okiadpcm.cpp: Add looped sample support, Allow reading current output without decoding

Fix initial values, Fix descriptions
qs1000.cpp: Add save state related to loop support (disabled currently)

src/devices/sound/okiadpcm.cpp

@@ -2,7 +2,7 @@
 // copyright-holders:Andrew Gardner,Aaron Giles
 /***************************************************************************
 
-    okiadpcm.h
+    okiadpcm.cpp
 
     OKI ADPCM emulation.
 
@@ -39,14 +39,15 @@ int oki_adpcm_state::s_diff_lookup[49*16];
 void oki_adpcm_state::reset()
 {
 	// reset the signal/step
-	m_signal = -2;
+	m_signal = m_loop_signal = 0;
-	m_step = 0;
+	m_step = m_loop_step = 0;
+	m_saved = false;
 }
 
 
 //-------------------------------------------------
-//  device_clock_changed - called if the clock
+//  clock - decode single nibble and update
-//  changes
+//  ADPCM output
 //-------------------------------------------------
 
 int16_t oki_adpcm_state::clock(uint8_t nibble)
@@ -72,6 +73,36 @@ int16_t oki_adpcm_state::clock(uint8_t nibble)
 }
 
 
+//-------------------------------------------------
+//  save - save current ADPCM state to buffer
+//-------------------------------------------------
+
+void oki_adpcm_state::save()
+{
+	if (!m_saved)
+	{
+		m_loop_signal = m_signal;
+		m_loop_step = m_step;
+		m_saved = true;
+	}
+}
+
+
+//-------------------------------------------------
+//  restore - restore previous ADPCM state
+//  from buffer
+//-------------------------------------------------
+
+void oki_adpcm_state::restore()
+{
+	if (m_saved)
+	{
+		m_signal = m_loop_signal;
+		m_step = m_loop_step;
+	}
+}
+
+
 //-------------------------------------------------
 //  compute_tables - precompute tables for faster
 //  sound generation
@@ -128,14 +159,15 @@ int oki_adpcm2_state::s_diff_lookup[49*16];
 void oki_adpcm2_state::reset()
 {
 	// reset the signal/step
-	m_signal = -2;
+	m_signal = m_loop_signal = -2;
-	m_step = 0;
+	m_step = m_loop_step = 0;
+	m_saved = false;
 }
 
 
 //-------------------------------------------------
-//  device_clock_changed - called if the clock
+//  clock - decode single nibble and update
-//  changes
+//  ADPCM output
 //-------------------------------------------------
 
 int16_t oki_adpcm2_state::clock(uint8_t nibble)
@@ -161,6 +193,36 @@ int16_t oki_adpcm2_state::clock(uint8_t nibble)
 }
 
 
+//-------------------------------------------------
+//  save - save current ADPCM state to buffer
+//-------------------------------------------------
+
+void oki_adpcm2_state::save()
+{
+	if (!m_saved)
+	{
+		m_loop_signal = m_signal;
+		m_loop_step = m_step;
+		m_saved = true;
+	}
+}
+
+
+//-------------------------------------------------
+//  restore - restore previous ADPCM state
+//  from buffer
+//-------------------------------------------------
+
+void oki_adpcm2_state::restore()
+{
+	if (m_saved)
+	{
+		m_signal = m_loop_signal;
+		m_step = m_loop_step;
+	}
+}
+
+
 //-------------------------------------------------
 //  compute_tables - precompute tables for faster
 //  sound generation

src/devices/sound/okiadpcm.h

@@ -24,9 +24,15 @@ public:
 
 	void reset();
 	int16_t clock(uint8_t nibble);
+	int16_t output() { return m_signal; }
+	void save();
+	void restore();
 
 	int32_t   m_signal;
 	int32_t   m_step;
+	int32_t   m_loop_signal;
+	int32_t   m_loop_step;
+	bool      m_saved;
 
 private:
 	static const int8_t s_index_shift[8];
@@ -48,9 +54,15 @@ public:
 
 	void reset();
 	int16_t clock(uint8_t nibble);
+	int16_t output() { return m_signal; }
+	void save();
+	void restore();
 
 	int32_t   m_signal;
 	int32_t   m_step;
+	int32_t   m_loop_signal;
+	int32_t   m_loop_step;
+	bool      m_saved;
 
 private:
 	static const int8_t s_index_shift[8];

src/devices/sound/qs1000.cpp

@@ -259,6 +259,9 @@ void qs1000_device::device_start()
 		save_item(NAME(m_channels[i].m_regs), i);
 		save_item(NAME(m_channels[i].m_adpcm.m_signal), i);
 		save_item(NAME(m_channels[i].m_adpcm.m_step), i);
+		save_item(NAME(m_channels[i].m_adpcm.m_loop_signal), i);
+		save_item(NAME(m_channels[i].m_adpcm.m_loop_step), i);
+		save_item(NAME(m_channels[i].m_adpcm.m_saved), i);
 	}
 }
 
@@ -505,7 +508,16 @@ void qs1000_device::sound_stream_update(sound_stream &stream, stream_sample_t **
 						chan.m_adpcm_addr++;
 
 						if (chan.m_start + chan.m_adpcm_addr >= chan.m_loop_end)
+						{
 							chan.m_adpcm_addr = chan.m_loop_start - chan.m_start;
+#if 0 // Looping disabled until envelopes work
+							chan.m_adpcm.restore();
+						}
+						if (chan.m_start + chan.m_adpcm_addr == chan.m_loop_start)
+						{
+							chan.m_adpcm.save();
+#endif
+						}
 
 						uint8_t data = read_byte(chan.m_start + (chan.m_adpcm_addr >> 1));
 						uint8_t nibble = (chan.m_adpcm_addr & 1 ? data : data >> 4) & 0xf;