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◆ main openmsx / src / sound / SN76489.hh
3.3 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef SN76489_HH
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#define SN76489_HH
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#include "ResampledSoundDevice.hh"
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#include "SimpleDebuggable.hh"
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#include <array>
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namespace openmsx {
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/** This class implements the Texas Instruments SN76489 sound chip.
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  * Unlike the AY-3-8910, this chip only performs sound synthesis.
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  *
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  * Resources used:
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  * - SN76489AN data sheet
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  *   http://map.grauw.nl/resources/sound/texas_instruments_sn76489an.pdf
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  * - Developer documentation on SMS Power!
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  *   http://www.smspower.org/Development/SN76489
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  * - John Kortink's reverse engineering results
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  *   http://www.zeridajh.org/articles/various/sn76489/index.htm
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  * - MAME's implementation
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  *   https://github.com/mamedev/mame/blob/master/src/devices/sound/sn76496.cpp
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  * - blueMSX's implementation
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  *   https://sourceforge.net/p/bluemsx/code/HEAD/tree/trunk/blueMSX/Src/SoundChips/SN76489.c
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  */
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class SN76489 final : public ResampledSoundDevice
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{
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public:
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	explicit SN76489(const DeviceConfig& config);
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	~SN76489();
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	// ResampledSoundDevice
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	void generateChannels(std::span<float*> buffers, unsigned num) override;
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	void reset(EmuTime time);
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	void write(uint8_t value, EmuTime time);
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	template<typename Archive>
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	void serialize(Archive& ar, unsigned version);
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private:
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	class NoiseShifter {
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	public:
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		/** Sets the feedback pattern and resets the shift register to the
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		  * initial state that matches that pattern.
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		  */
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		void initState(unsigned pattern, unsigned period);
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		/** Gets the current output of this shifter: 0 or 1.
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		  */
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		[[nodiscard]] unsigned getOutput() const;
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		/** Advances the shift register one step, to the next output.
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		  */
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		void advance();
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		/** Records that the shift register should be advanced multiple steps
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		  * before the next output is used.
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		  */
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		void queueAdvance(unsigned steps);
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		/** Advances the shift register by the number of steps that were queued.
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		  */
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		void catchUp();
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		template<typename Archive>
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		void serialize(Archive& ar, unsigned version);
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	private:
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		unsigned pattern;
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		unsigned period;
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		unsigned random;
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		unsigned stepsBehind;
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	};
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	/** Initialize registers, counters and other chip state.
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	  */
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	void initState();
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	/** Initialize noise shift register according to chip variant and noise
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	  * mode.
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	  */
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	void initNoise();
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	[[nodiscard]] uint16_t peekRegister(unsigned reg, EmuTime time) const;
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	void writeRegister(unsigned reg, uint16_t value, EmuTime time);
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	template<bool NOISE> void synthesizeChannel(
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		float*& buffer, unsigned num, unsigned generator);
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private:
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	NoiseShifter noiseShifter;
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	/** Register bank. The tone period registers (0, 2, 4) are 12 bits wide,
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	  * all other registers are 4 bits wide.
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	  */
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	std::array<uint16_t, 8> regs;
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	/** The last register written to (0-7).
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	  */
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	uint8_t registerLatch;
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	/** Frequency counter for each channel.
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	  * These count down and when they reach zero, the output flips and the
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	  * counter is re-loaded with the value of the period register.
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	  */
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	std::array<uint16_t, 4> counters;
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	/** Output flip-flop state (0 or 1) for each channel.
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	  */
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	std::array<uint8_t, 4> outputs;
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	struct Debuggable final : SimpleDebuggable {
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		Debuggable(MSXMotherBoard& motherBoard, const std::string& name);
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		[[nodiscard]] uint8_t read(unsigned address, EmuTime time) override;
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		void write(unsigned address, uint8_t value, EmuTime time) override;
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	} debuggable;
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};
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} // namespace openmsx
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#endif