More addressing modes for LDA
This commit is contained in:
Ivan Izaguirre
parent
925f76394f
commit
7e6b5012ca
82
execute.go
82
execute.go
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@ -14,53 +14,15 @@ const modeImmediate = 0
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const modeZeroPage = 1
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const modeZeroPageX = 3
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const modeAbsolute = 2
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const modeAbsoluteX = 4
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const modeAbsoluteY = 5
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// https://www.masswerk.at/6502/6502_instruction_set.html
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func opLDAimm(s *state, line []uint8) {
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opLDR(s, line, regA, modeImmediate)
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}
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func opLDAzpg(s *state, line []uint8) {
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opLDR(s, line, regA, modeZeroPage)
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}
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func opLDYimm(s *state, line []uint8) {
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opLDR(s, line, regY, modeImmediate)
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}
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func opLDAzpgX(s *state, line []uint8) {
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opLDR(s, line, regA, modeZeroPageX)
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}
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func opLDAabs(s *state, line []uint8) {
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opLDR(s, line, regA, modeAbsolute)
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}
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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 opLDR(s *state, line []uint8, reg int, mode int) {
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var value uint8
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switch mode {
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case modeImmediate:
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value = line[1]
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case modeZeroPage:
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address := line[1]
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value = s.memory[address]
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case modeZeroPageX:
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address := line[1] + s.registers.getRegister(regX)
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value = s.memory[address]
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case modeAbsolute:
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address := getWordInLine(line)
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value = s.memory[address]
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}
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s.registers.setRegister(reg, value)
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}
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type opFunc func(s *state, line []uint8, opcode opcode)
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type opcode struct {
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name string
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bytes int
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@ -70,18 +32,44 @@ type opcode struct {
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action opFunc
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}
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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 opLDRex(s *state, line []uint8, opcode opcode) {
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opLDR(s, line, opcode.reg, opcode.mode)
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func opLDR(s *state, line []uint8, opcode opcode) {
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var value uint8
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switch opcode.mode {
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case modeImmediate:
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value = line[1]
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case modeZeroPage:
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address := line[1]
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value = s.memory[address]
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case modeZeroPageX:
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address := line[1] + s.registers.getX()
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value = s.memory[address]
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case modeAbsolute:
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address := getWordInLine(line)
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value = s.memory[address]
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case modeAbsoluteX:
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address := getWordInLine(line) + uint16(s.registers.getX())
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value = s.memory[address]
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case modeAbsoluteY:
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address := getWordInLine(line) + uint16(s.registers.getY())
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value = s.memory[address]
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}
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s.registers.setRegister(opcode.reg, value)
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}
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var opcodes = [256]opcode{
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0x00: opcode{"BRK", 1, 7, modeImmediate, regNone, opNOP},
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0xA0: opcode{"LDY", -1, -1, modeImmediate, regY, opLDRex},
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0xA5: opcode{"LDA", 2, 3, modeZeroPage, regA, opLDRex},
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0xB5: opcode{"LDA", 2, 4, modeZeroPageX, regA, opLDRex},
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0xA9: opcode{"LDA", 2, 2, modeImmediate, regA, opLDRex},
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0xAD: opcode{"LDA", 3, 4, modeAbsolute, regA, opLDRex},
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0xA0: opcode{"LDY", 2, 2, modeImmediate, regY, opLDR},
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0xA5: opcode{"LDA", 2, 3, modeZeroPage, regA, opLDR},
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0xB5: opcode{"LDA", 2, 4, modeZeroPageX, regA, opLDR},
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0xA9: opcode{"LDA", 2, 2, modeImmediate, regA, opLDR},
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0xAD: opcode{"LDA", 3, 4, modeAbsolute, regA, opLDR},
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0xB9: opcode{"LDA", 3, 4, modeAbsoluteY, regA, opLDR}, // Extra cycles
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0xBD: opcode{"LDA", 3, 4, modeAbsoluteX, regA, opLDR}, // Extra cycles
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}
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func executeLine(s *state, line []uint8) {
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@ -7,47 +7,6 @@ import (
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func TestLDA(t *testing.T) {
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var s state
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opLDAimm(&s, []uint8{0xA9, 0x42})
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if s.registers.getA() != 0x42 {
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t.Error("Error in LDA #")
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}
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opLDYimm(&s, []uint8{0xA0, 0xFE})
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if s.registers.getY() != 0xFE {
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t.Error("Error in LDY #")
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}
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s.memory[0x38] = 0x87
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opLDAzpg(&s, []uint8{0xA5, 0x38})
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if s.registers.getA() != 0x87 {
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t.Error("Error in LDA zpg")
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}
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s.memory[0x57] = 0x90
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s.registers.setX(0x10)
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opLDAzpgX(&s, []uint8{0xB5, 0x47})
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if s.registers.getA() != 0x90 {
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t.Error("Error in LDA zpgX")
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}
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s.memory[0x38] = 0x12
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s.registers.setX(0x89)
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opLDAzpgX(&s, []uint8{0xB5, 0xAF})
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if s.registers.getA() != 0x12 {
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t.Error("Error in LDA zpgX with sero page overflow")
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}
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s.memory[0x1234] = 0x67
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opLDAabs(&s, []uint8{0xAD, 0x34, 0x12})
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if s.registers.getA() != 0x67 {
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t.Error("Error in LDA abs")
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}
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}
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func TestLDA2(t *testing.T) {
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var s state
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executeLine(&s, []uint8{0xA9, 0x42})
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if s.registers.getA() != 0x42 {
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t.Error("Error in LDA #")
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@ -68,7 +27,7 @@ func TestLDA2(t *testing.T) {
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s.registers.setX(0x10)
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executeLine(&s, []uint8{0xB5, 0x47})
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if s.registers.getA() != 0x90 {
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t.Error("Error in LDA zpgX")
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t.Error("Error in LDA zpg, X")
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}
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s.memory[0x38] = 0x12
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@ -84,4 +43,18 @@ func TestLDA2(t *testing.T) {
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t.Error("Error in LDA abs")
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}
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s.memory[0xC057] = 0x7E
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s.registers.setX(0x57)
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executeLine(&s, []uint8{0xBD, 0x00, 0xC0})
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if s.registers.getA() != 0x7E {
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t.Error("Error in LDA abs, X")
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}
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s.memory[0xD059] = 0x7A
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s.registers.setY(0x59)
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executeLine(&s, []uint8{0xB9, 0x00, 0xD0})
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if s.registers.getA() != 0x7A {
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t.Error("Error in LDA abs, Y")
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}
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}
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