mirror of https://github.com/ariejan/i6502.git
Clean up code / Refactorings
This commit is contained in:
Ariejan de Vroom
parent
6207a06423
commit
9ee72dc145
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@ -1,36 +0,0 @@
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package i6502
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// Addressing modes
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const (
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_ = iota
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absolute
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absoluteX
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absoluteY
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accumulator
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immediate
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implied
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indirect
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indirectX
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indirectY
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relative
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zeropage
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zeropageX
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zeropageY
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)
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var addressingNames = [...]string{
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"",
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"absolute",
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"absoluteX",
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"absoluteY",
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"accumulator",
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"immediate",
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"implied",
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"(indirect)",
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"(indirect,X)",
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"(indirect),Y",
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"relative",
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"zeropage",
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"zeropageX",
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"zeropageY",
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}
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316
cpu.go
316
cpu.go
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@ -3,8 +3,6 @@ package i6502
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import "fmt"
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type Cpu struct {
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bus *AddressBus // The address bus
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PC uint16 // 16-bit program counter
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P byte // Status Register
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SP byte // Stack Pointer
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@ -12,16 +10,20 @@ type Cpu struct {
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A byte // Accumulator
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X byte // X index register
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Y byte // Y index register
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Bus *AddressBus // The address bus
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}
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const (
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ResetVector = 0xFFFC // 0xFFFC-FFFD
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IrqVector = 0xFFFE // 0xFFFE-FFFF
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StackBase = 0x0100 // One page 0x0100-01FF
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)
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// Create an new Cpu instance with the specified AddressBus
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func NewCpu(bus *AddressBus) (*Cpu, error) {
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return &Cpu{bus: bus}, nil
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return &Cpu{Bus: bus}, nil
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}
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func (c *Cpu) String() string {
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@ -29,13 +31,13 @@ func (c *Cpu) String() string {
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return fmt.Sprintf(str, c.A, c.X, c.Y, c.SP, c.PC, c.P)
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}
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func (c *Cpu) HasAddressBus() bool {
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return c.bus != nil
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func (c *Cpu) hasAddressBus() bool {
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return c.Bus != nil
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}
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// Reset the CPU, emulating the RESB pin.
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func (c *Cpu) Reset() {
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c.PC = c.bus.Read16(ResetVector)
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c.PC = c.Bus.Read16(ResetVector)
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c.P = 0x34
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// Not specified, but let's clean up
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@ -57,14 +59,14 @@ func (c *Cpu) handleIrq(PC uint16) {
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c.setIrqDisable(true)
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c.PC = c.bus.Read16(IrqVector)
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c.PC = c.Bus.Read16(IrqVector)
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}
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// Load the specified program data at the given memory location
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// and point the Program Counter to the beginning of the program
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func (c *Cpu) LoadProgram(data []byte, location uint16) {
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for i, b := range data {
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c.bus.Write(location+uint16(i), b)
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c.Bus.Write(location+uint16(i), b)
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}
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c.PC = location
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@ -72,10 +74,8 @@ func (c *Cpu) LoadProgram(data []byte, location uint16) {
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// Execute the instruction pointed to by the Program Counter (PC)
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func (c *Cpu) Step() {
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// fmt.Println(c)
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instruction := c.readNextInstruction()
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c.PC += uint16(instruction.Size)
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// fmt.Println(instruction)
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c.execute(instruction)
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}
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@ -84,9 +84,9 @@ func (c *Cpu) execute(instruction Instruction) {
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case nop:
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break
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case adc:
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c.ADC(instruction)
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c.adc(instruction)
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case sbc:
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c.SBC(instruction)
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c.sbc(instruction)
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case sec:
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c.setCarry(true)
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case sed:
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@ -106,31 +106,40 @@ func (c *Cpu) execute(instruction Instruction) {
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case iny:
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c.setY(c.Y + 1)
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case inc:
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c.INC(instruction)
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c.inc(instruction)
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case dex:
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c.setX(c.X - 1)
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case dey:
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c.setY(c.Y - 1)
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case dec:
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c.DEC(instruction)
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c.dec(instruction)
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case lda:
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c.LDA(instruction)
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value := c.resolveOperand(instruction)
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c.setA(value)
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case ldx:
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c.LDX(instruction)
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value := c.resolveOperand(instruction)
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c.setX(value)
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case ldy:
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c.LDY(instruction)
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value := c.resolveOperand(instruction)
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c.setY(value)
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case ora:
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c.ORA(instruction)
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value := c.resolveOperand(instruction)
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c.setA(c.A | value)
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case and:
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c.AND(instruction)
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value := c.resolveOperand(instruction)
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c.setA(c.A & value)
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case eor:
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c.EOR(instruction)
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value := c.resolveOperand(instruction)
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c.setA(c.A ^ value)
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case sta:
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c.STA(instruction)
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address := c.memoryAddress(instruction)
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c.Bus.Write(address, c.A)
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case stx:
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c.STX(instruction)
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address := c.memoryAddress(instruction)
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c.Bus.Write(address, c.X)
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case sty:
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c.STY(instruction)
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address := c.memoryAddress(instruction)
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c.Bus.Write(address, c.Y)
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case tax:
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c.setX(c.A)
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case tay:
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@ -144,21 +153,28 @@ func (c *Cpu) execute(instruction Instruction) {
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case txs:
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c.SP = c.X
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case asl:
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c.ASL(instruction)
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c.asl(instruction)
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case lsr:
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c.LSR(instruction)
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c.lsr(instruction)
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case rol:
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c.ROL(instruction)
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c.rol(instruction)
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case ror:
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c.ROR(instruction)
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c.ror(instruction)
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case cmp:
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c.CMP(instruction)
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value := c.resolveOperand(instruction)
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c.setCarry(c.A >= value)
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c.setArithmeticFlags(c.A - value)
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case cpx:
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c.CPX(instruction)
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value := c.resolveOperand(instruction)
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c.setCarry(c.X >= value)
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c.setArithmeticFlags(c.X - value)
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case cpy:
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c.CPY(instruction)
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value := c.resolveOperand(instruction)
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c.setCarry(c.Y >= value)
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c.setArithmeticFlags(c.Y - value)
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case brk:
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c.BRK()
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c.setBreak(true)
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c.handleIrq(c.PC + 1)
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case bcc:
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if !c.getCarry() {
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c.branch(instruction)
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@ -192,7 +208,10 @@ func (c *Cpu) execute(instruction Instruction) {
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c.branch(instruction)
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}
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case bit:
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c.BIT(instruction)
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value := c.resolveOperand(instruction)
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c.setNegative((value & 0x80) != 0)
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c.setOverflow((value & 0x40) != 0)
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c.setZero((c.A & value) == 0)
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case php:
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c.stackPush(c.P | 0x30)
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case plp:
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@ -203,9 +222,11 @@ func (c *Cpu) execute(instruction Instruction) {
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value := c.stackPop()
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c.setA(value)
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case jmp:
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c.JMP(instruction)
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c.PC = c.memoryAddress(instruction)
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case jsr:
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c.JSR(instruction)
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c.stackPush(byte((c.PC - 1) >> 8))
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c.stackPush(byte(c.PC - 1))
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c.PC = c.memoryAddress(instruction)
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case rts:
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c.PC = (uint16(c.stackPop()) | uint16(c.stackPop())<<8) + 1
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case rti:
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@ -216,6 +237,27 @@ func (c *Cpu) execute(instruction Instruction) {
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}
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}
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func (c *Cpu) readNextInstruction() Instruction {
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// Read the opcode
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opcode := c.Bus.Read(c.PC)
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optype, ok := opTypes[opcode]
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if !ok {
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panic(fmt.Sprintf("Unknown or unimplemented opcode 0x%02X\n%s", opcode, c.String()))
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}
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instruction := Instruction{OpType: optype, Address: c.PC}
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switch instruction.Size {
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case 1: // Zero operand instruction
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case 2: // 8-bit operand
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instruction.Op8 = c.Bus.Read(c.PC + 1)
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case 3: // 16-bit operand
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instruction.Op16 = c.Bus.Read16(c.PC + 1)
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}
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return instruction
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}
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func (c *Cpu) branch(in Instruction) {
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relative := int8(in.Op8) // Signed!
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if relative >= 0 {
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@ -230,7 +272,7 @@ func (c *Cpu) resolveOperand(in Instruction) uint8 {
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case immediate:
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return in.Op8
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default:
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return c.bus.Read(c.memoryAddress(in))
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return c.Bus.Read(c.memoryAddress(in))
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}
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}
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@ -243,11 +285,11 @@ func (c *Cpu) memoryAddress(in Instruction) uint16 {
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case absoluteY:
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return in.Op16 + uint16(c.Y)
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case indirect:
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return c.bus.Read16(in.Op16)
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return c.Bus.Read16(in.Op16)
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case indirectX:
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return c.bus.Read16(uint16(in.Op8 + c.X))
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return c.Bus.Read16(uint16(in.Op8 + c.X))
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case indirectY:
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return c.bus.Read16(uint16(in.Op8)) + uint16(c.Y)
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return c.Bus.Read16(uint16(in.Op8)) + uint16(c.Y)
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case relative:
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panic("Relative addressing not yet implemented.")
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case zeropage:
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@ -260,3 +302,201 @@ func (c *Cpu) memoryAddress(in Instruction) uint16 {
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panic(fmt.Errorf("Unhandled addressing mode. Are you sure you are running a 6502 ROM?"))
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}
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}
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// Add Memory to Accumulator with Carry
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func (c *Cpu) adc(in Instruction) {
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operand := c.resolveOperand(in)
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carryIn := c.getCarryInt()
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if c.getDecimal() {
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c.adcDecimal(c.A, operand, carryIn)
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} else {
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c.adcNormal(c.A, operand, carryIn)
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}
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}
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// Substract memory from Accummulator with carry
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func (c *Cpu) sbc(in Instruction) {
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operand := c.resolveOperand(in)
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carryIn := c.getCarryInt()
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// fmt.Printf("SBC: A: 0x%02X V: 0x%02X C: %b D: %v\n", c.A, operand, carryIn, c.getDecimal())
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if c.getDecimal() {
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c.sbcDecimal(c.A, operand, carryIn)
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} else {
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c.adcNormal(c.A, ^operand, carryIn)
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}
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}
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func (c *Cpu) inc(in Instruction) {
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address := c.memoryAddress(in)
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value := c.Bus.Read(address) + 1
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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func (c *Cpu) dec(in Instruction) {
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address := c.memoryAddress(in)
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value := c.Bus.Read(address) - 1
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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func (c *Cpu) asl(in Instruction) {
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switch in.addressingId {
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case accumulator:
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c.setCarry((c.A >> 7) == 1)
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c.A <<= 1
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c.setArithmeticFlags(c.A)
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default:
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address := c.memoryAddress(in)
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value := c.Bus.Read(address)
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c.setCarry((value >> 7) == 1)
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value <<= 1
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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}
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func (c *Cpu) lsr(in Instruction) {
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switch in.addressingId {
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case accumulator:
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c.setCarry((c.A & 0x01) == 1)
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c.A >>= 1
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c.setArithmeticFlags(c.A)
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default:
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address := c.memoryAddress(in)
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value := c.Bus.Read(address)
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c.setCarry((value & 0x01) == 1)
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value >>= 1
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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}
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func (c *Cpu) rol(in Instruction) {
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carry := c.getCarryInt()
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switch in.addressingId {
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case accumulator:
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c.setCarry((c.A & 0x80) != 0)
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c.A = c.A<<1 | carry
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c.setArithmeticFlags(c.A)
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default:
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address := c.memoryAddress(in)
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value := c.Bus.Read(address)
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c.setCarry((value & 0x80) != 0)
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value = value<<1 | carry
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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}
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func (c *Cpu) ror(in Instruction) {
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carry := c.getCarryInt()
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switch in.addressingId {
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case accumulator:
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c.setCarry(c.A&0x01 == 1)
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c.A = c.A>>1 | carry<<7
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c.setArithmeticFlags(c.A)
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default:
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address := c.memoryAddress(in)
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value := c.Bus.Read(address)
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c.setCarry(value&0x01 == 1)
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value = value>>1 | carry<<7
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c.Bus.Write(address, value)
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c.setArithmeticFlags(value)
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}
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}
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// Performs regular, 8-bit addition
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func (c *Cpu) adcNormal(a uint8, b uint8, carryIn uint8) {
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result16 := uint16(a) + uint16(b) + uint16(carryIn)
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result := uint8(result16)
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carryOut := (result16 & 0x100) != 0
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overflow := (a^result)&(b^result)&0x80 != 0
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// Set the carry flag if we exceed 8-bits
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c.setCarry(carryOut)
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// Set the overflow bit
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c.setOverflow(overflow)
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// Store the resulting value (8-bits)
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c.setA(result)
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}
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// Performs addition in decimal mode
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func (c *Cpu) adcDecimal(a uint8, b uint8, carryIn uint8) {
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var carryB uint8 = 0
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low := (a & 0x0F) + (b & 0x0F) + carryIn
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if (low & 0xFF) > 9 {
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low += 6
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}
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if low > 15 {
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carryB = 1
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}
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high := (a >> 4) + (b >> 4) + carryB
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if (high & 0xFF) > 9 {
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high += 6
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}
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result := (low & 0x0F) | (high<<4)&0xF0
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c.setCarry(high > 15)
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c.setZero(result == 0)
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c.setNegative(false) // BCD never sets negative
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c.setOverflow(false) // BCD never sets overflow
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c.A = result
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}
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func (c *Cpu) sbcDecimal(a uint8, b uint8, carryIn uint8) {
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var carryB uint8 = 0
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if carryIn == 0 {
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carryIn = 1
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} else {
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carryIn = 0
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}
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low := (a & 0x0F) - (b & 0x0F) - carryIn
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if (low & 0x10) != 0 {
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low -= 6
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}
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if (low & 0x10) != 0 {
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carryB = 1
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}
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high := (a >> 4) - (b >> 4) - carryB
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if (high & 0x10) != 0 {
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high -= 6
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}
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result := (low & 0x0F) | (high << 4)
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c.setCarry((high & 0xFF) < 15)
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c.setZero(result == 0)
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c.setNegative(false) // BCD never sets negative
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c.setOverflow(false) // BCD never sets overflow
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c.A = result
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}
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func (c *Cpu) stackPush(data byte) {
|
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c.Bus.Write(StackBase+uint16(c.SP), data)
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c.SP -= 1
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}
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func (c *Cpu) stackPeek() byte {
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return c.Bus.Read(StackBase + uint16(c.SP+1))
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}
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|
||||
func (c *Cpu) stackPop() byte {
|
||||
c.SP += 1
|
||||
return c.Bus.Read(StackBase + uint16(c.SP))
|
||||
}
|
||||
|
|
|
|||
|
|
@ -1,271 +0,0 @@
|
|||
package i6502
|
||||
|
||||
// Add Memory to Accumulator with Carry
|
||||
func (c *Cpu) ADC(in Instruction) {
|
||||
operand := c.resolveOperand(in)
|
||||
carryIn := c.getCarryInt()
|
||||
|
||||
if c.getDecimal() {
|
||||
c.adcDecimal(c.A, operand, carryIn)
|
||||
} else {
|
||||
c.adcNormal(c.A, operand, carryIn)
|
||||
}
|
||||
}
|
||||
|
||||
// Substract memory from Accummulator with carry
|
||||
func (c *Cpu) SBC(in Instruction) {
|
||||
operand := c.resolveOperand(in)
|
||||
carryIn := c.getCarryInt()
|
||||
|
||||
// fmt.Printf("SBC: A: 0x%02X V: 0x%02X C: %b D: %v\n", c.A, operand, carryIn, c.getDecimal())
|
||||
|
||||
if c.getDecimal() {
|
||||
c.sbcDecimal(c.A, operand, carryIn)
|
||||
} else {
|
||||
c.adcNormal(c.A, ^operand, carryIn)
|
||||
}
|
||||
}
|
||||
|
||||
func (c *Cpu) INC(in Instruction) {
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address) + 1
|
||||
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
|
||||
func (c *Cpu) DEC(in Instruction) {
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address) - 1
|
||||
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
|
||||
func (c *Cpu) LDA(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setA(value)
|
||||
}
|
||||
|
||||
func (c *Cpu) LDX(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setX(value)
|
||||
}
|
||||
|
||||
func (c *Cpu) LDY(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setY(value)
|
||||
}
|
||||
|
||||
func (c *Cpu) ORA(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setA(c.A | value)
|
||||
}
|
||||
|
||||
func (c *Cpu) AND(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setA(c.A & value)
|
||||
}
|
||||
|
||||
func (c *Cpu) EOR(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setA(c.A ^ value)
|
||||
}
|
||||
|
||||
func (c *Cpu) STA(in Instruction) {
|
||||
address := c.memoryAddress(in)
|
||||
c.bus.Write(address, c.A)
|
||||
}
|
||||
|
||||
func (c *Cpu) STX(in Instruction) {
|
||||
address := c.memoryAddress(in)
|
||||
c.bus.Write(address, c.X)
|
||||
}
|
||||
|
||||
func (c *Cpu) STY(in Instruction) {
|
||||
address := c.memoryAddress(in)
|
||||
c.bus.Write(address, c.Y)
|
||||
}
|
||||
|
||||
func (c *Cpu) ASL(in Instruction) {
|
||||
switch in.addressingId {
|
||||
case accumulator:
|
||||
c.setCarry((c.A >> 7) == 1)
|
||||
c.A <<= 1
|
||||
c.setArithmeticFlags(c.A)
|
||||
default:
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address)
|
||||
c.setCarry((value >> 7) == 1)
|
||||
value <<= 1
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
}
|
||||
|
||||
func (c *Cpu) LSR(in Instruction) {
|
||||
switch in.addressingId {
|
||||
case accumulator:
|
||||
c.setCarry((c.A & 0x01) == 1)
|
||||
c.A >>= 1
|
||||
c.setArithmeticFlags(c.A)
|
||||
default:
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address)
|
||||
c.setCarry((value & 0x01) == 1)
|
||||
value >>= 1
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
}
|
||||
|
||||
func (c *Cpu) ROL(in Instruction) {
|
||||
carry := c.getCarryInt()
|
||||
|
||||
switch in.addressingId {
|
||||
case accumulator:
|
||||
c.setCarry((c.A & 0x80) != 0)
|
||||
c.A = c.A<<1 | carry
|
||||
c.setArithmeticFlags(c.A)
|
||||
default:
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address)
|
||||
c.setCarry((value & 0x80) != 0)
|
||||
value = value<<1 | carry
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
}
|
||||
|
||||
func (c *Cpu) ROR(in Instruction) {
|
||||
carry := c.getCarryInt()
|
||||
|
||||
switch in.addressingId {
|
||||
case accumulator:
|
||||
c.setCarry(c.A&0x01 == 1)
|
||||
c.A = c.A>>1 | carry<<7
|
||||
c.setArithmeticFlags(c.A)
|
||||
default:
|
||||
address := c.memoryAddress(in)
|
||||
value := c.bus.Read(address)
|
||||
c.setCarry(value&0x01 == 1)
|
||||
value = value>>1 | carry<<7
|
||||
c.bus.Write(address, value)
|
||||
c.setArithmeticFlags(value)
|
||||
}
|
||||
}
|
||||
|
||||
func (c *Cpu) CMP(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
// fmt.Printf("CMP A: 0x%02X V: 0x%02X\n", c.A, value)
|
||||
c.setCarry(c.A >= value)
|
||||
c.setArithmeticFlags(c.A - value)
|
||||
}
|
||||
|
||||
func (c *Cpu) CPX(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setCarry(c.X >= value)
|
||||
c.setArithmeticFlags(c.X - value)
|
||||
}
|
||||
|
||||
func (c *Cpu) CPY(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setCarry(c.Y >= value)
|
||||
c.setArithmeticFlags(c.Y - value)
|
||||
}
|
||||
|
||||
func (c *Cpu) BRK() {
|
||||
c.setBreak(true)
|
||||
c.handleIrq(c.PC + 1)
|
||||
}
|
||||
|
||||
func (c *Cpu) BIT(in Instruction) {
|
||||
value := c.resolveOperand(in)
|
||||
c.setNegative((value & 0x80) != 0)
|
||||
c.setOverflow((value & 0x40) != 0)
|
||||
c.setZero((c.A & value) == 0)
|
||||
}
|
||||
|
||||
func (c *Cpu) JMP(in Instruction) {
|
||||
c.PC = c.memoryAddress(in)
|
||||
}
|
||||
|
||||
func (c *Cpu) JSR(in Instruction) {
|
||||
c.stackPush(byte((c.PC - 1) >> 8))
|
||||
c.stackPush(byte(c.PC - 1))
|
||||
c.PC = c.memoryAddress(in)
|
||||
}
|
||||
|
||||
// Performs regular, 8-bit addition
|
||||
func (c *Cpu) adcNormal(a uint8, b uint8, carryIn uint8) {
|
||||
result16 := uint16(a) + uint16(b) + uint16(carryIn)
|
||||
result := uint8(result16)
|
||||
carryOut := (result16 & 0x100) != 0
|
||||
overflow := (a^result)&(b^result)&0x80 != 0
|
||||
|
||||
// Set the carry flag if we exceed 8-bits
|
||||
c.setCarry(carryOut)
|
||||
// Set the overflow bit
|
||||
c.setOverflow(overflow)
|
||||
// Store the resulting value (8-bits)
|
||||
c.setA(result)
|
||||
}
|
||||
|
||||
// Performs addition in decimal mode
|
||||
func (c *Cpu) adcDecimal(a uint8, b uint8, carryIn uint8) {
|
||||
var carryB uint8 = 0
|
||||
|
||||
low := (a & 0x0F) + (b & 0x0F) + carryIn
|
||||
if (low & 0xFF) > 9 {
|
||||
low += 6
|
||||
}
|
||||
if low > 15 {
|
||||
carryB = 1
|
||||
}
|
||||
|
||||
high := (a >> 4) + (b >> 4) + carryB
|
||||
if (high & 0xFF) > 9 {
|
||||
high += 6
|
||||
}
|
||||
|
||||
result := (low & 0x0F) | (high<<4)&0xF0
|
||||
|
||||
c.setCarry(high > 15)
|
||||
c.setZero(result == 0)
|
||||
c.setNegative(false) // BCD never sets negative
|
||||
c.setOverflow(false) // BCD never sets overflow
|
||||
|
||||
c.A = result
|
||||
}
|
||||
|
||||
func (c *Cpu) sbcDecimal(a uint8, b uint8, carryIn uint8) {
|
||||
var carryB uint8 = 0
|
||||
|
||||
if carryIn == 0 {
|
||||
carryIn = 1
|
||||
} else {
|
||||
carryIn = 0
|
||||
}
|
||||
|
||||
low := (a & 0x0F) - (b & 0x0F) - carryIn
|
||||
if (low & 0x10) != 0 {
|
||||
low -= 6
|
||||
}
|
||||
if (low & 0x10) != 0 {
|
||||
carryB = 1
|
||||
}
|
||||
|
||||
high := (a >> 4) - (b >> 4) - carryB
|
||||
if (high & 0x10) != 0 {
|
||||
high -= 6
|
||||
}
|
||||
|
||||
result := (low & 0x0F) | (high << 4)
|
||||
|
||||
c.setCarry((high & 0xFF) < 15)
|
||||
c.setZero(result == 0)
|
||||
c.setNegative(false) // BCD never sets negative
|
||||
c.setOverflow(false) // BCD never sets overflow
|
||||
|
||||
c.A = result
|
||||
}
|
||||
19
cpu_stack.go
19
cpu_stack.go
|
|
@ -1,19 +0,0 @@
|
|||
package i6502
|
||||
|
||||
const (
|
||||
StackBase = 0x0100
|
||||
)
|
||||
|
||||
func (c *Cpu) stackPush(data byte) {
|
||||
c.bus.Write(StackBase+uint16(c.SP), data)
|
||||
c.SP -= 1
|
||||
}
|
||||
|
||||
func (c *Cpu) stackPeek() byte {
|
||||
return c.bus.Read(StackBase + uint16(c.SP+1))
|
||||
}
|
||||
|
||||
func (c *Cpu) stackPop() byte {
|
||||
c.SP += 1
|
||||
return c.bus.Read(StackBase + uint16(c.SP))
|
||||
}
|
||||
|
|
@ -1,28 +0,0 @@
|
|||
package i6502
|
||||
|
||||
import (
|
||||
"github.com/stretchr/testify/assert"
|
||||
"testing"
|
||||
)
|
||||
|
||||
func TestStackPushPopPeek(t *testing.T) {
|
||||
assert := assert.New(t)
|
||||
cpu, _, _ := NewRamMachine()
|
||||
|
||||
assert.Equal(0xFF, cpu.SP)
|
||||
|
||||
cpu.stackPush(0x42)
|
||||
cpu.stackPush(0xA0)
|
||||
|
||||
assert.Equal(0xFD, cpu.SP)
|
||||
assert.Equal(0x42, cpu.bus.Read(0x1FF))
|
||||
assert.Equal(0xA0, cpu.bus.Read(0x1FE))
|
||||
|
||||
peekValue := cpu.stackPeek()
|
||||
assert.Equal(0xFD, cpu.SP)
|
||||
assert.Equal(0xA0, peekValue)
|
||||
|
||||
popValue := cpu.stackPop()
|
||||
assert.Equal(0xFE, cpu.SP)
|
||||
assert.Equal(0xA0, popValue)
|
||||
}
|
||||
445
cpu_test.go
445
cpu_test.go
File diff suppressed because it is too large
Load Diff
|
|
@ -30,24 +30,3 @@ func (i Instruction) String() (output string) {
|
|||
|
||||
return
|
||||
}
|
||||
|
||||
func (c *Cpu) readNextInstruction() Instruction {
|
||||
// Read the opcode
|
||||
opcode := c.bus.Read(c.PC)
|
||||
|
||||
optype, ok := opTypes[opcode]
|
||||
if !ok {
|
||||
panic(fmt.Sprintf("Unknown or unimplemented opcode 0x%02X\n%s", opcode, c.String()))
|
||||
}
|
||||
|
||||
instruction := Instruction{OpType: optype, Address: c.PC}
|
||||
switch instruction.Size {
|
||||
case 1: // Zero operand instruction
|
||||
case 2: // 8-bit operand
|
||||
instruction.Op8 = c.bus.Read(c.PC + 1)
|
||||
case 3: // 16-bit operand
|
||||
instruction.Op16 = c.bus.Read16(c.PC + 1)
|
||||
}
|
||||
|
||||
return instruction
|
||||
}
|
||||
|
|
|
|||
35
opcodes.go
35
opcodes.go
|
|
@ -1,5 +1,40 @@
|
|||
package i6502
|
||||
|
||||
// Addressing modes
|
||||
const (
|
||||
_ = iota
|
||||
absolute
|
||||
absoluteX
|
||||
absoluteY
|
||||
accumulator
|
||||
immediate
|
||||
implied
|
||||
indirect
|
||||
indirectX
|
||||
indirectY
|
||||
relative
|
||||
zeropage
|
||||
zeropageX
|
||||
zeropageY
|
||||
)
|
||||
|
||||
var addressingNames = [...]string{
|
||||
"",
|
||||
"absolute",
|
||||
"absoluteX",
|
||||
"absoluteY",
|
||||
"accumulator",
|
||||
"immediate",
|
||||
"implied",
|
||||
"(indirect)",
|
||||
"(indirect,X)",
|
||||
"(indirect),Y",
|
||||
"relative",
|
||||
"zeropage",
|
||||
"zeropageX",
|
||||
"zeropageY",
|
||||
}
|
||||
|
||||
// OpCode table
|
||||
const (
|
||||
_ = iota
|
||||
|
|
|
|||
Loading…
Reference in New Issue