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usbd_audio_drv_<codec-name>.h / usbd_audio_drv_<codec-name>.c
Prototype
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static void USBD_Audio_DrvStreamPlaybackTx (USBD_AUDIO_DRV *p_audio_drv,
CPU_INT08U terminal_id_link,
void *p_buf,
CPU_INT16U buf_len,
USBD_ERR *p_err);
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Arguments
p_audio_drv
Pointer to audio driver structure.
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This listing shows an example usage of this function.
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| Listing - USBD_Audio_DrvStreamPlaybackTx() Example Usage |
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| Listing - USBD_Audio_DrvStreamPlaybackTx() Example Usage |
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| language | cpp |
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| title | Listing - USBD_Audio_DrvStreamPlaybackTx() Example Usage |
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| linenumbers | true |
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#define DMA_CH_0 0u
#define DMA_MAX_NBR_CH_USED 2u
static CPU_INT08U DMA_AsHandleTbl[DMA_MAX_NBR_CH_USED];
static void USBD_Audio_DrvStreamPlaybackTx (USBD_AUDIO_DRV *p_audio_drv,
CPU_INT08U terminal_id_link,
void *p_buf,
CPU_INT16U buf_len,
USBD_ERR *p_err)
{
/* $$$$ Store ready playback buffer. */ (1)
/* $$$$ Prepare DMA transfer for initial buffer. */ (2)
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(1) The ready buffer provided by the audio class could be stored internally into the codec driver using any buffer memory management method (for example a circular buffer). Then the stored ready buffer could be retrieved by the audio peripheral ISR. | Tip |
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The Audio Peripheral Driver should support at least double-buffering to optimize the playback streaming. |
(2) If the Audio Peripheral driver support buffer queuing, you may accumulate a certain number of ready buffers (for instance, 2 buffers should be enough). When the buffers accumulation is done, you should prepare the initial DMA transfer. When the stream is launched, the next DMA transfer may be prepared in an interrupt context when the current DMA transfer completes. | Tip |
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If the peripheral managing audio data transfer can work with a DMA controller, we recommend using DMA transfers. It will improve overall audio performance by offloading the CPU. As opposed to CPU copies involved for FIFO transfers that would be time-consuming. |
(3) In case of error, you may return the error code USBD_ERR_TX. |