diff --git a/src/emu.js b/src/emu.js
index 7e486441..e98e93a4 100644
--- a/src/emu.js
+++ b/src/emu.js
@@ -643,3 +643,25 @@ function padBytes(data, len) {
   r.mem.set(data);
   return r.mem;
 }
+
+// TODO: better performance, check values
+function AddressDecoder(table) {
+  var self = this;
+  function makeFunction(lo, hi) {
+    var s = "";
+    for (var i=0; i<table.length; i++) {
+      var entry = table[i];
+      var start = entry[0];
+      var end = entry[1];
+      var mask = entry[2];
+      var func = entry[3];
+      self['__fn'+i] = func;
+      s += "if (a>=" + start + " && a<="+end + "){";
+      s += "a&="+(mask?mask:0xffff)+";";
+      s += "return this.__fn"+i+"(a,v)&0xff;}\n";
+    }
+    s += "return 0;"; // TODO: noise()?
+    return new Function('a', 'v', s);
+  }
+  return makeFunction(0x0, 0xffff).bind(self);
+}
diff --git a/src/platform/galaxian.js b/src/platform/galaxian.js
index fcf4c0bd..526b1448 100644
--- a/src/platform/galaxian.js
+++ b/src/platform/galaxian.js
@@ -150,72 +150,24 @@ var GalaxianPlatform = function(mainElement) {
     oram = new RAM(0x100);
 		outlatches = new RAM(0x8);
     membus = {
-      read: function(address) {
-        if (address < 0x4000) {
-          return (rom ? rom[address] : 0) & 0xff;
-        } else if (address < 0x4800) {
-          address &= 0x3ff;
-          return ram.mem[address] & 0xff;
-        } else if (address >= 0x5000 && address < 0x5800) {
-          address &= 0x3ff;
-          return vram.mem[address] & 0xff;
-        } else if (address >= 0x5800 && address < 0x6000) {
-          address &= 0xff;
-          return oram.mem[address] & 0xff;
-				} else if (address >= 0x6000 && address < 0x6800) {
-					address &= 0x7;
-					switch (address) {
-						case 0:
-							return inputs[0];
-					}
-				} else if (address >= 0x6800 && address < 0x7000) {
-					return inputs[1];
-				} else if (address >= 0x7000 && address < 0x7800) {
-					address &= 0x7;
-					switch (address) {
-						case 0:
-							return inputs[2];
-					}
-        } else if (address >= 0x7800 && address < 0x8000) {
-          watchdog_counter = INITIAL_WATCHDOG;
-        } else {
-					console.log("read", hex(address));
-          return 0;
-        }
-      },
-      write: function(address, value) {
-        //console.log("write", hex(address,4), hex(value,2));
-        if (address >= 0x4000 && address < 0x4800) {
-          address &= 0x3ff;
-          ram.mem[address] = value;
-        } else if (address >= 0x5000 && address < 0x5800) {
-          address &= 0x3ff;
-          vram.mem[address] = value;
-        } else if (address >= 0x5800 && address < 0x6000) {
-          address &= 0xff;
-          oram.mem[address] = value;
-				} else if (address >= 0x6000 && address < 0x6800) {
-					address &= 0x7;
-					outlatches.mem[address] = value;
-				} else if (address >= 0x6800 && address < 0x7000) {
-					address &= 0x7;
-					// TODO: sound
-        } else if (address >= 0x7000 && address < 0x7800) {
-					address &= 0x7;
-					switch (address) {
-						case 1:
-							interruptEnabled = value;
-							break;
-            case 4:
-              starsEnabled = value;
-              break;
-					}
-				} else if (address >= 0x7800 && address < 0x8000) {
-					// TODO: sound
-				} else {
-					console.log("write", hex(address), hex(value));
-				}
-      },
+      read: new AddressDecoder([
+				[0x0000, 0x3fff, 0,      function(a) { return rom ? rom[a] : null; }],
+				[0x4000, 0x47ff, 0x3ff,  function(a) { return ram.mem[a]; }],
+				[0x5000, 0x57ff, 0x3ff,  function(a) { return vram.mem[a]; }],
+				[0x5800, 0x5fff, 0xff,   function(a) { return oram.mem[a]; }],
+				[0x6000, 0x6000, 0,      function(a) { return inputs[0]; }],
+				[0x6800, 0x6800, 0,      function(a) { return inputs[1]; }],
+				[0x7000, 0x7000, 0,      function(a) { return inputs[2]; }],
+				[0x7800, 0x7800, 0,      function(a) { watchdog_counter = INITIAL_WATCHDOG; }],
+			]),
+			write: new AddressDecoder([
+				[0x4000, 0x47ff, 0x3ff,  function(a,v) { ram.mem[a] = v; }],
+				[0x5000, 0x57ff, 0x3ff,  function(a,v) { vram.mem[a] = v; }],
+				[0x5800, 0x5fff, 0xff,   function(a,v) { oram.mem[a] = v; }],
+				[0x6000, 0x67ff, 0x7,    function(a,v) { outlatches.mem[a] = v; }],
+				[0x7001, 0x7001, 0,      function(a,v) { interruptEnabled = v; }],
+				[0x7004, 0x7004, 0,      function(a,v) { starsEnabled = v; }],
+			]),
       isContended: function() { return false; },
     };
     iobus = {
@@ -323,7 +275,7 @@ var GalaxianPlatform = function(mainElement) {
     watchdog_counter = state.wdc;
 		interruptEnabled = state.ie;
     starsEnabled = state.se;
-    frameCounter = fc;
+    frameCounter = state.fc;
     inputs[0] = state.in0;
     inputs[1] = state.in1;
     inputs[2] = state.in2;
@@ -356,7 +308,6 @@ var GalaxianPlatform = function(mainElement) {
   this.pause = function() {
     timer.stop();
     audio.stop();
-    console.log(JSON.stringify(this.saveState()));
   }
   this.resume = function() {
     timer.start();
diff --git a/src/platform/spaceinv.js b/src/platform/spaceinv.js
index c3ae9e0c..b18efba7 100644
--- a/src/platform/spaceinv.js
+++ b/src/platform/spaceinv.js
@@ -46,29 +46,20 @@ var SpaceInvadersPlatform = function(mainElement) {
     ram = new RAM(0x2000);
     displayPCs = new Uint16Array(new ArrayBuffer(0x2000*2));
     membus = {
-      read: function(address) {
-        if (address < 0x2000) {
-          return (rom ? rom[address] : 0) & 0xff;
-        } else {
-          address &= 0x1fff;
-          return ram.mem[address] & 0xff;
-        }
-      },
-      write: function(address, value) {
-        //console.log("write", hex(address,4), hex(value,2));
-        if (address >= 0x2000) {
-          address &= 0x1fff;
-          value &= 0xff;
-          ram.mem[address] = value;
-          if (address >= 0x400) {
-						// TODO: dirty flags
-            var ofs = (address - 0x400)*8;
-            for (var i=0; i<8; i++)
-              pixels[ofs+i] = (value & (1<<i)) ? PIXEL_ON : PIXEL_OFF;
-            displayPCs[address] = cpu.getPC(); // save program counter
-          }
-        }
-      },
+      read: new AddressDecoder([
+				[0x0000, 0x1fff, 0x1fff, function(a) { return rom ? rom[a] : 0; }],
+				[0x2000, 0x3fff, 0x1fff, function(a) { return ram.mem[a]; }],
+			]),
+			write: new AddressDecoder([
+				[0x2000, 0x23ff, 0x3ff,  function(a,v) { ram.mem[a] = v; }],
+				[0x2400, 0x3fff, 0x1fff, function(a,v) {
+					ram.mem[a] = v;
+					var ofs = (a - 0x400)<<3;
+					for (var i=0; i<8; i++)
+						pixels[ofs+i] = (v & (1<<i)) ? PIXEL_ON : PIXEL_OFF;
+					displayPCs[a] = cpu.getPC(); // save program counter
+				}],
+			]),
       isContended: function() { return false; },
     };
     iobus = {
diff --git a/src/ui.js b/src/ui.js
index d0720a75..3938b0bf 100644
--- a/src/ui.js
+++ b/src/ui.js
@@ -381,6 +381,7 @@ worker.onmessage = function(e) {
     }
     if (rom_changed || trace_pending_at_pc) {
       // update editor annotations
+      // TODO: do incrementally for performance
       editor.clearGutter("gutter-info");
       editor.clearGutter("gutter-bytes");
       editor.clearGutter("gutter-offset");
diff --git a/test/cli/testdecoder.js b/test/cli/testdecoder.js
new file mode 100644
index 00000000..44308fa7
--- /dev/null
+++ b/test/cli/testdecoder.js
@@ -0,0 +1,33 @@
+
+var vm = require('vm');
+var fs = require('fs');
+var includeInThisContext = function(path) {
+    var code = fs.readFileSync(path);
+    vm.runInThisContext(code, path);
+};
+
+includeInThisContext("src/emu.js");
+
+function assert(b, msg) {
+  if (!b) { throw new Error(msg); }
+}
+function assertEquals(a,b) {
+  assert(a==b, a + " != " + b);
+}
+
+describe('Test address decoder', function() {
+  it('Should work empty', function() {
+    var decoder = new AddressDecoder([]);
+    assertEquals(0, decoder(0x1234));
+    assertEquals(0, decoder(0x123456));
+  });
+  it('Should work with 1 range', function() {
+    var decoder = new AddressDecoder([
+      [0x1000, 0x7fff, 0xff, function(a) { return a+2; }]
+    ]);
+    assertEquals(0, decoder(0xfff));
+    assertEquals(2, decoder(0x1000));
+    assertEquals(1, decoder(0x7fff));
+    assertEquals(0, decoder(0x8000));
+  });
+});