I2S (Inter-IC Sound) is a serial, synchronous communication protocol that is usually used for transmitting audio data between two digital audio devices.
{IDF_TARGET_NAME} contains {IDF_TARGET_I2S_NUM} I2S peripheral(s). These peripherals can be configured to input and output sample data via the I2S driver.
I2S0 output can be routed directly to the digital-to-analog converter's (DAC) output channels (GPIO 25 & GPIO 26) to produce direct analog output without involving any external I2S codecs. I2S0 can also be used for transmitting PDM (Pulse-density modulation) signals.
The I2S peripherals also support LCD mode for communicating data over a parallel bus, as used by some LCD displays and camera modules. LCD mode has the following operational modes:
For high accuracy clock applications, use the APLL_CLK clock source, which has the frequency range of 16 ~ 128 MHz. You can enable the APLL_CLK clock source by setting :cpp:member:`i2s_config_t::use_apll` to ``TRUE``.
If :cpp:member:`i2s_config_t::use_apll` = ``TRUE`` and :cpp:member:`i2s_config_t::fixed_mclk` > ``0``, then the master clock output frequency for I2S will be equal to the value of :cpp:member:`i2s_config_t::fixed_mclk`, which means that the mclk frequency is provided by the user, instead of being calculated by the driver.
The clock rate of the word select line, which is called audio left-right clock rate (LRCK) here, is always the divisor of the master clock output frequency and for which the following is always true: 0 < MCLK/LRCK/channels/bits_per_sample < 64.
Once the driver is installed, configure physical GPIO pins to which signals will be routed. For this, call the function :cpp:func`i2s_set_pin` and pass the following arguments to it:
- The structure :cpp:type:`i2s_pin_config_t` defining the GPIO pin numbers to which the driver should route the MCK, BCK, WS, DATA out, and DATA in signals. If you want to keep a currently allocated pin number for a specific signal, or if this signal is unused, then pass the macro :c:macro:`I2S_PIN_NO_CHANGE`. See the example below.
To retrieve received data, use the function :cpp:func:`i2s_read`. It will retrieve the data from the DMA Rx buffer, once the data is received by the I2S controller.
You can temporarily stop the I2S driver by calling the function :cpp:func:`i2s_stop`, which will disable the I2S Tx/Rx units until the function :cpp:func:`i2s_start` is called. If the function :cpp:func`i2s_driver_install` is used, the driver will start up automatically eliminating the need to call :cpp:func:`i2s_start`.
Deleting the Driver
^^^^^^^^^^^^^^^^^^^
If the established communication is no longer required, the driver can be removed to free allocated resources by calling :cpp:func:`i2s_driver_uninstall`.
I2S on {IDF_TARGET_NAME} support TDM mode, up to 16 channels are available in TDM mode. If you want to use TDM mode, set field ``channel_format`` of :cpp:type:`i2s_config_t` to ``I2S_CHANNEL_FMT_MULTIPLE``. Then enable the channels by setting ``chan_mask`` using masks in :cpp:type:`i2s_channel_t`, the number of active channels and total channels will be calculate automatically. Also you can set a particular total channel number for it, but it shouldn't be smaller than the largest channel you use.
If active channels are discrete, the inactive channels within total channels will be filled by a constant automatically. But if ``skip_msk`` is enabled, these inactive channels will be skiped.
For the applications that need a high frequency sample rate, sometimes the massive throughput of receiving data may cause data lost. Users can receive data lost event by registering an event queue handler to the driver during installation:
You will receive ``I2S_EVENT_RX_Q_OVF`` event when there are data lost.
Please follow these steps to prevent data lost:
1. Determine the interrupt interval. Generally, when data lost happened, the interval should be the bigger the better, it can help to reduce the interrupt times, i.e., ``dma_buf_len`` should be as big as possible while the DMA buffer size won't exceed its maximum value 4092. The relationships are::
2. Determine the ``dma_buf_count``. The ``dma_buf_count`` is decided by the max time of ``i2s_read`` polling cycle, all the received data are supposed to be stored between two ``i2s_read``. This cycle can be measured by a timer or an outputting gpio signal. The relationship is::
3. Determine the receiving buffer size. The receiving buffer that offered by user in ``i2s_read`` should be able to take all the data in all dma buffers, that means it should be bigger than the total size of all the dma buffers::
