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50 lines
1.3 KiB
C++
50 lines
1.3 KiB
C++
//
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// CartridgeActivisionStack.h
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// Clock Signal
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//
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// Created by Thomas Harte on 18/03/2017.
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// Copyright 2017 Thomas Harte. All rights reserved.
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//
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#ifndef Atari2600_ActivisionStack_hpp
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#define Atari2600_ActivisionStack_hpp
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namespace Atari2600::Cartridge {
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class ActivisionStack: public BusExtender {
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public:
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ActivisionStack(uint8_t *rom_base, std::size_t rom_size) :
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BusExtender(rom_base, rom_size),
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rom_ptr_(rom_base),
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last_opcode_(0x00) {}
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void perform_bus_operation(CPU::MOS6502::BusOperation operation, uint16_t address, uint8_t *value) {
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if(!(address & 0x1000)) return;
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// This is a bit of a hack; a real cartridge can't see either the sync or read lines, and can't see
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// address line 13. Instead it looks for a pattern in recent address accesses that would imply an
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// RST or JSR.
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if(operation == CPU::MOS6502::BusOperation::ReadOpcode && (last_opcode_ == 0x20 || last_opcode_ == 0x60)) {
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if(address & 0x2000) {
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rom_ptr_ = rom_base_;
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} else {
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rom_ptr_ = rom_base_ + 4096;
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}
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}
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if(isReadOperation(operation)) {
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*value = rom_ptr_[address & 4095];
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}
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if(operation == CPU::MOS6502::BusOperation::ReadOpcode) last_opcode_ = *value;
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}
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private:
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uint8_t *rom_ptr_;
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uint8_t last_opcode_;
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};
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}
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#endif /* Atari2600_CartridgeActivisionStack_hpp */
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