110 lines
3.5 KiB
C++
110 lines
3.5 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 "../Interrupt.hpp"
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#include "../Cpu65816.hpp"
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#define LOG_TAG "Cpu::executeBIT"
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/**
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* This file contains the implementation for all BIT OpCodes
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*/
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void Cpu65816::execute8BitBIT(OpCode &opCode) {
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const Address addressOfOpCodeData = getAddressOfOpCodeData(opCode);
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uint8_t value = mSystemBus.readByte(addressOfOpCodeData);
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bool isHighestBitSet = value & 0x80;
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bool isNextToHighestBitSet = value & 0x40;
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if (opCode.getAddressingMode() != AddressingMode::Immediate) {
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if (isHighestBitSet) mCpuStatus.setSignFlag();
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else mCpuStatus.clearSignFlag();
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if (isNextToHighestBitSet) mCpuStatus.setOverflowFlag();
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else mCpuStatus.clearOverflowFlag();
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}
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mCpuStatus.updateZeroFlagFrom8BitValue(value & Binary::lower8BitsOf(mA));
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}
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void Cpu65816::execute16BitBIT(OpCode &opCode) {
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const Address addressOfOpCodeData = getAddressOfOpCodeData(opCode);
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uint16_t value = mSystemBus.readTwoBytes(addressOfOpCodeData);
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bool isHighestBitSet = value & 0x8000;
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bool isNextToHighestBitSet = value & 0x4000;
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if (opCode.getAddressingMode() != AddressingMode::Immediate) {
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if (isHighestBitSet) mCpuStatus.setSignFlag();
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else mCpuStatus.clearSignFlag();
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if (isNextToHighestBitSet) mCpuStatus.setOverflowFlag();
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else mCpuStatus.clearOverflowFlag();
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}
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mCpuStatus.updateZeroFlagFrom16BitValue(value & mA);
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}
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void Cpu65816::executeBIT(OpCode &opCode) {
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if (accumulatorIs8BitWide()) {
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execute8BitBIT(opCode);
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} else {
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execute16BitBIT(opCode);
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addToCycles(1);
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}
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switch (opCode.getCode()) {
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case(0x89): // BIT Immediate
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{
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if (accumulatorIs16BitWide()) {
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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(0x2C): // BIT 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(0x24): // BIT 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(0x3C): // BIT 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(0x34): // BIT 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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LOG_UNEXPECTED_OPCODE(opCode);
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}
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}
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}
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