diff --git a/contexthub/1.2/Android.bp b/contexthub/1.2/Android.bp
index e819482..9722a97 100644
--- a/contexthub/1.2/Android.bp
+++ b/contexthub/1.2/Android.bp
@@ -6,6 +6,7 @@
     srcs: [
         "types.hal",
         "IContexthub.hal",
+        "IContexthubCallback.hal",
     ],
     interfaces: [
         "android.hardware.contexthub@1.0",
diff --git a/contexthub/1.2/IContexthub.hal b/contexthub/1.2/IContexthub.hal
index 819fc1d..3488b74 100644
--- a/contexthub/1.2/IContexthub.hal
+++ b/contexthub/1.2/IContexthub.hal
@@ -16,11 +16,41 @@
 
 package android.hardware.contexthub@1.2;
 
+import @1.0::Result;
 import @1.1::IContexthub;
 import @1.1::SettingValue;
+import IContexthubCallback;
 
 interface IContexthub extends @1.1::IContexthub {
     /**
+     * Register a callback for the HAL implementation to send asynchronous
+     * messages to the service from a context hub. There can be a maximum of
+     * one callback registered with the HAL. A call to this function when a
+     * callback has already been registered must override the previous
+     * registration.
+     *
+     * @param hubId    identifier for the hub
+     * @param callback an implementation of the IContextHubCallbacks
+     *
+     * @return result OK on success
+     *                BAD_VALUE if parameters are not valid
+     *
+     */
+    registerCallback_1_2(uint32_t hubId, IContexthubCallback cb) generates (Result result);
+
+    /**
+     * Send a message to a hub
+     *
+     * @param hubId identifier for hub to send message to
+     * @param msg   message to be sent
+     *
+     * @return result OK if successful, error code otherwise
+     *                BAD_VALUE if parameters are not valid
+     *                TRANSACTION_FAILED if message send failed
+     */
+    sendMessageToHub_1_2(uint32_t hubId, ContextHubMsg msg) generates (Result result);
+
+    /**
      * Notification sent by the framework to indicate that the user
      * has changed a setting.
      *
diff --git a/contexthub/1.2/IContexthubCallback.hal b/contexthub/1.2/IContexthubCallback.hal
new file mode 100644
index 0000000..0236160
--- /dev/null
+++ b/contexthub/1.2/IContexthubCallback.hal
@@ -0,0 +1,45 @@
+/*
+ * Copyright (C) 2020 The Android Open Source Project
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *      http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package android.hardware.contexthub@1.2;
+
+import @1.0::IContexthubCallback;
+
+interface IContexthubCallback extends @1.0::IContexthubCallback {
+    /**
+     * This callback is passed by the Contexthub service to the HAL
+     * implementation to allow the HAL to send asynchronous messages back
+     * to the service and registered clients of the ContextHub service.
+     *
+     * @param msg message that should be delivered to host app clients
+     *
+     */
+    handleClientMsg_1_2(ContextHubMsg msg);
+
+    /**
+     * This callback is passed by the Contexthub service to the HAL
+     * implementation to allow the HAL to send information about the
+     * currently loaded and active nanoapps on the hub.
+     *
+     * @param appInfo vector of HubAppinfo structure for each nanoApp
+     *                on the hub that can be enabled, disabled and
+     *                unloaded by the service. Any nanoApps that cannot
+     *                be controlled by the service must not be reported.
+     *                All nanoApps that can be controlled by the service
+     *                must be reported.
+     */
+    handleAppsInfo_1_2(vec<HubAppInfo> appInfo);
+};
diff --git a/contexthub/1.2/types.hal b/contexthub/1.2/types.hal
index 38f9f7a..e6c8acc 100644
--- a/contexthub/1.2/types.hal
+++ b/contexthub/1.2/types.hal
@@ -16,6 +16,8 @@
 
 package android.hardware.contexthub@1.2;
 
+import @1.0::ContextHubMsg;
+import @1.0::HubAppInfo;
 import @1.1::Setting;
 
 /**
@@ -32,3 +34,36 @@
     WIFI_AVAILABLE,
     AIRPLANE_MODE,
 };
+
+struct ContextHubMsg {
+    @1.0::ContextHubMsg msg_1_0;
+
+    /**
+     * The list of Android permissions that the sender of this message has at
+     * the time the message was sent.
+     *
+     * The HAL MUST drop messages to nanoapps if this list of permissions is not
+     * a superset of those of the receiving nanoapp(s).
+     *
+     * The framework MUST drop messages to host apps that don't have a superset
+     * of the permissions that the sending nanoapp is using.
+     */
+    vec<string> permissions;
+};
+
+struct HubAppInfo {
+    @1.0::HubAppInfo info_1_0;
+
+    /**
+     * The list of Android permissions used by this nanoapp. This list MUST
+     * correspond to the permissions required for an equivalent Android app to
+     * sample similar signals through the Android framework.
+     *
+     * For example, if a nanoapp used location-based signals, the permissions
+     * list MUST contains android.permission.ACCESS_FINE_LOCATION and
+     * android.permission.ACCESS_BACKGROUND_LOCATION. If it were to also list to
+     * audio data, it would require adding android.permission.RECORD_AUDIO to
+     * this list.
+     */
+    vec<string> permissions;
+};