izapple2/core6502/execute.go

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package core6502
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import "fmt"
// https://www.masswerk.at/6502/6502_instruction_set.html
// http://www.emulator101.com/reference/6502-reference.html
// https://www.csh.rit.edu/~moffitt/docs/6502.html#FLAGS
// https://ia800509.us.archive.org/18/items/Programming_the_6502/Programming_the_6502.pdf
// State represents the state of the simulated device
type State struct {
reg registers
mem Memory
cycles int64
opcodes *[256]opcode
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}
const (
vectorNMI uint16 = 0xfffa
vectorReset uint16 = 0xfffc
vectorBreak uint16 = 0xfffe
)
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type opcode struct {
name string
bytes uint8
cycles int
addressMode int
action opFunc
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}
type opFunc func(s *State, line []uint8, opcode opcode)
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func (s *State) executeLine(line []uint8) {
opcode := s.opcodes[line[0]]
if opcode.cycles == 0 {
panic(fmt.Sprintf("Unknown opcode 0x%02x\n", line[0]))
}
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opcode.action(s, line, opcode)
}
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// ExecuteInstruction transforms the state given after a single instruction is executed.
func (s *State) ExecuteInstruction(log bool) {
pc := s.reg.getPC()
opcodeID := s.mem.Peek(pc)
opcode := s.opcodes[opcodeID]
if opcode.cycles == 0 {
panic(fmt.Sprintf("Unknown opcode 0x%02x\n", opcodeID))
}
line := make([]uint8, opcode.bytes)
for i := uint8(0); i < opcode.bytes; i++ {
line[i] = s.mem.Peek(pc)
pc++
}
s.reg.setPC(pc)
if log {
fmt.Printf("%#04x %-12s: ", pc, lineString(line, opcode))
}
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opcode.action(s, line, opcode)
s.cycles += int64(opcode.cycles)
if log {
fmt.Printf("%v, [%02x]\n", s.reg, line)
}
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}
// Reset resets the processor state. Moves the program counter to the vector in 0cfffc.
func (s *State) Reset() {
startAddress := getWord(s.mem, vectorReset)
s.reg.setPC(startAddress)
}
func lineString(line []uint8, opcode opcode) string {
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t := opcode.name
switch opcode.addressMode {
case modeImplicit:
case modeImplicitX:
case modeImplicitY:
//Nothing
case modeAccumulator:
t += fmt.Sprintf(" A")
case modeImmediate:
t += fmt.Sprintf(" #%02x", line[1])
case modeZeroPage:
t += fmt.Sprintf(" $%02x", line[1])
case modeZeroPageX:
t += fmt.Sprintf(" $%02x,X", line[1])
case modeZeroPageY:
t += fmt.Sprintf(" $%02x,Y", line[1])
case modeRelative:
t += fmt.Sprintf(" *%+x", int8(line[1]))
case modeAbsolute:
t += fmt.Sprintf(" $%04x", getWordInLine(line))
case modeAbsoluteX:
t += fmt.Sprintf(" $%04x,X", getWordInLine(line))
case modeAbsoluteY:
t += fmt.Sprintf(" $%04x,Y", getWordInLine(line))
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case modeIndirect:
t += fmt.Sprintf(" ($%04x)", getWordInLine(line))
case modeIndexedIndirectX:
t += fmt.Sprintf(" ($%02x,X)", line[1])
case modeIndirectIndexedY:
t += fmt.Sprintf(" ($%02x),Y", line[1])
default:
t += "UNKNOWN MODE"
}
return t
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}