diff --git a/tridoraemu/cpu.go b/tridoraemu/cpu.go
index c0c7739..9d6b08d 100644
--- a/tridoraemu/cpu.go
+++ b/tridoraemu/cpu.go
@@ -125,7 +125,7 @@ func (c *CPU) step() error {
 	
 	Y := c.estack[c.ESP]
 
-	insWord, err := c.mem.read(c.PC)
+	insWord, err := c.mem.readIns(c.PC)
 	if err != nil { return err }
 	if c.PC % 4 == 0 {
 		insWord = insWord >> 16
diff --git a/tridoraemu/mem.go b/tridoraemu/mem.go
index 4765c8b..624c7bd 100644
--- a/tridoraemu/mem.go
+++ b/tridoraemu/mem.go
@@ -17,6 +17,12 @@ const IOSlotSize = 128
 
 const IOSlotCount = 16
 
+const DRAMStart = 65536
+
+const CacheAddrShift = 8
+
+const CacheWriteThrough = true
+
 type Mem struct {
 	ram [] word
 	iohandler [IOSlotCount] IOHandler
@@ -79,7 +85,7 @@ func (m *Mem) attachIO(h IOHandler, slot int) {
 	m.iohandler[slot] = h
 }
 
-func (m *Mem) read(byteaddr word) (word, error) {
+func (m *Mem) readRaw(byteaddr word) (word, error) {
 	if byteaddr >= IOStartAddr && byteaddr < RAMStartAddr {
 		ioslot := (byteaddr - IOStartAddr) / IOSlotSize
 		if m.iohandler[ioslot] != nil {
@@ -96,6 +102,14 @@ func (m *Mem) read(byteaddr word) (word, error) {
 	}
 }
 
+func (m *Mem) read(byteaddr word) (word, error) {
+	return m.readRaw(byteaddr);
+}
+
+func (m *Mem) readIns(byteaddr word) (word, error) {
+	return m.readRaw(byteaddr);
+}
+
 func (m *Mem) write(value word, byteaddr word) error {
 	if byteaddr < IOStartAddr {
 		return fmt.Errorf("Write to ROM area at %08X value %08X", byteaddr, value)
diff --git a/tridoraemu/tridoraemu.go b/tridoraemu/tridoraemu.go
index 88804b4..c148515 100644
--- a/tridoraemu/tridoraemu.go
+++ b/tridoraemu/tridoraemu.go
@@ -8,7 +8,8 @@ import (
 	"flag"
 	"time"
 	"github.com/hajimehoshi/ebiten/v2"
-	// "github.com/hajimehoshi/ebiten/v2/ebitenutil"
+	"github.com/hajimehoshi/ebiten/v2/ebitenutil"
+	"github.com/hajimehoshi/ebiten/v2/inpututil"
 	// "image/color"
 )
 
@@ -35,6 +36,7 @@ func idle(canGoIdle bool) {
 }
 
 type Game struct{
+		debug bool
 		x,y int
 		stepsPerFrame int
 		lastFrameDuration time.Duration
@@ -58,16 +60,23 @@ func (g *Game) Update() error {
 	}
 	g.lastFrameDuration = time.Since(startTime)
 
+	if inpututil.IsKeyJustReleased(ebiten.KeyF12) {
+		g.debug = !g.debug
+	}
+
 	return nil
 }
 
 func (g *Game) Draw(screen *ebiten.Image) {
 	screen.DrawImage(framebuffer.framebuffer, nil)
 
-	/*
-	buf := fmt.Sprintf("PC: %08X FP: %08X RP: %08X ESP: %2X\n%v", cpu.PC, cpu.FP, cpu.RP, cpu.ESP, g.lastFrameDuration)
-	ebitenutil.DebugPrint(screen, buf)
+	if g.debug {
+		buf := fmt.Sprintf("PC: %08X FP: %08X RP: %08X ESP: %2X  %v",
+			cpu.PC, cpu.FP, cpu.RP, cpu.ESP, g.lastFrameDuration)
+		ebitenutil.DebugPrint(screen, buf)
+	}
 
+	/*
 	screen.Set(g.x, g.y, color.RGBA{255,0,0,0})
 	screen.Set(g.x, g.y+1, color.RGBA{0,255,0,0})
 	screen.Set(g.x, g.y+2, color.RGBA{0,255,255,0})