mirror of https://github.com/stella-emu/stella.git
255 lines
7.6 KiB
C++
255 lines
7.6 KiB
C++
//============================================================================
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//
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// SSSS tt lll lll
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// SS SS tt ll ll
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// SS tttttt eeee ll ll aaaa
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// SSSS tt ee ee ll ll aa
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// SS tt eeeeee ll ll aaaaa -- "An Atari 2600 VCS Emulator"
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// SS SS tt ee ll ll aa aa
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// SSSS ttt eeeee llll llll aaaaa
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//
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// Copyright (c) 1995-2020 by Bradford W. Mott, Stephen Anthony
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// and the Stella Team
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//
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// See the file "License.txt" for information on usage and redistribution of
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// this file, and for a DISCLAIMER OF ALL WARRANTIES.
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//============================================================================
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#ifndef CARTRIDGE4A50_HXX
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#define CARTRIDGE4A50_HXX
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class System;
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#include "bspf.hxx"
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#include "Cart.hxx"
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#ifdef DEBUGGER_SUPPORT
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#include "Cart4A50Widget.hxx"
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#endif
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/**
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Bankswitching method as defined/created by John Payson (aka Supercat),
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documented at https://stella-emu.github.io/4A50.html.
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In this bankswitching scheme the 2600's 4K cartridge address space
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is broken into four segments. The first 2K segment accesses any 2K
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region of RAM, or of the first 32K of ROM. The second 1.5K segment
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accesses the first 1.5K of any 2K region of RAM, or of the last 32K
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of ROM. The 3rd 256 byte segment points to any 256 byte page of
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RAM or ROM. The last 256 byte segment always points to the last 256
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bytes of ROM.
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Because of the complexity of this scheme, the cart reports having
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only one actual bank, in which pieces of it can be swapped out in
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many different ways. It contains so many hotspots and possibilities
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for the ROM address space to change that we just consider the bank to
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have changed on every poke operation (for any RAM) or an actual bankswitch.
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NOTE: This scheme hasn't been fully implemented, and may never be (there
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is only one test ROM, and it hasn't been extended any further).
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In particular, the following functionality is missing:
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- hires helper functions
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- 1E00 page wrap
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@author Eckhard Stolberg & Stephen Anthony
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*/
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class Cartridge4A50 : public Cartridge
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{
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friend class Cartridge4A50Widget;
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public:
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/**
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Create a new cartridge using the specified image
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@param image Pointer to the ROM image
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@param size The size of the ROM image
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@param md5 The md5sum of the ROM image
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@param settings A reference to the various settings (read-only)
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*/
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Cartridge4A50(const ByteBuffer& image, size_t size, const string& md5,
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const Settings& settings);
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virtual ~Cartridge4A50() = default;
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public:
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/**
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Reset cartridge to its power-on state
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*/
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void reset() override;
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/**
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Install cartridge in the specified system. Invoked by the system
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when the cartridge is attached to it.
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@param system The system the device should install itself in
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*/
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void install(System& system) override;
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/**
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Patch the cartridge ROM.
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@param address The ROM address to patch
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@param value The value to place into the address
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@return Success or failure of the patch operation
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*/
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bool patch(uInt16 address, uInt8 value) override;
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/**
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Access the internal ROM image for this cartridge.
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@param size Set to the size of the internal ROM image data
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@return A pointer to the internal ROM image data
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*/
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const uInt8* getImage(size_t& size) const override;
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/**
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Save the current state of this cart to the given Serializer.
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@param out The Serializer object to use
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@return False on any errors, else true
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*/
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bool save(Serializer& out) const override;
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/**
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Load the current state of this cart from the given Serializer.
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@param in The Serializer object to use
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@return False on any errors, else true
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*/
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bool load(Serializer& in) override;
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/**
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Get a descriptor for the device name (used in error checking).
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@return The name of the object
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*/
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string name() const override { return "Cartridge4A50"; }
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#ifdef DEBUGGER_SUPPORT
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/**
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Get debugger widget responsible for accessing the inner workings
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of the cart.
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*/
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CartDebugWidget* debugWidget(GuiObject* boss, const GUI::Font& lfont,
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const GUI::Font& nfont, int x, int y, int w, int h) override
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{
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return new Cartridge4A50Widget(boss, lfont, nfont, x, y, w, h, *this);
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}
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#endif
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public:
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/**
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Get the byte at the specified address.
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@return The byte at the specified address
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*/
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uInt8 peek(uInt16 address) override;
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/**
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Change the byte at the specified address to the given value
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@param address The address where the value should be stored
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@param value The value to be stored at the address
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@return True if the poke changed the device address space, else false
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*/
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bool poke(uInt16 address, uInt8 value) override;
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private:
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#ifdef DEBUGGER_SUPPORT
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/**
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Query the given address type for the associated access flags.
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@param address The address to query
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*/
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Device::AccessFlags getAccessFlags(uInt16 address) const override;
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/**
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Change the given address to use the given access flags.
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@param address The address to modify
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@param flags A bitfield of AccessType directives for the given address
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*/
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void setAccessFlags(uInt16 address, Device::AccessFlags flags) override;
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#endif
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/**
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Check all possible hotspots
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*/
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void checkBankSwitch(uInt16 address, uInt8 value);
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/**
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Methods to perform all the ways that banks can be switched
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*/
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inline void bankROMLower(uInt16 value)
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{
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myIsRomLow = true;
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mySliceLow = value << 11;
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myBankChanged = true;
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}
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inline void bankRAMLower(uInt16 value)
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{
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myIsRomLow = false;
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mySliceLow = value << 11;
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myBankChanged = true;
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}
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inline void bankROMMiddle(uInt16 value)
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{
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myIsRomMiddle = true;
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mySliceMiddle = value << 11;
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myBankChanged = true;
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}
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inline void bankRAMMiddle(uInt16 value)
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{
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myIsRomMiddle = false;
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mySliceMiddle = value << 11;
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myBankChanged = true;
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}
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inline void bankROMHigh(uInt16 value)
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{
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myIsRomHigh = true;
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mySliceHigh = value << 8;
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myBankChanged = true;
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}
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inline void bankRAMHigh(uInt16 value)
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{
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myIsRomHigh = false;
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mySliceHigh = value << 8;
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myBankChanged = true;
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}
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private:
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// The 128K ROM image of the cartridge
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std::array<uInt8, 128_KB> myImage;
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// The 32K of RAM on the cartridge
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std::array<uInt8, 32_KB> myRAM;
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// (Actual) Size of the ROM image
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size_t mySize{0};
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// Indicates the slice mapped into each of the three segments
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uInt16 mySliceLow{0}; // index pointer for $1000-$17ff slice
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uInt16 mySliceMiddle{0}; // index pointer for $1800-$1dff slice
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uInt16 mySliceHigh{0}; // index pointer for $1e00-$1eff slice
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// Indicates whether the given slice is mapped to ROM or RAM
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bool myIsRomLow{true}; // true = ROM -- false = RAM at $1000-$17ff
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bool myIsRomMiddle{true}; // true = ROM -- false = RAM at $1800-$1dff
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bool myIsRomHigh{true}; // true = ROM -- false = RAM at $1e00-$1eFF
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// The previous address and data values (from peek and poke)
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uInt16 myLastAddress{0};
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uInt8 myLastData{0};
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private:
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// Following constructors and assignment operators not supported
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Cartridge4A50() = delete;
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Cartridge4A50(const Cartridge4A50&) = delete;
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Cartridge4A50(Cartridge4A50&&) = delete;
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Cartridge4A50& operator=(const Cartridge4A50&) = delete;
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Cartridge4A50& operator=(Cartridge4A50&&) = delete;
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};
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#endif
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