I2S (Inter-IC Sound) is a serial, synchronous communication protocol that is usually used for transmitting audio data between two digital audio devices.
Each I2S controller has the following features that can be configured using the I2S driver:
- Operation as system master or slave
- Capable of acting as transmitter or receiver
- Dedicated DMA controller that allows for streaming sample data without requiring the CPU to copy each data sample
Each controller can operate in half-duplex communication mode. Thus, the two controllers can be combined to establish full-duplex communication.
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 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.
..code-block:: c
static const i2s_pin_config_t pin_config = {
.bck_io_num = 26,
.ws_io_num = 25,
.data_out_num = 22,
.data_in_num = I2S_PIN_NO_CHANGE
};
i2s_set_pin(i2s_num, &pin_config);
Running I2S Communication
^^^^^^^^^^^^^^^^^^^^^^^^^
To perform a transmission:
- Prepare the data for sending
- Call the function :cpp:func:`i2s_write` and pass the data buffer address and data length to it
The function will write the data to the I2S DMA Tx buffer, and then the data will be transmitted automatically.
To retrieve received data, use the function :cpp:func:`i2s_read`. It will retrieve the data from the I2S 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`.
If the established communication is no longer required, the driver can be removed to free allocated resources by calling :cpp:func:`i2s_driver_uninstall`.
