I2S

I2S

About

I2S - Inter-IC Sound, correctly written I²S pronounced "eye-squared-ess", alternative notation is IIS. I²S is an electrical serial bus interface standard used for connecting digital audio devices together.

It is used to communicate PCM (Pulse-Code Modulation) audio data between integrated circuits in an electronic device. The I²S bus separates clock and serial data signals, resulting in simpler receivers than those required for asynchronous communications systems that need to recover the clock from the data stream.

Despite the similar name, I²S is unrelated and incompatible with the bidirectional I²C (IIC) bus.

The I²S bus consists of at least three lines:

.. note:: All lines can be attached to almost any pin and this change can occur even during operation.

• Bit clock line

  • Officially "continuous serial clock (SCK)". Typically written "bit clock (BCLK)".
  • In this library function parameter sck.

• Word clock line

  • Officially "word select (WS)". Typically called "left-right clock (LRCLK)" or "frame sync (FS)".
  • 0 = Left channel, 1 = Right channel
  • In this library function parameter ws.

• Data line

  • Officially "serial data (SD)", but can be called SDATA, SDIN, SDOUT, DACDAT, ADCDAT, etc.
  • Unlike Arduino I2S with single data pin switching between input and output, in ESP core driver use separate data line for input and output.
  • Output data line is called dout for function parameter.
  • Input data line is called din for function parameter.

It may also include a Master clock line:

• Master clock

  • Officially "master clock (MCLK)".
  • This is not a part of I2S bus, but is used to synchronize multiple I2S devices.
  • In this library function parameter mclk.

.. note:: Please check the ESP-IDF documentation <https://docs.espressif.com/projects/esp-idf/en/latest/esp32/api-reference/peripherals/i2s.html>_ for more details on the I2S peripheral for each ESP32 chip.

I2S Configuration

Master / Slave Mode

In Master mode (default) the device is generating clock signal sck and word select signal on ws.

In Slave mode the device listens on attached pins for the clock signal and word select - i.e. unless externally driven the pins will remain LOW. This mode is not supported yet.

Operation Modes

Setting the operation mode is done with function begin and is set by function parameter mode.

• I2S_MODE_STD In standard mode, there are always two sound channels, i.e., the left and right channels, which are called "slots". These slots support 8/16/24/32-bit width sample data. The communication format for the slots follows the Philips standard.

• I2S_MODE_TDM In Time Division Multiplexing mode (TDM), the number of sound channels is variable, and the width of each channel is fixed.

• I2S_MODE_PDM_TX PDM (Pulse-density Modulation) mode for the TX channel can convert PCM data into PDM format which always has left and right slots. PDM TX is only supported on I2S0 and it only supports 16-bit width sample data. It needs at least a CLK pin for clock signal and a DOUT pin for data signal.

• I2S_MODE_PDM_RX PDM (Pulse-density Modulation) mode for RX channel can receive PDM-format data and convert the data into PCM format. PDM RX is only supported on I2S0, and it only supports 16-bit width sample data. PDM RX needs at least a CLK pin for clock signal and a DIN pin for data signal.

Simplex / Duplex Mode

Due to the different clock sources the PDM modes are always in Simplex mode, using only one data pin.

The STD and TDM modes operate in the Duplex mode, using two separate data pins:

• Output pin dout for function parameter
• Input pin din for function parameter

In this mode, the driver is able to read and write simultaneously on each line and is suitable for applications like walkie-talkie or phone.

Data Bit Width

This is the number of bits in a channel sample. The data bit width is set by function parameter bits_cfg. The current supported values are:

• I2S_DATA_BIT_WIDTH_8BIT
• I2S_DATA_BIT_WIDTH_16BIT
• I2S_DATA_BIT_WIDTH_24BIT, requires the MCLK multiplier to be manually set to 384
• I2S_DATA_BIT_WIDTH_32BIT

Sample Rate

The sample rate is set by function parameter rate. It is the number of samples per second in Hz.

Slot Mode

The slot mode is set by function parameter ch. The current supported values are:

• I2S_SLOT_MODE_MONO I2S channel slot format mono. Transmit the same data in all slots for TX mode. Only receive the data in the first slots for RX mode.

• I2S_SLOT_MODE_STEREO I2S channel slot format stereo. Transmit different data in different slots for TX mode. Receive the data in all slots for RX mode.

Arduino-ESP32 I2S API

Initialization and deinitialization

Before initialization, set which pins you want to use.

begin (Master Mode) ^^^^^^^^^^^^^^^^^^^

Before usage choose which pins you want to use.

.. code-block:: arduino

bool begin(i2s_mode_t mode, uint32_t rate, i2s_data_bit_width_t bits_cfg, i2s_slot_mode_t ch, int8_t slot_mask=-1)

Parameters:

• [in] mode one of above mentioned operation mode, for example I2S_MODE_STD.

• [in] rate is the sampling rate in Hz, for example 16000.

• [in] bits_cfg is the number of bits in a channel sample, for example I2S_DATA_BIT_WIDTH_16BIT.

• [in] ch is the slot mode, for example I2S_SLOT_MODE_STEREO.

• [in] slot_mask is the slot mask, for example 0b11. This parameter is optional and defaults to -1 (not used).

This function will return true on success or fail in case of failure.

When failed, an error message will be printed if the correct log level is set.

end ^^^

Performs safe deinitialization - free buffers, destroy task, end driver operation, etc.

.. code-block:: arduino

void end()

Pin setup

The function to set the pins will depend on the operation mode.

setPins ^^^^^^^

Set the pins for the I2S interface when using the standard or TDM mode.

.. code-block:: arduino

void setPins(int8_t bclk, int8_t ws, int8_t dout, int8_t din=-1, int8_t mclk=-1)

Parameters:

• [in] bclk is the bit clock pin.

• [in] ws is the word select pin.

• [in] dout is the data output pin. Can be set to -1 if not used.

• [in] din is the data input pin. This parameter is optional and defaults to -1 (not used).

• [in] mclk is the master clock pin. This parameter is optional and defaults to -1 (not used).

setPinsPdmTx ^^^^^^^^^^^^

Set the pins for the I2S interface when using the PDM TX mode.

.. code-block:: arduino

void setPinsPdmTx(int8_t clk, int8_t dout0, int8_t dout1=-1)

Parameters:

• [in] clk is the clock pin.

• [in] dout0 is the data output pin 0.

• [in] dout1 is the data output pin 1. This parameter is optional and defaults to -1 (not used).

setPinsPdmRx ^^^^^^^^^^^^

Set the pins for the I2S interface when using the PDM RX mode.

.. code-block:: arduino

void setPinsPdmRx(int8_t clk, int8_t din0, int8_t din1=-1, int8_t din2=-1, int8_t din3=-1)

Parameters:

• [in] clk is the clock pin.

• [in] din0 is the data input pin 0.

• [in] din1 is the data input pin 1. This parameter is optional and defaults to -1 (not used).

• [in] din2 is the data input pin 2. This parameter is optional and defaults to -1 (not used).

• [in] din3 is the data input pin 3. This parameter is optional and defaults to -1 (not used).

setInverted ^^^^^^^^^^^

Set which pins have inverted logic when using the standard or TDM mode. Data pins cannot be inverted.

.. code-block:: arduino

void setInverted(bool bclk, bool ws, bool mclk=false)

Parameters:

• [in] bclk true if the bit clock pin is inverted. False otherwise.

• [in] ws true if the word select pin is inverted. False otherwise.

• [in] mclk true if the master clock pin is inverted. False otherwise. This parameter is optional and defaults to false.

setInvertedPdm ^^^^^^^^^^^^^^

Set which pins have inverted logic when using the PDM mode. Data pins cannot be inverted.

.. code-block:: arduino

void setInvertedPdm(bool clk)

Parameters:

• [in] clk true if the clock pin is inverted. False otherwise.

I2S Configuration

The I2S configuration can be changed during operation.

configureTX ^^^^^^^^^^^

Configure the I2S TX channel.

.. code-block:: arduino

bool configureTX(uint32_t rate, i2s_data_bit_width_t bits_cfg, i2s_slot_mode_t ch, int8_t slot_mask=-1)

Parameters:

• [in] rate is the sampling rate in Hz, for example 16000.

• [in] bits_cfg is the number of bits in a channel sample, for example I2S_DATA_BIT_WIDTH_16BIT.

• [in] ch is the slot mode, for example I2S_SLOT_MODE_STEREO.

• [in] slot_mask is the slot mask, for example 0b11. This parameter is optional and defaults to -1 (not used).

This function will return true on success or fail in case of failure.

When failed, an error message will be printed if the correct log level is set.

configureRX ^^^^^^^^^^^

Configure the I2S RX channel.

.. code-block:: arduino

bool configureRX(uint32_t rate, i2s_data_bit_width_t bits_cfg, i2s_slot_mode_t ch, i2s_rx_transform_t transform=I2S_RX_TRANSFORM_NONE)

Parameters:

• [in] rate is the sampling rate in Hz, for example 16000.

• [in] bits_cfg is the number of bits in a channel sample, for example I2S_DATA_BIT_WIDTH_16BIT.

• [in] ch is the slot mode, for example I2S_SLOT_MODE_STEREO.

• [in] transform is the transform mode, for example I2S_RX_TRANSFORM_NONE. This can be used to apply a transformation/conversion to the received data. The supported values are: I2S_RX_TRANSFORM_NONE (no transformation), I2S_RX_TRANSFORM_32_TO_16 (convert from 32 bits of data width to 16 bits) and I2S_RX_TRANSFORM_16_STEREO_TO_MONO (convert from stereo to mono when using 16 bits of data width).

This function will return true on success or fail in case of failure.

When failed, an error message will be printed if the correct log level is set.

txChan ^^^^^^

Get the TX channel handler pointer.

.. code-block:: arduino

i2s_chan_handle_t txChan()

txSampleRate ^^^^^^^^^^^^

Get the TX sample rate.

.. code-block:: arduino

uint32_t txSampleRate()

txDataWidth ^^^^^^^^^^^

Get the TX data width (8, 16 or 32 bits).

.. code-block:: arduino

i2s_data_bit_width_t txDataWidth()

txSlotMode ^^^^^^^^^^

Get the TX slot mode (stereo or mono).

.. code-block:: arduino

i2s_slot_mode_t txSlotMode()

rxChan ^^^^^^

Get the RX channel handler pointer.

.. code-block:: arduino

i2s_chan_handle_t rxChan()

rxSampleRate ^^^^^^^^^^^^

Get the RX sample rate.

.. code-block:: arduino

uint32_t rxSampleRate()

rxDataWidth ^^^^^^^^^^^

Get the RX data width (8, 16 or 32 bits).

.. code-block:: arduino

i2s_data_bit_width_t rxDataWidth()

rxSlotMode ^^^^^^^^^^

Get the RX slot mode (stereo or mono).

.. code-block:: arduino

i2s_slot_mode_t rxSlotMode()

I/O Operations

readBytes ^^^^^^^^^

Read a certain amount of data bytes from the I2S interface.

.. code-block:: arduino

size_t readBytes(char *buffer, size_t size)

Parameters:

• [in] buffer is the buffer to store the read data. The buffer must be at least size bytes long.

• [in] size is the number of bytes to read.

This function will return the number of bytes read.

read ^^^^

Read the next available byte from the I2S interface.

.. code-block:: arduino

int read()

This function will return the next available byte or -1 if no data is available or an error occurred.

write

There are two versions of the write function:

The first version writes a certain amount of data bytes to the I2S interface.

.. code-block:: arduino

size_t write(uint8_t *buffer, size_t size)

Parameters:

• [in] buffer is the buffer containing the data to be written.

• [in] size is the number of bytes to write from the buffer.

This function will return the number of bytes written.

The second version writes a single byte to the I2S interface.

.. code-block:: arduino

size_t write(uint8_t d)

Parameters:

• [in] d is the byte to be written.

This function will return 1 if the byte was written or 0 if an error occurred.

available ^^^^^^^^^

Get if there is data available to be read.

.. code-block:: arduino

int available()

This function will return I2S_READ_CHUNK_SIZE if there is data available to be read or -1 if not.

peek ^^^^

Get the next available byte from the I2S interface without removing it from the buffer. Currently not implemented.

.. code-block:: arduino

int peek()

This function will currently always return -1.

lastError ^^^^^^^^^

Get the last error code for an I/O operation on the I2S interface.

.. code-block:: arduino

int lastError()

recordWAV ^^^^^^^^^

Record a short PCM WAV to memory with the current RX settings. Returns a buffer that must be freed by the user.

.. code-block:: arduino

uint8_t * recordWAV(size_t rec_seconds, size_t * out_size)

Parameters:

• [in] rec_seconds is the number of seconds to record.

• [out] out_size is the size of the returned buffer in bytes.

This function will return a pointer to the buffer containing the recorded WAV data or NULL if an error occurred.

playWAV ^^^^^^^

Play a PCM WAV from memory with the current TX settings.

.. code-block:: arduino

void playWAV(uint8_t * data, size_t len)

Parameters:

• [in] data is the buffer containing the WAV data.

• [in] len is the size of the buffer in bytes.

playMP3 ^^^^^^^

Play a MP3 from memory with the current TX settings.

.. code-block:: arduino

bool playMP3(uint8_t *src, size_t src_len)

Parameters:

• [in] src is the buffer containing the MP3 data.

• [in] src_len is the size of the buffer in bytes.

This function will return true on success or false in case of failure.

When failed, an error message will be printed if the correct log level is set.

Sample code

.. code-block:: arduino

#include <ESP_I2S.h>

const int buff_size = 128; int available_bytes, read_bytes; uint8_t buffer[buff_size]; I2SClass I2S;

void setup() { I2S.setPins(5, 25, 26, 35, 0); //SCK, WS, SDOUT, SDIN, MCLK I2S.begin(I2S_MODE_STD, 16000, I2S_DATA_BIT_WIDTH_16BIT, I2S_SLOT_MODE_STEREO); I2S.read(); available_bytes = I2S.available(); if(available_bytes < buff_size) { read_bytes = I2S.readBytes(buffer, available_bytes); } else { read_bytes = I2S.readBytes(buffer, buff_size); } I2S.write(buffer, read_bytes); I2S.end(); }

void loop() {}