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214 lines
7.7 KiB
ReStructuredText
214 lines
7.7 KiB
ReStructuredText
I2S
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===
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Overview
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--------
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I2S (Inter-IC Sound) is a serial, synchronous communication protocol that is usually used for transmitting audio data between two digital audio devices.
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ESP32 integrates two I2S controllers, referred to as I2S0 and I2S1, both of which can be used for streaming audio and video digital data.
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An I2S bus consists of the following lines:
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- Bit clock line
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- Channel select line
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- Serial data line
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Each I2S controller has the following features that can be configured using the I2S driver:
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- Operation as system master or slave
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- Capable of acting as transmitter or receiver
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- Dedicated DMA controller that allows for streaming sample data without requiring the CPU to copy each data sample
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Each controller can operate in half-duplex communication mode. Thus, the two controllers can be combined to establish full-duplex communication.
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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.
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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:
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- LCD master transmitting mode
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- Camera slave receiving mode
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- ADC/DAC mode
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For more information, see the `ESP32 Technical Reference Manual <https://espressif.com/sites/default/files/documentation/esp32_technical_reference_manual_en.pdf#page=306>`_.
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.. note::
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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``.
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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.
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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.
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Functional Overview
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-------------------
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Installing the Driver
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^^^^^^^^^^^^^^^^^^^^^
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Install the I2S driver by calling the function :cpp:func`i2s_driver_install` and passing the following arguments:
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- Port number
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- The structure :cpp:type:`i2s_config_t` with defined communication parameters
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- Event queue size and handle
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Configuration example:
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.. code-block:: c
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static const int i2s_num = 0; // i2s port number
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static const i2s_config_t i2s_config = {
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.mode = I2S_MODE_MASTER | I2S_MODE_TX,
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.sample_rate = 44100,
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.bits_per_sample = 16,
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.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
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.communication_format = I2S_COMM_FORMAT_I2S | I2S_COMM_FORMAT_I2S_MSB,
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.intr_alloc_flags = 0, // default interrupt priority
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.dma_buf_count = 8,
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.dma_buf_len = 64,
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.use_apll = false
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};
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i2s_driver_install(I2S_NUM, &i2s_config, 0, NULL);
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Setting Communication Pins
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^^^^^^^^^^^^^^^^^^^^^^^^^^
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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:
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- Port number
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- 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.
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.. code-block:: c
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static const i2s_pin_config_t pin_config = {
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.bck_io_num = 26,
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.ws_io_num = 25,
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.data_out_num = 22,
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.data_in_num = I2S_PIN_NO_CHANGE
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};
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i2s_set_pin(i2s_num, &pin_config);
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Running I2S Communication
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^^^^^^^^^^^^^^^^^^^^^^^^^
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To perform a transmission:
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- Prepare the data for sending
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- Call the function :cpp:func:`i2s_write` and pass the data buffer address and data length to it
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The function will write the data to the I2S DMA Tx buffer, and then the data will be transmitted automatically.
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.. code-block:: c
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i2s_write(I2S_NUM, samples_data, ((bits+8)/16)*SAMPLE_PER_CYCLE*4, &i2s_bytes_write, 100);
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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.
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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`.
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Deleting the Driver
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^^^^^^^^^^^^^^^^^^^
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If the established communication is no longer required, the driver can be removed to free allocated resources by calling :cpp:func:`i2s_driver_uninstall`.
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Application Example
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-------------------
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A code example for the I2S driver can be found in the directory :example:`peripherals/i2s`.
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In addition, there are two short configuration examples for the I2S driver.
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I2S configuration
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^^^^^^^^^^^^^^^^^
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.. code-block:: c
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#include "driver/i2s.h"
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#include "freertos/queue.h"
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static const int i2s_num = 0; // i2s port number
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static const i2s_config_t i2s_config = {
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.mode = I2S_MODE_MASTER | I2S_MODE_TX,
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.sample_rate = 44100,
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.bits_per_sample = 16,
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.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
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.communication_format = I2S_COMM_FORMAT_I2S | I2S_COMM_FORMAT_I2S_MSB,
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.intr_alloc_flags = 0, // default interrupt priority
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.dma_buf_count = 8,
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.dma_buf_len = 64,
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.use_apll = false
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};
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static const i2s_pin_config_t pin_config = {
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.bck_io_num = 26,
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.ws_io_num = 25,
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.data_out_num = 22,
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.data_in_num = I2S_PIN_NO_CHANGE
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};
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...
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i2s_driver_install(i2s_num, &i2s_config, 0, NULL); //install and start i2s driver
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i2s_set_pin(i2s_num, &pin_config);
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i2s_set_sample_rates(i2s_num, 22050); //set sample rates
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i2s_driver_uninstall(i2s_num); //stop & destroy i2s driver
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Configuring I2S to use internal DAC for analog output
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^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
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.. code-block:: c
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#include "driver/i2s.h"
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#include "freertos/queue.h"
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static const int i2s_num = 0; // i2s port number
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static const i2s_config_t i2s_config = {
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.mode = I2S_MODE_MASTER | I2S_MODE_TX | I2S_MODE_DAC_BUILT_IN,
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.sample_rate = 44100,
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.bits_per_sample = 16, /* the DAC module will only take the 8bits from MSB */
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.channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
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.communication_format = I2S_COMM_FORMAT_I2S_MSB,
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.intr_alloc_flags = 0, // default interrupt priority
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.dma_buf_count = 8,
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.dma_buf_len = 64,
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.use_apll = false
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};
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...
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i2s_driver_install(i2s_num, &i2s_config, 0, NULL); //install and start i2s driver
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i2s_set_pin(i2s_num, NULL); //for internal DAC, this will enable both of the internal channels
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//You can call i2s_set_dac_mode to set built-in DAC output mode.
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//i2s_set_dac_mode(I2S_DAC_CHANNEL_BOTH_EN);
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i2s_set_sample_rates(i2s_num, 22050); //set sample rates
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i2s_driver_uninstall(i2s_num); //stop & destroy i2s driver
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API Reference
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-------------
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.. include:: /_build/inc/i2s.inc
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.. include:: /_build/inc/i2s_types.inc
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