iremga20: assume keyon is at reg 6 bit 1(not just any non-0 value), removed 2nd end of sample check, misc refactor and added notes (nw)

src/devices/sound/iremga20.cpp

@@ -3,8 +3,17 @@
 /*********************************************************
 
 Irem GA20 PCM Sound Chip
+80 pin QFP, label NANAO GA20 (Nanao Corporation was Irem's parent company)
 
-It's not currently known whether this chip is stereo.
+TODO:
+- It's not currently known whether this chip is stereo.
+- Is sample position base(regs 0,1) used while sample is playing, or
+  latched at key on? We've always emulated it the latter way.
+  gunforc2 seems to be the only game updating the address regs sometimes
+  while a sample is playing, but it doesn't seem intentional.
+- What is the 2nd sample address for? Is it end(cut-off) address, or
+  loop start address? Every game writes a value that's past sample end.
+- All games write either 0 or 2 to reg #6, do other bits have any function?
 
 
 Revisions:
@@ -26,7 +35,7 @@ Revisions:
 02-03-2007 R. Belmont
 - Cleaned up faux x86 assembly.
 
-09-25-2018 Valley Bell
+09-25-2018 Valley Bell & co
 - rewrote channel update to make data 0 act as sample terminator
 
 *********************************************************/
@@ -36,8 +45,6 @@ Revisions:
 
 #include <algorithm>
 
-#define MAX_VOL 256
-
 
 // device type definition
 DEFINE_DEVICE_TYPE(IREMGA20, iremga20_device, "iremga20", "Irem GA20")
@@ -66,26 +73,16 @@ iremga20_device::iremga20_device(const machine_config &mconfig, const char *tag,
 
 void iremga20_device::device_start()
 {
-	int i;
-
-	iremga20_reset();
-
-	std::fill(std::begin(m_regs), std::end(m_regs), 0);
-
 	m_stream = stream_alloc(0, 2, clock()/4);
 
 	save_item(NAME(m_regs));
-	for (i = 0; i < 4; i++)
+	for (int i = 0; i < 4; i++)
 	{
 		save_item(NAME(m_channel[i].rate), i);
-		save_item(NAME(m_channel[i].size), i);
-		save_item(NAME(m_channel[i].start), i);
 		save_item(NAME(m_channel[i].pos), i);
 		save_item(NAME(m_channel[i].frac), i);
 		save_item(NAME(m_channel[i].end), i);
 		save_item(NAME(m_channel[i].volume), i);
-		save_item(NAME(m_channel[i].pan), i);
-		save_item(NAME(m_channel[i].effect), i);
 		save_item(NAME(m_channel[i].play), i);
 	}
 }
@@ -97,7 +94,16 @@ void iremga20_device::device_start()
 
 void iremga20_device::device_reset()
 {
-	iremga20_reset();
+	std::fill(std::begin(m_regs), std::end(m_regs), 0);
+	for (int i = 0; i < 4; i++)
+	{
+		m_channel[i].rate = 0;
+		m_channel[i].pos = 0;
+		m_channel[i].frac = 0;
+		m_channel[i].end = 0;
+		m_channel[i].volume = 0;
+		m_channel[i].play = 0;
+	}
 }
 
 //-------------------------------------------------
@@ -142,12 +148,12 @@ void iremga20_device::sound_stream_update(sound_stream &stream, stream_sample_t
 				if (sample == 0x00) // check for sample end marker
 					ch.play = 0;
 				else
+				{
 					sampleout += (sample - 0x80) * (int32_t)ch.volume;
-				ch.frac += ch.rate;
+					ch.frac += ch.rate;
-				ch.pos += (ch.frac >> 24);
+					ch.pos += (ch.frac >> 24);
-				ch.frac &= ((1 << 24) - 1);
+					ch.frac &= ((1 << 24) - 1);
-				if (ch.pos >= ch.end)   // for safety (the actual chip probably doesn't check this)
+				}
-					ch.play = 0;
 			}
 		}
 
@@ -159,86 +165,64 @@ void iremga20_device::sound_stream_update(sound_stream &stream, stream_sample_t
 
 WRITE8_MEMBER( iremga20_device::irem_ga20_w )
 {
-	int channel;
-
-	//logerror("GA20:  Offset %02x, data %04x\n",offset,data);
-
 	m_stream->update();
 
-	channel = offset >> 3;
+	offset &= 0x1f;
-
 	m_regs[offset] = data;
+	int ch = offset >> 3;
+
+	// channel regs:
+	// 0,1: start address
+	// 2,3: end? address
+	// 4: rate
+	// 5: volume
+	// 6: control
+	// 7: voice status (read-only)
 
 	switch (offset & 0x7)
 	{
-		case 0: /* start address low */
-			m_channel[channel].start = ((m_channel[channel].start)&0xff000) | (data<<4);
-			break;
-
-		case 1: /* start address high */
-			m_channel[channel].start = ((m_channel[channel].start)&0x00ff0) | (data<<12);
-			break;
-
-		case 2: /* end? address low */
-			m_channel[channel].end = ((m_channel[channel].end)&0xff000) | (data<<4);
-			break;
-
-		case 3: /* end? address high */
-			m_channel[channel].end = ((m_channel[channel].end)&0x00ff0) | (data<<12);
-			break;
-
 		case 4:
-			m_channel[channel].rate = (1 << 24) / (256 - data);
+			m_channel[ch].rate = (1 << 24) / (256 - data);
 			break;
 
-		case 5: //AT: gain control
+		case 5:
-			m_channel[channel].volume = (data * MAX_VOL) / (data + 10);
+			m_channel[ch].volume = (data * 256) / (data + 10);
 			break;
 
-		case 6: //AT: this is always written 2(enabling both channels?)
+		case 6:
-			m_channel[channel].play = data;
+			// d1: key on/off
-			m_channel[channel].pos = m_channel[channel].start;
+			if (data & 2)
-			m_channel[channel].frac = 0;
+			{
+				m_channel[ch].play = 1;
+				m_channel[ch].pos = (m_regs[ch << 3 | 0] | m_regs[ch << 3 | 1] << 8) << 4;
+				m_channel[ch].end = (m_regs[ch << 3 | 2] | m_regs[ch << 3 | 3] << 8) << 4;
+				m_channel[ch].frac = 0;
+			}
+			else
+				m_channel[ch].play = 0;
+
+			// other: unknown/unused
+			// possibilities are: loop flag, left/right speaker(stereo)
 			break;
 	}
 }
 
 READ8_MEMBER( iremga20_device::irem_ga20_r )
 {
-	int channel;
-
 	m_stream->update();
 
-	channel = offset >> 3;
+	offset &= 0x1f;
+	int ch = offset >> 3;
 
 	switch (offset & 0x7)
 	{
-		case 7: // voice status.  bit 0 is 1 if active. (routine around 0xccc in rtypeleo)
+		case 7: // voice status. bit 0 is 1 if active. (routine around 0xccc in rtypeleo)
-			return m_channel[channel].play ? 1 : 0;
+			return m_channel[ch].play;
 
 		default:
-			logerror("GA20: read unk. register %d, channel %d\n", offset & 0xf, channel);
+			logerror("GA20: read unk. register %d, channel %d\n", offset & 0x7, ch);
 			break;
 	}
 
 	return 0;
 }
-
-
-void iremga20_device::iremga20_reset()
-{
-	int i;
-
-	for( i = 0; i < 4; i++ ) {
-	m_channel[i].rate = 0;
-	m_channel[i].size = 0;
-	m_channel[i].start = 0;
-	m_channel[i].pos = 0;
-	m_channel[i].frac = 0;
-	m_channel[i].end = 0;
-	m_channel[i].volume = 0;
-	m_channel[i].pan = 0;
-	m_channel[i].effect = 0;
-	m_channel[i].play = 0;
-	}
-}

src/devices/sound/iremga20.h

@@ -44,21 +44,15 @@ private:
 	struct channel_def
 	{
 		uint32_t rate;
-		uint32_t size;
-		uint32_t start;
 		uint32_t pos;
 		uint32_t frac;
 		uint32_t end;
 		uint32_t volume;
-		uint32_t pan;
-		uint32_t effect;
 		uint32_t play;
 	};
 
-	void iremga20_reset();
-
 	sound_stream *m_stream;
-	uint8_t m_regs[0x40/2];
+	uint8_t m_regs[0x20];
 	channel_def m_channel[4];
 };