diff --git a/src/cpu/6809.js b/src/cpu/6809.js
index fa7335aa..eb7b5e2d 100644
--- a/src/cpu/6809.js
+++ b/src/cpu/6809.js
@@ -2352,7 +2352,14 @@ return {
             Ts-=step();
         }
     },
+    runFrame: function(Tt){
+        while (T<Tt){
+          step();
+        }
+    },
     T:function(){return T;},
+    getTstates:function(){return T;},
+    setTstates:function(t){T=t;},
     reset: reset,
     init: function(bt,ba,tck){
         byteTo=bt;
diff --git a/src/emu.js b/src/emu.js
index 48c1a7fd..f06a30fe 100644
--- a/src/emu.js
+++ b/src/emu.js
@@ -544,8 +544,21 @@ function cpuStateToLongString_Z80(c) {
        ;
 }
 
+window.buildZ80({
+	applyContention: false // TODO???
+});
+
 var BaseZ80Platform = function() {
 
+  // TODO: refactor w/ platforms
+  this.newCPU = function(membus, iobus) {
+    return window.Z80({
+     display: {},
+     memory: membus,
+     ioBus: iobus
+   });
+  }
+
   var onBreakpointHit;
   var debugCondition;
   var debugSavedState = null;
@@ -686,6 +699,12 @@ function cpuStateToLongString_6809(c) {
 var Base6809Platform = function() {
   this.__proto__ = new BaseZ80Platform();
 
+  this.newCPU = function(membus) {
+    var cpu = new CPU6809();
+    cpu.init(membus.write, membus.read, 0);
+    return cpu;
+  }
+
 	this.runUntilReturn = function() {
     var self = this;
     var depth = 1;
diff --git a/src/platform/galaxian.js b/src/platform/galaxian.js
index 0c0c0d25..c9e6f21f 100644
--- a/src/platform/galaxian.js
+++ b/src/platform/galaxian.js
@@ -2,11 +2,6 @@
 var GALAXIAN_PRESETS = [
 ];
 
-// TODO: global???
-window.buildZ80({
-	applyContention: false
-});
-
 var GalaxianPlatform = function(mainElement) {
   var self = this;
   this.__proto__ = new BaseZ80Platform();
@@ -181,11 +176,7 @@ var GalaxianPlatform = function(mainElement) {
         console.log('IO write', hex(addr,4), hex(val,2));
     	}
     };
-    cpu = window.Z80({
-  		display: {},
-  		memory: membus,
-  		ioBus: iobus
-  	});
+    cpu = self.newCPU(membus, iobus);
     video = new RasterVideo(mainElement,264,264,{rotate:90});
 		audio = new MasterAudio();
     video.create();
diff --git a/src/platform/konamisound.js b/src/platform/konamisound.js
index c0114df3..80c40e8e 100644
--- a/src/platform/konamisound.js
+++ b/src/platform/konamisound.js
@@ -2,11 +2,6 @@
 var KONAMISOUND_PRESETS = [
 ];
 
-// TODO: global???
-window.buildZ80({
-	applyContention: false
-});
-
 var KonamiSoundPlatform = function(mainElement) {
   var self = this;
   this.__proto__ = new BaseZ80Platform();
diff --git a/src/platform/mw8080bw.js b/src/platform/mw8080bw.js
index cdb5d60d..5362aed1 100644
--- a/src/platform/mw8080bw.js
+++ b/src/platform/mw8080bw.js
@@ -5,11 +5,6 @@
 var MW8080BW_PRESETS = [
 ];
 
-// TODO: global???
-window.buildZ80({
-	applyContention: false
-});
-
 var Midway8080BWPlatform = function(mainElement) {
   var self = this;
   this.__proto__ = new BaseZ80Platform();
diff --git a/src/platform/vicdual.js b/src/platform/vicdual.js
index c1299881..e255e21f 100644
--- a/src/platform/vicdual.js
+++ b/src/platform/vicdual.js
@@ -2,11 +2,6 @@
 var VICDUAL_PRESETS = [
 ];
 
-// TODO: global???
-window.buildZ80({
-	applyContention: false
-});
-
 var VicDualPlatform = function(mainElement) {
   var self = this;
   this.__proto__ = new BaseZ80Platform();
diff --git a/src/platform/williams.js b/src/platform/williams.js
index 0bb11ef4..df8a094d 100644
--- a/src/platform/williams.js
+++ b/src/platform/williams.js
@@ -3,9 +3,9 @@
 var WILLIAMS_PRESETS = [
 ];
 
-var WilliamsPlatform = function(mainElement) {
+var WilliamsPlatform = function(mainElement, proto) {
   var self = this;
-  this.__proto__ = new Base6809Platform();
+  this.__proto__ = new (proto?proto:Base6809Platform)();
 
   var SCREEN_HEIGHT = 304;
   var SCREEN_WIDTH = 256;
@@ -76,7 +76,7 @@ var WilliamsPlatform = function(mainElement) {
     [0x400, 0x5ff, 0x1ff, function(a) { return nvram.mem[a]; }],
     [0x800, 0x800, 0,     function(a) { return video_counter; }],
     [0xc00, 0xc07, 0x7,   function(a) { return pia6821[a]; }],
-    [0x0,   0xfff, 0,     function(a) { console.log('ioread',hex(a)); }],
+    [0x0,   0xfff, 0,     function(a) { /*console.log('ioread',hex(a));*/ }],
   ]);
 
   var iowrite_defender = new AddressDecoder([
@@ -117,7 +117,7 @@ var WilliamsPlatform = function(mainElement) {
     [0x80c, 0x80f, 0x3,   function(a) { return pia6821[a+4]; }],
     [0xb00, 0xbff, 0,     function(a) { return video_counter; }],
     [0xc00, 0xfff, 0x3ff, function(a) { return nvram.mem[a]; }],
-    [0x0,   0xfff, 0,     function(a) { console.log('ioread',hex(a)); }],
+    [0x0,   0xfff, 0,     function(a) { /* console.log('ioread',hex(a)); */ }],
   ]);
 
   var iowrite_williams = new AddressDecoder([
@@ -172,7 +172,8 @@ var WilliamsPlatform = function(mainElement) {
     if (a) {
       blitregs[a] = v;
     } else {
-      doBlit(v);
+      var cycles = doBlit(v);
+      cpu.setTstates(cpu.getTstates() + cycles);
     }
   }
 
@@ -241,7 +242,8 @@ var WilliamsPlatform = function(mainElement) {
       curpix |= (solid & ~keepmask);
     else
       curpix |= (srcdata & ~keepmask);
-    memwrite_williams(dstaddr, curpix);
+    if (dstaddr < 0x9000) // can cause recursion otherwise
+      memwrite_williams(dstaddr, curpix);
   }
 
   var trace = false;
@@ -250,7 +252,7 @@ var WilliamsPlatform = function(mainElement) {
     var pc = cpu.getPC();
     if (!_traceinsns[pc]) {
       _traceinsns[pc] = 1;
-      console.log(hex(pc), cpu.T());
+      console.log(hex(pc), cpu.getTstates());
     }
   }
 
@@ -266,8 +268,7 @@ var WilliamsPlatform = function(mainElement) {
       read: memread_williams,
 			write: memwrite_williams,
     };
-    cpu = new CPU6809();
-    cpu.init(membus.write, membus.read, 0);
+    cpu = self.newCPU(membus);
     video = new RasterVideo(mainElement, SCREEN_WIDTH, SCREEN_HEIGHT, {rotate:-90});
     video.create();
 		$(video.canvas).click(function(e) {
@@ -287,21 +288,23 @@ var WilliamsPlatform = function(mainElement) {
       for (var quarter=0; quarter<4; quarter++) {
         video_counter = [0x00, 0x3c, 0xbc, 0xfc][quarter];
         if (membus.read != memread_defender || pia6821[7] == 0x3c) { // TODO?
-          cpu.interrupt();
-          //console.log(cpu.getPC());
+          if (cpu.interrupt)
+            cpu.interrupt();
+          if (cpu.requestInterrupt)
+            cpu.requestInterrupt();
         }
-        var targetTstates = cpu.T() + cpuCyclesPerFrame/4;
+        var targetTstates = cpu.getTstates() + cpuCyclesPerFrame/4;
         if (debugCond || trace) {
-          while (cpu.T() < targetTstates) {
+          while (cpu.getTstates() < targetTstates) {
             _trace();
             if (debugCond && debugCond()) {
               debugCond = null;
               break;
             }
-            cpu.steps(1);
+            cpu.runFrame(cpu.getTstates() + 1);
           }
         } else {
-          cpu.steps(cpuCyclesPerFrame);
+          cpu.runFrame(targetTstates);
         }
       }
       if (screenNeedsRefresh) {
@@ -320,6 +323,9 @@ var WilliamsPlatform = function(mainElement) {
   }
 
   this.loadROM = function(title, data) {
+    if (data.length > 2) {
+      rom = padBytes(data, 0xc000);
+    }
     // TODO
     self.reset();
   }
@@ -362,10 +368,16 @@ var WilliamsPlatform = function(mainElement) {
   this.reset = function() {
     cpu.reset();
     watchdog_counter = INITIAL_WATCHDOG;
+    banksel = 1;
   }
   this.readAddress = function(addr) {
     return membus.read(addr);
   }
 }
 
+var WilliamsZ80Platform = function(mainElement) {
+  this.__proto__ = new WilliamsPlatform(mainElement, BaseZ80Platform);
+}
+
 PLATFORMS['williams'] = WilliamsPlatform;
+PLATFORMS['williams-z80'] = WilliamsZ80Platform;
diff --git a/src/ui.js b/src/ui.js
index bde2d2cc..1168dbb9 100644
--- a/src/ui.js
+++ b/src/ui.js
@@ -907,6 +907,7 @@ function initPlatform() {
 
 function startPlatform() {
   initPlatform();
+  if (!PLATFORMS[platform_id]) throw Error("Invalid platform '" + platform_id + "'.");
   platform = new PLATFORMS[platform_id]($("#emulator")[0]);
   PRESETS = platform.getPresets();
   if (qs['file']) {
@@ -970,7 +971,8 @@ function startUI(loadplatform) {
     } else {
       // load and start platform object
       if (loadplatform) {
-        $.getScript('src/platform/' + platform_id + '.js', function() {
+        var scriptfn = 'src/platform/' + platform_id.split('-')[0] + '.js';
+        $.getScript(scriptfn, function() {
           console.log("loaded platform", platform_id);
           startPlatform();
         });
diff --git a/src/worker/workermain.js b/src/worker/workermain.js
index 661ea975..3c601699 100644
--- a/src/worker/workermain.js
+++ b/src/worker/workermain.js
@@ -19,6 +19,12 @@ var PLATFORM_PARAMS = {
     data_start: 0x4000,
     data_size: 0x400,
   },
+  'williams-z80': {
+    code_start: 0x0,
+    code_size: 0x9000,
+    data_start: 0x9000,
+    data_size: 0x3000,
+  },
 };
 
 var loaded = {}
@@ -639,7 +645,11 @@ function compileSDCC(code, platform) {
   if (msvc_errors.length) {
     return {errors:msvc_errors};
   }
-  var asmout = FS.readFile("main.asm", {encoding:'utf8'});
+  try {
+    var asmout = FS.readFile("main.asm", {encoding:'utf8'});
+  } catch (e) {
+    return {errors:[{line:1, msg:e+""}]};
+  }
   var warnings = msvc_errors;
   var result = assemblelinkSDASZ80(asmout, platform, true);
   result.asmlines = result.lines;
@@ -711,7 +721,7 @@ function preprocessMCPP(code, platform) {
   FS.writeFile("main.c", code, {encoding:'utf8'});
   MCPP.callMain([
     "-D", "__8BITWORKSHOP__",
-    "-D", platform.toUpperCase(),
+    "-D", platform.toUpperCase().replace('-','_'),
     "-I", "/share/include",
     "-Q",
     "main.c", "main.i"]);
@@ -725,7 +735,11 @@ function preprocessMCPP(code, platform) {
     var errout = FS.readFile("mcpp.err", {encoding:'utf8'});
     if (errout.length) {
       // //main.c:2: error: Can't open include file "stdiosd.h"
-      return {errors: extractErrors(/[^:]+:(\d+): (.+)/, errout.split("\n"))};
+      var errors = extractErrors(/[^:]+:(\d+): (.+)/, errout.split("\n"));
+      if (errors.length == 0) {
+        errors = [{line:1, msg:errout}];
+      }
+      return {errors: errors};
     }
   } catch (e) {
     //