diff --git a/soundtrigger/2.0/ISoundTriggerHwCallback.hal b/soundtrigger/2.0/ISoundTriggerHwCallback.hal
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+++ b/soundtrigger/2.0/ISoundTriggerHwCallback.hal
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+/*
+ * Copyright 2016 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.soundtrigger@2.0;
+
+import android.hardware.audio.common@2.0;
+
+interface ISoundTriggerHwCallback {
+    enum RecognitionStatus : uint32_t {
+        SUCCESS  = 0,
+        ABORT    = 1,
+        FAILURE  = 2,
+    };
+
+    enum SoundModelStatus : uint32_t {
+        UPDATED  = 0,
+    };
+
+    /*
+     * Generic recognition event sent via recognition callback
+     */
+    struct RecognitionEvent {
+        /* Recognition status e.g. SUCCESS */
+        RecognitionStatus status;
+        /* Sound model type for this event. e.g SoundModelType.TYPE_KEYPHRASE */
+        SoundModelType    type;
+        /* Handle of loaded sound model which triggered the event */
+        SoundModelHandle  model;
+        /* It is possible to capture audio from this */
+        /* utterance buffered by the implementation */
+        bool              captureAvailable;
+        /* Audio session ID. framework use */
+        int32_t           captureSession;
+        /* Delay in ms between end of model detection and start of audio
+        /* available for capture. A negative value is possible
+         * (e.g. if key phrase is also available for capture */
+        int32_t           captureDelayMs;
+        /* Duration in ms of audio captured before the start of the trigger.
+         * 0 if none. */
+        int32_t           capturePreambleMs;
+        /* The opaque data is the capture of the trigger sound */
+        bool              triggerInData;
+        /* Audio format of either the trigger in event data or to use for
+         * capture of the rest of the utterance */
+        AudioConfig       audioConfig;
+        /* Opaque event data */
+        vec<uint8_t>      data;
+    };
+
+    /*
+     * Specialized recognition event for key phrase recognitions
+     */
+    struct PhraseRecognitionEvent {
+        /* Common part of the recognition event */
+        RecognitionEvent common;
+        /* List of descriptors for each recognized key phrase */
+        vec<PhraseRecognitionExtra> phraseExtras;
+    };
+
+    /*
+     * Event sent via load sound model callback
+     */
+    struct ModelEvent {
+         /* Sound model status e.g. SoundModelStatus.UPDATED */
+        SoundModelStatus status;
+        /* Loaded sound model that triggered the event */
+        SoundModelHandle model;
+        /* Opaque event data, passed transparently by the framework */
+        vec<uint8_t>     data;
+    };
+
+    typedef int32_t CallbackCookie;
+
+    /*
+     * Callback method called by the HAL when the sound recognition triggers
+     * @param event A RecognitionEvent structure containing detailed results
+     *              of the recognition triggered
+     * @param cookie The cookie passed by the framework when recognition was
+     *               started (see ISoundtriggerHw.startRecognition()
+     */
+    recognitionCallback(RecognitionEvent event, CallbackCookie cookie);
+    /*
+     * Callback method called by the HAL when the sound model loading completes
+     * @param event A ModelEvent structure containing detailed results of the
+     *              model loading operation
+     * @param cookie The cookie passed by the framework when loading was
+     *               initiated (see ISoundtriggerHw.loadSoundModel()
+     */
+    soundModelCallback(ModelEvent event, CallbackCookie cookie);
+};