m65go2

package
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 Go to latest Published: Feb 28, 2019 License: GPL-2.0, GPL-2.0 Imports: 2 Imported by: 20

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m65go2

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A MOS 6502 simulator written in Go

Documentation

Overview

Package m65go2 simulates the MOS 6502 CPU

Index

Constants

View Source 
const (
	DefaultMemorySize uint32 = 65536
)

Variables

This section is empty.

Functions

func SamePage 

func SamePage(addr1 uint16, addr2 uint16) bool

Returns true iff the two addresses are located in the same page in memory. Two addresses are on the same page if their high bytes are both the same, i.e. 0x0101 and 0x0103 are on the same page but 0x0101 and 0203 are not.

Types

type BadOpCodeError 

type BadOpCodeError OpCode

Error type used to indicate that the CPU attempted to execute an invalid opcode

func (BadOpCodeError) Error 

func (b BadOpCodeError) Error() string

type BasicMemory 

type BasicMemory struct {
	M             []uint8
	DisableReads  bool
	DisableWrites bool
}

Represents the 6502 CPU's memory using a static array of uint8's.

func NewBasicMemory 

func NewBasicMemory(size uint32) *BasicMemory

Returns a pointer to a new BasicMemory with all memory initialized to zero.

func (*BasicMemory) Fetch 

func (mem *BasicMemory) Fetch(address uint16) (value uint8)

Returns the value stored at the given memory address

func (*BasicMemory) Reset 

func (mem *BasicMemory) Reset()

Resets all memory locations to zero

func (*BasicMemory) Store 

func (mem *BasicMemory) Store(address uint16, value uint8) (oldValue uint8)

Stores the value at the given memory address

type BrkOpCodeError 

type BrkOpCodeError OpCode

Error type used to indicate that the CPU executed a BRK instruction

func (BrkOpCodeError) Error 

func (b BrkOpCodeError) Error() string

type Index 

type Index uint8
const (
	X Index = iota
	Y
)

func (Index) String 

func (i Index) String() string

type Instruction 

type Instruction struct {
	Mneumonic string
	OpCode    OpCode
	Exec      func(*M6502) (status InstructionStatus)
}

Represents an instruction for the 6502 CPU. The Exec field implements the instruction and returns the total clock cycles to be consumed by the instruction.

type InstructionStatus 

type InstructionStatus uint16
const (
	PageCross InstructionStatus = 1 << iota
	Branched
)

type InstructionTable 

type InstructionTable struct {
	// contains filtered or unexported fields
}

Stores instructions understood by the 6502 CPU, indexed by opcode.

func NewInstructionTable 

func NewInstructionTable() InstructionTable

Returns a new, empty InstructionTable

func (InstructionTable) AddInstruction 

func (instructions InstructionTable) AddInstruction(inst *Instruction)

Adds an instruction to the InstructionTable

func (InstructionTable) Execute 

func (instructions InstructionTable) Execute(cpu *M6502, opcode OpCode) (cycles uint16)

Executes an instruction in the InstructionTable, returns number of cycles taken to execute

func (InstructionTable) InitInstructions 

func (instructions InstructionTable) InitInstructions()

Adds the 6502 CPU's instruction set to the InstructionTable.

func (InstructionTable) RemoveInstruction 

func (instructions InstructionTable) RemoveInstruction(opcode OpCode)

Removes any instruction with the given opcode

type Interrupt 

type Interrupt uint8
const (
	Irq Interrupt = iota
	Nmi
	Rst
)

type M6502 

type M6502 struct {
	Nmi          bool
	Irq          bool
	Rst          bool
	Registers    Registers        `json:"M6502Registers"`
	Memory       Memory           `json:"M6502Memory"`
	Instructions InstructionTable `json:"-"`
	// contains filtered or unexported fields
}

Represents the 6502 CPU.

func NewM6502 

func NewM6502(mem Memory) *M6502

Returns a pointer to a new CPU with the given Memory.

func (*M6502) Adc 

func (cpu *M6502) Adc(address uint16)

This instruction adds the contents of a memory location to the accumulator together with the carry bit. If overflow occurs the carry bit is set, this enables multiple byte addition to be performed. 

C 	Carry Flag 	  Set if overflow in bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Set if sign bit is incorrect
N 	Negative Flag 	  Set if bit 7 set

func (*M6502) Alr 

func (cpu *M6502) Alr(address uint16)

Unofficial

func (*M6502) Anc 

func (cpu *M6502) Anc(address uint16)

Unofficial

func (*M6502) And 

func (cpu *M6502) And(address uint16)

A logical AND is performed, bit by bit, on the accumulator contents using the contents of a byte of memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 set

func (*M6502) Arr 

func (cpu *M6502) Arr(address uint16)

Unofficial

func (*M6502) Asl 

func (cpu *M6502) Asl(address uint16)

This operation shifts all the bits of the memory contents one bit left. Bit 0 is set to 0 and bit 7 is placed in the carry flag. The effect of this operation is to multiply the memory contents by 2 (ignoring 2's complement considerations), setting the carry if the result will not fit in 8 bits. 

C 	Carry Flag 	  Set to contents of old bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) AslA 

func (cpu *M6502) AslA()

This operation shifts all the bits of the accumulator one bit left. Bit 0 is set to 0 and bit 7 is placed in the carry flag. The effect of this operation is to multiply the memory contents by 2 (ignoring 2's complement considerations), setting the carry if the result will not fit in 8 bits. 

C 	Carry Flag 	  Set to contents of old bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Axs 

func (cpu *M6502) Axs(address uint16)

Unofficial

func (*M6502) Bcc 

func (cpu *M6502) Bcc(address uint16, status *InstructionStatus)

If the carry flag is clear then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bcs 

func (cpu *M6502) Bcs(address uint16, status *InstructionStatus)

If the carry flag is set then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Beq 

func (cpu *M6502) Beq(address uint16, status *InstructionStatus)

If the zero flag is set then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bit 

func (cpu *M6502) Bit(address uint16)

This instructions is used to test if one or more bits are set in a target memory location. The mask pattern in A is ANDed with the value in memory to set or clear the zero flag, but the result is not kept. Bits 7 and 6 of the value from memory are copied into the N and V flags. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if the result if the AND is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Set to bit 6 of the memory value
N 	Negative Flag 	  Set to bit 7 of the memory value

func (*M6502) Bmi 

func (cpu *M6502) Bmi(address uint16, status *InstructionStatus)

If the negative flag is set then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bne 

func (cpu *M6502) Bne(address uint16, status *InstructionStatus)

If the zero flag is clear then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bpl 

func (cpu *M6502) Bpl(address uint16, status *InstructionStatus)

If the negative flag is clear then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Brk 

func (cpu *M6502) Brk()

The BRK instruction forces the generation of an interrupt request. The program counter and processor status are pushed on the stack then the IRQ interrupt vector at $FFFE/F is loaded into the PC and the break flag in the status set to one. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Set to 1
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bvc 

func (cpu *M6502) Bvc(address uint16, status *InstructionStatus)

If the overflow flag is clear then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Bvs 

func (cpu *M6502) Bvs(address uint16, status *InstructionStatus)

If the overflow flag is set then add the relative displacement to the program counter to cause a branch to a new location. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Clc 

func (cpu *M6502) Clc()

Set the carry flag to zero. 

C 	Carry Flag 	  Set to 0
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Cld 

func (cpu *M6502) Cld()

Set the decimal mode flag to zero. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Set to 0
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Cli 

func (cpu *M6502) Cli()

Clears the interrupt disable flag allowing normal interrupt requests to be serviced. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Set to 0
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Clv 

func (cpu *M6502) Clv()

Clears the interrupt disable flag allowing normal interrupt requests to be serviced. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Set to 0
N 	Negative Flag 	  Not affected

func (*M6502) Cmp 

func (cpu *M6502) Cmp(address uint16)

This instruction compares the contents of the accumulator with another memory held value and sets the zero and carry flags as appropriate. 

C 	Carry Flag 	  Set if A >= M
Z 	Zero Flag 	  Set if A = M
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Cpx 

func (cpu *M6502) Cpx(address uint16)

This instruction compares the contents of the X register with another memory held value and sets the zero and carry flags as appropriate. 

C 	Carry Flag 	  Set if X >= M
Z 	Zero Flag 	  Set if X = M
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Cpy 

func (cpu *M6502) Cpy(address uint16)

This instruction compares the contents of the Y register with another memory held value and sets the zero and carry flags as appropriate. 

C 	Carry Flag 	  Set if Y >= M
Z 	Zero Flag 	  Set if Y = M
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Dcp 

func (cpu *M6502) Dcp(address uint16)

Unofficial

func (*M6502) Dec 

func (cpu *M6502) Dec(address uint16)

Subtracts one from the value held at a specified memory location setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if result is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Dex 

func (cpu *M6502) Dex()

Subtracts one from the X register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if X is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of X is set

func (*M6502) Dey 

func (cpu *M6502) Dey()

Subtracts one from the Y register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if Y is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of Y is set

func (*M6502) DisableDecimalMode 

func (cpu *M6502) DisableDecimalMode()

func (*M6502) EnableDecode 

func (cpu *M6502) EnableDecode()

func (*M6502) Eor 

func (cpu *M6502) Eor(address uint16)

An exclusive OR is performed, bit by bit, on the accumulator contents using the contents of a byte of memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 set

func (*M6502) Execute 

func (cpu *M6502) Execute() (cycles uint16, error error)

Executes the instruction pointed to by the PC register in the number of cycles as returned by the instruction's Exec function. Returns the number of cycles executed and any error (such as BadOpCodeError).

func (*M6502) GetInterrupt 

func (cpu *M6502) GetInterrupt(which Interrupt) (state bool)

func (*M6502) Inc 

func (cpu *M6502) Inc(address uint16)

Adds one to the value held at a specified memory location setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if result is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) IndexToRegister 

func (cpu *M6502) IndexToRegister(which Index) uint8

func (*M6502) Interrupt 

func (cpu *M6502) Interrupt(which Interrupt, state bool)

func (*M6502) InterruptLine 

func (cpu *M6502) InterruptLine(which Interrupt) func(state bool)

func (*M6502) Inx 

func (cpu *M6502) Inx()

Adds one to the X register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if X is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of X is set

func (*M6502) Iny 

func (cpu *M6502) Iny()

Adds one to the Y register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if Y is zero
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of Y is set

func (*M6502) Isb 

func (cpu *M6502) Isb(address uint16)

Unofficial

func (*M6502) Jmp 

func (cpu *M6502) Jmp(address uint16)

Sets the program counter to the address specified by the operand. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Jsr 

func (cpu *M6502) Jsr(address uint16)

The JSR instruction pushes the address (minus one) of the return point on to the stack and then sets the program counter to the target memory address. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Lax 

func (cpu *M6502) Lax(address uint16)

Unofficial

Loads a byte of memory into the accumulator and X setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of A is set

func (*M6502) Lda 

func (cpu *M6502) Lda(address uint16)

Loads a byte of memory into the accumulator setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of A is set

func (*M6502) Ldx 

func (cpu *M6502) Ldx(address uint16)

Loads a byte of memory into the X register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if X = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of X is set

func (*M6502) Ldy 

func (cpu *M6502) Ldy(address uint16)

Loads a byte of memory into the Y register setting the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if Y = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of Y is set

func (*M6502) Lsr 

func (cpu *M6502) Lsr(address uint16)

Each of the bits in M is shift one place to the right. The bit that was in bit 0 is shifted into the carry flag. Bit 7 is set to zero. 

C 	Carry Flag 	  Set to contents of old bit 0
Z 	Zero Flag 	  Set if result = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) LsrA 

func (cpu *M6502) LsrA()

Each of the bits in A is shift one place to the right. The bit that was in bit 0 is shifted into the carry flag. Bit 7 is set to zero. 

C 	Carry Flag 	  Set to contents of old bit 0
Z 	Zero Flag 	  Set if result = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Nop 

func (cpu *M6502) Nop()

The NOP instruction causes no changes to the processor other than the normal incrementing of the program counter to the next instruction. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) NopAddress 

func (cpu *M6502) NopAddress(address uint16)

Unofficial

The NOP instruction causes no changes to the processor other than the normal incrementing of the program counter to the next instruction. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Ora 

func (cpu *M6502) Ora(address uint16)

An inclusive OR is performed, bit by bit, on the accumulator contents using the contents of a byte of memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 set

func (*M6502) PerformInterrupts 

func (cpu *M6502) PerformInterrupts() (cycles uint16)

func (*M6502) PerformIrq 

func (cpu *M6502) PerformIrq()

func (*M6502) PerformNmi 

func (cpu *M6502) PerformNmi()

func (*M6502) PerformRst 

func (cpu *M6502) PerformRst()

func (*M6502) Pha 

func (cpu *M6502) Pha()

Pushes a copy of the accumulator on to the stack. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Php 

func (cpu *M6502) Php()

Pushes a copy of the status flags on to the stack. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Pla 

func (cpu *M6502) Pla()

Pulls an 8 bit value from the stack and into the accumulator. The zero and negative flags are set as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of A is set

func (*M6502) Plp 

func (cpu *M6502) Plp()

Pulls an 8 bit value from the stack and into the processor flags. The flags will take on new states as determined by the value pulled. 

C 	Carry Flag 	  Set from stack
Z 	Zero Flag 	  Set from stack
I 	Interrupt Disable Set from stack
D 	Decimal Mode Flag Set from stack
B 	Break Command 	  Set from stack
V 	Overflow Flag 	  Set from stack
N 	Negative Flag 	  Set from stack

func (*M6502) Reset 

func (cpu *M6502) Reset()

Resets the CPU by resetting both the registers and memory.

func (*M6502) Rla 

func (cpu *M6502) Rla(address uint16)

Unofficial

func (*M6502) Rol 

func (cpu *M6502) Rol(address uint16)

Move each of the bits in A one place to the left. Bit 0 is filled with the current value of the carry flag whilst the old bit 7 becomes the new carry flag value. 

C 	Carry Flag 	  Set to contents of old bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) RolA 

func (cpu *M6502) RolA()

Move each of the bits in A one place to the left. Bit 0 is filled with the current value of the carry flag whilst the old bit 7 becomes the new carry flag value. 

C 	Carry Flag 	  Set to contents of old bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Ror 

func (cpu *M6502) Ror(address uint16)

Move each of the bits in M one place to the right. Bit 7 is filled with the current value of the carry flag whilst the old bit 0 becomes the new carry flag value. 

C 	Carry Flag 	  Set to contents of old bit 0
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) RorA 

func (cpu *M6502) RorA()

Move each of the bits in A one place to the right. Bit 7 is filled with the current value of the carry flag whilst the old bit 0 becomes the new carry flag value. 

C 	Carry Flag 	  Set to contents of old bit 0
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of the result is set

func (*M6502) Rra 

func (cpu *M6502) Rra(address uint16)

Unofficial

func (*M6502) Rti 

func (cpu *M6502) Rti()

The RTI instruction is used at the end of an interrupt processing routine. It pulls the processor flags from the stack followed by the program counter. 

C 	Carry Flag 	  Set from stack
Z 	Zero Flag 	  Set from stack
I 	Interrupt Disable Set from stack
D 	Decimal Mode Flag Set from stack
B 	Break Command 	  Set from stack
V 	Overflow Flag 	  Set from stack
N 	Negative Flag 	  Set from stack

func (*M6502) Rts 

func (cpu *M6502) Rts()

The RTS instruction is used at the end of a subroutine to return to the calling routine. It pulls the program counter (minus one) from the stack. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Run 

func (cpu *M6502) Run() (err error)

Executes instruction until Execute() returns an error.

func (*M6502) Sax 

func (cpu *M6502) Sax(address uint16)

Unofficial

func (*M6502) Sbc 

func (cpu *M6502) Sbc(address uint16)

This instruction subtracts the contents of a memory location to the accumulator together with the not of the carry bit. If overflow occurs the carry bit is clear, this enables multiple byte subtraction to be performed. 

C 	Carry Flag 	  Clear if overflow in bit 7
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Set if sign bit is incorrect
N 	Negative Flag 	  Set if bit 7 set

func (*M6502) Sec 

func (cpu *M6502) Sec()

Set the carry flag to one. 

C 	Carry Flag 	  Set to 1
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Sed 

func (cpu *M6502) Sed()

Set the decimal mode flag to one. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Set to 1
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Sei 

func (cpu *M6502) Sei()

Set the interrupt disable flag to one. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Set to 1
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Shx 

func (cpu *M6502) Shx(address uint16)

Unofficial

func (*M6502) Shy 

func (cpu *M6502) Shy(address uint16)

Unofficial

func (*M6502) Slo 

func (cpu *M6502) Slo(address uint16)

Unofficial

func (*M6502) Sre 

func (cpu *M6502) Sre(address uint16)

Unofficial

func (*M6502) Sta 

func (cpu *M6502) Sta(address uint16)

Stores the contents of the accumulator into memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Stx 

func (cpu *M6502) Stx(address uint16)

Stores the contents of the X register into memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Sty 

func (cpu *M6502) Sty(address uint16)

Stores the contents of the Y register into memory. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Tax 

func (cpu *M6502) Tax()

Copies the current contents of the accumulator into the X register and sets the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if X = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of X is set

func (*M6502) Tay 

func (cpu *M6502) Tay()

Copies the current contents of the accumulator into the Y register and sets the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if Y = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of Y is set

func (*M6502) ToggleDecode 

func (cpu *M6502) ToggleDecode() bool

func (*M6502) Tsx 

func (cpu *M6502) Tsx()

Copies the current contents of the stack register into the X register and sets the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if X = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of X is set

func (*M6502) Txa 

func (cpu *M6502) Txa()

Copies the current contents of the X register into the accumulator and sets the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of A is set

func (*M6502) Txs 

func (cpu *M6502) Txs()

Copies the current contents of the X register into the stack register. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Not affected
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Not affected

func (*M6502) Tya 

func (cpu *M6502) Tya()

Copies the current contents of the Y register into the accumulator and sets the zero and negative flags as appropriate. 

C 	Carry Flag 	  Not affected
Z 	Zero Flag 	  Set if A = 0
I 	Interrupt Disable Not affected
D 	Decimal Mode Flag Not affected
B 	Break Command 	  Not affected
V 	Overflow Flag 	  Not affected
N 	Negative Flag 	  Set if bit 7 of A is set

type Memory 

type Memory interface {
	Reset()                                             // Sets all memory locations to zero
	Fetch(address uint16) (value uint8)                 // Returns the value stored at the given memory address
	Store(address uint16, value uint8) (oldValue uint8) // Stores the value at the given memory address
}

Represents the RAM memory available to the 6502 CPU. Stores 8-bit values using a 16-bit address for a total of 65,536 possible 8-bit values.

type OpCode 

type OpCode uint8

Represents opcodes for the 6502 CPU

type Registers 

type Registers struct {
	A  uint8  // accumulator
	X  uint8  // index register X
	Y  uint8  // index register Y
	P  Status // processor status
	SP uint8  // stack pointer
	PC uint16 // program counter
}

The 6502's registers, all registers are 8-bit values except for PC which is 16-bits.

func NewRegisters 

func NewRegisters() (reg Registers)

Creates a new set of Registers. All registers are initialized to 0.

func (*Registers) Reset 

func (reg *Registers) Reset()

Resets all registers. Register P is initialized with only the I bit set, SP is initialized to 0xfd, PC is initialized to 0xfffc (the RESET vector) and all other registers are initialized to 0.

func (*Registers) String 

func (reg *Registers) String() string

Prints the values of each register to os.Stderr.

type Status 

type Status uint8

Flags used by P (Status) register 

const (
	C Status = 1 << iota // carry flag
	Z                    // zero flag
	I                    // interrupt disable
	D                    // decimal mode
	B                    // break command
	U                    // -UNUSED-
	V                    // overflow flag
	N                    // negative flag
)

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