diff --git a/docs/raspberry-pi.md b/docs/raspberry-pi.md
new file mode 100644
index 00000000..c770056f
--- /dev/null
+++ b/docs/raspberry-pi.md
@@ -0,0 +1,29 @@
+# Raspberry Pi and Raspbian
+
+It is possible to run the web editor or [command line interface](/cli) from Raspbian on Raspberry Pi 2 or 3.
+
+## Web editor
+
+The web editor requires to install IceWeasel (Firefox) as the built-in browser cannot handle it.
+
+```
+sudo apt-get install iceweasel
+```
+
+Once installed simply navigate to https://codethemicrobit.com or type
+
+```
+firefox https://codethemicrobit.com
+``` 
+
+## Command line
+
+The PXT command line also works on Raspbian and allows to run a local server and/or edit programs from any text editor.
+
+* Node.JS 6.0 needs installed
+
+To install all the tools, 
+
+```
+curl -s https://raw.githubusercontent.com/Microsoft/pxt-rpi/master/install.sh | sh -
+```
\ No newline at end of file
diff --git a/libs/microbit-bluetooth/_locales/microbit-bluetooth-jsdoc-strings.json b/libs/microbit-bluetooth/_locales/microbit-bluetooth-jsdoc-strings.json
index 74316739..1c243821 100644
--- a/libs/microbit-bluetooth/_locales/microbit-bluetooth-jsdoc-strings.json
+++ b/libs/microbit-bluetooth/_locales/microbit-bluetooth-jsdoc-strings.json
@@ -1,5 +1,4 @@
 {
-  "bluetooth": "Support for additional Bluetooth services.",
   "bluetooth.onBluetoothConnected": "Register code to run when the micro:bit is connected to over Bluetooth",
   "bluetooth.onBluetoothConnected|param|body": "Code to run when a Bluetooth connection is established",
   "bluetooth.onBluetoothDisconnected": "Register code to run when a bluetooth connection to the micro:bit is lost",
@@ -10,6 +9,7 @@
   "bluetooth.startLEDService": "Starts the Bluetooth LED service",
   "bluetooth.startMagnetometerService": "Starts the Bluetooth magnetometer service",
   "bluetooth.startTemperatureService": "Starts the Bluetooth temperature service",
+  "bluetooth.startUartService": "Starts the Bluetooth UART service",
   "bluetooth.uartRead": "Reads from the Bluetooth UART service buffer, returning its contents when the specified delimiter character is encountered.",
   "bluetooth.uartWrite": "Writes to the Bluetooth UART service buffer. From there the data is transmitted over Bluetooth to a connected device."
 }
\ No newline at end of file
diff --git a/libs/microbit-bluetooth/_locales/microbit-bluetooth-strings.json b/libs/microbit-bluetooth/_locales/microbit-bluetooth-strings.json
index 6c744fed..0fc2a04e 100644
--- a/libs/microbit-bluetooth/_locales/microbit-bluetooth-strings.json
+++ b/libs/microbit-bluetooth/_locales/microbit-bluetooth-strings.json
@@ -7,6 +7,7 @@
   "bluetooth.startLEDService|block": "bluetooth led service",
   "bluetooth.startMagnetometerService|block": "bluetooth magnetometer service",
   "bluetooth.startTemperatureService|block": "bluetooth temperature service",
+  "bluetooth.startUartService|block": "bluetooth uart service",
   "bluetooth.uartRead|block": "bluetooth uart read %del=bluetooth_uart_delimiter_conv",
   "bluetooth.uartWrite|block": "bluetooth uart write %data",
   "bluetooth|block": "bluetooth"
diff --git a/libs/microbit/_locales/microbit-jsdoc-strings.json b/libs/microbit/_locales/microbit-jsdoc-strings.json
index 1d33c526..81ff1d58 100644
--- a/libs/microbit/_locales/microbit-jsdoc-strings.json
+++ b/libs/microbit/_locales/microbit-jsdoc-strings.json
@@ -22,6 +22,8 @@
   "control": "Runtime and event utilities.",
   "control.inBackground": "Schedules code that run in the background.",
   "control.reset": "Resets the BBC micro:bit.",
+  "control.waitMicros": "Blocks the current fiber for the given microseconds",
+  "control.waitMicros|param|micros": "number of micro-seconds to wait. eg: 4",
   "game": "A single-LED sprite game engine",
   "game.addScore": "Adds points to the current score",
   "game.addScore|param|points": "amount of points to change, eg: 1",
@@ -52,9 +54,12 @@
   "input.onLogoDown|param|body": "TODO",
   "input.onLogoUp": "Attaches code to run when the logo is oriented upwards and the board is vertical.",
   "input.onLogoUp|param|body": "TODO",
-  "input.onPinPressed": "Do something when a pin(``P0``, ``P1`` or both ``P2``) is pressed.",
-  "input.onPinPressed|param|body": "TODO",
-  "input.onPinPressed|param|name": "TODO",
+  "input.onPinPressed": "Do something when a pin is pressed.",
+  "input.onPinPressed|param|body": "the code to run when the pin is pressed",
+  "input.onPinPressed|param|name": "the pin that needs to be pressed",
+  "input.onPinReleased": "Do something when a pin is released.",
+  "input.onPinReleased|param|body": "the code to run when the pin is released",
+  "input.onPinReleased|param|name": "the pin that needs to be released",
   "input.onScreenDown": "Attaches code to run when the screen is facing down.",
   "input.onScreenDown|param|body": "TODO",
   "input.onScreenUp": "Attaches code to run when the screen is facing up.",
@@ -152,6 +157,8 @@
   "pins.setPull": "Configures the pull of this pin.",
   "pins.setPull|param|name": "pin to set the pull mode on",
   "pins.setPull|param|pull": "one of the mbed pull configurations: PullUp, PullDown, PullNone ",
+  "pins.spiWrite": "Write to the SPI slave and return the response",
+  "pins.spiWrite|param|value": "Data to be sent to the SPI slave",
   "serial": "Reading and writing data over a serial connection.",
   "serial.readLine": "Reads a line of text from the serial port.",
   "serial.redirect": "Dynamically configuring the serial instance to use pins other than USBTX and USBRX.",
diff --git a/libs/microbit/_locales/microbit-strings.json b/libs/microbit/_locales/microbit-strings.json
index ae88c239..ddd6ab34 100644
--- a/libs/microbit/_locales/microbit-strings.json
+++ b/libs/microbit/_locales/microbit-strings.json
@@ -12,6 +12,7 @@
   "basic|block": "basic",
   "control.inBackground|block": "run in background",
   "control.reset|block": "reset",
+  "control.waitMicros|block": "wait (µs)%micros",
   "control|block": "control",
   "game.addScore|block": "change score by|%points",
   "game.gameOver|block": "game over",
@@ -28,7 +29,8 @@
   "input.magneticForce|block": "magnetic force (µT)|%NAME",
   "input.onButtonPressed|block": "on button|%NAME|pressed",
   "input.onGesture|block": "on |%NAME",
-  "input.onPinPressed|block": "on pin|%NAME|pressed",
+  "input.onPinPressed|block": "on pin %NAME|pressed",
+  "input.onPinReleased|block": "on pin %NAME|released",
   "input.pinIsPressed|block": "pin %NAME|is pressed",
   "input.rotation|block": "rotation (°)|%NAME",
   "input.runningTime|block": "running time (ms)",
@@ -41,6 +43,7 @@
   "led.point|block": "point|x %x|y %y",
   "led.setBrightness|block": "set brightness %value",
   "led.stopAnimation|block": "stop animation",
+  "led.toggle|block": "toggle|x %x|y %y",
   "led.unplot|block": "unplot|x %x|y %y",
   "led|block": "led",
   "music.beat|block": "%fraction|beat",
@@ -65,6 +68,7 @@
   "pins.servoSetPulse|block": "servo set pulse|pin %value|to (µs) %micros",
   "pins.servoWritePin|block": "servo write|pin %name|to %value",
   "pins.setPull|block": "set pull|pin %pin|to %pull",
+  "pins.spiWrite|block": "spi write %value",
   "pins|block": "pins",
   "serial.readLine|block": "serial read line",
   "serial.redirect|block": "serial redirect to|TX %tx|RX %rx|at baud rate %rate",
diff --git a/libs/microbit/core.cpp b/libs/microbit/core.cpp
index 79bfc6b9..4a8969eb 100644
--- a/libs/microbit/core.cpp
+++ b/libs/microbit/core.cpp
@@ -166,6 +166,7 @@ namespace Array_ {
     int removeElement(RefCollection *c, uint32_t x) { return c->removeElement(x); }
 }
 
+
 // Import some stuff directly
 namespace pxt {
   //%
@@ -181,10 +182,12 @@ namespace pxt {
   //%
   Action mkAction(int reflen, int totallen, int startptr);
   //%
-  RefRecord* mkRecord(int reflen, int totallen);
-  //%
   RefRecord* mkClassInstance(int offset);
   //%
+  void RefRecord_destroy(RefRecord *r);
+  //%
+  void RefRecord_print(RefRecord *r);
+  //%
   void debugMemLeaks();
   //%
   int incr(uint32_t e);
@@ -308,6 +311,72 @@ namespace pxtrt {
     }
   }
 
+  //%
+  RefMap *mkMap() {
+    return new RefMap();
+  }
+
+  //%
+  uint32_t mapGet(RefMap *map, uint32_t key) {
+    int i = map->findIdx(key);
+    if (i < 0) {
+      map->unref();
+      return 0;
+    }
+    uint32_t r = map->data[i].val;
+    map->unref();
+    return r;
+  }
+
+  //%
+  uint32_t mapGetRef(RefMap *map, uint32_t key) {
+    int i = map->findIdx(key);
+    if (i < 0) {
+      map->unref();
+      return 0;
+    }
+    uint32_t r = incr(map->data[i].val);
+    map->unref();
+    return r;
+  }
+
+  //%
+  void mapSet(RefMap *map, uint32_t key, uint32_t val) {
+    int i = map->findIdx(key);
+    if (i < 0) {
+      map->data.push_back({
+        key << 1,
+        val
+      });
+    } else {
+      if (map->data[i].key & 1) {
+        decr(map->data[i].val);
+        map->data[i].key = key << 1;
+      }
+      map->data[i].val = val;
+    }
+    map->unref();
+  }
+
+  //%
+  void mapSetRef(RefMap *map, uint32_t key, uint32_t val) {
+    int i = map->findIdx(key);
+    if (i < 0) {
+      map->data.push_back({
+        (key << 1) | 1,
+        val
+      });
+    } else {
+      if (map->data[i].key & 1) {
+        decr(map->data[i].val);
+      } else {
+        map->data[i].key = (key << 1) | 1;
+      }
+      map->data[i].val = val;
+    }
+    map->unref();      
+  }
+
   //
   // Debugger
   //
diff --git a/libs/microbit/pxtparts.json b/libs/microbit/pxtparts.json
index cf0f73f1..63cf9a5e 100644
--- a/libs/microbit/pxtparts.json
+++ b/libs/microbit/pxtparts.json
@@ -1,78 +1,126 @@
 { 
-    "ledmatrix": {
-        "visual": "ledmatrix",
-        "breadboardColumnsNeeded": 8,
-        "breadboardStartRow": "h",
-        "pinAllocation": {
-            "type": "auto",
-            "gpioPinsNeeded": [5, 5]
+     "buttonpair": {
+        "simulationBehavior": "buttonpair",
+        "visual": {
+            "builtIn": "buttonpair",
+            "width": 75,
+            "height": 45,
+            "pinDistance": 15,
+            "pinLocations": [
+                {"x": 0, "y": 0},
+                {"x": 30, "y": 45},
+                {"x": 45, "y": 0},
+                {"x": 75, "y": 45}
+            ]
         },
-        "assemblyStep": 0,
-        "wires": [
-            {"start": ["breadboard", "j", 0], "end": ["GPIO", 5], "color": "purple", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 1], "end": ["GPIO", 6], "color": "purple", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 2], "end": ["GPIO", 7], "color": "purple", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 3], "end": ["GPIO", 8], "color": "purple", "assemblyStep": 1},
-            {"start": ["breadboard", "a", 7], "end": ["GPIO", 9], "color": "purple", "assemblyStep": 1},
-            {"start": ["breadboard", "a", 0], "end": ["GPIO", 0], "color": "green", "assemblyStep": 2},
-            {"start": ["breadboard", "a", 1], "end": ["GPIO", 1], "color": "green", "assemblyStep": 2},
-            {"start": ["breadboard", "a", 2], "end": ["GPIO", 2], "color": "green", "assemblyStep": 2},
-            {"start": ["breadboard", "a", 3], "end": ["GPIO", 3], "color": "green", "assemblyStep": 2},
-            {"start": ["breadboard", "j", 4], "end": ["GPIO", 4], "color": "green", "assemblyStep": 2}
-        ]
-    },
-    "buttonpair": {
-        "visual": "buttonpair",
-        "breadboardColumnsNeeded": 6,
-        "breadboardStartRow": "f",
-        "pinAllocation": {
-            "type": "predefined",
-            "pins": ["P13", "P12"]
+        "numberOfPins": 4,
+        "pinDefinitions": [
+            {"target": "P14", "style": "male", "orientation": "-Z"},
+            {"target": "ground", "style": "male", "orientation": "-Z"},
+            {"target": "P15", "style": "male", "orientation": "-Z"},
+            {"target": "ground", "style": "male", "orientation": "-Z"}
+        ],
+        "instantiation": {
+            "kind": "singleton"
         },
-        "assemblyStep": 0,
-        "wires": [
-            {"start": ["breadboard", "j", 0], "end": ["GPIO", 0], "color": "yellow", "assemblyStep": 1},
-            {"start": ["breadboard", "a", 2], "end": "ground", "color": "blue", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 3], "end": ["GPIO", 1], "color": "orange", "assemblyStep": 2},
-            {"start": ["breadboard", "a", 5], "end": "ground", "color": "blue", "assemblyStep": 2}
+        "assembly": [
+            {"part": true},
+            {"pinIndices": [0, 1]},
+            {"pinIndices": [2, 3]}
         ]
     },
     "neopixel": {
-        "visual": "neopixel",
-        "breadboardColumnsNeeded": 5,
-        "breadboardStartRow": "h",
-        "pinAllocation": {
-            "type": "factoryfunction",
-            "functionName": "neopixel.create",
-            "pinArgPositions": [0],
-            "otherArgPositions": [1]
+        "simulationBehavior": "neopixel",
+        "visual": {
+            "builtIn": "neopixel",
+            "width": 58,
+            "height": 113,
+            "pinDistance": 9,
+            "pinLocations": [
+                {"x": 10, "y": 0},
+                {"x": 19, "y": 0},
+                {"x": 28, "y": 0}
+            ]
         },
-        "assemblyStep": 0,
-        "wires": [
-            {"start": ["breadboard", "j", 1], "end": "ground", "color": "blue", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 2], "end": "threeVolt", "color": "red", "assemblyStep": 2},
-            {"start": ["breadboard", "j", 3], "end": ["GPIO", 0], "color": "green", "assemblyStep": 2}
+        "numberOfPins": 3,
+        "pinDefinitions": [
+            {"target": {"pinInstantiationIdx": 0}, "style": "solder", "orientation": "+Z"},
+            {"target": "threeVolt", "style": "solder", "orientation": "+Z"},
+            {"target": "ground", "style": "solder", "orientation": "+Z"}
+        ],
+        "instantiation": {
+            "kind": "function",
+            "fullyQualifiedName": "neopixel.create",
+            "argumentRoles": [
+                {"pinInstantiationIdx": 0, "partParameter": "pin"},
+                {"partParameter": "mode"}
+            ]
+        },
+        "assembly": [
+            {"part": true, "pinIndices": [2]},
+            {"pinIndices": [0, 1]}
+        ]
+    },
+    "ledmatrix": {
+        "visual": {
+            "builtIn": "ledmatrix",
+            "width": 105,
+            "height": 105,
+            "pinDistance": 15,
+            "pinLocations": [
+                {"x": 0, "y": 0},
+                {"x": 15, "y": 0},
+                {"x": 30, "y": 0},
+                {"x": 45, "y": 0},
+                {"x": 105, "y": 105},
+                {"x": 0, "y": 105},
+                {"x": 15, "y": 105},
+                {"x": 30, "y": 105},
+                {"x": 45, "y": 105},
+                {"x": 60, "y": 0}
+            ]
+        },
+        "simulationBehavior": "ledmatrix",
+        "numberOfPins": 10,
+        "instantiation": {"kind": "singleton"},
+        "pinDefinitions": [
+            {"target": "P6", "style": "male", "orientation": "-Z", "colorGroup": 0},
+            {"target": "P7", "style": "male", "orientation": "-Z", "colorGroup": 0},
+            {"target": "P8", "style": "male", "orientation": "-Z", "colorGroup": 0},
+            {"target": "P9", "style": "male", "orientation": "-Z", "colorGroup": 0},
+            {"target": "P10", "style": "male", "orientation": "-Z", "colorGroup": 0},
+            {"target": "P12", "style": "male", "orientation": "-Z", "colorGroup": 1},
+            {"target": "P13", "style": "male", "orientation": "-Z", "colorGroup": 1},
+            {"target": "P16", "style": "male", "orientation": "-Z", "colorGroup": 1},
+            {"target": "P19", "style": "male", "orientation": "-Z", "colorGroup": 1},
+            {"target": "P20", "style": "male", "orientation": "-Z", "colorGroup": 1}
+        ],
+        "assembly": [
+            {"part": true},
+            {"pinIndices": [0, 1, 2, 3, 4]},
+            {"pinIndices": [5, 6, 7, 8, 9]}
         ]
     },
     "speaker": {
+        "numberOfPins": 2,
         "visual": {
             "image": "/parts/speaker.svg",
             "width": 500,
             "height": 500,
-            "firstPin": [180, 135],
-            "pinDist": 70,
-            "extraColumnOffset": 1
+            "pinDistance": 70,
+            "pinLocations": [
+                {"x": 180, "y": 135},
+                {"x": 320, "y": 135}
+            ]
         },
-        "breadboardColumnsNeeded": 5,
-        "breadboardStartRow": "f",
-        "pinAllocation": {
-            "type": "auto",
-            "gpioPinsNeeded": 1
-        },
-        "assemblyStep": 0,
-        "wires": [
-            {"start": ["breadboard", "j", 1], "end": ["GPIO", 0], "color": "#ff80fa", "assemblyStep": 1},
-            {"start": ["breadboard", "j", 3], "end": "ground", "color": "blue", "assemblyStep": 1}
+        "pinDefinitions": [
+            {"target": "P0", "style": "male", "orientation": "-Z"},
+            {"target": "ground", "style": "male", "orientation": "-Z"}
+        ],
+        "instantiation": {"kind": "singleton"},
+        "assembly": [
+            {"part": true, "pinIndices": [0]},
+            {"pinIndices": [1]}
         ]
     }
 }
\ No newline at end of file
diff --git a/package.json b/package.json
index e5b1f815..96940a41 100644
--- a/package.json
+++ b/package.json
@@ -1,6 +1,6 @@
 {
   "name": "pxt-microbit",
-  "version": "0.3.78",
+  "version": "0.3.85",
   "description": "micro:bit target for PXT",
   "keywords": [
     "JavaScript",
@@ -29,6 +29,6 @@
     "typescript": "^1.8.7"
   },
   "dependencies": {
-    "pxt-core": "0.3.92"
+    "pxt-core": "0.3.97"
   }
 }
diff --git a/pxtarget.json b/pxtarget.json
index 8d9a9ef3..e83414f6 100644
--- a/pxtarget.json
+++ b/pxtarget.json
@@ -76,6 +76,7 @@
     "simulator": {
         "autoRun": true,
         "aspectRatio": 1.22,
+        "parts": true,
         "partsAspectRatio": 0.69,
         "builtinParts": {
             "accelerometer": true,
@@ -91,7 +92,7 @@
         "yottaTarget": "bbc-microbit-classic-gcc",
         "yottaCorePackage": "pxt-microbit-core",
         "githubCorePackage": "microsoft/pxt-microbit-core",
-        "gittag": "v0.4.2",
+        "gittag": "v0.5.0",
         "serviceId": "ws"
     },
     "serial": {
@@ -147,4 +148,4 @@
         "userVoiceApiKey": "WEkkIGaj1WtJnSUF59iwaA",
         "userVoiceForumId": 402381
     }
-}
\ No newline at end of file
+}
diff --git a/sim/allocator.ts b/sim/allocator.ts
index b7bd09b2..cb1acaaa 100644
--- a/sim/allocator.ts
+++ b/sim/allocator.ts
@@ -1,60 +1,81 @@
-
 namespace pxsim {
-    export interface AllocatorOpts {
+    const GROUND_COLOR = "blue";
+    const POWER_COLOR = "red";
+
+     export interface AllocatorOpts {
         boardDef: BoardDefinition,
-        cmpDefs: Map<PartDefinition>,
+        partDefs: Map<PartDefinition>,
+        partsList: string[]
         fnArgs: any,
-        getBBCoord: (loc: BBRowCol) => visuals.Coord,
-        cmpList: string[]
+        // Used for finding the nearest available power pins
+        getBBCoord: (loc: BBLoc) => visuals.Coord,
     };
     export interface AllocatorResult {
-        powerWires: WireInst[],
-        components: CmpAndWireInst[]
+        partsAndWires: PartAndWiresInst[],
     }
-
-    export interface CmpAndWireInst {
-        component: CmpInst,
-        wires: WireInst[]
-    }
-    export interface CmpInst {
+    export interface PartInst {
         name: string,
-        breadboardStartColumn: number,
-        breadboardStartRow: string,
-        assemblyStep: number,
-        visual: string | PartVisualDefinition,
-        microbitPins: string[],
-        otherArgs?: string[],
+        simulationBehavior?: string,
+        visual: PartVisualDefinition,
+        bbFit: PartBBFit,
+        startColumnIdx: number,
+        startRowIdx: number,
+        breadboardConnections: BBLoc[],
+        params: Map<string>,
     }
     export interface WireInst {
         start: Loc,
         end: Loc,
         color: string,
-        assemblyStep: number
     };
-    interface PartialCmpAlloc {
+    export interface AssemblyStep {
+        part?: boolean,
+        wireIndices?: number[],
+    }
+    export interface PartAndWiresInst {
+        part?: PartInst,
+        wires?: WireInst[],
+        assembly: AssemblyStep[],
+    }
+    export interface PartBBFit {
+        xOffset: number,
+        yOffset: number,
+        rowCount: number,
+        colCount: number,
+    }
+    interface PinBBFit {
+        partRelativeColIdx: number,
+        partRelativeRowIdx: number,
+        xOffset: number,
+        yOffset: number,
+    }
+    interface PinIR {
+        loc: XY,
+        def: PartPinDefinition,
+        target: PinTarget,
+        bbFit: PinBBFit,
+    }
+    interface PartIR {
         name: string,
         def: PartDefinition,
-        pinsAssigned: string[],
-        pinsNeeded: number | number[],
-        breadboardColumnsNeeded: number,
-        otherArgs?: string[],
-    }
-
-    interface AllocLocOpts {
-        nearestBBPin?: BBRowCol,
-        startColumn?: number,
-        cmpGPIOPins?: string[],
+        partParams: Map<string>,
+        pins: PinIR[],
+        bbFit: PartBBFit,
     };
-    interface AllocWireOpts {
-        startColumn: number,
-        cmpGPIOPins: string[],
-    }
-    interface AllocBlock {
-        cmpIdx: number,
-        cmpBlkIdx: number,
-        gpioNeeded: number,
-        gpioAssigned: string[]
+    interface PartPlacement extends PartIR {
+        startColumnIdx: number,
+        startRowIdx: number,
+    };
+    type WireIRLoc = PinTarget | BBLoc;
+    interface WireIR {
+        pinIdx: number,
+        start: WireIRLoc,
+        end: WireIRLoc,
+        color: string,
     }
+    interface PartIRAndWireIRs extends PartPlacement {
+        wires: WireIR[],
+    };
     interface PowerUsage {
         topGround: boolean,
         topThreeVolt: boolean,
@@ -63,18 +84,27 @@ namespace pxsim {
         singleGround: boolean,
         singleThreeVolt: boolean,
     }
-    function isOnBreadboardBottom(location: WireLocationDefinition) {
+    interface AllocLocOpts {
+        referenceBBPin?: BBLoc,
+    };
+    interface AllocWireOpts {
+        //TODO: port
+        startColumn: number,
+        partGPIOPins: string[],
+    }
+    function isOnBreadboardBottom(location: WireIRLoc) {
         let isBot = false;
-        if (location[0] === "breadboard") {
-            let row = <string>location[1];
+        if (typeof location !== "string" && (<BBLoc>location).type === "breadboard") {
+            let bbLoc = <BBLoc>location;
+            let row = bbLoc.row;
             isBot = 0 <= ["a", "b", "c", "d", "e"].indexOf(row);
         }
         return isBot;
     }
     const arrCount = (a: boolean[]) => a.reduce((p, n) => p + (n ? 1 : 0), 0);
     const arrAny = (a: boolean[]) => arrCount(a) > 0;
-    function computePowerUsage(wireDef: WireDefinition): PowerUsage {
-        let ends = [wireDef.start, wireDef.end];
+    function computePowerUsage(wire: WireIR): PowerUsage {
+        let ends = [wire.start, wire.end];
         let endIsGround = ends.map(e => e === "ground");
         let endIsThreeVolt = ends.map(e => e === "threeVolt");
         let endIsBot = ends.map(e => isOnBreadboardBottom(e));
@@ -115,10 +145,21 @@ namespace pxsim {
     function copyDoubleArray(a: string[][]) {
          return a.map(b => b.map(p => p));
     }
-    function readPin(arg: string): string {
+    function merge2<A, B>(a: A, b: B): A & B {
+        let res: any = {};
+        for (let aKey in a)
+            res[aKey] = (<any>a)[aKey];
+        for (let bKey in b)
+            res[bKey] = (<any>b)[bKey];
+        return <A & B>res;
+    }
+    function merge3<A, B, C>(a: A, b: B, c: C): A & B & C {
+        return merge2(merge2(a, b), c);
+    }
+    function readPin(arg: string): MicrobitPin {
         U.assert(!!arg, "Invalid pin: " + arg);
         let pin = arg.split("DigitalPin.")[1];
-        return pin;
+        return <MicrobitPin>pin;
     }
     function mkReverseMap(map: {[key: string]: string}) {
         let origKeys: string[] = [];
@@ -135,25 +176,239 @@ namespace pxsim {
         }
         return newMap;
     }
+    function isConnectedToBB(pin: PartPinDefinition): boolean {
+        return pin.orientation === "-Z" && pin.style === "male";
+    }
     class Allocator {
+        //TODO: better handling of allocation errors
         private opts: AllocatorOpts;
         private availablePowerPins = {
             top: {
-                threeVolt: mkRange(26, 51).map(n => <BBRowCol>["+", `${n}`]),
-                ground: mkRange(26, 51).map(n => <BBRowCol>["-", `${n}`]),
+                threeVolt: mkRange(26, 51).map(n => <BBLoc>{type: "breadboard", row: "+", col: `${n}`}),
+                ground: mkRange(26, 51).map(n => <BBLoc>{type: "breadboard", row: "-", col: `${n}`}),
             },
             bottom: {
-                threeVolt: mkRange(1, 26).map(n => <BBRowCol>["+", `${n}`]),
-                ground: mkRange(1, 26).map(n => <BBRowCol>["-", `${n}`]),
+                threeVolt: mkRange(1, 26).map(n => <BBLoc>{type: "breadboard", row: "+", col: `${n}`}),
+                ground: mkRange(1, 26).map(n => <BBLoc>{type: "breadboard", row: "-", col: `${n}`}),
             },
         };
         private powerUsage: PowerUsage;
+        private availableWireColors: string[];
 
         constructor(opts: AllocatorOpts) {
             this.opts = opts;
         }
 
-        private allocateLocation(location: WireLocationDefinition, opts: AllocLocOpts): Loc {
+        private allocPartIRs(def: PartDefinition, name: string, bbFit: PartBBFit): PartIR[] {
+            let partIRs: PartIR[] = [];
+            let mkIR = (def: PartDefinition, name: string, instPins?: PinTarget[], partParams?: Map<string>): PartIR => {
+                let pinIRs: PinIR[] = [];
+                for (let i = 0; i < def.numberOfPins; i++) {
+                    let pinDef = def.pinDefinitions[i];
+                    let pinTarget: PinTarget;
+                    if (typeof pinDef.target === "string") {
+                        pinTarget = <PinTarget>pinDef.target;
+                    } else {
+                        let instIdx = (<PinInstantiationIdx>pinDef.target).pinInstantiationIdx;
+                        U.assert(!!instPins && instPins[instIdx] !== undefined,
+                            `No pin found for PinInstantiationIdx: ${instIdx}. (Is the part missing an ArguementRole or "trackArgs=" annotations?)`);
+                        pinTarget = instPins[instIdx];
+                    }
+                    let pinLoc = def.visual.pinLocations[i];
+                    let adjustedY = bbFit.yOffset + pinLoc.y;
+                    let relativeRowIdx = Math.round(adjustedY / def.visual.pinDistance);
+                    let relativeYOffset = adjustedY - relativeRowIdx * def.visual.pinDistance;
+                    let adjustedX = bbFit.xOffset + pinLoc.x;
+                    let relativeColIdx = Math.round(adjustedX / def.visual.pinDistance);
+                    let relativeXOffset = adjustedX - relativeColIdx * def.visual.pinDistance;
+                    let pinBBFit: PinBBFit = {
+                        partRelativeRowIdx: relativeRowIdx,
+                        partRelativeColIdx: relativeColIdx,
+                        xOffset: relativeXOffset,
+                        yOffset: relativeYOffset
+                    };
+                    pinIRs.push({
+                        def: pinDef,
+                        loc: pinLoc,
+                        target: pinTarget,
+                        bbFit: pinBBFit,
+                    });
+                }
+                return {
+                    name: name,
+                    def: def,
+                    pins: pinIRs,
+                    partParams: partParams || {},
+                    bbFit: bbFit
+                };
+            };
+            if (def.instantiation.kind === "singleton") {
+                partIRs.push(mkIR(def, name));
+            } else if (def.instantiation.kind === "function") {
+                let fnAlloc = def.instantiation as PartFunctionDefinition;
+                let fnNm = fnAlloc.fullyQualifiedName;
+                let callsitesTrackedArgs = <string[]>this.opts.fnArgs[fnNm];
+                U.assert(!!callsitesTrackedArgs && !!callsitesTrackedArgs.length, "Failed to read pin(s) from callsite for: " + fnNm);
+                callsitesTrackedArgs.forEach(fnArgsStr => {
+                    let fnArgsSplit = fnArgsStr.split(",");
+                    U.assert(fnArgsSplit.length === fnAlloc.argumentRoles.length,
+                        `Mismatch between number of arguments at callsite (function name: ${fnNm}) vs number of argument roles in part definition (part: ${name}).`);
+                    let instPins: PinTarget[] = [];
+                    let paramArgs: Map<string> = {};
+                    fnArgsSplit.forEach((arg, idx) => {
+                        let role = fnAlloc.argumentRoles[idx];
+                        if (role.partParameter !== undefined) {
+                            paramArgs[role.partParameter] = arg;
+                        }
+                        if (role.pinInstantiationIdx !== undefined) {
+                            let instIdx = role.pinInstantiationIdx;
+                            let pin = readPin(arg);
+                            instPins[instIdx] = pin;
+                        }
+                    });
+                    partIRs.push(mkIR(def, name, instPins, paramArgs));
+                });
+            }
+            return partIRs;
+        }
+        private computePartDimensions(def: PartDefinition, name: string): PartBBFit {
+            let pinLocs = def.visual.pinLocations;
+            let pinDefs = def.pinDefinitions;
+            let numPins = def.numberOfPins;
+            U.assert(pinLocs.length === numPins, `Mismatch between "numberOfPins" and length of "visual.pinLocations" for "${name}"`);
+            U.assert(pinDefs.length === numPins, `Mismatch between "numberOfPins" and length of "pinDefinitions" for "${name}"`);
+            U.assert(numPins > 0, `Part "${name}" has no pins`);
+            let pins = pinLocs.map((loc, idx) => merge3({idx: idx}, loc, pinDefs[idx]));
+            let bbPins = pins.filter(p => p.orientation === "-Z");
+            let hasBBPins = bbPins.length > 0;
+            let pinDist = def.visual.pinDistance;
+            let xOff: number;
+            let yOff: number;
+            let colCount: number;
+            let rowCount: number;
+            if (hasBBPins) {
+                let refPin = bbPins[0];
+                let refPinColIdx = Math.ceil(refPin.x / pinDist);
+                let refPinRowIdx = Math.ceil(refPin.y / pinDist);
+                xOff = refPinColIdx * pinDist - refPin.x;
+                yOff = refPinRowIdx * pinDist - refPin.y;
+                colCount = Math.ceil((xOff + def.visual.width) / pinDist) + 1;
+                rowCount = Math.ceil((yOff + def.visual.height) / pinDist) + 1;
+            } else {
+                colCount = Math.ceil(def.visual.width / pinDist);
+                rowCount = Math.ceil(def.visual.height / pinDist);
+                xOff = colCount * pinDist - def.visual.width;
+                yOff = rowCount * pinDist - def.visual.height;
+            }
+            return {
+                xOffset: xOff,
+                yOffset: yOff,
+                rowCount: rowCount,
+                colCount: colCount
+            };
+        }
+        private allocColumns(colCounts: {colCount: number}[]): number[] {
+            let partsCount = colCounts.length;
+            const totalColumnsCount = visuals.BREADBOARD_MID_COLS; //TODO allow multiple breadboards
+            let totalSpaceNeeded = colCounts.map(d => d.colCount).reduce((p, n) => p + n, 0);
+            let extraSpace = totalColumnsCount - totalSpaceNeeded;
+            if (extraSpace <= 0) {
+                console.log("Not enough breadboard space!");
+                //TODO
+            }
+            let padding = Math.floor(extraSpace / (partsCount - 1 + 2));
+            let partSpacing = padding; //Math.floor(extraSpace/(partsCount-1));
+            let totalPartPadding = extraSpace - partSpacing * (partsCount - 1);
+            let leftPadding = Math.floor(totalPartPadding / 2);
+            let rightPadding = Math.ceil(totalPartPadding / 2);
+            let nextAvailableCol = 1 + leftPadding;
+            let partStartCol = colCounts.map(part => {
+                let col = nextAvailableCol;
+                nextAvailableCol += part.colCount + partSpacing;
+                return col;
+            });
+            return partStartCol;
+        }
+        private placeParts(parts: PartIR[]): PartPlacement[] {
+            const totalRowsCount = visuals.BREADBOARD_MID_ROWS + 2; // 10 letters + 2 for the middle gap
+            let startColumnIndices = this.allocColumns(parts.map(p => p.bbFit));
+            let startRowIndicies = parts.map(p => {
+                let extraRows = totalRowsCount - p.bbFit.rowCount;
+                let topPad = Math.floor(extraRows / 2);
+                let startIdx = topPad;
+                if (startIdx > 4)
+                    startIdx = 4;
+                if (startIdx < 1)
+                    startIdx = 1;
+                return startIdx;
+            });
+            let placements = parts.map((p, idx) => {
+                let row = startRowIndicies[idx];
+                let col = startColumnIndices[idx];
+                return merge2({startColumnIdx: col, startRowIdx: row}, p);
+            });
+            return placements;
+        }
+        private nextColor(): string {
+            if (!this.availableWireColors || this.availableWireColors.length <= 0) {
+                this.availableWireColors = visuals.GPIO_WIRE_COLORS.map(c => c);
+            }
+            return this.availableWireColors.pop();
+        }
+        private allocWireIRs(part: PartPlacement): PartIRAndWireIRs {
+            let groupToColor: string[] = [];
+            let wires: WireIR[] = part.pins.map((pin, pinIdx) => {
+                let end = pin.target;
+                let start: WireIRLoc;
+                let colIdx = part.startColumnIdx + pin.bbFit.partRelativeColIdx;
+                let colName = visuals.getColumnName(colIdx);
+                let pinRowIdx = part.startRowIdx + pin.bbFit.partRelativeRowIdx;
+                if (pinRowIdx >= 7) //account for middle gap
+                    pinRowIdx -= 2;
+                if (isConnectedToBB(pin.def)) {
+                    //make a wire from bb top or bottom to target
+                    let connectedToTop = pinRowIdx < 5;
+                    let rowName = connectedToTop ? "j" : "a";
+                    start = {
+                        type: "breadboard",
+                        row: rowName,
+                        col: colName,
+                    };
+                } else {
+                    //make a wire directly from pin to target
+                    let rowName = visuals.getRowName(pinRowIdx);
+                    start = {
+                        type: "breadboard",
+                        row: rowName,
+                        col: colName,
+                        xOffset: pin.bbFit.xOffset / part.def.visual.pinDistance,
+                        yOffset: pin.bbFit.yOffset / part.def.visual.pinDistance
+                    }
+                }
+                let color: string;
+                if (end === "ground") {
+                    color = GROUND_COLOR;
+                } else if (end === "threeVolt") {
+                    color = POWER_COLOR;
+                } else if (typeof pin.def.colorGroup === "number") {
+                    if (groupToColor[pin.def.colorGroup]) {
+                        color = groupToColor[pin.def.colorGroup];
+                    } else {
+                        color = groupToColor[pin.def.colorGroup] = this.nextColor();
+                    }
+                } else {
+                    color = this.nextColor()
+                }
+                return {
+                    start: start,
+                    end: end,
+                    color: color,
+                    pinIdx: pinIdx,
+                }
+            });
+            return merge2(part, {wires: wires});
+        }
+        private allocLocation(location: WireIRLoc, opts: AllocLocOpts): Loc {
             if (location === "ground" || location === "threeVolt") {
                 //special case if there is only a single ground or three volt pin in the whole build
                 if (location === "ground" && this.powerUsage.singleGround) {
@@ -164,8 +419,8 @@ namespace pxsim {
                     return {type: "dalboard", pin: boardThreeVoltPin};
                 }
 
-                U.assert(!!opts.nearestBBPin);
-                let nearestCoord = this.opts.getBBCoord(opts.nearestBBPin);
+                U.assert(!!opts.referenceBBPin);
+                let nearestCoord = this.opts.getBBCoord(opts.referenceBBPin);
                 let firstTopAndBot = [
                     this.availablePowerPins.top.ground[0] || this.availablePowerPins.top.threeVolt[0],
                     this.availablePowerPins.bottom.ground[0] || this.availablePowerPins.bottom.threeVolt[0]
@@ -177,7 +432,7 @@ namespace pxsim {
                     //TODO
                 }
                 let nearTop = visuals.findClosestCoordIdx(nearestCoord, firstTopAndBot) == 0;
-                let barPins: BBRowCol[];
+                let barPins: BBLoc[];
                 if (nearTop) {
                     if (location === "ground") {
                         barPins = this.availablePowerPins.top.ground;
@@ -203,17 +458,9 @@ namespace pxsim {
                     this.availablePowerPins.bottom.ground.splice(closestPinIdx, 1);
                     this.availablePowerPins.bottom.threeVolt.splice(closestPinIdx, 1);
                 }
-                return {type: "breadboard", rowCol: pin};
-            } else if (location[0] === "breadboard") {
-                U.assert(!!opts.startColumn);
-                let row = <string>location[1];
-                let col = (<number>location[2] + opts.startColumn).toString();
-                return {type: "breadboard", rowCol: [row, col]}
-            } else if (location[0] === "GPIO") {
-                U.assert(!!opts.cmpGPIOPins);
-                let idx = <number>location[1];
-                let pin = opts.cmpGPIOPins[idx];
-                return {type: "dalboard", pin: pin};
+                return pin;
+            } else if ((<BBLoc>location).type === "breadboard") {
+                return <BBLoc>location;
             } else if (location === "MOSI" || location === "MISO" || location === "SCK") {
                 if (!this.opts.boardDef.spiPins)
                     console.debug("No SPI pin mappings found!");
@@ -225,12 +472,15 @@ namespace pxsim {
                 let pin = (<any>this.opts.boardDef.i2cPins)[location as string] as string;
                 return {type: "dalboard", pin: pin};
             } else {
-                //TODO
-                U.assert(false);
-                return null;
+                //it must be a MicrobitPin
+                U.assert(typeof location === "string", "Unknown location type: " + location);
+                let mbPin = <MicrobitPin>location;
+                let boardPin = this.opts.boardDef.gpioPinMap[mbPin];
+                U.assert(!!boardPin, "Unknown pin: " + location);
+                return {type: "dalboard", pin: boardPin};
             }
         }
-        private getBoardGroundPin() {
+        private getBoardGroundPin(): string {
             let boardGround = this.opts.boardDef.groundPins[0] || null;
             if (!boardGround) {
                 console.log("No available ground pin on board!");
@@ -238,7 +488,7 @@ namespace pxsim {
             }
             return boardGround;
         }
-        private getBoardThreeVoltPin() {
+        private getBoardThreeVoltPin(): string {
             let threeVoltPin = this.opts.boardDef.threeVoltPins[0] || null;
             if (!threeVoltPin) {
                 console.log("No available 3.3V pin on board!");
@@ -246,14 +496,14 @@ namespace pxsim {
             }
             return threeVoltPin;
         }
-        private allocatePowerWires(powerUsage: PowerUsage): WireInst[] {
+        private allocPowerWires(powerUsage: PowerUsage): PartAndWiresInst {
             let boardGroundPin = this.getBoardGroundPin();
             let threeVoltPin = this.getBoardThreeVoltPin();
-            let topLeft: BBRowCol = ["-", "26"];
-            let botLeft: BBRowCol = ["-", "1"];
-            let topRight: BBRowCol = ["-", "50"];
-            let botRight: BBRowCol = ["-", "25"];
-            let top: BBRowCol, bot: BBRowCol;
+            const topLeft: BBLoc = {type: "breadboard", row: "-", col: "26"};
+            const botLeft: BBLoc = {type: "breadboard", row: "-", col: "1"};
+            const topRight: BBLoc = {type: "breadboard", row: "-", col: "50"};
+            const botRight: BBLoc = {type: "breadboard", row: "-", col: "25"};
+            let top: BBLoc, bot: BBLoc;
             if (this.opts.boardDef.attachPowerOnRight) {
                 top = topRight;
                 bot = botRight;
@@ -261,296 +511,162 @@ namespace pxsim {
                 top = topLeft;
                 bot = botLeft;
             }
-            const GROUND_COLOR = "blue";
-            const POWER_COLOR = "red";
-            const wires: WireInst[] = [];
-            let groundStep = 0;
-            let threeVoltStep = (powerUsage.bottomGround || powerUsage.topGround) ? 1 : 0;
+            let groundWires: WireInst[] = [];
+            let threeVoltWires: WireInst[] = [];
             if (powerUsage.bottomGround && powerUsage.topGround) {
                 //bb top - <==> bb bot -
-                wires.push({
-                    start: this.allocateLocation("ground", {nearestBBPin: top}),
-                    end: this.allocateLocation("ground", {nearestBBPin: bot}),
-                    color: GROUND_COLOR, assemblyStep: groundStep
+                groundWires.push({
+                    start: this.allocLocation("ground", {referenceBBPin: top}),
+                    end: this.allocLocation("ground", {referenceBBPin: bot}),
+                    color: GROUND_COLOR,
                 });
             }
             if (powerUsage.topGround) {
                 //board - <==> bb top -
-                wires.push({
-                    start: this.allocateLocation("ground", {nearestBBPin: top}),
+                groundWires.push({
+                    start: this.allocLocation("ground", {referenceBBPin: top}),
                     end: {type: "dalboard", pin: boardGroundPin},
-                    color: GROUND_COLOR, assemblyStep: groundStep
+                    color: GROUND_COLOR,
                 });
             } else if (powerUsage.bottomGround) {
                 //board - <==> bb bot -
-                wires.push({
-                    start: this.allocateLocation("ground", {nearestBBPin: bot}),
+                groundWires.push({
+                    start: this.allocLocation("ground", {referenceBBPin: bot}),
                     end: {type: "dalboard", pin: boardGroundPin},
-                    color: GROUND_COLOR, assemblyStep: groundStep
+                    color: GROUND_COLOR,
                 });
             }
             if (powerUsage.bottomThreeVolt && powerUsage.bottomGround) {
                 //bb top + <==> bb bot +
-                wires.push({
-                    start: this.allocateLocation("threeVolt", {nearestBBPin: top}),
-                    end: this.allocateLocation("threeVolt", {nearestBBPin: bot}),
-                    color: POWER_COLOR, assemblyStep: threeVoltStep
+                threeVoltWires.push({
+                    start: this.allocLocation("threeVolt", {referenceBBPin: top}),
+                    end: this.allocLocation("threeVolt", {referenceBBPin: bot}),
+                    color: POWER_COLOR,
                 });
             }
             if (powerUsage.topThreeVolt) {
                 //board + <==> bb top +
-                wires.push({
-                    start: this.allocateLocation("threeVolt", {nearestBBPin: top}),
+                threeVoltWires.push({
+                    start: this.allocLocation("threeVolt", {referenceBBPin: top}),
                     end: {type: "dalboard", pin: threeVoltPin},
-                    color: POWER_COLOR, assemblyStep: threeVoltStep
+                    color: POWER_COLOR,
                 });
             } else if (powerUsage.bottomThreeVolt) {
                 //board + <==> bb bot +
-                wires.push({
-                    start: this.allocateLocation("threeVolt", {nearestBBPin: bot}),
+                threeVoltWires.push({
+                    start: this.allocLocation("threeVolt", {referenceBBPin: bot}),
                     end: {type: "dalboard", pin: threeVoltPin},
-                    color: POWER_COLOR, assemblyStep: threeVoltStep
+                    color: POWER_COLOR,
                 });
             }
-            return wires;
+            let assembly: AssemblyStep[] = [];
+            if (groundWires.length > 0)
+                assembly.push({wireIndices: groundWires.map((w, i) => i)});
+            let numGroundWires = groundWires.length;
+            if (threeVoltWires.length > 0)
+                assembly.push({wireIndices: threeVoltWires.map((w, i) => i + numGroundWires)});
+            return {
+                wires: groundWires.concat(threeVoltWires),
+                assembly: assembly
+            };
         }
-        private allocateWire(wireDef: WireDefinition, opts: AllocWireOpts): WireInst {
-            let ends = [wireDef.start, wireDef.end];
+        private allocWire(wireIR: WireIR): WireInst {
+            let ends = [wireIR.start, wireIR.end];
             let endIsPower = ends.map(e => e === "ground" || e === "threeVolt");
             //allocate non-power first so we know the nearest pin for the power end
-            let endInsts = ends.map((e, idx) => !endIsPower[idx] ? this.allocateLocation(e, opts) : null)
+            let endInsts = ends.map((e, idx) => !endIsPower[idx] ? this.allocLocation(e, {}) : null)
             //allocate power pins closest to the other end of the wire
             endInsts = endInsts.map((e, idx) => {
                 if (e)
                     return e;
                 let locInst = <BBLoc>endInsts[1 - idx]; // non-power end
-                let l = this.allocateLocation(ends[idx], {
-                    nearestBBPin: locInst.rowCol,
-                    startColumn: opts.startColumn,
-                    cmpGPIOPins: opts.cmpGPIOPins,
+                let l = this.allocLocation(ends[idx], {
+                    referenceBBPin: locInst,
                 });
                 return l;
             });
-            return {start: endInsts[0], end: endInsts[1], color: wireDef.color, assemblyStep: wireDef.assemblyStep};
+            return {start: endInsts[0], end: endInsts[1], color: wireIR.color};
         }
-        private allocatePartialCmps(): PartialCmpAlloc[] {
-            let cmpNmAndDefs = this.opts.cmpList.map(cmpName => <[string, PartDefinition]>[cmpName, this.opts.cmpDefs[cmpName]]).filter(d => !!d[1]);
-            let cmpNmsList = cmpNmAndDefs.map(p => p[0]);
-            let cmpDefsList = cmpNmAndDefs.map(p => p[1]);
-            let partialCmps: PartialCmpAlloc[] = [];
-            cmpDefsList.forEach((def, idx) => {
-                let nm = cmpNmsList[idx];
-                if (def.pinAllocation.type === "predefined") {
-                    let mbPins = (<PredefinedPinAlloc>def.pinAllocation).pins;
-                    let pinsAssigned = mbPins.map(p => this.opts.boardDef.gpioPinMap[p]);
-                    partialCmps.push({
-                        name: nm,
-                        def: def,
-                        pinsAssigned: pinsAssigned,
-                        pinsNeeded: 0,
-                        breadboardColumnsNeeded: def.breadboardColumnsNeeded,
-                    });
-                } else if (def.pinAllocation.type === "factoryfunction") {
-                    let fnPinAlloc = (<FactoryFunctionPinAlloc>def.pinAllocation);
-                    let fnNm = fnPinAlloc.functionName;
-                    let fnsAndArgs = <string[]>this.opts.fnArgs[fnNm];
-                    let success = false;
-                    if (fnsAndArgs && fnsAndArgs.length) {
-                        let pinArgPoses = fnPinAlloc.pinArgPositions;
-                        let otherArgPoses = fnPinAlloc.otherArgPositions || [];
-                        fnsAndArgs.forEach(fnArgsStr => {
-                            let fnArgsSplit = fnArgsStr.split(",");
-                            let pinArgs: string[] = [];
-                            pinArgPoses.forEach(i => {
-                                pinArgs.push(fnArgsSplit[i]);
-                            });
-                            let mbPins = pinArgs.map(arg => readPin(arg));
-                            let otherArgs: string[] = [];
-                            otherArgPoses.forEach(i => {
-                                otherArgs.push(fnArgsSplit[i]);
-                            });
-                            let pinsAssigned = mbPins.map(p => this.opts.boardDef.gpioPinMap[p]);
-                            partialCmps.push({
-                                name: nm,
-                                def: def,
-                                pinsAssigned: pinsAssigned,
-                                pinsNeeded: 0,
-                                breadboardColumnsNeeded: def.breadboardColumnsNeeded,
-                                otherArgs: otherArgs.length ? otherArgs : null,
-                            });
-                        });
-                    } else {
-                        // failed to find pin allocation from callsites
-                        console.debug("Failed to read pin(s) from callsite for: " + fnNm);
-                        let pinsNeeded = fnPinAlloc.pinArgPositions.length;
-                        partialCmps.push({
-                            name: nm,
-                            def: def,
-                            pinsAssigned: [],
-                            pinsNeeded: pinsNeeded,
-                            breadboardColumnsNeeded: def.breadboardColumnsNeeded,
-                        });
+        private allocPart(ir: PartPlacement): PartInst {
+            let bbConnections = ir.pins
+                .filter(p => isConnectedToBB(p.def))
+                .map(p => {
+                    let rowIdx = ir.startRowIdx + p.bbFit.partRelativeRowIdx;
+                    if (rowIdx >= 7) //account for middle gap
+                        rowIdx -= 2;
+                    let rowName = visuals.getRowName(rowIdx);
+                    let colIdx = ir.startColumnIdx + p.bbFit.partRelativeColIdx;
+                    let colName = visuals.getColumnName(colIdx);
+                    return <BBLoc>{
+                        type: "breadboard",
+                        row: rowName,
+                        col: colName,
                     }
-                } else if (def.pinAllocation.type === "auto") {
-                    let pinsNeeded = (<AutoPinAlloc>def.pinAllocation).gpioPinsNeeded;
-                    partialCmps.push({
-                        name: nm,
-                        def: def,
-                        pinsAssigned: [],
-                        pinsNeeded: pinsNeeded,
-                        breadboardColumnsNeeded: def.breadboardColumnsNeeded,
-                    });
-                }
-            });
-            return partialCmps;
-        }
-        private allocateGPIOPins(partialCmps: PartialCmpAlloc[]): string[][] {
-            let availableGPIOBlocks = copyDoubleArray(this.opts.boardDef.gpioPinBlocks);
-            let sortAvailableGPIOBlocks = () => availableGPIOBlocks.sort((a, b) => a.length - b.length); //smallest blocks first
-            // determine blocks needed
-            let blockAssignments: AllocBlock[] = [];
-            let preassignedPins: string[] = [];
-            partialCmps.forEach((cmp, idx) => {
-                if (cmp.pinsAssigned && cmp.pinsAssigned.length) {
-                    //already assigned
-                    blockAssignments.push({cmpIdx: idx, cmpBlkIdx: 0, gpioNeeded: 0, gpioAssigned: cmp.pinsAssigned});
-                    preassignedPins = preassignedPins.concat(cmp.pinsAssigned);
-                } else if (cmp.pinsNeeded) {
-                    if (typeof cmp.pinsNeeded === "number") {
-                        //individual pins
-                        for (let i = 0; i < cmp.pinsNeeded; i++) {
-                            blockAssignments.push(
-                                {cmpIdx: idx, cmpBlkIdx: 0, gpioNeeded: 1, gpioAssigned: []});
-                        }
-                    } else {
-                        //blocks of pins
-                        let blocks = <number[]>cmp.pinsNeeded;
-                        blocks.forEach((numNeeded, blkIdx) => {
-                            blockAssignments.push(
-                                {cmpIdx: idx, cmpBlkIdx: blkIdx, gpioNeeded: numNeeded, gpioAssigned: []});
-                        });
-                    }
-                }
-            });
-            // remove assigned blocks
-            availableGPIOBlocks.forEach(blks => {
-                for (let i = blks.length - 1; 0 <= i; i--) {
-                    let pin = blks[i];
-                    if (0 <= preassignedPins.indexOf(pin)) {
-                        blks.splice(i, 1);
-                    }
-                }
-            });
-            // sort by size of blocks
-            let sortBlockAssignments = () => blockAssignments.sort((a, b) => b.gpioNeeded - a.gpioNeeded); //largest blocks first
-            // allocate each block
-            if (0 < blockAssignments.length && 0 < availableGPIOBlocks.length) {
-                do {
-                    sortBlockAssignments();
-                    sortAvailableGPIOBlocks();
-                    let assignment = blockAssignments[0];
-                    let smallestAvailableBlockThatFits: string[];
-                    for (let j = 0; j < availableGPIOBlocks.length; j++) {
-                        smallestAvailableBlockThatFits = availableGPIOBlocks[j];
-                        if (assignment.gpioNeeded <= availableGPIOBlocks[j].length) {
-                            break;
-                        }
-                    }
-                    if (!smallestAvailableBlockThatFits || smallestAvailableBlockThatFits.length <= 0) {
-                        break; // out of pins
-                    }
-                    while (0 < assignment.gpioNeeded && 0 < smallestAvailableBlockThatFits.length) {
-                        assignment.gpioNeeded--;
-                        let pin = smallestAvailableBlockThatFits[0];
-                        smallestAvailableBlockThatFits.splice(0, 1);
-                        assignment.gpioAssigned.push(pin);
-                    }
-                    sortBlockAssignments();
-                } while (0 < blockAssignments[0].gpioNeeded);
-            }
-            if (0 < blockAssignments.length && 0 < blockAssignments[0].gpioNeeded) {
-                console.debug("Not enough GPIO pins!");
-                return null;
-            }
-            let cmpGPIOPinBlocks: string[][][] = partialCmps.map((def, cmpIdx) => {
-                if (!def)
-                    return null;
-                let assignments = blockAssignments.filter(a => a.cmpIdx === cmpIdx);
-                let gpioPins: string[][] = [];
-                for (let i = 0; i < assignments.length; i++) {
-                    let a = assignments[i];
-                    let blk = gpioPins[a.cmpBlkIdx] || (gpioPins[a.cmpBlkIdx] = []);
-                    a.gpioAssigned.forEach(p => blk.push(p));
-                }
-                return gpioPins;
-            });
-            let cmpGPIOPins = cmpGPIOPinBlocks.map(blks => blks.reduce((p, n) => p.concat(n), []));
-            return cmpGPIOPins;
-        }
-        private allocateColumns(partialCmps: PartialCmpAlloc[]): number[] {
-            let componentsCount = partialCmps.length;
-            let totalAvailableSpace = 30; //TODO allow multiple breadboards
-            let totalSpaceNeeded = partialCmps.map(d => d.breadboardColumnsNeeded).reduce((p, n) => p + n, 0);
-            let extraSpace = totalAvailableSpace - totalSpaceNeeded;
-            if (extraSpace <= 0) {
-                console.log("Not enough breadboard space!");
-                //TODO
-            }
-            let padding = Math.floor(extraSpace / (componentsCount - 1 + 2));
-            let componentSpacing = padding; //Math.floor(extraSpace/(componentsCount-1));
-            let totalCmpPadding = extraSpace - componentSpacing * (componentsCount - 1);
-            let leftPadding = Math.floor(totalCmpPadding / 2);
-            let rightPadding = Math.ceil(totalCmpPadding / 2);
-            let nextAvailableCol = 1 + leftPadding;
-            let cmpStartCol = partialCmps.map(cmp => {
-                let col = nextAvailableCol;
-                nextAvailableCol += cmp.breadboardColumnsNeeded + componentSpacing;
-                return col;
-            });
-            return cmpStartCol;
-        }
-        private allocateComponent(partialCmp: PartialCmpAlloc, startColumn: number, microbitPins: string[]): CmpInst {
-            return {
-                name: partialCmp.name,
-                breadboardStartColumn: startColumn,
-                breadboardStartRow: partialCmp.def.breadboardStartRow,
-                assemblyStep: partialCmp.def.assemblyStep,
-                visual: partialCmp.def.visual,
-                microbitPins: microbitPins,
-                otherArgs: partialCmp.otherArgs,
-            };
-        }
-        public allocateAll(): AllocatorResult {
-            let cmpList = this.opts.cmpList;
-            let basicWires: WireInst[] = [];
-            let cmpsAndWires: CmpAndWireInst[] = [];
-            if (cmpList.length > 0) {
-                let partialCmps = this.allocatePartialCmps();
-                let allWireDefs = partialCmps.map(p => p.def.wires).reduce((p, n) => p.concat(n), []);
-                let allPowerUsage = allWireDefs.map(w => computePowerUsage(w));
-                this.powerUsage = mergePowerUsage(allPowerUsage);
-                basicWires = this.allocatePowerWires(this.powerUsage);
-                let cmpGPIOPins = this.allocateGPIOPins(partialCmps);
-                let reverseMap = mkReverseMap(this.opts.boardDef.gpioPinMap);
-                let cmpMicrobitPins = cmpGPIOPins.map(pins => pins.map(p => reverseMap[p]));
-                let cmpStartCol = this.allocateColumns(partialCmps);
-                let cmps = partialCmps.map((c, idx) => this.allocateComponent(c, cmpStartCol[idx], cmpMicrobitPins[idx]));
-                let wires = partialCmps.map((c, idx) => c.def.wires.map(d => this.allocateWire(d, {
-                    cmpGPIOPins: cmpGPIOPins[idx],
-                    startColumn: cmpStartCol[idx],
-                })));
-                cmpsAndWires = cmps.map((c, idx) => {
-                    return {component: c, wires: wires[idx]}
                 });
+            let part: PartInst = {
+                name: ir.name,
+                visual: ir.def.visual,
+                bbFit: ir.bbFit,
+                startColumnIdx: ir.startColumnIdx,
+                startRowIdx: ir.startRowIdx,
+                breadboardConnections: bbConnections,
+                params: ir.partParams,
+                simulationBehavior: ir.def.simulationBehavior
+            }
+            return part;
+        }
+        public allocAll(): AllocatorResult {
+            let partNmAndDefs = this.opts.partsList
+                .map(partName => {return {name: partName, def: this.opts.partDefs[partName]}})
+                .filter(d => !!d.def);
+            if (partNmAndDefs.length > 0) {
+                let partNmsList = partNmAndDefs.map(p => p.name);
+                let partDefsList = partNmAndDefs.map(p => p.def);
+                let dimensions = partNmAndDefs.map(nmAndPart => this.computePartDimensions(nmAndPart.def, nmAndPart.name));
+                let partIRs: PartIR[] = [];
+                partNmAndDefs.forEach((nmAndDef, idx) => {
+                    let dims = dimensions[idx];
+                    let irs = this.allocPartIRs(nmAndDef.def, nmAndDef.name, dims);
+                    partIRs = partIRs.concat(irs);
+                })
+                let partPlacements = this.placeParts(partIRs);
+                let partsAndWireIRs = partPlacements.map(p => this.allocWireIRs(p));
+                let allWireIRs = partsAndWireIRs.map(p => p.wires).reduce((p, n) => p.concat(n), []);
+                let allPowerUsage = allWireIRs.map(w => computePowerUsage(w));
+                this.powerUsage = mergePowerUsage(allPowerUsage);
+                let basicWires = this.allocPowerWires(this.powerUsage);
+                let partsAndWires: PartAndWiresInst[] = partsAndWireIRs.map((irs, idx) => {
+                    let part = this.allocPart(irs);
+                    let wires = irs.wires.map(w => this.allocWire(w));
+                    let pinIdxToWireIdx: number[] = [];
+                    irs.wires.forEach((wIR, idx) => {
+                        pinIdxToWireIdx[wIR.pinIdx] = idx;
+                    });
+                    let assembly: AssemblyStep[] = irs.def.assembly.map(stepDef => {
+                        return {
+                            part: stepDef.part,
+                            wireIndices: (stepDef.pinIndices || []).map(i => pinIdxToWireIdx[i])
+                        }
+                    });
+                    return {
+                        part: part,
+                        wires: wires,
+                        assembly: assembly
+                    }
+                });
+                let all = [basicWires].concat(partsAndWires);
+                return {
+                    partsAndWires: all
+                }
+            } else {
+                return {
+                    partsAndWires: []
+                }
             }
-            return {
-                powerWires: basicWires,
-                components: cmpsAndWires
-            };
         }
     }
 
     export function allocateDefinitions(opts: AllocatorOpts): AllocatorResult {
-        return new Allocator(opts).allocateAll();
+        return new Allocator(opts).allocAll();
     }
 }
\ No newline at end of file
diff --git a/sim/dalboard.ts b/sim/dalboard.ts
index b95f354b..8ab23f27 100644
--- a/sim/dalboard.ts
+++ b/sim/dalboard.ts
@@ -84,8 +84,8 @@ namespace pxsim {
             let viewHost = new visuals.BoardHost({
                 state: this,
                 boardDef: boardDef,
-                cmpsList: cmpsList,
-                cmpDefs: cmpDefs,
+                partsList: cmpsList,
+                partDefs: cmpDefs,
                 fnArgs: fnArgs,
                 maxWidth: "100%",
                 maxHeight: "100%",
diff --git a/sim/definitions.ts b/sim/definitions.ts
index 154f4001..2d29b786 100644
--- a/sim/definitions.ts
+++ b/sim/definitions.ts
@@ -53,7 +53,7 @@ namespace pxsim {
         marginWhenBreadboarding: [0, 0, 80, 0],
     }
 
-    export const builtinComponentSimVisual: Map<() => visuals.IBoardComponent<any>> = {
+    export const builtinComponentSimVisual: Map<() => visuals.IBoardPart<any>> = {
         "buttonpair": () => new visuals.ButtonPairView(),
         "ledmatrix": () => new visuals.LedMatrixView(),
         "neopixel": () => new visuals.NeoPixelView(),
diff --git a/sim/instructions/instructions.ts b/sim/instructions/instructions.ts
index 1a91b9c3..63e60d5f 100644
--- a/sim/instructions/instructions.ts
+++ b/sim/instructions/instructions.ts
@@ -20,7 +20,7 @@ namespace pxsim.instructions {
     const LBL_LEFT_PAD = 5;
     const REQ_WIRE_HEIGHT = 45;
     const REQ_CMP_HEIGHT = 55;
-    const REQ_CMP_SCALE = 0.5 * 4;
+    const REQ_CMP_SCALE = 0.5 * 3;
     type Orientation = "landscape" | "portrait";
     const ORIENTATION: Orientation = "portrait";
     const PPI = 96.0;
@@ -59,7 +59,7 @@ namespace pxsim.instructions {
                 border-color: ${BORDER_COLOR};
                 border-style: solid;
                 border-radius: ${BORDER_RADIUS}px;
-                display: block;
+                display: inline-block;
                 width: ${PANEL_WIDTH}px;
                 height: ${PANEL_HEIGHT}px;
                 position: relative;
@@ -284,18 +284,18 @@ namespace pxsim.instructions {
         div.appendChild(svgEl);
         return div;
     }
-    function mkCmpDiv(cmp: "wire" | string | PartVisualDefinition, opts: mkCmpDivOpts): HTMLElement {
+    function mkCmpDiv(cmp: "wire" | PartVisualDefinition, opts: mkCmpDivOpts): HTMLElement {
         let el: visuals.SVGElAndSize;
         if (cmp == "wire") {
-            //TODO: support non-croc wire parts
             el = visuals.mkWirePart([0, 0], opts.wireClr || "red", opts.crocClips);
-        } else if (typeof cmp == "string") {
-            let builtinVis = <string>cmp;
-            let cnstr = builtinComponentPartVisual[builtinVis];
-            el = cnstr([0, 0]);
         } else {
             let partVis = <PartVisualDefinition>cmp;
-            el = visuals.mkGenericPartSVG(partVis);
+            if (typeof partVis.builtIn == "string") {
+                let cnstr = builtinComponentPartVisual[partVis.builtIn];
+                el = cnstr([0, 0]);
+            } else {
+                el = visuals.mkGenericPartSVG(partVis);
+            }
         }
         return wrapSvg(el, opts);
     }
@@ -305,40 +305,33 @@ namespace pxsim.instructions {
         fnArgs: any,
         allAlloc: AllocatorResult,
         stepToWires: WireInst[][],
-        stepToCmps: CmpInst[][]
+        stepToCmps: PartInst[][]
         allWires: WireInst[],
-        allCmps: CmpInst[],
+        allCmps: PartInst[],
         lastStep: number,
         colorToWires: Map<WireInst[]>,
         allWireColors: string[],
     };
     function mkBoardProps(allocOpts: AllocatorOpts): BoardProps {
         let allocRes = allocateDefinitions(allocOpts);
-        let {powerWires, components} = allocRes;
         let stepToWires: WireInst[][] = [];
-        let stepToCmps: CmpInst[][] = [];
-        powerWires.forEach(w => {
-            let step = w.assemblyStep + 1;
-            (stepToWires[step] || (stepToWires[step] = [])).push(w)
-        });
-        let getMaxStep = (ns: { assemblyStep: number }[]) => ns.reduce((m, n) => Math.max(m, n.assemblyStep), 0);
-        let stepOffset = powerWires.length > 0 ? getMaxStep(powerWires) + 2 : 1;
-        components.forEach(cAndWs => {
-            let {component, wires} = cAndWs;
-            let cStep = component.assemblyStep + stepOffset;
-            let arr = stepToCmps[cStep] || (stepToCmps[cStep] = []);
-            arr.push(component);
-            let wSteps = wires.map(w => w.assemblyStep + stepOffset);
-            wires.forEach((w, i) => {
-                let wStep = wSteps[i];
-                let arr = stepToWires[wStep] || (stepToWires[wStep] = []);
-                arr.push(w);
+        let stepToCmps: PartInst[][] = [];
+        let stepOffset = 0;
+        allocRes.partsAndWires.forEach(cAndWs => {
+            let part = cAndWs.part;
+            let wires = cAndWs.wires;
+            cAndWs.assembly.forEach((step, idx) => {
+                if (step.part && part)
+                    stepToCmps[stepOffset + idx] = [part]
+                if (step.wireIndices && step.wireIndices.length > 0 && wires)
+                    stepToWires[stepOffset + idx] = step.wireIndices.map(i => wires[i])
             })
-            stepOffset = Math.max(cStep, wSteps.reduce((m, n) => Math.max(m, n), 0)) + 1;
+            stepOffset += cAndWs.assembly.length;
         });
-        let lastStep = stepOffset - 1;
-        let allCmps = components.map(p => p.component);
-        let allWires = powerWires.concat(components.map(p => p.wires).reduce((p, n) => p.concat(n), []));
+        let numSteps = stepOffset;
+        let lastStep = numSteps - 1;
+        let allCmps = allocRes.partsAndWires.map(r => r.part).filter(p => !!p);
+        let allWires = allocRes.partsAndWires.map(r => r.wires || []).reduce((p, n) => p.concat(n), []);
         let colorToWires: Map<WireInst[]> = {}
         let allWireColors: string[] = [];
         allWires.forEach(w => {
@@ -350,7 +343,7 @@ namespace pxsim.instructions {
         });
         return {
             boardDef: allocOpts.boardDef,
-            cmpDefs: allocOpts.cmpDefs,
+            cmpDefs: allocOpts.partDefs,
             fnArgs: allocOpts.fnArgs,
             allAlloc: allocRes,
             stepToWires: stepToWires,
@@ -368,7 +361,7 @@ namespace pxsim.instructions {
             state: state,
             boardDef: boardDef,
             forceBreadboard: true,
-            cmpDefs: cmpDefs,
+            partDefs: cmpDefs,
             maxWidth: `${width}px`,
             fnArgs: fnArgs,
             wireframe: buildMode,
@@ -397,6 +390,19 @@ namespace pxsim.instructions {
         }
 
         for (let i = 0; i <= step; i++) {
+            let cmps = props.stepToCmps[i];
+            if (cmps) {
+                cmps.forEach(partInst => {
+                    let cmp = board.addPart(partInst)
+                    //last step
+                    if (i === step) {
+                        //highlight locations pins
+                        partInst.breadboardConnections.forEach(bbLoc => board.highlightBreadboardPin(bbLoc));
+                        svg.addClass(cmp.element, "notgrayed");
+                    }
+                });
+            }
+
             let wires = props.stepToWires[i];
             if (wires) {
                 wires.forEach(w => {
@@ -405,13 +411,12 @@ namespace pxsim.instructions {
                     if (i === step) {
                         //location highlights
                         if (w.start.type == "breadboard") {
-                            let lbls = board.highlightBreadboardPin((<BBLoc>w.start).rowCol);
+                            let lbls = board.highlightBreadboardPin((<BBLoc>w.start));
                         } else {
                             board.highlightBoardPin((<BoardLoc>w.start).pin);
                         }
                         if (w.end.type == "breadboard") {
-                            let [row, col] = (<BBLoc>w.end).rowCol;
-                            let lbls = board.highlightBreadboardPin((<BBLoc>w.end).rowCol);
+                            let lbls = board.highlightBreadboardPin((<BBLoc>w.end));
                         } else {
                             board.highlightBoardPin((<BoardLoc>w.end).pin);
                         }
@@ -420,24 +425,6 @@ namespace pxsim.instructions {
                     }
                 });
             }
-            let cmps = props.stepToCmps[i];
-            if (cmps) {
-                cmps.forEach(cmpInst => {
-                    let cmp = board.addComponent(cmpInst)
-                    let colOffset = (<any>cmpInst.visual).breadboardStartColIdx || 0;
-                    let rowCol: BBRowCol = [`${cmpInst.breadboardStartRow}`, `${colOffset + cmpInst.breadboardStartColumn}`];
-                    //last step
-                    if (i === step) {
-                        board.highlightBreadboardPin(rowCol);
-                        if (cmpInst.visual === "buttonpair") {
-                            //TODO: don't specialize this
-                            let rowCol2: BBRowCol = [`${cmpInst.breadboardStartRow}`, `${cmpInst.breadboardStartColumn + 3}`];
-                            board.highlightBreadboardPin(rowCol2);
-                        }
-                        svg.addClass(cmp.element, "notgrayed");
-                    }
-                });
-            }
         }
     }
     function mkPanel() {
@@ -463,7 +450,7 @@ namespace pxsim.instructions {
         cmps.forEach(c => {
             let quant = 1;
             // TODO: don't special case this
-            if (c.visual === "buttonpair") {
+            if (c.visual.builtIn === "buttonpair") {
                 quant = 2;
             }
             let cmp = mkCmpDiv(c.visual, {
@@ -516,7 +503,7 @@ namespace pxsim.instructions {
         let wires = (props.stepToWires[step] || []);
         let mkLabel = (loc: Loc) => {
             if (loc.type === "breadboard") {
-                let [row, col] = (<BBLoc>loc).rowCol;
+                let {row, col} = (<BBLoc>loc);
                 return `(${row},${col})`
             } else
                 return (<BoardLoc>loc).pin;
@@ -536,17 +523,23 @@ namespace pxsim.instructions {
         });
         let cmps = (props.stepToCmps[step] || []);
         cmps.forEach(c => {
-            let l: BBRowCol = [`${c.breadboardStartRow}`, `${c.breadboardStartColumn}`];
-            let locs = [l];
-            if (c.visual === "buttonpair") {
+            let locs: BBLoc[];
+            if (c.visual.builtIn === "buttonpair") {
                 //TODO: don't special case this
-                let l2: BBRowCol = [`${c.breadboardStartRow}`, `${c.breadboardStartColumn + 3}`];
-                locs.push(l2);
+                locs = [c.breadboardConnections[0], c.breadboardConnections[2]]
+            } else {
+                locs = [c.breadboardConnections[0]];
             }
             locs.forEach((l, i) => {
-                let [row, col] = l;
+                let topLbl: string;
+                if (l) {
+                    let {row, col} = l;
+                    topLbl = `(${row},${col})`;
+                } else {
+                    topLbl = "";
+                }
                 let cmp = mkCmpDiv(c.visual, {
-                    top: `(${row},${col})`,
+                    top: topLbl,
                     topSize: LOC_LBL_SIZE,
                     cmpHeight: REQ_CMP_HEIGHT,
                     cmpScale: REQ_CMP_SCALE
@@ -656,8 +649,8 @@ ${tsPackage}
         activeComponents.sort();
         let props = mkBoardProps({
             boardDef: boardDef,
-            cmpDefs: cmpDefs,
-            cmpList: activeComponents,
+            partDefs: cmpDefs,
+            partsList: activeComponents,
             fnArgs: fnArgs,
             getBBCoord: dummyBreadboard.getCoord.bind(dummyBreadboard)
         });
diff --git a/sim/simlib.ts b/sim/simlib.ts
index 5e855eb5..1bdb3d91 100644
--- a/sim/simlib.ts
+++ b/sim/simlib.ts
@@ -3,10 +3,18 @@
 /// <reference path="../libs/microbit/dal.d.ts"/>
 
 namespace pxsim {
-    export type BBRowCol = [/*row*/string, /*column*/string];
     export type BoardPin = string;
-    export interface BBLoc { type: "breadboard", rowCol: BBRowCol };
-    export interface BoardLoc { type: "dalboard", pin: BoardPin };
+    export interface BBLoc {
+        type: "breadboard",
+        row: string,
+        col: string
+        xOffset?: number,
+        yOffset?: number
+    };
+    export interface BoardLoc {
+        type: "dalboard",
+        pin: BoardPin
+    };
     export type Loc = BBLoc | BoardLoc;
 
     export function initRuntimeWithDalBoard() {
@@ -197,11 +205,12 @@ namespace pxsim.visuals {
         return minIdx;
     }
 
-    export interface IBoardComponent<T> {
+    export interface IBoardPart<T> {
         style: string,
         element: SVGElement,
+        overElement?: SVGElement,
         defs: SVGElement[],
-        init(bus: EventBus, state: T, svgEl: SVGSVGElement, gpioPins: string[], otherArgs: string[]): void, //NOTE: constructors not supported in interfaces
+        init(bus: EventBus, state: T, svgEl: SVGSVGElement, otherParams: Map<string>): void, //NOTE: constructors not supported in interfaces
         moveToCoord(xy: Coord): void,
         updateState(): void,
         updateTheme(): void,
@@ -224,7 +233,8 @@ namespace pxsim.visuals {
     }
 
     export type WireColor =
-        "black" | "white" | "gray" | "purple" | "blue" | "green" | "yellow" | "orange" | "red" | "brown";
+        "black" | "white" | "gray" | "purple" | "blue" | "green" | "yellow" | "orange" | "red" | "brown" | "pink";
+    export const GPIO_WIRE_COLORS = ["pink", "green", "purple", "orange", "yellow"];
     export const WIRE_COLOR_MAP: Map<string> = {
         black: "#514f4d",
         white: "#fcfdfc",
@@ -236,6 +246,7 @@ namespace pxsim.visuals {
         orange: "#fdb262",
         red: "#f44f43",
         brown: "#c89764",
+        pink: "#ff80fa"
     }
     export function mapWireColor(clr: WireColor | string): string {
         return WIRE_COLOR_MAP[clr] || clr;
diff --git a/sim/visuals/boardhost.ts b/sim/visuals/boardhost.ts
index fdbffb50..5adf86fc 100644
--- a/sim/visuals/boardhost.ts
+++ b/sim/visuals/boardhost.ts
@@ -2,8 +2,8 @@ namespace pxsim.visuals {
     export interface BoardHostOpts {
         state: DalBoard,
         boardDef: BoardDefinition,
-        cmpsList?: string[],
-        cmpDefs: Map<PartDefinition>,
+        partsList?: string[],
+        partDefs: Map<PartDefinition>,
         fnArgs: any,
         forceBreadboard?: boolean,
         maxWidth?: string,
@@ -11,13 +11,15 @@ namespace pxsim.visuals {
         wireframe?: boolean
     }
     export class BoardHost {
-        private components: IBoardComponent<any>[] = [];
+        private parts: IBoardPart<any>[] = [];
         private wireFactory: WireFactory;
         private breadboard: Breadboard;
         private fromBBCoord: (xy: Coord) => Coord;
         private fromMBCoord: (xy: Coord) => Coord;
         private boardView: BoardView;
         private view: SVGSVGElement;
+        private partGroup: SVGGElement;
+        private partOverGroup: SVGGElement;
         private style: SVGStyleElement;
         private defs: SVGDefsElement;
         private state: DalBoard;
@@ -26,7 +28,7 @@ namespace pxsim.visuals {
         constructor(opts: BoardHostOpts) {
             this.state = opts.state;
             let onboardCmps = opts.boardDef.onboardComponents || [];
-            let activeComponents = (opts.cmpsList || []).filter(c => onboardCmps.indexOf(c) < 0);
+            let activeComponents = (opts.partsList || []).filter(c => onboardCmps.indexOf(c) < 0);
             activeComponents.sort();
             this.useCrocClips = opts.boardDef.useCrocClips;
 
@@ -68,6 +70,8 @@ namespace pxsim.visuals {
                 this.fromMBCoord = composition.toHostCoord1;
                 this.fromBBCoord = composition.toHostCoord2;
                 let pinDist = composition.scaleUnit;
+                this.partGroup = over;
+                this.partOverGroup = <SVGGElement>svg.child(this.view, "g");
 
                 this.style = <SVGStyleElement>svg.child(this.view, "style", {});
                 this.defs = <SVGDefsElement>svg.child(this.view, "defs", {});
@@ -76,16 +80,18 @@ namespace pxsim.visuals {
 
                 let allocRes = allocateDefinitions({
                     boardDef: opts.boardDef,
-                    cmpDefs: opts.cmpDefs,
+                    partDefs: opts.partDefs,
                     fnArgs: opts.fnArgs,
                     getBBCoord: this.breadboard.getCoord.bind(this.breadboard),
-                    cmpList: activeComponents,
+                    partsList: activeComponents,
                 });
 
                 this.addAll(allocRes);
             } else {
                 let el = this.boardView.getView().el;
                 this.view = el;
+                this.partGroup = <SVGGElement>svg.child(this.view, "g");
+                this.partOverGroup = <SVGGElement>svg.child(this.view, "g");
                 if (opts.maxWidth)
                     svg.hydrate(this.view, { width: opts.maxWidth });
                 if (opts.maxHeight)
@@ -99,7 +105,7 @@ namespace pxsim.visuals {
             this.boardView.highlightPin(pinNm);
         }
 
-        public highlightBreadboardPin(rowCol: BBRowCol) {
+        public highlightBreadboardPin(rowCol: BBLoc) {
             this.breadboard.highlightLoc(rowCol);
         }
 
@@ -120,10 +126,10 @@ namespace pxsim.visuals {
         }
 
         private updateState() {
-            this.components.forEach(c => c.updateState());
+            this.parts.forEach(c => c.updateState());
         }
 
-        private getBBCoord(rowCol: BBRowCol) {
+        private getBBCoord(rowCol: BBLoc) {
             let bbCoord = this.breadboard.getCoord(rowCol);
             return this.fromBBCoord(bbCoord);
         }
@@ -134,7 +140,7 @@ namespace pxsim.visuals {
         public getLocCoord(loc: Loc): Coord {
             let coord: Coord;
             if (loc.type === "breadboard") {
-                let rowCol = (<BBLoc>loc).rowCol;
+                let rowCol = (<BBLoc>loc);
                 coord = this.getBBCoord(rowCol);
             } else {
                 let pinNm = (<BoardLoc>loc).pin;
@@ -147,47 +153,62 @@ namespace pxsim.visuals {
             return coord;
         }
 
-        public addComponent(cmpDesc: CmpInst): IBoardComponent<any> {
-            let cmp: IBoardComponent<any> = null;
+        public addPart(partInst: PartInst): IBoardPart<any> {
+            let part: IBoardPart<any> = null;
             let colOffset = 0;
-            if (typeof cmpDesc.visual === "string") {
-                let builtinVisual = cmpDesc.visual as string;
-                let cnstr = builtinComponentSimVisual[builtinVisual];
-                let stateFn = builtinComponentSimState[builtinVisual];
-                cmp = cnstr();
-                cmp.init(this.state.bus, stateFn(this.state), this.view, cmpDesc.microbitPins, cmpDesc.otherArgs);
+            if (partInst.simulationBehavior) {
+                //TODO: seperate simulation behavior from builtin visual
+                let builtinBehavior = partInst.simulationBehavior;
+                let cnstr = builtinComponentSimVisual[builtinBehavior];
+                let stateFn = builtinComponentSimState[builtinBehavior];
+                part = cnstr();
+                part.init(this.state.bus, stateFn(this.state), this.view, partInst.params);
             } else {
-                let vis = cmpDesc.visual as PartVisualDefinition;
-                cmp = new GenericPart(vis);
-                colOffset = vis.extraColumnOffset || 0;
+                let vis = partInst.visual as PartVisualDefinition;
+                part = new GenericPart(vis);
             }
-            this.components.push(cmp);
-            this.view.appendChild(cmp.element);
-            if (cmp.defs)
-                cmp.defs.forEach(d => this.defs.appendChild(d));
-            this.style.textContent += cmp.style || "";
-            let rowCol = <BBRowCol>[`${cmpDesc.breadboardStartRow}`, `${colOffset + cmpDesc.breadboardStartColumn}`];
+            this.parts.push(part);
+            this.partGroup.appendChild(part.element);
+            if (part.overElement)
+                this.partOverGroup.appendChild(part.overElement);
+            if (part.defs)
+                part.defs.forEach(d => this.defs.appendChild(d));
+            this.style.textContent += part.style || "";
+            let colIdx = partInst.startColumnIdx;
+            let rowIdx = partInst.startRowIdx;
+            let row = getRowName(rowIdx);
+            let col = getColumnName(colIdx);
+            let xOffset = partInst.bbFit.xOffset / partInst.visual.pinDistance;
+            let yOffset = partInst.bbFit.yOffset  / partInst.visual.pinDistance;
+            let rowCol = <BBLoc>{
+                type: "breadboard",
+                row: row,
+                col: col,
+                xOffset: xOffset,
+                yOffset: yOffset
+            };
             let coord = this.getBBCoord(rowCol);
-            cmp.moveToCoord(coord);
+            part.moveToCoord(coord);
             let getCmpClass = (type: string) => `sim-${type}-cmp`;
-            let cls = getCmpClass(name);
-            svg.addClass(cmp.element, cls);
-            svg.addClass(cmp.element, "sim-cmp");
-            cmp.updateTheme();
-            cmp.updateState();
-            return cmp;
+            let cls = getCmpClass(partInst.name);
+            svg.addClass(part.element, cls);
+            svg.addClass(part.element, "sim-cmp");
+            part.updateTheme();
+            part.updateState();
+            return part;
         }
         public addWire(inst: WireInst): Wire {
             return this.wireFactory.addWire(inst.start, inst.end, inst.color, this.useCrocClips);
         }
-        public addAll(basicWiresAndCmpsAndWires: AllocatorResult) {
-            let {powerWires, components} = basicWiresAndCmpsAndWires;
-            powerWires.forEach(w => this.addWire(w));
-            components.forEach((cAndWs, idx) => {
-                let {component, wires} = cAndWs;
-                wires.forEach(w => this.addWire(w));
-                this.addComponent(component);
-            });
+        public addAll(allocRes: AllocatorResult) {
+            allocRes.partsAndWires.forEach(pAndWs => {
+                let part = pAndWs.part;
+                if (part)
+                    this.addPart(part)
+                let wires = pAndWs.wires;
+                if (wires)
+                    wires.forEach(w => this.addWire(w));
+            })
         }
     }
 }
\ No newline at end of file
diff --git a/sim/visuals/breadboard.ts b/sim/visuals/breadboard.ts
index f213cf39..f9f88978 100644
--- a/sim/visuals/breadboard.ts
+++ b/sim/visuals/breadboard.ts
@@ -80,7 +80,8 @@ namespace pxsim.visuals {
             fill: #BBB;
         }
         .grayed .sim-bb-pin {
-            fill: #BBB;
+            fill:none;
+            stroke: #BBB;
         }
         .grayed .sim-bb-label {
             fill: #BBB;
@@ -106,10 +107,10 @@ namespace pxsim.visuals {
         }
         `
     // Pin rows and coluns
-    const MID_ROWS = 10;
+    export const BREADBOARD_MID_ROWS = 10;
+    export const BREADBOARD_MID_COLS = 30;
     const MID_ROW_GAPS = [4, 4];
-    const MID_ROW_AND_GAPS = MID_ROWS + MID_ROW_GAPS.length;
-    const MID_COLS = 30;
+    const MID_ROW_AND_GAPS = BREADBOARD_MID_ROWS + MID_ROW_GAPS.length;
     const BAR_ROWS = 2;
     const BAR_COLS = 25;
     const POWER_ROWS = BAR_ROWS * 2;
@@ -117,14 +118,14 @@ namespace pxsim.visuals {
     const BAR_COL_GAPS = [4, 9, 14, 19];
     const BAR_COL_AND_GAPS = BAR_COLS + BAR_COL_GAPS.length;
     // Essential dimensions
-    const WIDTH = PIN_DIST * (MID_COLS + 3);
+    const WIDTH = PIN_DIST * (BREADBOARD_MID_COLS + 3);
     const HEIGHT = PIN_DIST * (MID_ROW_AND_GAPS + POWER_ROWS + 5.5);
     const MID_RATIO = 2.0 / 3.0;
     const BAR_RATIO = (1.0 - MID_RATIO) * 0.5;
     const MID_HEIGHT = HEIGHT * MID_RATIO;
     const BAR_HEIGHT = HEIGHT * BAR_RATIO;
     // Pin grids
-    const MID_GRID_WIDTH = (MID_COLS - 1) * PIN_DIST;
+    const MID_GRID_WIDTH = (BREADBOARD_MID_COLS - 1) * PIN_DIST;
     const MID_GRID_HEIGHT = (MID_ROW_AND_GAPS - 1) * PIN_DIST;
     const MID_GRID_X = (WIDTH - MID_GRID_WIDTH) / 2.0;
     const MID_GRID_Y = BAR_HEIGHT + (MID_HEIGHT - MID_GRID_HEIGHT) / 2.0;
@@ -151,6 +152,10 @@ namespace pxsim.visuals {
     const SMALL_CHANNEL_HEIGHT = PIN_DIST * 0.05;
     // Background
     const BACKGROUND_ROUNDING = PIN_DIST * 0.3;
+    // Row and column helpers
+    const alphabet = "abcdefghij".split("").reverse();
+    export function getColumnName(colIdx: number): string { return `${colIdx + 1}` };
+    export function getRowName(rowIdx: number): string { return alphabet[rowIdx] };
 
     export interface GridPin {
         el: SVGElement,
@@ -320,12 +325,14 @@ namespace pxsim.visuals {
                 return null;
             return pin;
         }
-        public getCoord(rowCol: BBRowCol): Coord {
-            let [row, col] = rowCol;
+        public getCoord(rowCol: BBLoc): Coord {
+            let {row, col, xOffset, yOffset} = rowCol;
             let pin = this.getPin(row, col);
             if (!pin)
                 return null;
-            return [pin.cx, pin.cy];
+            let xOff = (xOffset || 0) * PIN_DIST;
+            let yOff = (yOffset || 0) * PIN_DIST;
+            return [pin.cx + xOff, pin.cy + yOff];
         }
 
         public getPinDist() {
@@ -370,14 +377,11 @@ namespace pxsim.visuals {
             mkChannel(BAR_HEIGHT + MID_HEIGHT, SMALL_CHANNEL_HEIGHT);
 
             //-----pins
-            const getMidTopOrBot = (rowIdx: number) => rowIdx < MID_ROWS / 2.0 ? "b" : "t";
+            const getMidTopOrBot = (rowIdx: number) => rowIdx < BREADBOARD_MID_ROWS / 2.0 ? "b" : "t";
             const getBarTopOrBot = (colIdx: number) => colIdx < POWER_COLS / 2.0 ? "b" : "t";
-            const alphabet = "abcdefghij".split("").reverse();
-            const getColName = (colIdx: number) => `${colIdx + 1}`;
-            const getMidRowName = (rowIdx: number) => alphabet[rowIdx];
             const getMidGroupName = (rowIdx: number, colIdx: number) => {
                 let botOrTop = getMidTopOrBot(rowIdx);
-                let colNm = getColName(colIdx);
+                let colNm = getColumnName(colIdx);
                 return `${botOrTop}${colNm}`;
             };
             const getBarRowName = (rowIdx: number) => rowIdx === 0 ? "-" : "+";
@@ -391,13 +395,13 @@ namespace pxsim.visuals {
             let midGridRes = mkGrid({
                 xOffset: MID_GRID_X,
                 yOffset: MID_GRID_Y,
-                rowCount: MID_ROWS,
-                colCount: MID_COLS,
+                rowCount: BREADBOARD_MID_ROWS,
+                colCount: BREADBOARD_MID_COLS,
                 pinDist: PIN_DIST,
                 mkPin: mkBBPin,
                 mkHoverPin: mkBBHoverPin,
-                getRowName: getMidRowName,
-                getColName: getColName,
+                getRowName: getRowName,
+                getColName: getColumnName,
                 getGroupName: getMidGroupName,
                 rowIdxsWithGap: MID_ROW_GAPS,
             });
@@ -414,7 +418,7 @@ namespace pxsim.visuals {
                 mkPin: mkBBPin,
                 mkHoverPin: mkBBHoverPin,
                 getRowName: getBarRowName,
-                getColName: getColName,
+                getColName: getColumnName,
                 getGroupName: getBarGroupName,
                 colIdxsWithGap: BAR_COL_GAPS,
             });
@@ -432,7 +436,7 @@ namespace pxsim.visuals {
                 mkPin: mkBBPin,
                 mkHoverPin: mkBBHoverPin,
                 getRowName: getBarRowName,
-                getColName: getColName,
+                getColName: getColumnName,
                 getGroupName: getBarGroupName,
                 colIdxsWithGap: BAR_COL_GAPS.map(g => g + BAR_COLS),
             });
@@ -459,39 +463,39 @@ namespace pxsim.visuals {
             const mkBBLabelAtPin = (row: string, col: string, xOffset: number, yOffset: number, txt: string, group?: string): GridLabel => {
                 let size = PIN_LBL_SIZE;
                 let rotation = LBL_ROTATION;
-                let loc = this.getCoord([row, col]);
+                let loc = this.getCoord({type: "breadboard", row: row, col: col});
                 let [cx, cy] = loc;
                 let t = mkBBLabel(cx + xOffset, cy + yOffset, size, rotation, txt, group);
                 return t;
             }
 
             //columns
-            for (let colIdx = 0; colIdx < MID_COLS; colIdx++) {
-                let colNm = getColName(colIdx);
+            for (let colIdx = 0; colIdx < BREADBOARD_MID_COLS; colIdx++) {
+                let colNm = getColumnName(colIdx);
                 //top
                 let rowTIdx = 0;
-                let rowTNm = getMidRowName(rowTIdx);
+                let rowTNm = getRowName(rowTIdx);
                 let groupT = getMidGroupName(rowTIdx, colIdx);
                 let lblT = mkBBLabelAtPin(rowTNm, colNm, 0, -PIN_DIST, colNm, groupT);
                 this.allLabels.push(lblT);
                 //bottom
-                let rowBIdx = MID_ROWS - 1;
-                let rowBNm = getMidRowName(rowBIdx);
+                let rowBIdx = BREADBOARD_MID_ROWS - 1;
+                let rowBNm = getRowName(rowBIdx);
                 let groupB = getMidGroupName(rowBIdx, colIdx);
                 let lblB = mkBBLabelAtPin(rowBNm, colNm, 0, +PIN_DIST, colNm, groupB);
                 this.allLabels.push(lblB);
             }
             //rows
-            for (let rowIdx = 0; rowIdx < MID_ROWS; rowIdx++) {
-                let rowNm = getMidRowName(rowIdx);
+            for (let rowIdx = 0; rowIdx < BREADBOARD_MID_ROWS; rowIdx++) {
+                let rowNm = getRowName(rowIdx);
                 //top
                 let colTIdx = 0;
-                let colTNm = getColName(colTIdx);
+                let colTNm = getColumnName(colTIdx);
                 let lblT = mkBBLabelAtPin(rowNm, colTNm, -PIN_DIST, 0, rowNm);
                 this.allLabels.push(lblT);
                 //top
-                let colBIdx = MID_COLS - 1;
-                let colBNm = getColName(colBIdx);
+                let colBIdx = BREADBOARD_MID_COLS - 1;
+                let colBNm = getColumnName(colBIdx);
                 let lblB = mkBBLabelAtPin(rowNm, colBNm, +PIN_DIST, 0, rowNm);
                 this.allLabels.push(lblB);
             }
@@ -634,8 +638,8 @@ namespace pxsim.visuals {
             return {el: this.bb, y: 0, x: 0, w: WIDTH, h: HEIGHT};
         }
 
-        public highlightLoc(rowCol: BBRowCol) {
-            let [row, col] = rowCol;
+        public highlightLoc(rowCol: BBLoc) {
+            let {row, col} = rowCol;
             let pin = this.rowColToPin[row][col];
             let {cx, cy} = pin;
             let lbls = this.rowColToLbls[row][col];
diff --git a/sim/visuals/buttonpair.ts b/sim/visuals/buttonpair.ts
index 9ae5e7f4..2e326d52 100644
--- a/sim/visuals/buttonpair.ts
+++ b/sim/visuals/buttonpair.ts
@@ -92,7 +92,7 @@ namespace pxsim.visuals {
                 pointer-events:none;
             }
             `;
-    export class ButtonPairView implements IBoardComponent<ButtonPairState> {
+    export class ButtonPairView implements IBoardPart<ButtonPairState> {
         public element: SVGElement;
         public defs: SVGElement[];
         public style = BUTTON_PAIR_STYLE;
diff --git a/sim/visuals/genericpart.ts b/sim/visuals/genericpart.ts
index e31eee72..e14599b5 100644
--- a/sim/visuals/genericpart.ts
+++ b/sim/visuals/genericpart.ts
@@ -5,13 +5,13 @@ namespace pxsim.visuals {
             image: partVisual.image,
             width: partVisual.width,
             height: partVisual.height,
-            imageUnitDist: partVisual.pinDist,
+            imageUnitDist: partVisual.pinDistance,
             targetUnitDist: PIN_DIST
         });
         return imgAndSize;
     }
 
-    export class GenericPart implements IBoardComponent<any> {
+    export class GenericPart implements IBoardPart<any> {
         public style: string = "";
         public element: SVGElement;
         defs: SVGElement[] = [];
@@ -19,11 +19,6 @@ namespace pxsim.visuals {
         constructor(partVisual: PartVisualDefinition) {
             let imgAndSize = mkGenericPartSVG(partVisual);
             let img = imgAndSize.el;
-            let scaleFn = mkScaleFn(partVisual.pinDist, PIN_DIST);
-            let [pinX, pinY] = partVisual.firstPin;
-            let left = -scaleFn(pinX);
-            let top = -scaleFn(pinY);
-            translateEl(img, [left, top]); // So that 0,0 is on the first pin
             this.element = svg.elt("g");
             this.element.appendChild(img);
         }
@@ -33,7 +28,7 @@ namespace pxsim.visuals {
         }
 
         //unused
-        init(bus: EventBus, state: any, svgEl: SVGSVGElement, gpioPins: string[], otherArgs: string[]): void { }
+        init(bus: EventBus, state: any, svgEl: SVGSVGElement): void { }
         updateState(): void { }
         updateTheme(): void { }
     }
diff --git a/sim/visuals/ledmatrix.ts b/sim/visuals/ledmatrix.ts
index 971cbde8..44239a52 100644
--- a/sim/visuals/ledmatrix.ts
+++ b/sim/visuals/ledmatrix.ts
@@ -68,7 +68,7 @@ namespace pxsim.visuals {
             }
             `
 
-    export class LedMatrixView implements IBoardComponent<LedMatrixState> {
+    export class LedMatrixView implements IBoardPart<LedMatrixState> {
         private background: SVGElement;
         private ledsOuter: SVGElement[];
         private leds: SVGElement[];
diff --git a/sim/visuals/neopixel.ts b/sim/visuals/neopixel.ts
index 6a8c45d8..86777300 100644
--- a/sim/visuals/neopixel.ts
+++ b/sim/visuals/neopixel.ts
@@ -102,26 +102,17 @@ namespace pxsim.visuals {
         });
         return { el: img, x: l, y: t, w: w, h: h };
     }
-    export class NeoPixel implements SVGAndSize<SVGCircleElement> {
-        public el: SVGCircleElement;
-        public w: number;
-        public h: number;
-        public x: number;
-        public y: number;
-        public cx: number;
+    export class NeoPixel {
+        public el: SVGElement;
         public cy: number;
 
         constructor(xy: Coord = [0, 0]) {
-            let circle = <SVGCircleElement>svg.elt("circle");
+            let el = <SVGElement>svg.elt("rect");
             let r = PIXEL_RADIUS;
             let [cx, cy] = xy;
-            svg.hydrate(circle, { cx: cx, cy: cy, r: r, class: "sim-neopixel" });
-            this.el = circle;
-            this.w = r * 2;
-            this.h = r * 2;
-            this.x = cx - r;
-            this.y = cy - r;
-            this.cx = cx;
+            let y = cy - r;
+            svg.hydrate(el, { x: "-50%", y: y, width: "100%", height: r * 2, class: "sim-neopixel" });
+            this.el = el;
             this.cy = cy;
         }
 
@@ -200,9 +191,15 @@ namespace pxsim.visuals {
         }
     };
 
-    function gpioPinToPinNumber(gpioPin: string): number {
-        let pinNumStr = gpioPin.split("P")[1];
-        let pinNum = Number(pinNumStr) + 7 /*MICROBIT_ID_IO_P0; TODO: don't hardcode this, import enums.d.ts*/;
+    function digitalPinToPinNumber(gpioPin: string): number {
+        const MICROBIT_ID_IO_P0 = 7; //TODO: don't hardcode this, import enums.d.ts
+        if (gpioPin == "*") {
+            return MICROBIT_ID_IO_P0;
+        }
+        let pinSplit = gpioPin.split("DigitalPin.P");
+        U.assert(pinSplit.length === 2, "Unknown format for pin (for NeoPixel): " + gpioPin);
+        let pinNumStr = pinSplit[1];
+        let pinNum = Number(pinNumStr) + MICROBIT_ID_IO_P0;
         return pinNum
     }
     function parseNeoPixelMode(modeStr: string): NeoPixelMode {
@@ -222,7 +219,7 @@ namespace pxsim.visuals {
         return mode;
     }
 
-    export class NeoPixelView implements IBoardComponent<NeoPixelState> {
+    export class NeoPixelView implements IBoardPart<NeoPixelState> {
         public style: string = `
             .sim-neopixel-canvas {
             }
@@ -240,6 +237,7 @@ namespace pxsim.visuals {
             }
         `;
         public element: SVGElement;
+        public overElement: SVGElement;
         public defs: SVGElement[];
         private state: NeoPixelState;
         private canvas: NeoPixelCanvas;
@@ -249,22 +247,24 @@ namespace pxsim.visuals {
         private pin: number;
         private mode: NeoPixelMode;
 
-        public init(bus: EventBus, state: NeoPixelState, svgEl: SVGSVGElement, gpioPins: string[], otherArgs: string[]): void {
-            U.assert(otherArgs.length === 1, "NeoPixels assumes a RGB vs RGBW mode is passed to it");
-            let modeStr = otherArgs[0];
+        public init(bus: EventBus, state: NeoPixelState, svgEl: SVGSVGElement, otherParams: Map<string>): void {
+            U.assert(!!otherParams["mode"], "NeoPixels assumes a RGB vs RGBW mode is passed to it");
+            U.assert(!!otherParams["pin"], "NeoPixels assumes a pin is passed to it");
+            let modeStr = otherParams["mode"];
             this.mode = parseNeoPixelMode(modeStr);
             this.state = state;
             this.stripGroup = <SVGGElement>svg.elt("g");
             this.element = this.stripGroup;
-            let pinStr = gpioPins[0];
-            this.pin = gpioPinToPinNumber(pinStr);
+            let pinStr = otherParams["pin"];
+            this.pin = digitalPinToPinNumber(pinStr);
             this.lastLocation = [0, 0];
             let part = mkNeoPixelPart();
             this.part = part;
             this.stripGroup.appendChild(part.el);
             let canvas = new NeoPixelCanvas(this.pin);
             this.canvas = canvas;
-            let canvasG = svg.child(this.stripGroup, "g", { class: "sim-neopixel-canvas-parent" });
+            let canvasG = svg.elt("g", { class: "sim-neopixel-canvas-parent" });
+            this.overElement = canvasG;
             canvasG.appendChild(canvas.canvas);
             this.updateStripLoc();
         }
@@ -276,6 +276,7 @@ namespace pxsim.visuals {
         }
         private updateStripLoc() {
             let [x, y] = this.lastLocation;
+            U.assert(typeof x === "number" && typeof y === "number", "invalid x,y for NeoPixel strip");
             this.canvas.setLoc([x + CANVAS_LEFT, y + CANVAS_TOP]);
             svg.hydrate(this.part.el, { transform: `translate(${x} ${y})` }); //TODO: update part's l,h, etc.
         }
diff --git a/sim/visuals/wiring.ts b/sim/visuals/wiring.ts
index d5a0b693..b527b805 100644
--- a/sim/visuals/wiring.ts
+++ b/sim/visuals/wiring.ts
@@ -455,7 +455,7 @@ namespace pxsim.visuals {
             let wireEls: Wire;
             if (withCrocs && end.type == "dalboard") {
                 let boardPin = (<BoardLoc>end).pin;
-                if (boardPin == "P0" || boardPin == "P1" || boardPin == "P0" || boardPin == "GND" || boardPin == "+3v3" ) {
+                if (boardPin == "P0" || boardPin == "P1" || boardPin == "P2" || boardPin == "GND" || boardPin == "+3v3" ) {
                     //HACK
                     wireEls = this.drawWireWithCrocs(startLoc, endLoc, color);
                 } else {