Support for BRK, JMP, JSR, RTI and RTS
This commit is contained in:
Ivan Izaguirre
parent
e43a0a9ae1
commit
7f9aea24e9
105
execute.go
105
execute.go
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@ -22,6 +22,7 @@ const modeIndirectIndexedY = 8
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const modeAccumulator = 9
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const modeRegisterX = 10
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const modeRegisterY = 11
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const modeIndirect = 12
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// https://www.masswerk.at/6502/6502_instruction_set.html
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// http://www.emulator101.com/reference/6502-reference.html
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@ -32,8 +33,7 @@ func getWordInLine(line []uint8) uint16 {
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return uint16(line[1]) + 0x100*uint16(line[2])
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}
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func resolveWithAddressMode(s *state, line []uint8, addressMode int) (value uint8, setValue func(uint8)) {
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var address uint16
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func resolveWithAddressMode(s *state, line []uint8, addressMode int) (value uint8, address uint16, setValue func(uint8)) {
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hasAddress := true
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register := regNone
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@ -68,6 +68,9 @@ func resolveWithAddressMode(s *state, line []uint8, addressMode int) (value uint
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case modeIndexedIndirectX:
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addressAddress := uint8(line[1] + s.registers.getX())
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address = s.memory.getZeroPageWord(addressAddress)
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case modeIndirect:
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addressAddress := getWordInLine(line)
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address = s.memory.getWord(addressAddress)
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case modeIndirectIndexedY:
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address = s.memory.getZeroPageWord(line[1]) +
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uint16(s.registers.getY())
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@ -98,8 +101,6 @@ type opcode struct {
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type opFunc func(s *state, line []uint8, opcode opcode)
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func opNOP(s *state, line []uint8, opcode opcode) {}
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func buildOpTransfer(regSrc int, regDst int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value := s.registers.getRegister(regSrc)
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@ -112,7 +113,7 @@ func buildOpTransfer(regSrc int, regDst int) opFunc {
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func buildOpIncDec(addressMode int, inc bool) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, setValue := resolveWithAddressMode(s, line, addressMode)
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value, _, setValue := resolveWithAddressMode(s, line, addressMode)
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if inc {
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value++
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} else {
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@ -125,7 +126,7 @@ func buildOpIncDec(addressMode int, inc bool) opFunc {
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func buildShift(addressMode int, isLeft bool, isRotate bool) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, setValue := resolveWithAddressMode(s, line, addressMode)
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value, _, setValue := resolveWithAddressMode(s, line, addressMode)
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oldCarry := s.registers.getFlagBit(flagC)
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var carry bool
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@ -150,7 +151,7 @@ func buildShift(addressMode int, isLeft bool, isRotate bool) opFunc {
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func buildOpLoad(addressMode int, regDst int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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s.registers.setRegister(regDst, value)
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s.registers.updateFlagZN(value)
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}
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@ -158,7 +159,7 @@ func buildOpLoad(addressMode int, regDst int) opFunc {
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func buildOpStore(addressMode int, regSrc int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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_, setValue := resolveWithAddressMode(s, line, addressMode)
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_, _, setValue := resolveWithAddressMode(s, line, addressMode)
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value := s.registers.getRegister(regSrc)
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setValue(value)
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}
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@ -183,7 +184,7 @@ func buildOpBranch(flag uint8, value bool) opFunc {
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func buildOpBit(addressMode int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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acc := s.registers.getA()
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s.registers.updateFlag(flagZ, value&acc == 0)
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s.registers.updateFlag(flagN, value&(1<<7) != 0)
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@ -193,7 +194,7 @@ func buildOpBit(addressMode int) opFunc {
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func buildOpCompare(addressMode int, reg int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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reference := s.registers.getRegister(reg)
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s.registers.updateFlagZN(reference - value)
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s.registers.updateFlag(flagC, reference >= value)
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@ -206,7 +207,7 @@ func operationXor(a uint8, b uint8) uint8 { return a ^ b }
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func buildOpLogic(addressMode int, operation func(uint8, uint8) uint8) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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result := operation(value, s.registers.getA())
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s.registers.setA(result)
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s.registers.updateFlagZN(result)
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@ -215,9 +216,10 @@ func buildOpLogic(addressMode int, operation func(uint8, uint8) uint8) opFunc {
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func buildOpAdd(addressMode int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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if s.registers.getFlag(flagD) {
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// TODO BCD
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// TODO BCD. See http://www.6502.org/tutorials/decimal_mode.html
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} else {
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total := uint16(s.registers.getA()) +
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uint16(value) +
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@ -232,7 +234,7 @@ func buildOpAdd(addressMode int) opFunc {
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func buildOpSub(addressMode int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value, _ := resolveWithAddressMode(s, line, addressMode)
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value, _, _ := resolveWithAddressMode(s, line, addressMode)
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if s.registers.getFlag(flagD) {
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// TODO BCD
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} else {
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@ -249,38 +251,79 @@ func buildOpSub(addressMode int) opFunc {
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const stackAddress uint16 = 0x0100
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func pushByte(s *state, value uint8) {
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adresss := stackAddress + uint16(s.registers.getSP())
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s.memory[adresss] = value
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s.registers.setSP(s.registers.getSP() - 1)
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}
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func pullByte(s *state) uint8 {
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s.registers.setSP(s.registers.getSP() + 1)
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adresss := stackAddress + uint16(s.registers.getSP())
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return s.memory[adresss]
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}
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func pushWord(s *state, value uint16) {
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pushByte(s, uint8(value>>8))
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pushByte(s, uint8(value))
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}
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func pullWord(s *state) uint16 {
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return uint16(pullByte(s)) +
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(uint16(pullByte(s)) << 8)
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}
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func buildOpPush(reg int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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value := s.registers.getRegister(reg)
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adresss := stackAddress + uint16(s.registers.getSP())
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s.memory[adresss] = value
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s.registers.setSP(s.registers.getSP() - 1)
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pushByte(s, s.registers.getRegister(reg))
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}
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}
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func buildOpPull(reg int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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s.registers.setSP(s.registers.getSP() + 1)
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adresss := stackAddress + uint16(s.registers.getSP())
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value := s.memory[adresss]
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s.registers.setRegister(reg, value)
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s.registers.setRegister(reg, pullByte(s))
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}
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}
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/*
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TODO:
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http://www.6502.org/tutorials/decimal_mode.html
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func buildOpJump(addressMode int) opFunc {
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return func(s *state, line []uint8, opcode opcode) {
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_, address, _ := resolveWithAddressMode(s, line, addressMode)
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s.registers.setPC(address)
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}
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}
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BRK
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func opNOP(s *state, line []uint8, opcode opcode) {}
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JMP
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JSR
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RTI
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RTS
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func opJSR(s *state, line []uint8, opcode opcode) {
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pushWord(s, s.registers.getPC())
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s.registers.setPC(getWordInLine(line))
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}
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*/
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func opRTI(s *state, line []uint8, opcode opcode) {
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s.registers.setP(pullByte(s))
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s.registers.setPC(pullWord(s))
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}
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func opRTS(s *state, line []uint8, opcode opcode) {
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s.registers.setPC(pullWord(s) + 1) // TODO: Do we really need to add 1?
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}
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func opBRK(s *state, line []uint8, opcode opcode) {
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s.registers.setFlag(flagI)
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pushWord(s, s.registers.getPC()+1) // TODO: De we have to add 1 or 2?
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pushByte(s, s.registers.getP())
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s.registers.setPC(s.memory.getWord(0xFFFE))
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}
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var opcodes = [256]opcode{
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0x00: opcode{"BRK", 1, 7, opBRK},
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0x4C: opcode{"JMP", 3, 3, buildOpJump(modeAbsolute)},
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0x6C: opcode{"JMP", 3, 3, buildOpJump(modeIndirect)},
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0x20: opcode{"JSR", 3, 6, opJSR},
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0x40: opcode{"RTI", 1, 6, opRTI},
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0x60: opcode{"RTS", 1, 6, opRTS},
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0x48: opcode{"PHA", 1, 3, buildOpPush(regA)},
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0x08: opcode{"PHP", 1, 3, buildOpPush(regP)},
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0x68: opcode{"PLA", 1, 4, buildOpPull(regA)},
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