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#define  DMA_CH_1                                  1u 
#define  DMA_MAX_NBR_CH_USED                       2u
static   CPU_INT08U  DMA_AsHandleTbl[DMA_MAX_NBR_CH_USED];
 
static  CPU_BOOLEAN  USBD_Audio_DrvStreamStart (USBD_AUDIO_DRV  *p_audio_drv,
                                                CPU_INT08U       as_handle,
                                                CPU_INT08U       terminal_id_link)
{
    CPU_INT16U   buf_len;
    CPU_INT08U  *p_buf;


    (void)&p_audio_drv;

    if (terminal_id_link != Mic_OT_USB_IN_ID) {                               (1)
        return (DEF_FAIL);
    }

    DMA_AsHandleTbl[DMA_CH_1] = as_handle;                                    (2)
																
    /* $$$$ Enable record operations on audio chip if needed. */              (3)

    p_buf = (CPU_INT08U *)USBD_Audio_RecordBufGet(as_handle,                  (4)
                                                 &buf_len);
    if (p_buf == (CPU_INT08U *)0) {
        return (DEF_FAIL);
    }
 
    /* $$$$ Prepare initial DMA transfer. */							      (5)

    return (DEF_OK);
}

(1) You can verify if the stream processing is intended for the record path by checking the terminal ID associated to this stream. The function may be used to process also a playback stream. In that case, the terminal ID will differentiate the different streams.

(2) You should save the AudioStreaming interface handle locally to be used by the ISR managing audio data transfer. This handle is used by the functions USBD_Audio_RecordBufGet(), USBD_Audio_RecordRxCmpl and USBD_Audio_RecordBufFree().

(3) You may have to enable the record operations on the audio chip. It could be enabling some clocks, enabling some modules, etc. It may require sending a series of I2C commands for registers access,

(4) Call USBD_Audio_RecordBufGet() to get an empty record buffer.

(5) With this buffer, prepare the initial DMA transfer.

#define  DMA_CH_0                                  0u 
#define  DMA_MAX_NBR_CH_USED                       2u
static   CPU_INT08U  DMA_AsHandleTbl[DMA_MAX_NBR_CH_USED];
 
static  CPU_BOOLEAN  USBD_Audio_DrvStreamStart (USBD_AUDIO_DRV  *p_audio_drv,
                                                CPU_INT08U       as_handle,
                                                CPU_INT08U       terminal_id_link)
{
    CPU_INT16U   buf_len;
    CPU_INT08U  *p_buf;


    (void)&p_audio_drv;

    if (terminal_id_link != Speaker_IT_USB_OUT_ID) {						  (1)
        return (DEF_FAIL);
    }

    DMA_AsHandleTbl[DMA_CH_0] = as_handle;                                    (2)
																              
    /* $$$$ Enable playback operations on audio chip if needed. */            (3)


    USBD_Audio_PlaybackTxCmpl(as_handle);                                     (4)
    USBD_Audio_PlaybackTxCmpl(as_handle);

    return (DEF_OK);
}

(1) You can verify if the stream processing is intended for the playback path by checking the terminal ID associated to this stream. The function may be used to process also a record stream. In that case, the terminal ID will differentiate the different streams.

(2) You should save the AudioStreaming interface handle locally to be used by the ISR managing audio data transfer. This handle is used by the functions USBD_Audio_PlaybackTxCmpl and USBD_Audio_PlaybackBufFree().

(3) You may have to enable the playback operations on the audio chip. It could be enabling some clocks, enabling some modules, etc. It may require sending a series of I2C commands for registers access,

(4) Signal to the playback task the number of ready buffers that can be queued by calling USBD_Audio_PlaybackTxCmpl(). In this example, 2 playback buffers ready to be consumed can be queued. The playback task will receive 2 events CODEC XFER CMPL and will call USBD_Audio_DrvStreamPlaybackTx to provide to the code driver ready buffers. The codec driver could initiate for instance a DMA transfer from USBD_Audio_DrvStreamPlaybackTx() to start the streaming.