Inter-IC Sound (I2S)

Overview

I2S (Inter-IC Sound) is a serial, synchronous communication protocol that is usually used for transmitting audio data between two digital audio devices.

ESP32-S2 contains one I2S peripheral(s). These peripherals can be configured to input and output sample data via the I2S driver.

An I2S bus consists of the following lines:

  • Master clock line (operational)

  • Bit clock line

  • Channel select line

  • Serial data line

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

  • 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.

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:

  • LCD master transmitting mode

  • Camera slave receiving mode

  • ADC/DAC mode

For more information, see ESP32-S2 Technical Reference Manual > I2S Controller (I2S) > LCD Mode [PDF].

Note

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 i2s_config_t::use_apll to TRUE.

If i2s_config_t::use_apll = TRUE and i2s_config_t::fixed_mclk > 0, then the master clock output frequency for I2S will be equal to the value of 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.

Functional Overview

Installing the Driver

Install the I2S driver by calling the function :cpp:func`i2s_driver_install` and passing the following arguments:

  • Port number

  • The structure i2s_config_t with defined communication parameters

  • Event queue size and handle

Once :cpp:func`i2s_driver_install` returns ESP_OK, it means I2S has started.

Configuration example:

static const int i2s_num = 0; // i2s port number

i2s_config_t i2s_config = {
    .mode = I2S_MODE_MASTER | I2S_MODE_TX,
    .sample_rate = 44100,
    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
    .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
    .communication_format = I2S_COMM_FORMAT_STAND_I2S
    .tx_desc_auto_clear = false,
    .dma_buf_count = 8,
    .dma_buf_len = 64,
    .use_apll = false,
    .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1  // Interrupt level 1, default 0
};

i2s_driver_install(I2S_NUM, &i2s_config, 0, NULL);

Setting Communication Pins

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:

  • Port number

  • The structure 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 I2S_PIN_NO_CHANGE. See the example below.

Note

MCK only takes effect in I2S_MODE_MASTER mode.

static const i2s_pin_config_t pin_config = {
    .mck_io_num = 0,
    .bck_io_num = 4,
    .ws_io_num = 5,
    .data_out_num = 18,
    .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 i2s_write() and pass the data buffer address and data length to it

The function will write the data to the DMA Tx buffer, and then the data will be transmitted automatically.

i2s_write(I2S_NUM, samples_data, ((bits+8)/16)*SAMPLE_PER_CYCLE*4, &i2s_bytes_write, 100);

To retrieve received data, use the function i2s_read(). It will retrieve the data from the DMA Rx buffer, once the data is received by the I2S controller.

i2s_read(I2S_NUM, data_recv, ((bits+8)/16)*SAMPLE_PER_CYCLE*4, &i2s_bytes_read, 100);

You can temporarily stop the I2S driver by calling the function i2s_stop(), which will disable the I2S Tx/Rx units until the function 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 i2s_start().

Deleting the Driver

If the established communication is no longer required, the driver can be removed to free allocated resources by calling i2s_driver_uninstall().

Application Example

A code example for the I2S driver can be found in the directory peripherals/i2s.

In addition, there is a short configuration examples for the I2S driver.

I2S configuration

Example for general usage.

#include "driver/i2s.h"

static const int i2s_num = 0; // i2s port number

i2s_config_t i2s_config = {
    .mode = I2S_MODE_MASTER | I2S_MODE_TX,
    .sample_rate = 44100,
    .bits_per_sample = I2S_BITS_PER_SAMPLE_16BIT,
    .channel_format = I2S_CHANNEL_FMT_RIGHT_LEFT,
    .communication_format = I2S_COMM_FORMAT_STAND_I2S
    .tx_desc_auto_clear = false,
    .dma_buf_count = 8,
    .dma_buf_len = 64,
    .use_apll = false,
    .intr_alloc_flags = ESP_INTR_FLAG_LEVEL1  // Interrupt level 1, default 0
};

static const i2s_pin_config_t pin_config = {
    .bck_io_num = 4,
    .ws_io_num = 5,
    .data_out_num = 18,
    .data_in_num = I2S_PIN_NO_CHANGE
};

i2s_driver_install(i2s_num, &i2s_config, 0, NULL);   //install and start i2s driver
i2s_set_pin(i2s_num, &pin_config);

...
/* You can reset parameters by calling 'i2s_set_clk'
 *
 * The low 16 bits are the valid data bits in one chan and the high 16 bits are
 * the total bits in one chan. If high 16 bits is smaller than low 16 bits, it will
 * be set to a same value as low 16 bits.
 */
uint32_t bits_cfg = (I2S_BITS_PER_CHAN_32BIT << 16) | I2S_BITS_PER_SAMPLE_16BIT;
i2s_set_clk(i2s_num, 22050, bits_cfg, I2S_CHANNEL_STEREO);
...

i2s_driver_uninstall(i2s_num); //stop & destroy i2s driver

API Reference

Functions

esp_err_t i2s_set_pin(i2s_port_t i2s_num, const i2s_pin_config_t *pin)

Set I2S pin number.

Inside the pin configuration structure, set I2S_PIN_NO_CHANGE for any pin where the current configuration should not be changed.

Note

The I2S peripheral output signals can be connected to multiple GPIO pads. However, the I2S peripheral input signal can only be connected to one GPIO pad.

Parameters
  • i2s_num: I2S port number

  • pin: I2S Pin structure, or NULL to set 2-channel 8-bit internal DAC pin configuration (GPIO25 & GPIO26)

Note

if *pin is set as NULL, this function will initialize both of the built-in DAC channels by default. if you don’t want this to happen and you want to initialize only one of the DAC channels, you can call i2s_set_dac_mode instead.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

  • ESP_FAIL IO error

esp_err_t i2s_driver_install(i2s_port_t i2s_num, const i2s_config_t *i2s_config, int queue_size, void *i2s_queue)

Install and start I2S driver.

This function must be called before any I2S driver read/write operations.

Parameters
  • i2s_num: I2S port number

  • i2s_config: I2S configurations - see i2s_config_t struct

  • queue_size: I2S event queue size/depth.

  • i2s_queue: I2S event queue handle, if set NULL, driver will not use an event queue.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

  • ESP_ERR_NO_MEM Out of memory

  • ESP_ERR_NOT_FOUND I2S port is not found or has been installed by others (e.g. LCD i80)

esp_err_t i2s_driver_uninstall(i2s_port_t i2s_num)

Uninstall I2S driver.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

  • ESP_ERR_INVALID_STATE I2S port has been uninstalled by others (e.g. LCD i80)

Parameters
  • i2s_num: I2S port number

esp_err_t i2s_write(i2s_port_t i2s_num, const void *src, size_t size, size_t *bytes_written, TickType_t ticks_to_wait)

Write data to I2S DMA transmit buffer.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

Parameters
  • i2s_num: I2S port number

  • src: Source address to write from

  • size: Size of data in bytes

  • [out] bytes_written: Number of bytes written, if timeout, the result will be less than the size passed in.

  • ticks_to_wait: TX buffer wait timeout in RTOS ticks. If this many ticks pass without space becoming available in the DMA transmit buffer, then the function will return (note that if the data is written to the DMA buffer in pieces, the overall operation may still take longer than this timeout.) Pass portMAX_DELAY for no timeout.

esp_err_t i2s_write_expand(i2s_port_t i2s_num, const void *src, size_t size, size_t src_bits, size_t aim_bits, size_t *bytes_written, TickType_t ticks_to_wait)

Write data to I2S DMA transmit buffer while expanding the number of bits per sample. For example, expanding 16-bit PCM to 32-bit PCM.

Format of the data in source buffer is determined by the I2S configuration (see i2s_config_t).

Parameters
  • i2s_num: I2S port number

  • src: Source address to write from

  • size: Size of data in bytes

  • src_bits: Source audio bit

  • aim_bits: Bit wanted, no more than 32, and must be greater than src_bits

  • [out] bytes_written: Number of bytes written, if timeout, the result will be less than the size passed in.

  • ticks_to_wait: TX buffer wait timeout in RTOS ticks. If this many ticks pass without space becoming available in the DMA transmit buffer, then the function will return (note that if the data is written to the DMA buffer in pieces, the overall operation may still take longer than this timeout.) Pass portMAX_DELAY for no timeout.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

esp_err_t i2s_read(i2s_port_t i2s_num, void *dest, size_t size, size_t *bytes_read, TickType_t ticks_to_wait)

Read data from I2S DMA receive buffer.

Note

If the built-in ADC mode is enabled, we should call i2s_adc_enable and i2s_adc_disable around the whole reading process, to prevent the data getting corrupted.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

Parameters
  • i2s_num: I2S port number

  • dest: Destination address to read into

  • size: Size of data in bytes

  • [out] bytes_read: Number of bytes read, if timeout, bytes read will be less than the size passed in.

  • ticks_to_wait: RX buffer wait timeout in RTOS ticks. If this many ticks pass without bytes becoming available in the DMA receive buffer, then the function will return (note that if data is read from the DMA buffer in pieces, the overall operation may still take longer than this timeout.) Pass portMAX_DELAY for no timeout.

esp_err_t i2s_set_sample_rates(i2s_port_t i2s_num, uint32_t rate)

Set sample rate used for I2S RX and TX.

The bit clock rate is determined by the sample rate and i2s_config_t configuration parameters (number of channels, bits_per_sample).

bit_clock = rate * (number of channels) * bits_per_sample

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

  • ESP_ERR_NO_MEM Out of memory

Parameters
  • i2s_num: I2S port number

  • rate: I2S sample rate (ex: 8000, 44100…)

esp_err_t i2s_stop(i2s_port_t i2s_num)

Stop I2S driver.

There is no need to call i2s_stop() before calling i2s_driver_uninstall().

Disables I2S TX/RX, until i2s_start() is called.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

Parameters
  • i2s_num: I2S port number

esp_err_t i2s_start(i2s_port_t i2s_num)

Start I2S driver.

It is not necessary to call this function after i2s_driver_install() (it is started automatically), however it is necessary to call it after i2s_stop().

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

Parameters
  • i2s_num: I2S port number

esp_err_t i2s_zero_dma_buffer(i2s_port_t i2s_num)

Zero the contents of the TX DMA buffer.

Pushes zero-byte samples into the TX DMA buffer, until it is full.

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

Parameters
  • i2s_num: I2S port number

esp_err_t i2s_set_clk(i2s_port_t i2s_num, uint32_t rate, uint32_t bits_cfg, i2s_channel_t ch)

Set clock & bit width used for I2S RX and TX.

Similar to i2s_set_sample_rates(), but also sets bit width.

  1. stop i2s;

  2. calculate mclk, bck, bck_factor

  3. malloc dma buffer;

  4. start i2s

Return

  • ESP_OK Success

  • ESP_ERR_INVALID_ARG Parameter error

  • ESP_ERR_NO_MEM Out of memory

Parameters
  • i2s_num: I2S port number

  • rate: I2S sample rate (ex: 8000, 44100…)

  • bits_cfg: I2S bits configuration the low 16 bits is for data bits per sample in one channel (see ‘i2s_bits_per_sample_t’) the high 16 bits is for total bits in one channel (see ‘i2s_bits_per_chan_t’) high 16bits =0 means same as the bits per sample.

  • ch: I2S channel, (I2S_CHANNEL_MONO, I2S_CHANNEL_STEREO or specific channel in TDM mode)

float i2s_get_clk(i2s_port_t i2s_num)

get clock set on particular port number.

Return

  • actual clock set by i2s driver

Parameters
  • i2s_num: I2S port number

Structures

struct i2s_pin_config_t

I2S pin number for i2s_set_pin.

Public Members

int mck_io_num

MCK in out pin

int bck_io_num

BCK in out pin

int ws_io_num

WS in out pin

int data_out_num

DATA out pin

int data_in_num

DATA in pin

struct i2s_driver_config_t

I2S driver configuration parameters.

Public Members

i2s_mode_t mode

I2S work mode

uint32_t sample_rate

I2S sample rate

i2s_bits_per_sample_t bits_per_sample

I2S sample bits in one channel

i2s_channel_fmt_t channel_format

I2S channel format.

i2s_comm_format_t communication_format

I2S communication format

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

int dma_buf_count

I2S DMA Buffer Count

int dma_buf_len

I2S DMA Buffer Length

bool use_apll

I2S using APLL as main I2S clock, enable it to get accurate clock

bool tx_desc_auto_clear

I2S auto clear tx descriptor if there is underflow condition (helps in avoiding noise in case of data unavailability)

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

i2s_mclk_multiple_t mclk_multiple

The multiple of I2S master clock(MCLK) to sample rate

i2s_bits_per_chan_t bits_per_chan

I2S total bits in one channel, only take effect when larger than ‘bits_per_sample’, default ‘0’ means equal to ‘bits_per_sample’

struct i2s_event_t

Event structure used in I2S event queue.

Public Members

i2s_event_type_t type

I2S event type

size_t size

I2S data size for I2S_DATA event

Macros

I2S_PIN_NO_CHANGE

Use in i2s_pin_config_t for pins which should not be changed

Type Definitions

typedef i2s_driver_config_t i2s_config_t
typedef intr_handle_t i2s_isr_handle_t

Enumerations

enum i2s_port_t

I2S port number, the max port number is (I2S_NUM_MAX -1).

Values:

I2S_NUM_0 = 0

I2S port 0

I2S_NUM_MAX

I2S port max

enum i2s_event_type_t

I2S event queue types.

Values:

I2S_EVENT_DMA_ERROR
I2S_EVENT_TX_DONE

I2S DMA finish sent 1 buffer

I2S_EVENT_RX_DONE

I2S DMA finish received 1 buffer

I2S_EVENT_TX_Q_OVF

I2S DMA sent queue overflow

I2S_EVENT_RX_Q_OVF

I2S DMA receive queue overflow

I2S_EVENT_MAX

I2S event max index

Enumerations

enum i2s_bits_per_sample_t

I2S bit width per sample.

Values:

I2S_BITS_PER_SAMPLE_8BIT = 8

data bit-width: 8

I2S_BITS_PER_SAMPLE_16BIT = 16

data bit-width: 16

I2S_BITS_PER_SAMPLE_24BIT = 24

data bit-width: 24

I2S_BITS_PER_SAMPLE_32BIT = 32

data bit-width: 32

enum i2s_bits_per_chan_t

I2S bit width per chan.

Values:

I2S_BITS_PER_CHAN_DEFAULT = (0)

channel bit-width equals to data bit-width

I2S_BITS_PER_CHAN_8BIT = (8)

channel bit-width: 8

I2S_BITS_PER_CHAN_16BIT = (16)

channel bit-width: 16

I2S_BITS_PER_CHAN_24BIT = (24)

channel bit-width: 24

I2S_BITS_PER_CHAN_32BIT = (32)

channel bit-width: 32

enum i2s_channel_t

I2S channel.

Values:

I2S_CHANNEL_MONO = (0x01 << 31) | 0x03

I2S channel (mono), two channel enabled. In this mode, you only need to send one channel data but the fifo will copy same data for another channel automatically, then both channels will transmit same data. The highest bit is for differentiating I2S_CHANNEL_STEREO since they both use two channels

I2S_CHANNEL_STEREO = 0x03

I2S channel (stereo), two channel enabled. In this mode, two channels will transmit different data.

enum i2s_comm_format_t

I2S communication standard format.

Values:

I2S_COMM_FORMAT_STAND_I2S = 0X01

I2S communication I2S Philips standard, data launch at second BCK

I2S_COMM_FORMAT_STAND_MSB = 0X02

I2S communication MSB alignment standard, data launch at first BCK

I2S_COMM_FORMAT_STAND_PCM_SHORT = 0x04

PCM Short standard, also known as DSP mode. The period of synchronization signal (WS) is 1 bck cycle.

I2S_COMM_FORMAT_STAND_PCM_LONG = 0x0C

PCM Long standard. The period of synchronization signal (WS) is channel_bit*bck cycles.

I2S_COMM_FORMAT_STAND_MAX

standard max

I2S_COMM_FORMAT_I2S = 0x01

I2S communication format I2S, correspond to I2S_COMM_FORMAT_STAND_I2S

I2S_COMM_FORMAT_I2S_MSB = 0x01

I2S format MSB, (I2S_COMM_FORMAT_I2S |I2S_COMM_FORMAT_I2S_MSB) correspond to I2S_COMM_FORMAT_STAND_I2S

I2S_COMM_FORMAT_I2S_LSB = 0x02

I2S format LSB, (I2S_COMM_FORMAT_I2S |I2S_COMM_FORMAT_I2S_LSB) correspond to I2S_COMM_FORMAT_STAND_MSB

I2S_COMM_FORMAT_PCM = 0x04

I2S communication format PCM, correspond to I2S_COMM_FORMAT_STAND_PCM_SHORT

I2S_COMM_FORMAT_PCM_SHORT = 0x04

PCM Short, (I2S_COMM_FORMAT_PCM | I2S_COMM_FORMAT_PCM_SHORT) correspond to I2S_COMM_FORMAT_STAND_PCM_SHORT

I2S_COMM_FORMAT_PCM_LONG = 0x08

PCM Long, (I2S_COMM_FORMAT_PCM | I2S_COMM_FORMAT_PCM_LONG) correspond to I2S_COMM_FORMAT_STAND_PCM_LONG

enum i2s_channel_fmt_t

I2S channel format type.

Values:

I2S_CHANNEL_FMT_RIGHT_LEFT

Separated left and right channel

I2S_CHANNEL_FMT_ALL_RIGHT

Load right channel data in both two channels

I2S_CHANNEL_FMT_ALL_LEFT

Load left channel data in both two channels

I2S_CHANNEL_FMT_ONLY_RIGHT

Only load data in right channel (mono mode)

I2S_CHANNEL_FMT_ONLY_LEFT

Only load data in left channel (mono mode)

enum i2s_mode_t

I2S Mode.

Values:

I2S_MODE_MASTER = (0x1 << 0)

Master mode

I2S_MODE_SLAVE = (0x1 << 1)

Slave mode

I2S_MODE_TX = (0x1 << 2)

TX mode

I2S_MODE_RX = (0x1 << 3)

RX mode

I2S_MODE_PDM = (0x1 << 6)

I2S PDM mode

enum i2s_clock_src_t

I2S source clock.

Values:

I2S_CLK_D2CLK = 0

Clock from PLL_D2_CLK(160M)

I2S_CLK_APLL

Clock from APLL

enum i2s_mclk_multiple_t

The multiple of mclk to sample rate.

Values:

I2S_MCLK_MULTIPLE_DEFAULT = 0

Default value. mclk = sample_rate * 256

I2S_MCLK_MULTIPLE_128 = 128

mclk = sample_rate * 128

I2S_MCLK_MULTIPLE_256 = 256

mclk = sample_rate * 256

I2S_MCLK_MULTIPLE_384 = 384

mclk = sample_rate * 384