c140.cpp: add sample status readback, fixes engine sound in suzuka 8 hours, final lap and four trax game series (#8080)

src/devices/sound/c140.cpp

@@ -463,10 +463,23 @@ void c219_device::sound_stream_update(sound_stream &stream, std::vector<read_str
 	}
 }
 
+inline u8 c140_device::keyon_status_read(u16 offset)
+{
+	m_stream->update();
+	C140_VOICE const &v = m_voi[offset >> 4];
+	// suzuka 8 hours and final lap games reads from here,
+	// expecting bit 6 to be an inprogress sample flag.
+	// four trax also expects bit 4 high for some specific channels to make engine noises to work properly
+	// (sounds kinda bogus when player crashes in an object and jump spin, needs real HW verification)
+	return (v.key ? 0x40 : 0x00) | (v.mode & 0x3f);
+}
+
 
 u8 c140_device::c140_r(offs_t offset)
 {
 	offset &= 0x1ff;
+	if ((offset & 0xf) == 0x5)
+		return keyon_status_read(offset);
 	return m_REG[offset];
 }
 
@@ -540,6 +553,11 @@ void c140_device::c140_w(offs_t offset, u8 data)
 u8 c219_device::c219_r(offs_t offset)
 {
 	offset &= 0x1ff;
+	// assume same as c140
+	// TODO: what happens here on reading unmapped voice regs?
+	if ((offset & 0xf) == 0x5)
+		return keyon_status_read(offset);
+
 	return m_REG[offset];
 }
 

src/devices/sound/c140.h

@@ -97,6 +97,8 @@ protected:
 	C140_VOICE m_voi[MAX_VOICE];
 
 	emu_timer *m_int1_timer;
+	
+	u8 keyon_status_read(u16 offset);
 };
 
 class c219_device : public c140_device