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@@ -97,8 +97,22 @@ typedef struct {
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i2s_channel_fmt_t channel_format; /*!< I2S channel format.*/
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i2s_comm_format_t communication_format; /*!< I2S communication format */
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int intr_alloc_flags; /*!< Flags used to allocate the interrupt. One or multiple (ORred) ESP_INTR_FLAG_* values. See esp_intr_alloc.h for more info */
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- int dma_buf_count; /*!< I2S DMA Buffer Count */
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- int dma_buf_len; /*!< I2S DMA Buffer Length */
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+ int dma_buf_count; /**< The total number of DMA buffers to receive/transmit data.
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+ * A descriptor includes some information such as buffer address,
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+ * the address of the next descriptor, and the buffer length.
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+ * Since one descriptor points to one buffer, therefore, 'dma_desc_num' can be interpreted as the total number of DMA buffers used to store data from DMA interrupt.
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+ * Notice that these buffers are internal to'i2s_read' and descriptors are created automatically inside of the I2S driver.
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+ * Users only need to set the buffer number while the length is derived from the parameter described below.
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+ */
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+ int dma_buf_len; /**< Number of frames in a DMA buffer.
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+ * A frame means the data of all channels in a WS cycle.
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+ * The real_dma_buf_size = dma_buf_len * chan_num * bits_per_chan / 8.
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+ * For example, if two channels in stereo mode (i.e., 'channel_format' is set to 'I2S_CHANNEL_FMT_RIGHT_LEFT') are active,
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+ * and each channel transfers 32 bits (i.e., 'bits_per_sample' is set to 'I2S_BITS_PER_CHAN_32BIT'),
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+ * then the total number of bytes of a frame is 'channel_format' * 'bits_per_sample' = 2 * 32 / 8 = 8 bytes.
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+ * We assume that the current 'dma_buf_len' is 100, then the real length of the DMA buffer is 8 * 100 = 800 bytes.
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+ * Note that the length of an internal real DMA buffer shouldn't be greater than 4092.
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+ */
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bool use_apll; /*!< I2S using APLL as main I2S clock, enable it to get accurate clock */
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bool tx_desc_auto_clear; /*!< I2S auto clear tx descriptor if there is underflow condition (helps in avoiding noise in case of data unavailability) */
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int fixed_mclk; /*!< I2S using fixed MCLK output. If use_apll = true and fixed_mclk > 0, then the clock output for i2s is fixed and equal to the fixed_mclk value. If fixed_mclk set, mclk_multiple won't take effect */
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laokaiyao