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More addressing modes for LDA

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This commit is contained in:
Ivan Izaguirre 2019-01-27 09:25:33 +01:00
parent 925f76394f
commit 7e6b5012ca
2 changed files with 50 additions and 89 deletions
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82
execute.go
View File

@ -14,53 +14,15 @@ const modeImmediate = 0
const modeZeroPage = 1
const modeZeroPageX = 3
const modeAbsolute = 2
const modeAbsoluteX = 4
const modeAbsoluteY = 5
// https://www.masswerk.at/6502/6502_instruction_set.html
func opLDAimm(s *state, line []uint8) {
opLDR(s, line, regA, modeImmediate)
}
func opLDAzpg(s *state, line []uint8) {
opLDR(s, line, regA, modeZeroPage)
}
func opLDYimm(s *state, line []uint8) {
opLDR(s, line, regY, modeImmediate)
}
func opLDAzpgX(s *state, line []uint8) {
opLDR(s, line, regA, modeZeroPageX)
}
func opLDAabs(s *state, line []uint8) {
opLDR(s, line, regA, modeAbsolute)
}
func getWordInLine(line []uint8) uint16 {
return uint16(line[1]) + 0x100*uint16(line[2])
}
func opLDR(s *state, line []uint8, reg int, mode int) {
var value uint8
switch mode {
case modeImmediate:
value = line[1]
case modeZeroPage:
address := line[1]
value = s.memory[address]
case modeZeroPageX:
address := line[1] + s.registers.getRegister(regX)
value = s.memory[address]
case modeAbsolute:
address := getWordInLine(line)
value = s.memory[address]
}
s.registers.setRegister(reg, value)
}
type opFunc func(s *state, line []uint8, opcode opcode)
type opcode struct {
name string
bytes int
@ -70,18 +32,44 @@ type opcode struct {
action opFunc
}
type opFunc func(s *state, line []uint8, opcode opcode)
func opNOP(s *state, line []uint8, opcode opcode) {}
func opLDRex(s *state, line []uint8, opcode opcode) {
opLDR(s, line, opcode.reg, opcode.mode)
func opLDR(s *state, line []uint8, opcode opcode) {
var value uint8
switch opcode.mode {
case modeImmediate:
value = line[1]
case modeZeroPage:
address := line[1]
value = s.memory[address]
case modeZeroPageX:
address := line[1] + s.registers.getX()
value = s.memory[address]
case modeAbsolute:
address := getWordInLine(line)
value = s.memory[address]
case modeAbsoluteX:
address := getWordInLine(line) + uint16(s.registers.getX())
value = s.memory[address]
case modeAbsoluteY:
address := getWordInLine(line) + uint16(s.registers.getY())
value = s.memory[address]
}
s.registers.setRegister(opcode.reg, value)
}
var opcodes = [256]opcode{
0x00: opcode{"BRK", 1, 7, modeImmediate, regNone, opNOP},
0xA0: opcode{"LDY", -1, -1, modeImmediate, regY, opLDRex},
0xA5: opcode{"LDA", 2, 3, modeZeroPage, regA, opLDRex},
0xB5: opcode{"LDA", 2, 4, modeZeroPageX, regA, opLDRex},
0xA9: opcode{"LDA", 2, 2, modeImmediate, regA, opLDRex},
0xAD: opcode{"LDA", 3, 4, modeAbsolute, regA, opLDRex},
0xA0: opcode{"LDY", 2, 2, modeImmediate, regY, opLDR},
0xA5: opcode{"LDA", 2, 3, modeZeroPage, regA, opLDR},
0xB5: opcode{"LDA", 2, 4, modeZeroPageX, regA, opLDR},
0xA9: opcode{"LDA", 2, 2, modeImmediate, regA, opLDR},
0xAD: opcode{"LDA", 3, 4, modeAbsolute, regA, opLDR},
0xB9: opcode{"LDA", 3, 4, modeAbsoluteY, regA, opLDR}, // Extra cycles
0xBD: opcode{"LDA", 3, 4, modeAbsoluteX, regA, opLDR}, // Extra cycles
}
func executeLine(s *state, line []uint8) {

57
execute_test.go
View File

@ -7,47 +7,6 @@ import (
func TestLDA(t *testing.T) {
var s state
opLDAimm(&s, []uint8{0xA9, 0x42})
if s.registers.getA() != 0x42 {
t.Error("Error in LDA #")
}
opLDYimm(&s, []uint8{0xA0, 0xFE})
if s.registers.getY() != 0xFE {
t.Error("Error in LDY #")
}
s.memory[0x38] = 0x87
opLDAzpg(&s, []uint8{0xA5, 0x38})
if s.registers.getA() != 0x87 {
t.Error("Error in LDA zpg")
}
s.memory[0x57] = 0x90
s.registers.setX(0x10)
opLDAzpgX(&s, []uint8{0xB5, 0x47})
if s.registers.getA() != 0x90 {
t.Error("Error in LDA zpgX")
}
s.memory[0x38] = 0x12
s.registers.setX(0x89)
opLDAzpgX(&s, []uint8{0xB5, 0xAF})
if s.registers.getA() != 0x12 {
t.Error("Error in LDA zpgX with sero page overflow")
}
s.memory[0x1234] = 0x67
opLDAabs(&s, []uint8{0xAD, 0x34, 0x12})
if s.registers.getA() != 0x67 {
t.Error("Error in LDA abs")
}
}
func TestLDA2(t *testing.T) {
var s state
executeLine(&s, []uint8{0xA9, 0x42})
if s.registers.getA() != 0x42 {
t.Error("Error in LDA #")
@ -68,7 +27,7 @@ func TestLDA2(t *testing.T) {
s.registers.setX(0x10)
executeLine(&s, []uint8{0xB5, 0x47})
if s.registers.getA() != 0x90 {
t.Error("Error in LDA zpgX")
t.Error("Error in LDA zpg, X")
}
s.memory[0x38] = 0x12
@ -84,4 +43,18 @@ func TestLDA2(t *testing.T) {
t.Error("Error in LDA abs")
}
s.memory[0xC057] = 0x7E
s.registers.setX(0x57)
executeLine(&s, []uint8{0xBD, 0x00, 0xC0})
if s.registers.getA() != 0x7E {
t.Error("Error in LDA abs, X")
}
s.memory[0xD059] = 0x7A
s.registers.setY(0x59)
executeLine(&s, []uint8{0xB9, 0x00, 0xD0})
if s.registers.getA() != 0x7A {
t.Error("Error in LDA abs, Y")
}
}