bbd: Add support for a continuously-varying frequency to avoid abusing the sound manager.

src/devices/sound/bbd.cpp

@@ -17,7 +17,9 @@ bbd_device_base<Entries, Outputs>::bbd_device_base(const machine_config &mconfig
 	device_t(mconfig, type, tag, owner, clock),
 	device_sound_interface(mconfig, *this),
 	m_stream(nullptr),
-	m_curpos(0)
+	m_curpos(0),
+	m_cv_handler(*this),
+	m_next_bbdtime(attotime::zero)
 {
 	std::fill_n(&m_buffer[0], Entries, 0);
 }
@@ -30,8 +32,16 @@ bbd_device_base<Entries, Outputs>::bbd_device_base(const machine_config &mconfig
 template<int Entries, int Outputs>
 void bbd_device_base<Entries, Outputs>::device_start()
 {
+	m_cv_handler.resolve();
+
+	if (m_cv_handler.isnull())
 		m_stream = stream_alloc(1, Outputs, sample_rate());
+	else
+		m_stream = stream_alloc(1, Outputs, SAMPLE_RATE_OUTPUT_ADAPTIVE, STREAM_DISABLE_INPUT_RESAMPLING);
+
 	save_item(NAME(m_buffer));
+	save_item(NAME(m_curpos));
+	save_item(NAME(m_next_bbdtime));
 }
 
 
@@ -56,6 +66,8 @@ void bbd_device_base<Entries, Outputs>::sound_stream_update(sound_stream &stream
 	// BBDs that I've seen so far typically have 2 outputs, with the first outputting
 	// sample n-1 and the second outputting sampe n; if chips with more outputs
 	// or other taps turn up, this logic will need to be made more flexible
+	if (m_cv_handler.isnull())
+	{
 		for (int sampindex = 0; sampindex < outputs[0].samples(); sampindex++)
 		{
 			for (int outnum = 0; outnum < Outputs; outnum++)
@@ -64,6 +76,41 @@ void bbd_device_base<Entries, Outputs>::sound_stream_update(sound_stream &stream
 			m_curpos = (m_curpos + 1) % Entries;
 		}
 	}
+	else
+	{
+		read_stream_view in(inputs[0], m_next_bbdtime);
+		attotime intime = in.start_time();
+		attotime outtime = outputs[0].start_time();
+		int inpos = 0;
+
+		// loop until all outputs generated
+		for (int sampindex = 0; sampindex < outputs[0].samples(); sampindex++)
+		{
+			// we need to process some more BBD input
+			while (outtime >= m_next_bbdtime)
+			{
+				// find the input sample that overlaps our start time
+				while (intime + in.sample_period() < m_next_bbdtime)
+				{
+					inpos++;
+					intime += in.sample_period();
+				}
+
+				// copy that to the buffer
+				m_buffer[m_curpos] = in.get(inpos);
+				m_curpos = (m_curpos + 1) % std::size(m_buffer);
+
+				// advance the end time of this BBD sample
+				m_next_bbdtime += attotime(0, m_cv_handler(m_next_bbdtime));
+			}
+
+			// copy the most recently-generated BBD data
+			for (int outnum = 0; outnum < Outputs; outnum++)
+				outputs[outnum].put(sampindex, outputval(outnum - (Outputs - 1)));
+			outtime += outputs[0].sample_period();
+		}
+	}
+}
 
 
 //**************************************************************************

src/devices/sound/bbd.h

@@ -14,13 +14,19 @@
 template<int Entries, int Outputs>
 class bbd_device_base : public device_t, public device_sound_interface
 {
+public:
+	// configuration
+	template <typename... T> void set_cv_handler(T &&... args)
+	{
+		m_cv_handler.set(std::forward<T>(args)...);
+	}
+
 protected:
+	using cv_delegate = device_delegate<attoseconds_t (attotime const &)>;
+
 	// internal constructor
 	bbd_device_base(const machine_config &mconfig, const char *tag, device_t *owner, uint32_t clock, device_type type);
 
-	// override to convert clock to sample rate
-	virtual u32 sample_rate() const { return clock(); }
-
 	// device-level overrides
 	virtual void device_start() override;
 	virtual void device_clock_changed() override;
@@ -29,9 +35,15 @@ protected:
 	virtual void sound_stream_update(sound_stream &stream, std::vector<read_stream_view> const &inputs, std::vector<write_stream_view> &outputs) override;
 
 protected:
+	// override to convert clock to sample rate
+	stream_buffer::sample_t outputval(s32 index) const { return m_buffer[m_curpos + Entries + index]; }
+	virtual u32 sample_rate() const { return clock(); }
+
 	sound_stream *          m_stream;
 	u32                     m_curpos;
-	stream_buffer::sample_t m_buffer[Entries];
+	cv_delegate             m_cv_handler;
+	attotime                m_next_bbdtime;
+	stream_buffer::sample_t m_buffer[Entries + 1];
 };