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◆ main openmsx / src / video / ADVram.hh
2.3 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef ADVRAM_HH
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#define ADVRAM_HH
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#include "MSXDevice.hh"
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namespace openmsx {
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class VDP;
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class VDPVRAM;
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/** Implementation of direct cpu access to VRAM.  ADVram (Accesso
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  * Direito à Vram is a rare hardware modification that allows the
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  * CPU to access the video ram in the same way as ordinary ram.
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  */
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class ADVram final : public MSXDevice
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{
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public:
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	explicit ADVram(const DeviceConfig& config);
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	/** This method is called on reset.  Reset the mapper register and
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	 * the planar bit, if the device is configured with an enable bit
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	 * then that bit is reset as well.
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	 */
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	void reset(EmuTime time) override;
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	/** Read a byte from an IO port, change mode bits.  The planar bit
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	 * and possibly the enable bit are set according to address lines
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	 * that are normally ignored for IO reads.  Returns 255.
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	 */
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	[[nodiscard]] uint8_t readIO(uint16_t port, EmuTime time) override;
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	// default peekIO() implementation is ok.
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	/** Write a byte to a given IO port, set mapper register.  */
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	void writeIO(uint16_t port, uint8_t value, EmuTime time) override;
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	/** Read a byte from a location in the video ram at a certain
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	 * time.  If the device is enabled then the value returned comes
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	 * from the video ram, otherwise it returns 255.
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	 */
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	[[nodiscard]] uint8_t readMem(uint16_t address, EmuTime time) override;
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	/** Write a given byte at a certain time to a given location in
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	 * the video ram.  If the device is enabled then the write is
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	 * redirected to the video ram, if it is not, nothing happens.
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	 */
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	void writeMem(uint16_t address, uint8_t value, EmuTime time) override;
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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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	void init() override;
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	[[nodiscard]] inline unsigned calcAddress(uint16_t address) const;
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private:
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	VDP* vdp = nullptr;
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	VDPVRAM* vram = nullptr;
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	/** Bit mask applied to logical addresses, reflects vram size.  */
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	/*const*/ unsigned mask;
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	/** Base address of selected page in vram.  */
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	unsigned baseAddr;
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	/** True if ADVram device is enabled.  */
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	bool enabled;
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	/** True if ADVram device can be switched on or off by performing
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		IO-reads.  */
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	const bool hasEnable;
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	/** True if address bits are shuffled as is appropriate for screen
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		7 and higher.  */
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	bool planar;
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};
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} // namespace openmsx
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#endif // ADVRAM_HH