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# 3.3.2.3.6 Enabling Audio Stream

An audio stream must be enabled before doing any data transfer operation. An audio stream enable or disable can be scheduled by using USB_HOST_AUDIO_V1_0_StreamEnable or USB_HOST_AUDIO_V1_0_StreamEnable functions. Return values of these function indicates if the request has been placed successfully or failed. When the audio stream enable request is completed, stream event handler generates an event USB_HOST_AUDIO_V1_0_STREAM_EVENT_ENABLE_COMPLETE. Similarly it generates an event USB_HOST_AUDIO_V1_0_STREAM_EVENT_DISABLE_COMPLETE when stream disable is complete. The event data USB_HOST_AUDIO_V1_0_STREAM_EVENT_ENABLE_COMPLETE_DATA has details like request handle and termination status. The requestStatus member of the USB_HOST_AUDIO_V1_0_STREAM_EVENT_ENABLE_COMPLETE_DATA indicates if the request was success or failed. When audio stream multiple audio streams with an audio stream group cannot be enabled at the same time. The following code shows an example of how an Audio Stream is enabled.

    /* This code shows an example of enabling an audio stream */
    /* Specify the Audio Stream format details that this application supports */
    const APP_USB_HOST_AUDIO_STREAM_FORTMAT audioSpeakerStreamFormat =
    {

        .streamDirection = USB_HOST_AUDIO_V1_0_DIRECTION_OUT,
        .format = USB_AUDIO_FORMAT_PCM,
        .nChannels = 2,
        .bitResolution = 16,
        .subFrameSize = 2,
        .samplingRate = 48000
    };

    bool isAudioDeviceAttached = false;
    bool isStreamEnabled = false;
    USB_HOST_AUDIO_V1_0_OBJ audioDeviceObj;

    /*************************************************************
     * Audio Stream Event Handler function.
     ************************************************************/

    USB_HOST_AUDIO_V1_0_STREAM_EVENT_RESPONSE APP_USBHostAudioStreamEventHandler
    (
        USB_HOST_AUDIO_V1_0_STREAM_HANDLE streamHandle,
        USB_HOST_AUDIO_V1_0_STREAM_EVENT event,
        void * eventData,
        uintptr_t context
    )
    {
        USB_HOST_AUDIO_V1_0_STREAM_EVENT_WRITE_COMPLETE_DATA * writeCompleteEventData;
        switch(event)
        {
            case USB_HOST_AUDIO_V1_0_STREAM_EVENT_DISABLE_COMPLETE:

                break;

            case USB_HOST_AUDIO_V1_0_STREAM_EVENT_ENABLE_COMPLETE:
                /* Check eventData result member to know if stream enable is complete */
                    isStreamEnabled = true;

                break;
            case USB_HOST_AUDIO_V1_0_STREAM_EVENT_WRITE_COMPLETE:

                break;
            default:
                break;
        }
        return USB_HOST_AUDIO_V1_0_STREAM_EVENT_RESPONSE_NONE;
    }
    /*************************************************************/
    /* Function to search for a specific Audio Stream */
    /************************************************************/
    USB_HOST_AUDIO_V1_0_STREAM_OBJ App_USBHostAudioSpeakerStreamFind
    (
        USB_HOST_AUDIO_V1_0_OBJ audioDeviceObj,
        APP_USB_HOST_AUDIO_STREAM_FORTMAT audioStream,
        uint8_t* numberofStreamGroups
    )
    {
        USB_HOST_AUDIO_V1_0_RESULT result;
        USB_HOST_AUDIO_V1_0_STREAM_INFO streamInfo;

        /* Get Number of Stream Groups */
        *numberofStreamGroups = USB_HOST_AUDIO_V1_0_NumberOfStreamGroupsGet(audioDeviceObj);
        if (*numberofStreamGroups == 0)
        {
            return (USB_HOST_AUDIO_V1_0_STREAM_OBJ)0;
        }
        /* Get the First Stream Information in the Stream Group */
        result = USB_HOST_AUDIO_V1_0_StreamGetFirst(appData.audioDeviceObj, 0, &streamInfo);
        if (result == USB_HOST_AUDIO_V1_0_RESULT_SUCCESS)
        {
             /* Compare Audio Stream info */
              if ((streamInfo.format == audioStream.format)
                && (streamInfo.streamDirection == audioStream.streamDirection)
                        && (streamInfo.nChannels == audioStream.nChannels)
                        && (streamInfo.bitResolution == audioStream.bitResolution)
                        && (streamInfo.subFrameSize == audioStream.subFrameSize))
            {
                return streamInfo.streamObj;
            }
        }
        return (USB_HOST_AUDIO_V1_0_STREAM_OBJ)0;
    }

    /*************************************************************/
    /* Audio attach event listener function */
    /************************************************************/
    void APP_USBHostAudioAttachEventListener
    (
        USB_HOST_AUDIO_V1_0_OBJ audioObj,
        USB_HOST_AUDIO_V1_0_EVENT event,
        uintptr_t context
    )
    {
        /* This function gets called when the Audio v1.0 device is attached/detached. In this
         * example we let the application know that a device is attached and we
         * store the Audio v1.0 device object. This object will be required to open the
         * device. */
        switch (event)
        {
            case USB_HOST_AUDIO_V1_0_EVENT_ATTACH:
                if (isAudioDeviceAttached == false)
                {
                    isAudioDeviceAttached = true;
                    audioDeviceObj = audioObj;
                }
                else
                {
                    /* This application supports only one Audio Device . Handle Error Here.*/
                }
            break;
            case USB_HOST_AUDIO_V1_0_EVENT_DETACH:
                if (isAudioDeviceAttached == true)
                {
                    /* This means the device was detached. There is no event data
                     * associated with this event.*/
                    isAudioDeviceAttached = false;
                    break;
                }
            break;
        }
    }

    /*************************************************************/
    /* Audio Tasks function */
    /************************************************************/
    void APP_Tasks ( void )
    {
        USB_HOST_AUDIO_V1_0_RESULT audioResult;
        USB_HOST_AUDIO_V1_0_STREAM_RESULT streamResult;

        /* Check the application's current state. */
        switch ( appData.state )
        {
            case APP_STATE_BUS_ENABLE:

                /* Register a callback for Audio Device Attach. */
                audioResult = USB_HOST_AUDIO_V1_0_AttachEventHandlerSet
                              (
                                  &APP_USBHostAudioAttachEventListener,
                                  (uintptr_t)0
                              );

                if (audioResult == USB_HOST_AUDIO_V1_0_RESULT_SUCCESS )
                {
                    /* Set Host Event Handler */
                    USB_HOST_EventHandlerSet(APP_USBHostEventHandler, 0);
                    USB_HOST_BusEnable(0);
                    /* Advance application state */
                    appData.state = APP_STATE_WAIT_FOR_BUS_ENABLE_COMPLETE;
                }
                break;

            case APP_STATE_WAIT_FOR_BUS_ENABLE_COMPLETE:
                if(USB_HOST_BusIsEnabled(0))
                {
                    appData.state = APP_STATE_WAIT_FOR_DEVICE_ATTACH;
                }
                break;

            case APP_STATE_WAIT_FOR_DEVICE_ATTACH:
                /* Check if an Audio Device has been attached  */
                if(appData.isAudioDeviceAttached == true)
                {
                    appData.nAudioStreamGroups = 0;
                    /* Find an Audio Stream matching to our requirement */
                    appData.ouStreamObj = App_USBHostAudioSpeakerStreamFind
                                          (
                                              appData.audioDeviceObj,
                                              audioSpeakerStreamFormat,
                                              &appData.nAudioStreamGroups
                                          );
                    if (appData.nAudioStreamGroups == 0)
                    {
                        appData.state = APP_STATE_ERROR;
                        break;
                    }

                    /* Open Audio Stream */
                    appData.outStreamHandle = USB_HOST_AUDIO_V1_0_StreamOpen
                                              (
                                                  appData.ouStreamObj
                                              );

                    if (appData.outStreamHandle == USB_HOST_AUDIO_V1_0_STREAM_HANDLE_INVALID)
                    {
                        appData.state = APP_STATE_ERROR;
                        break;
                    }

                    /* Set Stream Event Handler  */
                    streamResult = USB_HOST_AUDIO_V1_0_StreamEventHandlerSet
                                   (
                                       appData.outStreamHandle,
                                       APP_USBHostAudioStreamEventHandler,
                                       (uintptr_t)appData.ouStreamObj
                                   );

                    if (streamResult != USB_HOST_AUDIO_V1_0_STREAM_SUCCESS)
                    {
                        appData.state = APP_STATE_ERROR;
                        break;
                    }
                    appData.state = APP_STATE_ENABLE_AUDIO_STREAM;
                }
                break;

                case  APP_STATE_ENABLE_AUDIO_STREAM:
                    isStreamEnableComplete = false;
                     /* Set default interface setting of the streaming interface */
                    streamResult = USB_HOST_AUDIO_V1_0_StreamEnable
                                   (
                                       appData.outStreamHandle,
                                       &appData.requestHandle
                                   );
                    if (streamResult != USB_HOST_AUDIO_V1_0_STREAM_SUCCESS)
                    {
                        appData.state = APP_STATE_ERROR;
                        break;
                    }
                    appData.state = APP_STATE_WAIT_FOR_ENABLE_AUDIO_STREAM;
                break;
            case  APP_STATE_WAIT_FOR_ENABLE_AUDIO_STREAM:
                if (isStreamEnabled == true)
                {
                    /* stream enable complete*/
                }
                break;

            default:
                break;
        }
    }