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# 3.3.2.3.7 Setting the Desired Audio Stream Sampling Rate

Sampling rate of an audio stream can be set using USB_HOST_AUDIO_V1_0_StreamSamplingRateSet function. Supported sampling rates for an audio stream is returned as part of USB_HOST_AUDIO_V1_0_STREAM_INFO by the USB_HOST_AUDIO_V1_0_StreamGetFirst and USB_HOST_AUDIO_V1_0_StreamGetNextfunctions. Return values of these function indicates if the request has been placed successfully or failed. When the set sampling rate request is completed the stream event handler generates an event USB_HOST_AUDIO_V1_0_STREAM_EVENT_SAMPLING_RATE_SET_COMPLETE. The event data USB_HOST_AUDIO_V1_0_STREAM_EVENT_SAMPLING_RATE_SET_COMPLETE_DATA has request handle and the requestStatus which indicates the set sampling request was accepted by the device or failed. The following code shows an example of how sampling rates can be set in an audio stream.

    /* This code shows an example of Set sampling rate to 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;
    bool isSampleRateSetComplete = 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;

             case USB_HOST_AUDIO_V1_0_STREAM_EVENT_SAMPLING_RATE_SET_COMPLETE:
                    /* Check eventData result member to know if stream enable is complete */
                    isSampleRateSetComplete = true;

                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)
                {
                    /* Set sampling rate 48000 Hz */
                    isSampleRateSetComplete = false;
                    streamResult = USB_HOST_AUDIO_V1_0_StreamSamplingRateSet
                                   (
                                       appData.outStreamHandle,
                                       &appData.requestHandle,
                                       48000
                                   );
                    if (streamResult != USB_HOST_AUDIO_V1_0_STREAM_SUCCESS)
                    {
                        appData.state = APP_STATE_ERROR;
                        break;
                    }
                    appData.state = APP_STATE_WAIT_FOR_SAMPLE_RATE_SET_COMPLETE;

                }
                break;
            case  APP_STATE_WAIT_FOR_SAMPLE_RATE_SET_COMPLETE:
                if (isSampleRateSetComplete == true)
                {
                    /* Set sampling rate completed */
                }
            default:
                break;
        }
    }