Initial commit for basics need a refresher.

cmd/asm/main.go

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+package main
+
+import "fmt"
+
+func main() {
+	fmt.Println("hi compiler")
+}

cmd/sim/main.go

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+package main
+
+import (
+	"fmt"
+
+	"jh/gomos/internal/bus"
+	"jh/gomos/internal/cpu"
+)
+
+func main() {
+	fmt.Println("--- 6502 Simulator Starting ---")
+
+	// Initialize the Bus
+	b := bus.New()
+
+	// Initialize CPU and "plug in" the Bus
+	c := &cpu.CPU{Bus: b}
+	c.Reset()
+
+	// Run for 10 cycles to verify the "Fetch" works
+	for range 10 {
+		c.Step()
+	}
+
+	fmt.Println("--- Simulation Complete ---")
+}

go.mod

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+module jh/gomos
+
+go 1.26.1

internal/bus/bus.go

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+package bus
+
+type MainBus struct {
+	// add ram etc here
+}
+
+func New() *MainBus {
+	return &MainBus{}
+}
+
+// Just a test read for now, need to figure wtf is happening...
+func (b *MainBus) Read(address uint16) uint8 {
+	// Just testing with NOPs
+	return 0xEA
+}
+
+func (b *MainBus) Write(address uint16, data uint8) {
+	// Need to write data to the actual ram.
+}
+

internal/cpu/cpu.go

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+package cpu
+
+import "fmt"
+
+const ARCH = "MOS6502"
+
+// bits for the status register
+const (
+	FlagCarry     = 1 << 0 // Bit 0
+	FlagZero      = 1 << 1 // Bit 1
+	FlagInterrupt = 1 << 2 // Bit 2
+	FlagDecimal   = 1 << 3 // Bit 3
+	FlagBreak     = 1 << 4 // Bit 4
+	FlagUnused    = 1 << 5 // Bit 5
+	FlagOverflow  = 1 << 6 // Bit 6
+	FlagNegative  = 1 << 7 // Bit 7
+)
+
+type Bus interface {
+	Read(address uint16) uint8
+}
+
+type CPU struct {
+	A      uint8  // Accumulator
+	X      uint8  // X Register
+	Y      uint8  // Y Register
+	PC     uint16 // Program Counter
+	SP     uint8  // Stack Pointer
+	Status uint8  // Status Flags
+	Bus    Bus    // Connection to the Bus
+}
+
+func (c *CPU) Reset() {
+	c.A = 0
+	c.X = 0
+	c.Y = 0
+	c.SP = 0xFD
+	c.Status = 0x24 
+	c.PC = 0x0000
+}
+
+// Small helper func to flip the status register bits
+func (c *CPU) setFlag(flag uint8, set bool) {
+	if set {
+		c.Status |= flag
+	} else {
+		c.Status &= ^flag
+	}
+}
+
+// fetch -> decode -> execute cycle
+func (c *CPU) Step() {
+	// fetch with program counter and bus memory
+	opcode := c.Bus.Read(c.PC)
+
+	fmt.Printf("Executing at PC: %04X | Opcode: %02X\n", c.PC, opcode)
+
+	// decode + exe need to split this out to handle all instructions etc
+	// Look at : https://www.ahl27.com/posts/2023/01/6502-emu1/
+	switch opcode {
+	case 0xEA: //NOP
+		// does nothing its a no op
+	default:
+		fmt.Printf("Unknown opcode: %02X\n", opcode)
+	}
+
+	// Move the Program counter
+	c.PC++
+}
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