A too low value will cause clipping, while
// too high will cause quantization noise.
#define EMPHASIS_OUTPUT_SHIFT 1

// device type definition
DEFINE_DEVICE_TYPE(ZSG2, zsg2_device, "zsg2", "ZOOM ZSG-2")

//-------------------------------------------------
//  zsg2_device - constructor
//-------------------------------------------------

zsg2_device::zsg2_device(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock)
	: device_t(mconfig, ZSG2, tag, owner, clock)
	, device_sound_interface(mconfig, *this)
	, m_mem_base(*this, DEVICE_SELF)
	, m_read_address(0)
	, m_ext_read_handler(*this)
{
}

//-------------------------------------------------
//  device_start - device-specific startup
//-------------------------------------------------

void zsg2_device::device_start()
{
	m_ext_read_handler.resolve();

	memset(&m_chan, 0, sizeof(m_chan));

	m_stream = stream_alloc(0, 4, clock() / 768);

	m_mem_blocks = m_mem_base.length();
	m_mem_copy = make_unique_clear<uint32_t[]>(m_mem_blocks);
	m_full_samples = make_unique_clear<int16_t[]>(m_mem_blocks * 4 + 4); // +4 is for empty block

	// register for savestates
	save_pointer(NAME(m_mem_copy), m_mem_blocks / sizeof(uint32_t));
	save_pointer(NAME(m_full_samples), (m_mem_blocks * 4 + 4) / sizeof(int16_t));
	save_item(NAME(m_read_address));

	// Generate the output gain table. Assuming -1dB per step for now.
	for (int i = 1; i < 32; i++)
	{
		double val = pow(10, -(31 - i) / 20.) * 65535.;
		m_gain_tab[i] = val;
	}
	m_gain_tab[0] = 0;

	for (int ch = 0; ch < 48; ch++)
	{
		save_item(NAME(m_chan[ch].v), ch);
		save_item(NAME(m_chan[ch].status), ch);
		save_item(NAME(m_chan[ch].cur_pos), ch);
		save_item(NAME(m_chan[ch].step_ptr), ch);
		save_item(NAME(m_chan[ch].step), ch);
		save_item(NAME(m_chan[ch].start_pos), ch);
		save_item(NAME(m_chan[ch].end_pos), ch);
		save_item(NAME(m_chan[ch].loop_pos), ch);
		save_item(NAME(m_chan[ch].page), ch);

		save_item(NAME(m_chan[ch].vol), ch);
		save_item(NAME(m_chan[ch].vol_initial), ch);
		save_item(NAME(m_chan[ch].vol_target), ch);
		save_item(NAME(m_chan[ch].vol_delta), ch);

		save_item(NAME(m_chan[ch].output_cutoff), ch);
		save_item(NAME(m_chan[ch].output_cutoff_initial), ch);
		save_item(NAME(m_chan[ch].output_cutoff_target), ch);
		save_item(NAME(m_chan[ch].output_cutoff_delta), ch);

		save_item(NAME(m_chan[ch].emphasis_filter_state), ch);
		save_item(NAME(m_chan[ch].output_filter_state), ch);

		save_item(NAME(m_chan[ch].output_gain), ch);

		save_item(NAME(m_chan[ch].samples), ch);
	}

	save_item(NAME(m_sample_count));
}

//-------------------------------------------------
//  device_reset - device-specific reset
//-------------------------------------------------

void zsg2_device::device_reset()
{
	m_read_address = 0;

	// stop playing and clear all channels
	control_w(4, 0xffff);
	control_w(5, 0xffff);
	control_w(6, 0xffff);

	for (int ch = 0; ch < 48; ch++)
		for (int reg = 0; reg < 0x10; reg++)
			chan_w(ch, reg, 0);
	m_sample_count = 0;

#if 0
	for (int i = 0; i < m_mem_blocks; i++)
		prepare_samples(i);

	FILE* f;

	f = fopen("zoom_samples.bin","wb");
	fwrite(m_mem_copy.get(),1,m_mem_blocks*4,f);
	fclose(f);

	f = fopen("zoom_samples.raw","wb");
	fwrite(m_full_samples.get(),2,m_mem_blocks*4,f);
	fclose(f);
#endif
}

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

uint32_t zsg2_device::read_memory(uint32_t offset)
{
	if (offset >= m_mem_blocks)
		return 0;

	if (m_ext_read_handler.isnull())
		return m_mem_base[offset];

	return m_ext_read_handler(offset);
}

int16_t *zsg2_device::prepare_samples(uint32_t offset)
{
	uint32_t block = read_memory(offset);

	if (block == 0)
		return &m_full_samples[m_mem_blocks]; // overflow or 0

	if (block == m_mem_copy[offset])
		return &m_full_samples[offset * 4]; // cached

	m_mem_copy[offset] = block;
	offset *= 4;

	// decompress 32 bit block to 4 16-bit samples
	// 42222222 51111111 60000000 ssss3333
	m_full_samples[offset|0] = block >> 8 & 0x7f;
	m_full_samples[offset|1] = block >> 16 & 0x7f;
	m_full_samples[offset|2] = block >> 24 & 0x7f;
	m_full_samples[offset|3] = (block >> (8+1) & 0x40) | (block >> (16+2) & 0x20) | (block >> (24+3) & 0x10) | (block & 0xf);

	// sign-extend and shift
	uint8_t shift = block >> 4 & 0xf;
	for (int i = offset; i < (offset + 4); i++)
	{
		m_full_samples[i] <<= 9;
		m_full_samples[i] >>= shift;
	}

	return &m_full_samples[offset];
}

// Fill the buffer with filtered samples
void zsg2_device::filter_samples(zchan *ch)
{
	int16_t *raw_samples = prepare_samples(ch->page | ch->cur_pos);
	ch->samples[0] = ch->samples[4]; // we want to remember the last sample

	for (int i = 0; i < 4; i++)
	{
		ch->emphasis_filter_state += raw_samples[i]-((ch->emphasis_filter_state+EMPHASIS_ROUNDING)>>EMPHASIS_FILTER_SHIFT);

		int32_t sample = ch->emphasis_filter_state >> EMPHASIS_OUTPUT_SHIFT;
		ch->samples[i+1] = std::min<int32_t>(std::max<int32_t>(sample, -32768), 32767);
	}
}

//-------------------------------------------------
//  sound_stream_update - handle a stream update
//-------------------------------------------------

void zsg2_device::sound_stream_update(sound_stream &stream, std::vector<read_stream_view> const &inputs, std::vector<write_stream_view> &outputs)
{
	for (int i = 0; i < outputs[0].samples(); i++)
	{
		int32_t mix[4] = {};

		// loop over all channels
		for (auto & elem : m_chan)
		{
			if(~elem.status & STATUS_ACTIVE)
				continue;

			elem.step_ptr += elem.step;
			if (elem.step_ptr & 0xffff0000)
			{
				if (++elem.cur_pos >= elem.end_pos)
				{
					// loop sample
					elem.cur_pos = elem.loop_pos;
					if ((elem.cur_pos + 1) >= elem.end_pos)
					{
						// end of sample
						elem.vol = 0; //this should help the channel allocation just a bit
						elem.status &= ~STATUS_ACTIVE;
						continue;
					}
				}

				if(elem.cur_pos == elem.start_pos)
					elem.emphasis_filter_state = EMPHASIS_INITIAL_BIAS;

				elem.step_ptr &= 0xffff;
				filter_samples(&elem);
			}

			uint8_t sample_pos = elem.step_ptr >> 14 & 3;
			int32_t sample = elem.samples[sample_pos];

			// linear interpolation (hardware certainly does something similar)
			sample += ((uint16_t)(elem.step_ptr<<2&0xffff) * (int16_t)(elem.samples[sample_pos+1] - sample))>>16;

			// another filter...
			elem.output_filter_state += (sample - (elem.output_filter_state>>16)) * elem.output_cutoff;
			sample = elem.output_filter_state >> 16;

			// To prevent DC bias, we need to slowly discharge the filter when the output filter cutoff is 0
			if(!elem.output_cutoff)
				elem.output_filter_state >>= 1;

			sample = (sample * elem.vol)>>16;

			for(int output=0; output<4; output++)
			{
				int output_gain = elem.output_gain[output] & 0x1f; // left / right
				int32_t output_sample = sample;

				if (elem.output_gain[output] & 0x80) // perhaps ?
					output_sample = -output_sample;

				mix[output] += (output_sample * m_gain_tab[output_gain&0x1f]) >> 16;
			}

			// Apply ramping every other update
			// It's possible key on is handled on the other sample
			if(m_sample_count & 1)
			{
				elem.vol = ramp(elem.vol, elem.vol_target, elem.vol_delta);
				elem.output_cutoff = ramp(elem.output_cutoff, elem.output_cutoff_target, elem.output_cutoff_delta);
			}
		}

		for(int output=0; output<4; output++)
			outputs[output].put_int_clamp(i, mix[output], 32768);
	}
	m_sample_count++;
}

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

void zsg2_device::chan_w(int ch, int reg, uint16_t data)
{
	switch (reg)
	{
		case 0x0:
			// lo byte: unknown, 0 on most games
			// hi byte: start address low
			m_chan[ch].start_pos = (m_chan[ch].start_pos & 0xff00) | (data >> 8 & 0xff);
			break;

		case 0x1:
			// lo byte: start address high
			// hi byte: address page
			m_chan[ch].start_pos = (m_chan[ch].start_pos & 0x00ff) | (data << 8 & 0xff00);
			m_chan[ch].page = data << 8 & 0xff0000;
			break;

		case 0x2:
			// no function? always 0
			break;

		case 0x3:
			// unknown, always 0x0400. is this a flag?
			m_chan[ch].status &= 0x8000;
			m_chan[ch].status |= data & 0x7fff;
			break;

		case 0x4:
			// frequency
			m_chan[ch].step = data + 1;
			break;

		case 0x5:
			// lo byte: loop address low
			// hi byte: right output gain (direct)
			m_chan[ch].loop_pos = (m_chan[ch].loop_pos & 0xff00) | (data & 0xff);
			m_chan[ch].output_gain[3] = data >> 8;
			break;

		case 0x6:
			// end address
			m_chan[ch].end_pos = data;
			break;

		case 0x7:
			// lo byte: loop address high
			// hi byte: left output gain (direct)
			m_chan[ch].loop_pos = (m_chan[ch].loop_pos & 0x00ff) | (data << 8 & 0xff00);
			m_chan[ch].output_gain[2] = data >> 8;
			break;

		case 0x8:
			// IIR lowpass time constant (initial, latched on key on)
			m_chan[ch].output_cutoff_initial = data;
			break;

		case 0x9:
			// writes 0 at key on
			m_chan[ch].output_cutoff = data;
			break;

		case 0xa:
			// volume (initial, latched on key on)
			m_chan[ch].vol_initial = data;
			break;

		case 0xb:
			// writes 0 at key on
			m_chan[ch].vol = data;
			break;

		case 0xc:
			// IIR lowpass time constant (target)
			m_chan[ch].output_cutoff_target = data;
			break;

		case 0xd:
			// hi byte: DSP channel 1 (chorus) gain
			// lo byte: Filter ramping speed
			m_chan[ch].output_gain[1] = data >> 8;
			m_chan[ch].output_cutoff_delta = get_ramp(data & 0xff);
			break;

		case 0xe:
			// volume target
			m_chan[ch].vol_target = data;
			break;

		case 0xf:
			// hi byte: DSP channel 0 (reverb) gain
			// lo byte: Volume ramping speed
			m_chan[ch].output_gain[0] = data >> 8;
			m_chan[ch].vol_delta = get_ramp(data & 0xff);
			break;

		default:
			break;
	}

	m_chan[ch].v[reg] = data;
}

uint16_t zsg2_device::chan_r(int ch, int reg)
{
	switch (reg)
	{
		case 0x3:
			// no games read from this.
			return m_chan[ch].status;
		case 0x9:
			// pretty certain, though no games actually read from this.
			return m_chan[ch].output_cutoff;
		case 0xb: // Only later games (taitogn) read this register...
			// GNet games use some of the flags to decide which channels to kill when
			// all the channels are busy. (take raycris song #23 as an example)
			return m_chan[ch].vol;
		default:
			break;
	}

	return m_chan[ch].v[reg];
}

// Convert ramping register value to something more usable.
// Upper 4 bits is a shift amount, lower 4 bits is a 2's complement value.
// Get ramp amount by sign extending the low 4 bits, XOR by 8, then
// shifting it by the upper 4 bits.
// CPU uses a lookup table (stored in gdarius sound cpu ROM at 0x6332) to
// calculate this value, for now I'm generating an opproximate inverse.
int16_t zsg2_device::get_ramp(uint8_t val)
{
	int16_t frac = val<<12; // sign extend
	frac = ((frac>>12) ^ 8) << (val >> 4);
	return (frac >> 4);
}

inline uint16_t zsg2_device::ramp(uint16_t current, uint16_t target, int16_t delta)
{
	int32_t rampval = current + delta;
	if(delta < 0 && rampval < target)
		rampval = target;
	else if(delta >= 0 && rampval > target)
		rampval = target;

	return rampval;
}

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

void zsg2_device::control_w(int reg, uint16_t data)
{
	switch (reg)
	{
		case 0x00: case 0x01: case 0x02:
		{
			// key on
			int base = (reg & 3) << 4;
			for (int i = 0; i < 16; i++)
			{
				if (data & (1 << i))
				{
					int ch = base | i;
					m_chan[ch].status |= STATUS_ACTIVE;
					m_chan[ch].cur_pos = m_chan[ch].start_pos - 1;
					m_chan[ch].step_ptr = 0x10000;
					// Ignoring the "initial volume" for now because it causes lots of clicking
					m_chan[ch].vol = 0; // m_chan[ch].vol_initial;
					m_chan[ch].vol_delta = 0x0400; // register 06 ?
					m_chan[ch].output_cutoff = m_chan[ch].output_cutoff_initial;
					m_chan[ch].output_filter_state = 0;
				}
			}
			break;
		}

		case 0x04: case 0x05: case 0x06:
		{
			// key off
			int base = (reg & 3) << 4;
			for (int i = 0; i < 16; i++)
			{
				if (data & (1 << i))
				{
					int ch = base | i;
					m_chan[ch].vol = 0;
					m_chan[ch].status &= ~STATUS_ACTIVE;
				}
			}
			break;
		}

//      case 0x0c: //These registers are sometimes written to by the CPU. Unknown purpose.
//          break;
//      case 0x0d:
//          break;
//      case 0x10:
//          break;

//      case 0x18:
//          break;

		case 0x1c:
			// rom readback address low (low 2 bits always 0)
			if (data & 3) popmessage("ZSG2 address %04X, contact MAMEdev", data);
			m_read_address = (m_read_address & 0x3fffc000) | (data >> 2 & 0x00003fff);
			break;
		case 0x1d:
			// rom readback address high
			m_read_address = (m_read_address & 0x00003fff) | (data << 14 & 0x3fffc000);
			break;

		default:
			if(reg < 0x20)
				m_reg[reg] = data;
			logerror("ZSG2 control   %02X = %04X\n", reg, data & 0xffff);
			break;
	}
}

uint16_t zsg2_device::control_r(int reg)
{
	switch (reg)
	{
		case 0x14:
			// memory bus busy?
			// right before reading memory, it polls until low 8 bits are 0
			return 0;

		case 0x1e:
			// rom readback word low
			return read_memory(m_read_address) & 0xffff;
		case 0x1f:
			// rom readback word high
			return read_memory(m_read_address) >> 16;

		default:
			if(reg < 0x20)
				return m_reg[reg];
			break;
	}

	return 0;
}

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

void zsg2_device::write(offs_t offset, uint16_t data, uint16_t mem_mask)
{
	// we only support full 16-bit accesses
	if (mem_mask != 0xffff)
	{
		popmessage("ZSG2 write mask %04X, contact MAMEdev", mem_mask);
		return;
	}

	m_stream->update();

	if (offset < 0x300)
	{
		int chan = offset >> 4;
		int reg = offset & 0xf;

		chan_w(chan, reg, data);
	}
	else
	{
		control_w(offset - 0x300, data);
	}
}

uint16_t zsg2_device::read(offs_t offset, uint16_t mem_mask)
{
	// we only support full 16-bit accesses
	if (mem_mask != 0xffff)
	{
		popmessage("ZSG2 read mask %04X, contact MAMEdev", mem_mask);
		return 0;
	}

	if (offset < 0x300)
	{
		int chan = offset >> 4;
		int reg = offset & 0xf;

		return chan_r(chan, reg);
	}
	else
	{
		return control_r(offset - 0x300);
	}
}