diff --git a/gb/cartridge.go b/gb/cartridge.go
new file mode 100644
index 0000000..f13c48d
--- /dev/null
+++ b/gb/cartridge.go
@@ -0,0 +1,301 @@
+package gb
+
+import (
+	"bytes"
+	"encoding/binary"
+	"io"
+	"log"
+	"os"
+)
+
+// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0104-0133--nintendo-logo
+var expectedLogo = [48]byte{
+	0xCE, 0xED, 0x66, 0x66, 0xCC, 0x0D, 0x00, 0x0B,
+	0x03, 0x73, 0x00, 0x83, 0x00, 0x0C, 0x00, 0x0D,
+	0x00, 0x08, 0x11, 0x1F, 0x88, 0x89, 0x00, 0x0E,
+	0xDC, 0xCC, 0x6E, 0xE6, 0xDD, 0xDD, 0xD9, 0x99,
+	0xBB, 0xBB, 0x67, 0x63, 0x6E, 0x0E, 0xEC, 0xCC,
+	0xDD, 0xDC, 0x99, 0x9F, 0xBB, 0xB9, 0x33, 0x3E,
+}
+
+// Cartridge types
+// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0147--cartridge-type
+var cartridgeTypes = map[byte]string{
+	0x00: "ROM ONLY",
+	0x01: "MBC1",
+	0x02: "MBC1+RAM",
+	0x03: "MBC1+RAM+BATTERY",
+	0x05: "MBC2",
+	0x06: "MBC2+BATTERY",
+	0x08: "ROM+RAM 9",
+	0x09: "ROM+RAM+BATTERY 9",
+	0x0B: "MMM01",
+	0x0C: "MMM01+RAM",
+	0x0D: "MMM01+RAM+BATTERY",
+	0x0F: "MBC3+TIMER+BATTERY",
+	0x10: "MBC3+TIMER+RAM+BATTERY 10",
+	0x11: "MBC3",
+	0x12: "MBC3+RAM 10",
+	0x13: "MBC3+RAM+BATTERY 10",
+	0x19: "MBC5",
+	0x1A: "MBC5+RAM",
+	0x1B: "MBC5+RAM+BATTERY",
+	0x1C: "MBC5+RUMBLE",
+	0x1D: "MBC5+RUMBLE+RAM",
+	0x1E: "MBC5+RUMBLE+RAM+BATTERY",
+	0x20: "MBC6",
+	0x22: "MBC7+SENSOR+RUMBLE+RAM+BATTERY",
+	0xFC: "POCKET CAMERA",
+	0xFD: "BANDAI TAMA5",
+	0xFE: "HuC3",
+	0xFF: "HuC1+RAM+BATTERY",
+}
+
+// RAM sizes
+// https://gbdev.io/pandocs/The_Cartridge_Header.html#0149--ram-size
+var ramSizes = map[byte]string{
+	0x00: "0 - No RAM",
+	0x01: "UNUSED VALUE",
+	0x02: "8 KiB - 1 bank",
+	0x03: "32 KiB - 4 banks of 8 KiB each",
+	0x04: "128 KiB 16 banks of 8 KiB each",
+	0x05: "64 KiB  8 banks of 8 KiB each",
+}
+
+// Old licensees
+// https://gbdev.io/pandocs/The_Cartridge_Header.html#014b--old-licensee-code
+var oldLicensees = map[byte]string{
+	0x00: "None",
+	0x01: "Nintendo",
+	0x08: "Capcom",
+	0x09: "HOT-B",
+	0x0A: "Jaleco",
+	0x0B: "Coconuts Japan",
+	0x0C: "Elite Systems",
+	0x13: "EA (Electronic Arts)",
+	0x18: "Hudson Soft",
+	0x19: "ITC Entertainment",
+	0x1A: "Yanoman",
+	0x1D: "Japan Clary",
+	0x1F: "Virgin Games Ltd.3",
+	0x24: "PCM Complete",
+	0x25: "San-X",
+	0x28: "Kemco",
+	0x29: "SETA Corporation",
+	0x30: "Infogrames5",
+	0x31: "Nintendo",
+	0x32: "Bandai",
+	0x33: "Indicates that the New licensee code should be used instead.",
+	0x34: "Konami",
+	0x35: "HectorSoft",
+	0x38: "Capcom",
+	0x39: "Banpresto",
+	0x3C: "Entertainment Interactive (stub)",
+	0x3E: "Gremlin",
+	0x41: "Ubi Soft1",
+	0x42: "Atlus",
+	0x44: "Malibu Interactive",
+	0x46: "Angel",
+	0x47: "Spectrum HoloByte",
+	0x49: "Irem",
+	0x4A: "Virgin Games Ltd.3",
+	0x4D: "Malibu Interactive",
+	0x4F: "U.S. Gold",
+	0x50: "Absolute",
+	0x51: "Acclaim Entertainment",
+	0x52: "Activision",
+	0x53: "Sammy USA Corporation",
+	0x54: "GameTek",
+	0x55: "Park Place13",
+	0x56: "LJN",
+	0x57: "Matchbox",
+	0x59: "Milton Bradley Company",
+	0x5A: "Mindscape",
+	0x5B: "Romstar",
+	0x5C: "Naxat Soft14",
+	0x5D: "Tradewest",
+	0x60: "Titus Interactive",
+	0x61: "Virgin Games Ltd.3",
+	0x67: "Ocean Software",
+	0x69: "EA (Electronic Arts)",
+	0x6E: "Elite Systems",
+	0x6F: "Electro Brain",
+	0x70: "Infogrames5",
+	0x71: "Interplay Entertainment",
+	0x72: "Broderbund",
+	0x73: "Sculptured Software6",
+	0x75: "The Sales Curve Limited7",
+	0x78: "THQ",
+	0x79: "Accolade15",
+	0x7A: "Triffix Entertainment",
+	0x7C: "MicroProse",
+	0x7F: "Kemco",
+	0x80: "Misawa Entertainment",
+	0x83: "LOZC G.",
+	0x86: "Tokuma Shoten",
+	0x8B: "Bullet-Proof Software2",
+	0x8C: "Vic Tokai Corp.16",
+	0x8E: "Ape Inc.17",
+	0x8F: "I'Max18",
+	0x91: "Chunsoft Co.8",
+	0x92: "Video System",
+	0x93: "Tsubaraya Productions",
+	0x95: "Varie",
+	0x96: "Yonezawa19/S'Pal",
+	0x97: "Kemco",
+	0x99: "Arc",
+	0x9A: "Nihon Bussan",
+	0x9B: "Tecmo",
+	0x9C: "Imagineer",
+	0x9D: "Banpresto",
+	0x9F: "Nova",
+	0xA1: "Hori Electric",
+	0xA2: "Bandai",
+	0xA4: "Konami",
+	0xA6: "Kawada",
+	0xA7: "Takara",
+	0xA9: "Technos Japan",
+	0xAA: "Broderbund",
+	0xAC: "Toei Animation",
+	0xAD: "Toho",
+	0xAF: "Namco",
+	0xB0: "Acclaim Entertainment",
+	0xB1: "ASCII Corporation or Nexsoft",
+	0xB2: "Bandai",
+	0xB4: "Square Enix",
+	0xB6: "HAL Laboratory",
+	0xB7: "SNK",
+	0xB9: "Pony Canyon",
+	0xBA: "Culture Brain",
+	0xBB: "Sunsoft",
+	0xBD: "Sony Imagesoft",
+	0xBF: "Sammy Corporation",
+	0xC0: "Taito",
+	0xC2: "Kemco",
+	0xC3: "Square",
+	0xC4: "Tokuma Shoten",
+	0xC5: "Data East",
+	0xC6: "Tonkin House",
+	0xC8: "Koei",
+	0xC9: "UFL",
+	0xCA: "Ultra Games",
+	0xCB: "VAP, Inc.",
+	0xCC: "Use Corporation",
+	0xCD: "Meldac",
+	0xCE: "Pony Canyon",
+	0xCF: "Angel",
+	0xD0: "Taito",
+	0xD1: "SOFEL (Software Engineering Lab)",
+	0xD2: "Quest",
+	0xD3: "Sigma Enterprises",
+	0xD4: "ASK Kodansha Co.",
+	0xD6: "Naxat Soft14",
+	0xD7: "Copya System",
+	0xD9: "Banpresto",
+	0xDA: "Tomy",
+	0xDB: "LJN",
+	0xDD: "Nippon Computer Systems",
+	0xDE: "Human Ent.",
+	0xDF: "Altron",
+	0xE0: "Jaleco",
+	0xE1: "Towa Chiki",
+	0xE2: "Yutaka # Needs more info",
+	0xE3: "Varie",
+	0xE5: "Epoch",
+	0xE7: "Athena",
+	0xE8: "Asmik Ace Entertainment",
+	0xE9: "Natsume",
+	0xEA: "King Records",
+	0xEB: "Atlus",
+	0xEC: "Epic/Sony Records",
+	0xEE: "IGS",
+	0xF0: "A Wave",
+	0xF3: "Extreme Entertainment",
+	0xFF: "LJN",
+}
+
+type ROMHeader struct {
+	EntryPoint [4]byte
+	Logo       [48]byte
+	// NOTE(m): Assuming "old" cartridges here. This may cause problems with newer cartridges.
+	// See https://gbdev.io/pandocs/The_Cartridge_Header.html#0134-0143--title
+	Title                [16]byte
+	NewLicenseeCode      [2]byte
+	SGBFlag              byte
+	CartridgeType        byte
+	ROMSize              byte
+	RAMSize              byte
+	DestinationCode      byte
+	OldLicenseeCode      byte
+	MaskROMVersionNumber byte
+	HeaderChecksum       byte
+	GlobalChecksum       [2]byte
+}
+
+type Cartridge struct {
+	Filename    string
+	Mapper      string
+	Title       string
+	Licensee    string
+	SGBSupport  bool
+	ROMSize     int
+	RAMSize     string
+	Destination string
+	Version     int
+}
+
+func InsertCartridge(path string) *Cartridge {
+	file, err := os.Open(path)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer file.Close()
+	cartridge := Cartridge{Filename: file.Name()}
+
+	// Jump to start of header
+	_, err = file.Seek(0x0100, io.SeekStart)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Read header
+	var header ROMHeader
+	err = binary.Read(file, binary.LittleEndian, &header)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	// Validate the ROM by checking presence of the Nintendo logo
+	if header.Logo != expectedLogo {
+		log.Fatal("Invalid ROM file: No valid logo found!")
+	}
+
+	// Convert some header values
+	cartridge.Title = string(bytes.Trim(header.Title[:], "\x00"))
+	cartridge.Mapper = cartridgeTypes[header.CartridgeType]
+	if header.OldLicenseeCode == 0x33 {
+		// FIXME(m): Support new licensee codes
+		cartridge.Licensee = "Indicates that the New licensee code should be used instead."
+	} else {
+		cartridge.Licensee = oldLicensees[header.OldLicenseeCode]
+	}
+	cartridge.SGBSupport = (header.SGBFlag == 0x03)
+	cartridge.ROMSize = 32 * (1 << header.ROMSize)
+	cartridge.RAMSize = ramSizes[header.RAMSize]
+	switch header.DestinationCode {
+	case 0x00:
+		cartridge.Destination = "Japan (and possibly overseas)"
+	case 0x01:
+		cartridge.Destination = "Overseas only"
+	default:
+		cartridge.Destination = "UNKNOWN"
+	}
+	cartridge.Version = int(header.MaskROMVersionNumber)
+
+	// TODO(m): Verify header checksum
+
+	// NOTE(m): Ignoring global checksum which is not used, except by one emulator.
+	// See https://gbdev.io/pandocs/The_Cartridge_Header.html#014e-014f--global-checksum
+
+	return &cartridge
+}
diff --git a/gb/console.go b/gb/console.go
new file mode 100644
index 0000000..e66ebe6
--- /dev/null
+++ b/gb/console.go
@@ -0,0 +1,17 @@
+package gb
+
+type Console struct {
+	Cartridge *Cartridge
+}
+
+func NewConsole(path string) (*Console, error) {
+	cartridge := InsertCartridge(path)
+
+	console := Console{cartridge}
+
+	return &console, nil
+}
+
+func (console *Console) Update(dt uint64) {
+	console.StepSeconds(dt)
+}
diff --git a/main.go b/main.go
index bdea31a..9b83c00 100644
--- a/main.go
+++ b/main.go
@@ -1,127 +1,16 @@
 package main
 
 import (
-	"fmt"
-	"log"
-	"runtime"
-
-	"github.com/veandco/go-sdl2/sdl"
-	"github.com/veandco/go-sdl2/ttf"
+	"gb-player/ui"
 )
 
-var renderer *sdl.Renderer
-var font *ttf.Font
-
-func init() {
-	runtime.LockOSThread()
-}
-
 func main() {
-	if err := sdl.Init(sdl.INIT_EVERYTHING); err != nil {
-		log.Fatal(err)
-	}
-	defer sdl.Quit()
+	// FIXME(m): Allow specifying rom file on command line
+	// if len(os.Args) != 2 {
+	// 	log.Fatalln("No rom file specified")
+	// }
+	// romPath := os.Args[1]
+	romPath := "rom.gb"
 
-	if err := ttf.Init(); err != nil {
-		log.Fatal((err))
-	}
-	defer ttf.Quit()
-
-	window, err := sdl.CreateWindow(
-		"GB Player",
-		sdl.WINDOWPOS_UNDEFINED,
-		sdl.WINDOWPOS_UNDEFINED,
-		800, 600,
-		sdl.WINDOW_SHOWN)
-	if err != nil {
-		panic(err)
-	}
-	defer window.Destroy()
-
-	renderer, err = sdl.CreateRenderer(window, -1, 0)
-	if err != nil {
-		panic(err)
-	}
-	defer renderer.Destroy()
-	renderer.RenderSetVSync(true)
-
-	font, err = ttf.OpenFont("SourceCodePro.ttf", 18)
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer font.Close()
-	font.SetStyle(ttf.STYLE_BOLD)
-
-	var fps float64
-	var frameCount uint32
-	var startTicks = sdl.GetTicks64()
-	var now uint64
-	var last uint64
-
-	cartridge := Insert("rom.gb")
-	fmt.Println(cartridge)
-
-	running := true
-	for running {
-		for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
-			switch event.(type) {
-			case *sdl.QuitEvent:
-				println("Quit")
-				running = false
-			}
-		}
-
-		last = now
-		now = sdl.GetPerformanceCounter()
-		deltaTime := float64((now - last) * 1000.0 / sdl.GetPerformanceFrequency())
-		_ = deltaTime
-
-		// Clear screen
-		renderer.SetDrawColor(0x63, 0x94, 0xED, 0xff)
-		renderer.Clear()
-
-		// Update state
-		rect := sdl.Rect{X: 100, Y: 100, W: 200, H: 150}
-		renderer.SetDrawColor(0, 0, 255, 255)
-		renderer.FillRect(&rect)
-
-		drawDebugWindow(fps)
-
-		// Present to screen
-		renderer.Present()
-
-		// Calculate framerate
-		frameCount++
-		currentTicks := sdl.GetTicks64()
-		elapsed := currentTicks - startTicks
-
-		if elapsed >= 1000 {
-			fps = float64(frameCount) / (float64(elapsed) / 1000.0)
-
-			// Reset counters
-			frameCount = 0
-			startTicks = currentTicks
-		}
-	}
-}
-
-func drawDebugWindow(fps float64) {
-	var textSurface *sdl.Surface
-	var textTexture *sdl.Texture
-
-	// FPS
-	textSurface, err := font.RenderUTF8Blended(fmt.Sprintf("FPS: %.2f", fps), sdl.Color{R: 0, G: 0, B: 0, A: 255})
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer textSurface.Free()
-
-	textTexture, err = renderer.CreateTextureFromSurface(textSurface)
-	if err != nil {
-		log.Fatal(err)
-	}
-	defer textTexture.Destroy()
-
-	textRect := sdl.Rect{X: 0, Y: 0, W: textSurface.W, H: textSurface.H}
-	renderer.Copy(textTexture, nil, &textRect)
+	ui.Run(romPath)
 }
diff --git a/ui/controller.go b/ui/controller.go
new file mode 100644
index 0000000..5679ce1
--- /dev/null
+++ b/ui/controller.go
@@ -0,0 +1,86 @@
+package ui
+
+import (
+	"gb-player/gb"
+
+	"github.com/veandco/go-sdl2/sdl"
+)
+
+type Controller struct {
+	renderer  *sdl.Renderer
+	view      *View
+	timestamp uint64
+}
+
+func NewController(renderer *sdl.Renderer) *Controller {
+	controller := Controller{}
+	controller.renderer = renderer
+	return &controller
+}
+
+func (c *Controller) Start(path string) {
+	console := gb.NewConsole(path)
+	c.view = NewView(c, console)
+	c.Run()
+}
+
+func (c *Controller) Step() {
+	timestamp := sdl.GetTicks64()
+	dt := timestamp - c.timestamp
+	c.view.Update(timestamp, dt)
+}
+
+func (c *Controller) Run() {
+	var fps float64
+	var frameCount uint32
+	var startTicks = sdl.GetTicks64()
+	var now, last uint64
+
+	// cartridge := gb.Insert(romPath)
+	// fmt.Println(cartridge)
+
+	running := true
+	for running {
+		for event := sdl.PollEvent(); event != nil; event = sdl.PollEvent() {
+			switch event.(type) {
+			case *sdl.QuitEvent:
+				println("Quit")
+				running = false
+			}
+		}
+
+		last = now
+		now = sdl.GetPerformanceCounter()
+		deltaTime := float64((now - last) * 1000.0 / sdl.GetPerformanceFrequency())
+		_ = deltaTime
+
+		// Clear screen
+		renderer.SetDrawColor(0x63, 0x94, 0xED, 0xff)
+		renderer.Clear()
+
+		// Update state
+		c.Step()
+		rect := sdl.Rect{X: 100, Y: 100, W: 200, H: 150}
+		renderer.SetDrawColor(0, 0, 255, 255)
+		renderer.FillRect(&rect)
+
+		drawDebugWindow(fps)
+
+		// Present to screen
+		renderer.Present()
+
+		// Calculate framerate
+		frameCount++
+		currentTicks := sdl.GetTicks64()
+		elapsed := currentTicks - startTicks
+
+		if elapsed >= 1000 {
+			fps = float64(frameCount) / (float64(elapsed) / 1000.0)
+
+			// Reset counters
+			frameCount = 0
+			startTicks = currentTicks
+		}
+	}
+
+}
diff --git a/ui/run.go b/ui/run.go
new file mode 100644
index 0000000..4b328d7
--- /dev/null
+++ b/ui/run.go
@@ -0,0 +1,75 @@
+package ui
+
+import (
+	"fmt"
+	"log"
+	"runtime"
+
+	"github.com/veandco/go-sdl2/sdl"
+	"github.com/veandco/go-sdl2/ttf"
+)
+
+var renderer *sdl.Renderer
+var font *ttf.Font
+
+func init() {
+	runtime.LockOSThread()
+}
+
+func Run(romPath string) {
+	if err := sdl.Init(sdl.INIT_EVERYTHING); err != nil {
+		log.Fatal(err)
+	}
+	defer sdl.Quit()
+
+	if err := ttf.Init(); err != nil {
+		log.Fatal((err))
+	}
+	defer ttf.Quit()
+
+	window, err := sdl.CreateWindow(
+		"GB Player",
+		sdl.WINDOWPOS_UNDEFINED,
+		sdl.WINDOWPOS_UNDEFINED,
+		800, 600,
+		sdl.WINDOW_SHOWN)
+	if err != nil {
+		panic(err)
+	}
+	defer window.Destroy()
+
+	renderer, err = sdl.CreateRenderer(window, -1, 0)
+	if err != nil {
+		panic(err)
+	}
+	defer renderer.Destroy()
+	renderer.RenderSetVSync(true)
+
+	font, err = ttf.OpenFont("SourceCodePro.ttf", 18)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer font.Close()
+	font.SetStyle(ttf.STYLE_BOLD)
+
+	controller := NewController(renderer)
+	controller.Start(romPath)
+}
+
+func drawDebugWindow(fps float64) {
+	// FPS
+	textSurface, err := font.RenderUTF8Blended(fmt.Sprintf("FPS: %.2f", fps), sdl.Color{R: 0, G: 0, B: 0, A: 255})
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer textSurface.Free()
+
+	textTexture, err := renderer.CreateTextureFromSurface(textSurface)
+	if err != nil {
+		log.Fatal(err)
+	}
+	defer textTexture.Destroy()
+
+	textRect := sdl.Rect{X: 0, Y: 0, W: textSurface.W, H: textSurface.H}
+	renderer.Copy(textTexture, nil, &textRect)
+}
diff --git a/ui/view.go b/ui/view.go
new file mode 100644
index 0000000..499b478
--- /dev/null
+++ b/ui/view.go
@@ -0,0 +1,14 @@
+package ui
+
+import (
+	"gb-player/gb"
+)
+
+type View struct {
+	controller *Controller
+	console    *gb.Console
+}
+
+func NewView(controller *Controller, console *gb.Console) *View {
+	return &View{controller, console}
+}