static uint8_t  usbd_audio_Init (void  *pdev, uint8_t cfgidx)
{  
    /* Open EP OUT/IN */
    DCD_EP_Open(pdev, AUDIO_OUT_EP, AUDIO_OUT_PACKET, USB_OTG_EP_ISOC);
    DCD_EP_Open(pdev, AUDIO_IN_EP, AUDIO_IN_PACKET, USB_OTG_EP_ISOC);
    
        DCD_EP_Tx (pdev, AUDIO_IN_EP, bufs, 3);
        
    /* Initialize the Audio output Hardware layer */
    if (AUDIO_OUT_fops.Init(USBD_AUDIO_FREQ, DEFAULT_VOLUME, 0) != USBD_OK){ return USBD_FAIL; }

    /* Prepare Out endpoint to receive audio data */
    DCD_EP_PrepareRx(pdev, AUDIO_OUT_EP, (uint8_t*)IsocOutBuff, AUDIO_OUT_PACKET);

    return USBD_OK;
}

/* Configuration 1 */
0x09, /* bLength */
USB_CONFIGURATION_DESCRIPTOR_TYPE, /* bDescriptorType */
LOBYTE(AUDIO_CONFIG_DESC_SIZE), /* wTotalLength 118 bytes*/
HIBYTE(AUDIO_CONFIG_DESC_SIZE),
0x02, /* bNumInterfaces */
0x01, /* bConfigurationValue */
0x00, /* iConfiguration */
0xC0, /* bmAttributes BUS Powred*/
0x32, /* bMaxPower = 100 mA*/
/* 09 byte*/

/* USB Speaker Standard interface descriptor */
AUDIO_INTERFACE_DESC_SIZE, /* bLength */
USB_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
0x00, /* bInterfaceNumber */
0x00, /* bAlternateSetting */
0x00, /* bNumEndpoints */
USB_DEVICE_CLASS_AUDIO, /* bInterfaceClass */
AUDIO_SUBCLASS_AUDIOCONTROL, /* bInterfaceSubClass */
AUDIO_PROTOCOL_UNDEFINED, /* bInterfaceProtocol */
0x00, /* iInterface */
/* 09 byte*/

/* USB Speaker Class-specific AC Interface Descriptor */
AUDIO_INTERFACE_DESC_SIZE, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_CONTROL_HEADER, /* bDescriptorSubtype */
0x00, /* 1.00 */ /* bcdADC */
0x01,
0x27, /* wTotalLength = 39*/
0x00,
0x01, /* bInCollection */
0x01, /* baInterfaceNr */
/* 09 byte*/

/* USB Speaker Input Terminal Descriptor */
AUDIO_INPUT_TERMINAL_DESC_SIZE, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_CONTROL_INPUT_TERMINAL, /* bDescriptorSubtype */
0x01, /* bTerminalID */
0x01, /* wTerminalType AUDIO_TERMINAL_USB_STREAMING 0x0101 */
0x01,
0x00, /* bAssocTerminal */
0x02, /* bNrChannels */
0x03, /* wChannelConfig 0x0003 - Left&Right; 0x0000 - Mono; 0x0004 - FrontCenter */
0x00,
0x00, /* iChannelNames */
0x00, /* iTerminal */
/* 12 byte*/

/* USB Speaker Audio Feature Unit Descriptor */
0x09, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_CONTROL_FEATURE_UNIT, /* bDescriptorSubtype */
AUDIO_OUT_STREAMING_CTRL, /* bUnitID */
0x01, /* bSourceID */
0x01, /* bControlSize */
AUDIO_CONTROL_MUTE, /* bmaControls(0) */
0x00, /* bmaControls(1) */
0x00, /* iTerminal */
/* 09 byte*/

/*USB Speaker Output Terminal Descriptor */
0x09, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_CONTROL_OUTPUT_TERMINAL, /* bDescriptorSubtype */
0x03, /* bTerminalID */
0x02, /* wTerminalType 0x0302, headphones*/
0x03,
0x00, /* bAssocTerminal */
0x02, /* bSourceID */
0x00, /* iTerminal */
/* 09 byte*/

/* USB Speaker Standard AS Interface Descriptor - Audio Streaming Zero Bandwith */
/* Interface 1, Alternate Setting 0 */
AUDIO_INTERFACE_DESC_SIZE, /* bLength */
USB_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
0x01, /* bInterfaceNumber */
0x00, /* bAlternateSetting */
0x00, /* bNumEndpoints */
USB_DEVICE_CLASS_AUDIO, /* bInterfaceClass */
AUDIO_SUBCLASS_AUDIOSTREAMING, /* bInterfaceSubClass */
AUDIO_PROTOCOL_UNDEFINED, /* bInterfaceProtocol */
0x00, /* iInterface */
/* 09 byte*/

/* USB Speaker Standard AS Interface Descriptor - Audio Streaming Operational */
/* Interface 1, Alternate Setting 1 */
AUDIO_INTERFACE_DESC_SIZE, /* bLength */
USB_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
0x01, /* bInterfaceNumber */
0x01, /* bAlternateSetting */
0x02, /* bNumEndpoints */
USB_DEVICE_CLASS_AUDIO, /* bInterfaceClass */
AUDIO_SUBCLASS_AUDIOSTREAMING, /* bInterfaceSubClass */
AUDIO_PROTOCOL_UNDEFINED, /* bInterfaceProtocol */
0x00, /* iInterface */
/* 09 byte*/

/* USB Speaker Audio Streaming Interface Descriptor */
AUDIO_STREAMING_INTERFACE_DESC_SIZE, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_STREAMING_GENERAL, /* bDescriptorSubtype */
0x01, /* bTerminalLink */
0x00, /* bDelay */
0x01, /* wFormatTag AUDIO_FORMAT_PCM 0x0001*/
0x00,
/* 07 byte*/

/* USB Speaker Audio Type I Format Interface Descriptor */
0x0B, /* bLength */
AUDIO_INTERFACE_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_STREAMING_FORMAT_TYPE, /* bDescriptorSubtype */
AUDIO_FORMAT_TYPE_I, /* bFormatType */
0x02, /* bNrChannels */
AUDIO_FRAME_SIZE, /* bSubFrameSize; bytes per frame */
AUDIO_BITRESOLUTION, /* bBitResolution; bits per sample */
0x01, /* bSamFreqType only one frequency supported */
SAMPLE_FREQ(USBD_AUDIO_FREQ), /* Audio sampling frequency coded on 3 bytes */
/* 11 byte*/


/* Endpoint 1 - Standard Descriptor */
AUDIO_STANDARD_ENDPOINT_DESC_SIZE, /* bLength */
USB_ENDPOINT_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_OUT_EP, /* bEndpointAddress 1 out endpoint, 0х01*/
USB_ENDPOINT_TYPE_ISOCHRONOUS | (1<<2), /* bmAttributes, isochronus, async */
AUDIO_PACKET_SZE(USBD_AUDIO_FREQ), /* wMaxPacketSize in Bytes (Freq(Samples)*2(Stereo)*2(HalfWord)) */
0x01, /* bInterval */
0x01, /* bRefresh */
AUDIO_IN_EP, /* bSynchAddress */
/* 09 byte*/

/* Endpoint - Audio Streaming Descriptor*/
AUDIO_STREAMING_ENDPOINT_DESC_SIZE, /* bLength */
AUDIO_ENDPOINT_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_ENDPOINT_GENERAL, /* bDescriptor */
0x00, /* bmAttributes, default 0x00 */
0x00, /* bLockDelayUnits */
0x00, /* wLockDelay */
0x00,
/* 07 byte*/


/* Endpoint 2 - Standard Descriptor, FB */
AUDIO_STANDARD_ENDPOINT_DESC_SIZE, /* bLength */
USB_ENDPOINT_DESCRIPTOR_TYPE, /* bDescriptorType */
AUDIO_IN_EP, /* bEndpointAddress 2, in FB endpoint, 0х81*/
USB_ENDPOINT_TYPE_ISOCHRONOUS|(1<<4), /* bmAttributes, feedback endpoint(explict) */
0x03, 0x00, /* wMaxPacketSize in Bytes */
0x01, /* bInterval */
0x05, /* bRefresh */
0x00, /* bSynchAddress */
/* 09 byte*/