FruitMachine-Swift/FruitMachine/M6502/CPUState.swift

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//
// CPUState.swift
// FruitMachine
//
// Created by Christopher Rohl on 7/19/17.
// Copyright © 2017 Christopher Rohl. All rights reserved.
//
import Cocoa
enum CPUExceptions : Error {
case invalidInstruction
}
struct StatusRegister {
var negative: Bool //N - 0x80
var overflow: Bool //V - 0x40
// - 0x20
var brk: Bool //B - 0x10
var decimal: Bool //D - 0x08
var irq_disable: Bool //I - 0x04
var zero: Bool //Z - 0x02
var carry: Bool //C - 0x01
func asString() -> String {
var str = ""
if(negative) {
str += "N"
} else {
str += "-"
}
if(overflow) {
str += "V"
} else {
str += "-"
}
str += "-" //0x20 is unassigned
if(brk) {
str += "B"
} else {
str += "-"
}
if(decimal) {
str += "D"
} else {
str += "-"
}
if(irq_disable) {
str += "I"
} else {
str += "-"
}
if(zero) {
str += "Z"
} else {
str += "-"
}
return str
}
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mutating func fromByte(state: UInt8) {
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negative = (state & 0x80 == 0x80)
overflow = (state & 0x40 == 0x40)
brk = (state & 0x10 == 0x10)
decimal = (state & 0x08 == 0x08)
irq_disable = (state & 0x04 == 0x04)
zero = (state & 0x02 == 0x02)
carry = (state & 0x01 == 0x01)
}
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func asByte() -> UInt8 {
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var val: UInt8 = 0x20 //unused bit is hardwired to 1
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if(negative) {
val |= 0x80
}
if(overflow) {
val |= 0x40
}
if(brk) {
val |= 0x10
}
if(decimal) {
val |= 0x08
}
if(irq_disable) {
val |= 0x04
}
if(zero) {
val |= 0x02
}
if(carry) {
val |= 0x01
}
return val
}
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}
class CPUState: NSObject {
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let NMI_VECTOR: UInt16 = 0xFFFA
let RESET_VECTOR: UInt16 = 0xFFFC
let IRQ_VECTOR: UInt16 = 0xFFFE
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static var sharedInstance = CPUState()
var cycles: Int
var instruction_register: UInt8
var accumulator: UInt8
var index_x: UInt8
var index_y: UInt8
var stack_pointer: UInt8
var program_counter: UInt16
var status_register: StatusRegister
var page_boundary_crossed: Bool
var memoryInterface: MemoryInterface
var branch_was_taken: Bool
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override init() {
cycles = 0
instruction_register = 0
accumulator = 0
index_x = 0
index_y = 0
stack_pointer = 0
program_counter = 0
status_register = StatusRegister(negative: false, overflow: false, brk: false, decimal: false, irq_disable: false, zero: false, carry: false)
memoryInterface = MemoryInterface()
//Some instructions incur a 1-cycle penalty if crossing a page boundary.
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page_boundary_crossed = false
//Branches incur a 1-cycle penalty if taken plus the page boundary penalty if necessary.
branch_was_taken = false
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}
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func disassemble(fromAddress: UInt16, length: UInt16) -> [Disassembly] {
var disassembly: [Disassembly] = [Disassembly]()
var currentAddress: UInt16 = fromAddress
let endAddress: UInt16 = fromAddress + length
while(currentAddress < endAddress) {
let instruction = memoryInterface.readByte(offset: currentAddress)
let operation = InstructionTable[instruction]
var data = [UInt8]()
if(operation != nil) {
for index in 1...operation!.bytes {
data.append(memoryInterface.readByte(offset:currentAddress + UInt16(index)))
}
disassembly.append(Disassembly(instruction: operation, address: currentAddress, data: data))
currentAddress = currentAddress + UInt16(operation!.bytes)
} else {
currentAddress = currentAddress + 1
}
}
return disassembly
}
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func getOperandByte() -> UInt8 {
//Returns the operand byte after the current instruction byte.
return memoryInterface.readByte(offset: program_counter + 1)
}
func getOperandWord() -> UInt16 {
var word: UInt16
let low = memoryInterface.readByte(offset: program_counter + 1)
let high = memoryInterface.readByte(offset: program_counter + 2)
word = UInt16(high)
word = word << 8
word |= UInt16(low)
return word
}
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func getInstructionBytes(atAddress: UInt16) -> [UInt8] {
var bytes = [UInt8]()
let instruction = memoryInterface.readByte(offset: atAddress)
let operation = InstructionTable[instruction]
if(operation != nil){
for offset in 0...operation!.bytes {
bytes.append(memoryInterface.readByte(offset: atAddress + UInt16(offset)))
}
}
return bytes
}
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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]
if(operation == nil) {
throw CPUExceptions.invalidInstruction
}
operation!.action(CPUState.sharedInstance, operation!.addressingMode)
self.cycles += operation!.cycles
if(self.page_boundary_crossed) {
self.cycles += 1
self.page_boundary_crossed = false
}
if(self.branch_was_taken) {
self.cycles += 1
self.branch_was_taken = false
}
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if(operation!.mnemonic != "JMP") {
self.program_counter = UInt16(Int(self.program_counter) + operation!.bytes)
}
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}
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func performReset() {
program_counter = memoryInterface.readWord(offset: RESET_VECTOR)
stack_pointer = 0xFF
status_register.irq_disable = true
}
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func updateNegativeFlag(value: UInt8) {
status_register.negative = (value & 0x80 == 0x80)
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}
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func updateZeroFlag(value: UInt8) {
status_register.zero = (value == 0)
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}
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}