70 lines
2.0 KiB
C++
70 lines
2.0 KiB
C++
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#include "CPU.h"
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#include <stdexcept>
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#include <iostream>
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#include <iomanip>
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#include <stdlib.h>
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#include <array>
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CPU::CPU(std::shared_ptr<Bus> bus) : m_Bus(bus), m_Context({m_Instruction, m_InstructionPointer, m_Flags, m_Registers, m_Bus}){
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m_InstructionPointer = 0x00008000;
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for(int i = 0; i < 16; i++)
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{
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m_Registers[i] = 0;
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}
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}
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void CPU::Step(){
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FetchDecode();
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Execute();
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}
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void CPU::FetchDecode(){
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std::cout << "Fetching instruction: " << std::hex << m_InstructionPointer << std::endl;
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m_InstructionRaw = m_Bus->AccessX<uint64_t>(m_InstructionPointer); // Slice of 8 bytes.
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std::cout << "Context window fetched: " << std::hex << m_InstructionRaw << std::endl; // Start Decode Instruction
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uint64_t first_byte = m_InstructionRaw & 0xFF;
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std::cout << "Decoded first byte: " << std::hex << first_byte << std::endl;
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Opcode opcode = static_cast<Opcode>(first_byte);
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if(first_byte >= 0xB8 && first_byte <= 0xBF)
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{
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m_Instruction.m_Operand1 = first_byte - 0xB8;
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opcode = Opcode::MOV_R_IMM32;
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}
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switch(opcode){
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case Opcode::NOP: m_Instruction.m_Length = 1; break;
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case Opcode::HLT: m_Instruction.m_Length = 1; break;
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case Opcode::MOV_R_IMM32:
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m_Instruction.m_Operand2 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + 1);
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m_Instruction.m_Length = 5;
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break;
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case Opcode::ADD_RM32_R32:
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m_Instruction.m_Operand1 = m_Bus->AccessX<uint8_t>(m_InstructionPointer + 1);
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m_Instruction.m_Operand2 = m_Bus->AccessX<uint32_t>(m_InstructionPointer + 2);
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m_Instruction.m_Length = 6;
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break;
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default:
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std::runtime_error("Decode encountered unexpected opcode.");
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break;
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}
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m_Instruction.m_Opcode = opcode;
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m_InstructionPointer += m_Instruction.m_Length;
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}
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void CPU::Execute(){
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std::cout << "Executing... \n";
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uint8_t opcode_value = static_cast<uint8_t>(m_Instruction.m_Opcode);
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auto& exec_table = GetExecutorTable();
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if(exec_table[opcode_value])
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{
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exec_table[opcode_value](m_Context);
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return;
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}
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throw std::runtime_error("Opcode not found!");
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}
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