95 lines
2.7 KiB
C++
95 lines
2.7 KiB
C++
/*
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* This file is part of the 65816 Emulator Library.
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* Copyright (c) 2018 Francesco Rigoni.
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*
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* https://github.com/FrancescoRigoni/Lib65816
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*
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* This program is free software: you can redistribute it and/or modify
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* it under the terms of the GNU General Public License as published by
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* the Free Software Foundation, version 3.
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*
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* This program is distributed in the hope that it will be useful, but
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* WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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* General Public License for more details.
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*
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* You should have received a copy of the GNU General Public License
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* along with this program. If not, see <http://www.gnu.org/licenses/>.
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*/
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#include "../Cpu65816.hpp"
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#include <cmath>
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#define LOG_TAG "Cpu::executeLDY"
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/**
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* This file contains implementations for all LDY OpCodes.
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*/
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void Cpu65816::executeLDY8Bit(OpCode &opCode) {
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Address opCodeDataAddress = getAddressOfOpCodeData(opCode);
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uint8_t value = mSystemBus.readByte(opCodeDataAddress);
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Binary::setLower8BitsOf16BitsValue(&mY, value);
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mCpuStatus.updateSignAndZeroFlagFrom8BitValue(value);
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}
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void Cpu65816::executeLDY16Bit(OpCode &opCode) {
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Address opCodeDataAddress = getAddressOfOpCodeData(opCode);
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mY = mSystemBus.readTwoBytes(opCodeDataAddress);
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mCpuStatus.updateSignAndZeroFlagFrom16BitValue(mY);
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}
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void Cpu65816::executeLDY(OpCode &opCode) {
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if (indexIs16BitWide()) {
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executeLDY16Bit(opCode);
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addToCycles(1);
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} else {
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executeLDY8Bit(opCode);
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}
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switch (opCode.getCode()) {
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case (0xA0): // LDY Immediate
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{
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if (indexIs16BitWide()) {
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addToProgramAddress(1);
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}
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addToProgramAddressAndCycles(2, 2);
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break;
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}
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case (0xAC): // LDY Absolute
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{
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addToProgramAddressAndCycles(3, 4);
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break;
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}
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case (0xA4): // LDY Direct Page
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{
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if (Binary::lower8BitsOf(mD) != 0) {
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addToCycles(1);
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}
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addToProgramAddressAndCycles(2, 3);
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break;
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}
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case (0xBC): // LDY Absolute Indexed, X
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{
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if (opCodeAddressingCrossesPageBoundary(opCode)) {
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addToCycles(1);
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}
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addToProgramAddressAndCycles(3, 4);
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break;
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}
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case (0xB4): // LDY Direct Page Indexed, X
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{
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if (Binary::lower8BitsOf(mD) != 0) {
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addToCycles(1);
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}
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addToProgramAddressAndCycles(2, 4);
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break;
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}
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default:
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{
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LOG_UNEXPECTED_OPCODE(opCode);
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}
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}
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}
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