144 lines
3.7 KiB
Swift
144 lines
3.7 KiB
Swift
//
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// CPUState.swift
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// FruitMachine
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//
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// Created by Christopher Rohl on 7/19/17.
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// Copyright © 2017 Christopher Rohl. All rights reserved.
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//
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import Cocoa
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enum CPUExceptions : Error {
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case invalidInstruction
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}
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struct StatusRegister {
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var negative: Bool //N - 0x80
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var overflow: Bool //V - 0x40
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// - 0x20
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var brk: Bool //B - 0x10
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var decimal: Bool //D - 0x08
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var irq_disable: Bool //I - 0x04
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var zero: Bool //Z - 0x02
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var carry: Bool //C - 0x01
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mutating func fromByte(state: UInt8) {
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negative = (state & 0x80 == 0x80)
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overflow = (state & 0x40 == 0x40)
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brk = (state & 0x10 == 0x10)
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decimal = (state & 0x08 == 0x08)
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irq_disable = (state & 0x04 == 0x04)
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zero = (state & 0x02 == 0x02)
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carry = (state & 0x01 == 0x01)
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}
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func asByte() -> UInt8 {
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var val: UInt8 = 0x00
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if(negative) {
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val |= 0x80
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}
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if(overflow) {
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val |= 0x40
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}
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if(brk) {
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val |= 0x10
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}
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if(decimal) {
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val |= 0x08
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}
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if(irq_disable) {
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val |= 0x04
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}
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if(zero) {
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val |= 0x02
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}
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if(carry) {
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val |= 0x01
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}
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return val
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}
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}
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class CPUState: NSObject {
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static var sharedInstance = CPUState()
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var cycles: Int
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var instruction_register: UInt8
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var accumulator: UInt8
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var index_x: UInt8
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var index_y: UInt8
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var stack_pointer: UInt8
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var program_counter: UInt16
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var status_register: StatusRegister
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var page_boundary_crossed: Bool
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var memoryInterface: MemoryInterface
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override init() {
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cycles = 0
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instruction_register = 0
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accumulator = 0
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index_x = 0
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index_y = 0
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stack_pointer = 0
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program_counter = 0
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status_register = StatusRegister(negative: false, overflow: false, brk: false, decimal: false, irq_disable: false, zero: false, carry: false)
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memoryInterface = MemoryInterface()
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page_boundary_crossed = false
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}
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func getOperandByte() -> UInt8 {
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//Returns the operand byte after the current instruction byte.
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return memoryInterface.readByte(offset: program_counter + 1)
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}
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func getOperandWord() -> UInt16 {
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var word: UInt16
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let low = memoryInterface.readByte(offset: program_counter + 1)
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let high = memoryInterface.readByte(offset: program_counter + 2)
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word = UInt16(high)
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word = word << 8
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word |= UInt16(low)
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return word
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}
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func executeNextInstruction() throws {
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instruction_register = memoryInterface.readByte(offset: program_counter)
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let operation = InstructionTable[instruction_register]
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if(operation == nil) {
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throw CPUExceptions.invalidInstruction
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}
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operation!.action(CPUState.sharedInstance, operation!.addressingMode)
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self.cycles += operation!.cycles
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if(self.page_boundary_crossed) {
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self.cycles += 1
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self.page_boundary_crossed = false
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}
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if(operation!.mnemonic != "JMP") {
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self.program_counter = UInt16(Int(self.program_counter) + operation!.bytes)
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}
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}
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func updateNegativeFlag(value: UInt8) {
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status_register.negative = (value & 0x80 == 0x80)
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}
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func updateZeroFlag(value: UInt8) {
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status_register.zero = (value == 0)
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}
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}
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