C352: implement volume ramping, rewrite mulaw algorithm

- implement volume ramping behavior and confirmed with recording of
  real hardware (Tekken 3)
- rewrote mulaw algorithm. This is not quite perfect yet but is closer
  to recordings and sounds a bit clearer (example: Time Crisis)

src/devices/sound/c352.cpp

@@ -72,14 +72,18 @@ void c352_device::fetch_sample(c352_voice_t* v)
 	}
 	else
 	{
-		int8_t s;
+		int8_t s, s2;
 
 		s = (int8_t)read_byte(v->pos);
 
+		v->sample = s<<8;
 		if(v->flags & C352_FLG_MULAW)
-			v->sample = m_mulaw_table[(uint8_t)s];
+		{
-		else
+			s2 = (s&0x7f)>>4;
-			v->sample = s<<8;
+
+			v->sample = ((s2*s2)<<4) - (~(s2<<1)) * (s&0x0f);
+			v->sample = (s&0x80) ? (~v->sample)<<5 : v->sample<<5;
+		}
 
 		uint16_t pos = v->pos&0xffff;
 
@@ -120,11 +124,18 @@ void c352_device::fetch_sample(c352_voice_t* v)
 	}
 }
 
+void c352_device::ramp_volume(c352_voice_t* v,int ch,uint8_t val)
+{
+    int16_t vol_delta = v->curr_vol[ch] - val;
+    if(vol_delta != 0)
+        v->curr_vol[ch] += (vol_delta>0) ? -1 : 1;
+}
+
 void c352_device::sound_stream_update(sound_stream &stream, stream_sample_t **inputs, stream_sample_t **outputs, int samples)
 {
-
 	int i,j;
 	int16_t s;
+	int32_t next_counter;
 	stream_sample_t *buffer_fl = outputs[0];
 	stream_sample_t *buffer_fr = outputs[1];
 	stream_sample_t *buffer_rl = outputs[2];
@@ -145,13 +156,22 @@ void c352_device::sound_stream_update(sound_stream &stream, stream_sample_t **in
 
 			if(v->flags & C352_FLG_BUSY)
 			{
-				v->counter += v->freq;
+				next_counter = v->counter+v->freq;
 
-				if(v->counter > 0x10000)
+				if(next_counter & 0x10000)
 				{
-					v->counter &= 0xffff;
 					fetch_sample(v);
 				}
+								
+				if((next_counter^v->counter) & 0x18000)
+				{
+					ramp_volume(v,0,v->vol_f>>8);
+					ramp_volume(v,1,v->vol_f&0xff);
+					ramp_volume(v,2,v->vol_r>>8);
+					ramp_volume(v,3,v->vol_r&0xff);
+				}
+				
+				v->counter = next_counter&0xffff;
 
 				s = v->sample;
 
@@ -161,12 +181,12 @@ void c352_device::sound_stream_update(sound_stream &stream, stream_sample_t **in
 			}
 
 			// Left
-			out[0] += ((v->flags & C352_FLG_PHASEFL) ? -s * (v->vol_f>>8) : s * (v->vol_f>>8))>>8;
+			out[0] += (((v->flags & C352_FLG_PHASEFL) ? -s : s) * v->curr_vol[0])>>8;
-			out[2] += ((v->flags & C352_FLG_PHASERL) ? -s * (v->vol_r>>8) : s * (v->vol_r>>8))>>8;
+			out[2] += (((v->flags & C352_FLG_PHASEFR) ? -s : s) * v->curr_vol[2])>>8;
 
 			// Right
-			out[1] += ((v->flags & C352_FLG_PHASEFR) ? -s * (v->vol_f&0xff) : s * (v->vol_f&0xff))>>8;
+			out[1] += (((v->flags & C352_FLG_PHASERL) ? -s : s) * v->curr_vol[1])>>8;
-			out[3] += ((v->flags & C352_FLG_PHASEFR) ? -s * (v->vol_r&0xff) : s * (v->vol_r&0xff))>>8;
+			out[3] += (((v->flags & C352_FLG_PHASERL) ? -s : s) * v->curr_vol[3])>>8;
 		}
 
 		*buffer_fl++ = (int16_t) (out[0]>>3);
@@ -174,8 +194,6 @@ void c352_device::sound_stream_update(sound_stream &stream, stream_sample_t **in
 		*buffer_rl++ = (int16_t) (out[2]>>3);
 		*buffer_rr++ = (int16_t) (out[3]>>3);
 	}
-
-
 }
 
 uint16_t c352_device::read_reg16(unsigned long address)
@@ -196,6 +214,8 @@ uint16_t c352_device::read_reg16(unsigned long address)
 
 	if(address < 0x100)
 		return *((uint16_t*)&m_c352_v[address/8]+reg_map[address%8]);
+	else if(address == 0x200)
+		return m_control;
 	else
 		return 0;
 
@@ -222,11 +242,13 @@ void c352_device::write_reg16(unsigned long address, unsigned short val)
 
 	if(address < 0x100)
 	{
-		//printf("w %04lx,%04x, %d\n", address, val, reg_map[address&7]);
 		*((uint16_t*)&m_c352_v[address/8]+reg_map[address%8]) = val;
 	}
 	else if(address == 0x200)
+	{
 		m_control = val;
+		logerror("C352 control register write: %04x\n",val);
+	}
 	else if(address == 0x202) // execute keyons/keyoffs
 	{
 		for(i=0;i<32;i++)
@@ -237,16 +259,18 @@ void c352_device::write_reg16(unsigned long address, unsigned short val)
 
 				m_c352_v[i].sample = 0;
 				m_c352_v[i].last_sample = 0;
-				m_c352_v[i].counter = 0x10000;
+				m_c352_v[i].counter = 0xffff;
 
 				m_c352_v[i].flags |= C352_FLG_BUSY;
 				m_c352_v[i].flags &= ~(C352_FLG_KEYON|C352_FLG_LOOPHIST);
-
+				
-				//printf("voice %d : pos= %08x\n",i,m_c352_v[i].pos);
+				m_c352_v[i].curr_vol[0] = m_c352_v[i].curr_vol[1] = 0;
+				m_c352_v[i].curr_vol[2] = m_c352_v[i].curr_vol[3] = 0;
 			}
 			else if(m_c352_v[i].flags & C352_FLG_KEYOFF)
 			{
 				m_c352_v[i].flags &= ~(C352_FLG_BUSY|C352_FLG_KEYOFF);
+				m_c352_v[i].counter = 0xffff;
 			}
 		}
 	}
@@ -264,27 +288,11 @@ void c352_device::device_clock_changed()
 void c352_device::device_start()
 {
 	int i;
-	double x_max = 32752.0;
+	
-	double y_max = 127.0;
-	double u = 10.0;
-
 	m_sample_rate_base = clock() / m_divider;
 
 	m_stream = machine().sound().stream_alloc(*this, 0, 4, m_sample_rate_base);
 
-	// generate mulaw table for mulaw format samples
-	for (i = 0; i < 256; i++)
-	{
-			double y = (double) (i & 0x7f);
-			double x = (exp (y / y_max * log (1.0 + u)) - 1.0) * x_max / u;
-
-			if (i & 0x80)
-			{
-				x = -x;
-			}
-			m_mulaw_table[i] = (uint16_t)x;
-	}
-
 	// register save state info
 	for (i = 0; i < 32; i++)
 	{
@@ -294,6 +302,7 @@ void c352_device::device_start()
 		save_item(NAME(m_c352_v[i].last_sample), i);
 		save_item(NAME(m_c352_v[i].vol_f), i);
 		save_item(NAME(m_c352_v[i].vol_r), i);
+		save_item(NAME(m_c352_v[i].curr_vol), i);
 		save_item(NAME(m_c352_v[i].freq), i);
 		save_item(NAME(m_c352_v[i].flags), i);
 		save_item(NAME(m_c352_v[i].wave_bank), i);
@@ -303,7 +312,6 @@ void c352_device::device_start()
 	}
 	save_item(NAME(m_random));
 	save_item(NAME(m_control));
-
 }
 
 void c352_device::device_reset()
@@ -325,7 +333,6 @@ WRITE16_MEMBER( c352_device::write )
 {
 	if (mem_mask == 0xffff)
 	{
-		//printf("%04x: %04x\n", offset, data);
 		write_reg16(offset, data);
 	}
 	else

src/devices/sound/c352.h

@@ -81,6 +81,8 @@ private:
 
 		uint16_t vol_f;
 		uint16_t vol_r;
+		uint8_t curr_vol[4];
+		
 		uint16_t freq;
 		uint16_t flags;
 
@@ -95,12 +97,12 @@ private:
 	int m_divider;
 
 	c352_voice_t m_c352_v[32];
-	int16_t m_mulaw_table[256];
 
 	uint16_t m_random;
 	uint16_t m_control; // control flags, purpose unknown.
 
 	void fetch_sample(c352_voice_t* v);
+	void ramp_volume(c352_voice_t* v,int ch,uint8_t val);
 
 	unsigned short read_reg16(unsigned long address);
 	void write_reg16(unsigned long address, unsigned short val);