diff --git a/libs/core/_locales/core-jsdoc-strings.json b/libs/core/_locales/core-jsdoc-strings.json
index 9b296a2d54b..e7cd982dd77 100644
--- a/libs/core/_locales/core-jsdoc-strings.json
+++ b/libs/core/_locales/core-jsdoc-strings.json
@@ -324,6 +324,8 @@
   "control.raiseEvent|param|src": "ID of the MicroBit Component that generated the event e.g. MICROBIT_ID_BUTTON_A.",
   "control.raiseEvent|param|value": "Component specific code indicating the cause of the event.",
   "control.ramSize": "Returns estimated size of memory in bytes.",
+  "control.rawOnEvent": "Registers an event handler.",
+  "control.rawUnregisterEvent": "Unregisters an event handler.",
   "control.reset": "Resets the BBC micro:bit.",
   "control.runInParallel": "Run other code in the parallel.",
   "control.runtimeWarning": "Display warning in the simulator.",
diff --git a/libs/core/codal.cpp b/libs/core/codal.cpp
index b1d3dc2b9df..b8ce34da6dd 100644
--- a/libs/core/codal.cpp
+++ b/libs/core/codal.cpp
@@ -102,6 +102,16 @@ void registerWithDal(int id, int event, Action a, int flags) {
     registerGCPtr(a);
 }
 
+// relies on making sure Action a is kept alive in STS
+void rawRegisterWithDal(int id, int event, Action a, int flags) {
+    uBit.messageBus.listen(id, event, dispatchForeground, a, (uint16_t) flags);
+}
+
+void rawUnregisterWithDal(int id, int event) {
+    uBit.messageBus.ignore(id, event, dispatchForeground);
+}
+
+
 void fiberDone(void *a) {
     decr((Action)a);
     unregisterGCPtr((Action)a);
diff --git a/libs/core/control.cpp b/libs/core/control.cpp
index 031c37e7b92..2d93c98c6d5 100644
--- a/libs/core/control.cpp
+++ b/libs/core/control.cpp
@@ -312,6 +312,23 @@ namespace control {
         registerWithDal(src, value, handler, (int)flags);
     }
 
+    /**
+     * Registers an event handler.
+     */
+    //%
+    void rawOnEvent(int src, int value, Action handler, int flags = 0) {
+        if (!flags) flags = ::EventFlags::QueueIfBusy;
+        rawRegisterWithDal(src, value, handler, (int)flags);
+    }
+
+    /**
+     * Unregisters an event handler.
+     */
+    //%
+    void rawUnregisterEvent(int src, int value) {
+        rawUnregisterWithDal(src, value);
+    }
+
     /**
     * Gets the value of the last event executed on the bus
     */
diff --git a/libs/core/shims.d.ts b/libs/core/shims.d.ts
index 6d4cdaaa8ed..8baca0673ef 100644
--- a/libs/core/shims.d.ts
+++ b/libs/core/shims.d.ts
@@ -420,6 +420,18 @@ declare namespace control {
     //% blockExternalInputs=1 flags.defl=0 shim=control::onEvent
     function onEvent(src: int32, value: int32, handler: () => void, flags?: int32): void;
 
+    /**
+     * Registers an event handler.
+     */
+    //% flags.defl=0 shim=control::rawOnEvent
+    function rawOnEvent(src: int32, value: int32, handler: () => void, flags?: int32): void;
+
+    /**
+     * Unregisters an event handler.
+     */
+    //% shim=control::rawUnregisterEvent
+    function rawUnregisterEvent(src: int32, value: int32): void;
+
     /**
      * Gets the value of the last event executed on the bus
      */
diff --git a/sim/state/misc.ts b/sim/state/misc.ts
index 83a9a662af4..128cb5da564 100644
--- a/sim/state/misc.ts
+++ b/sim/state/misc.ts
@@ -46,6 +46,21 @@ namespace pxsim.control {
         pxtcore.registerWithDal(id, evid, handler, flags)
     }
 
+    export function rawOnEvent(id: number, evid: number, handler: RefAction, flags: number) {
+        if (id == DAL.MICROBIT_ID_BUTTON_AB) {
+            const b = board().buttonPairState;
+            if (!b.usesButtonAB) {
+                b.usesButtonAB = true;
+                runtime.queueDisplayUpdate();
+            }
+        }
+        pxtcore.registerWithDal(id, evid, handler, flags)
+    }
+
+    export function rawUnregisterEvent(id: number, evid: number) {
+        // TODO
+    }
+
     export function eventTimestamp() {
         return board().bus.getLastEventTime()
     }
diff --git a/targetconfig.json b/targetconfig.json
index 33ddcae1ed3..34b1dbd7702 100644
--- a/targetconfig.json
+++ b/targetconfig.json
@@ -9,7 +9,7 @@
                 "tags": [ "Lights and Display" ],
                 "simx": {
                     "sha": "0825d56f78528c57af100a96abdfe2162f59945a",
-                    "devUrl": "http://localhost:3000"
+                    "devUrl": "https://microbit-apps.github.io/display-shield/"
                 }
             },
             "microsoft/pxt-microturtle": {