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I2S

Overview

The I2S (Inter-IC Sound) API provides support for the standard I2S interface as well as common non-standard extensions such as PCM Short/Long Frame Sync and Left/Right Justified Data Formats.

Configuration Options

Related configuration options:

API Reference

group i2s_interface

I2S (Inter-IC Sound) Interface.

The I2S API provides support for the standard I2S interface standard as well as common non-standard extensions such as PCM Short/Long Frame Sync, Left/Right Justified Data Format.

Defines

I2S_FMT_DATA_FORMAT_SHIFT

Data Format bit field position.

I2S_FMT_DATA_FORMAT_MASK

Data Format bit field mask.

I2S_FMT_DATA_FORMAT_I2S

Standard I2S Data Format.

Serial data is transmitted in two’s complement with the MSB first. Both Word Select (WS) and Serial Data (SD) signals are sampled on the rising edge of the clock signal (SCK). The MSB is always sent one clock period after the WS changes. Left channel data are sent first indicated by WS = 0, followed by right channel data indicated by WS = 1. 

   -. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
SCK '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '
   -.                               .-------------------------------.
WS  '-------------------------------'                               '----
   -.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.
SD  |   |MSB|   |...|   |LSB| x |...| x |MSB|   |...|   |LSB| x |...| x |
   -'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'
        | Left channel                  | Right channel                 |

I2S_FMT_DATA_FORMAT_PCM_SHORT

PCM Short Frame Sync Data Format.

Serial data is transmitted in two’s complement with the MSB first. Both Word Select (WS) and Serial Data (SD) signals are sampled on the falling edge of the clock signal (SCK). The falling edge of the frame sync signal (WS) indicates the start of the PCM word. The frame sync is one clock cycle long. An arbitrary number of data words can be sent in one frame. 

     .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
SCK -' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-
     .---.                                                       .---.
WS  -'   '-                                                     -'   '-
    -.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---
SD   |   |MSB|   |...|   |LSB|MSB|   |...|   |LSB|MSB|   |...|   |LSB|
    -'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---
         | Word 1            | Word 2            | Word 3  |  Word n |

I2S_FMT_DATA_FORMAT_PCM_LONG

PCM Long Frame Sync Data Format.

Serial data is transmitted in two’s complement with the MSB first. Both Word Select (WS) and Serial Data (SD) signals are sampled on the falling edge of the clock signal (SCK). The rising edge of the frame sync signal (WS) indicates the start of the PCM word. The frame sync has an arbitrary length, however it has to fall before the start of the next frame. An arbitrary number of data words can be sent in one frame. 

     .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
SCK -' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-
         .--- ---.    ---.        ---.                               .---
WS      -'       '-      '-          '-                             -'
    -.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---
SD   |   |MSB|   |...|   |LSB|MSB|   |...|   |LSB|MSB|   |...|   |LSB|
    -'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---
         | Word 1            | Word 2            | Word 3  |  Word n |

I2S_FMT_DATA_FORMAT_LEFT_JUSTIFIED

Left Justified Data Format.

Serial data is transmitted in two’s complement with the MSB first. Both Word Select (WS) and Serial Data (SD) signals are sampled on the rising edge of the clock signal (SCK). The bits within the data word are left justified such that the MSB is always sent in the clock period following the WS transition. Left channel data are sent first indicated by WS = 1, followed by right channel data indicated by WS = 0. 

     .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
SCK -' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-
       .-------------------------------.                               .-
WS  ---'                               '-------------------------------'
    ---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.-
SD     |MSB|   |...|   |LSB| x |...| x |MSB|   |...|   |LSB| x |...| x |
    ---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'-
       | Left channel                  | Right channel                 |

I2S_FMT_DATA_FORMAT_RIGHT_JUSTIFIED

Right Justified Data Format.

Serial data is transmitted in two’s complement with the MSB first. Both Word Select (WS) and Serial Data (SD) signals are sampled on the rising edge of the clock signal (SCK). The bits within the data word are right justified such that the LSB is always sent in the clock period preceding the WS transition. Left channel data are sent first indicated by WS = 1, followed by right channel data indicated by WS = 0. 

     .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-. .-.
SCK -' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-' '-
       .-------------------------------.                               .-
WS  ---'                               '-------------------------------'
    ---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.---.-
SD     | x |...| x |MSB|   |...|   |LSB| x |...| x |MSB|   |...|   |LSB|
    ---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'---'-
       | Left channel                  | Right channel                 |

I2S_FMT_DATA_ORDER_MSB

Send MSB first

I2S_FMT_DATA_ORDER_LSB

Send LSB first

I2S_FMT_DATA_ORDER_INV

Invert bit ordering, send LSB first

I2S_FMT_CLK_FORMAT_SHIFT

Data Format bit field position.

I2S_FMT_CLK_FORMAT_MASK

Data Format bit field mask.

I2S_FMT_BIT_CLK_INV

Invert bit clock

I2S_FMT_FRAME_CLK_INV

Invert frame clock

I2S_FMT_CLK_NF_NB

NF represents “Normal Frame” whereas IF represents “Inverted Frame” NB represents “Normal Bit Clk” whereas IB represents “Inverted Bit clk”

I2S_FMT_CLK_NF_IB
I2S_FMT_CLK_IF_NB
I2S_FMT_CLK_IF_IB
I2S_OPT_BIT_CLK_CONT

Run bit clock continuously

I2S_OPT_BIT_CLK_GATED

Run bit clock when sending data only

I2S_OPT_BIT_CLK_MASTER

I2S driver is bit clock master

I2S_OPT_BIT_CLK_SLAVE

I2S driver is bit clock slave

I2S_OPT_FRAME_CLK_MASTER

I2S driver is frame clock master

I2S_OPT_FRAME_CLK_SLAVE

I2S driver is frame clock slave

I2S_OPT_LOOPBACK

Loop back mode.

In loop back mode RX input will be connected internally to TX output. This is used primarily for testing.

I2S_OPT_PINGPONG

Ping pong mode.

In ping pong mode TX output will keep alternating between a ping buffer and a pong buffer. This is normally used in audio streams when one buffer is being populated while the other is being played (DMAed) and vice versa. So, in this mode, 2 sets of buffers fixed in size are used. Static Arrays are used to achieve this and hence they are never freed.

Typedefs

typedef uint8_t i2s_fmt_t
typedef uint8_t i2s_opt_t

Enums

enum i2s_dir

I2C Direction.

Values:

enumerator I2S_DIR_RX

Receive data

enumerator I2S_DIR_TX

Transmit data

enumerator I2S_DIR_BOTH

Both receive and transmit data

enum i2s_state

Interface state

Values:

enumerator I2S_STATE_NOT_READY

The interface is not ready. 

   The interface was initialized but is not yet ready to receive /
   transmit data. Call i2s_configure() to configure interface and change
   its state to READY.

enumerator I2S_STATE_READY

The interface is ready to receive / transmit data.

enumerator I2S_STATE_RUNNING

The interface is receiving / transmitting data.

enumerator I2S_STATE_STOPPING

The interface is draining its transmit queue.

enumerator I2S_STATE_ERROR

TX buffer underrun or RX buffer overrun has occurred.

enum i2s_trigger_cmd

Trigger command

Values:

enumerator I2S_TRIGGER_START

Start the transmission / reception of data. 

   If I2S_DIR_TX is set some data has to be queued for transmission by
   the i2s_write() function. This trigger can be used in READY state
   only and changes the interface state to RUNNING.

enumerator I2S_TRIGGER_STOP

Stop the transmission / reception of data. 

   Stop the transmission / reception of data at the end of the current
   memory block. This trigger can be used in RUNNING state only and at
   first changes the interface state to STOPPING. When the current TX /
   RX block is transmitted / received the state is changed to READY.
   Subsequent START trigger will resume transmission / reception where
   it stopped.

enumerator I2S_TRIGGER_DRAIN

Empty the transmit queue. 

   Send all data in the transmit queue and stop the transmission.
   If the trigger is applied to the RX queue it has the same effect as
   I2S_TRIGGER_STOP. This trigger can be used in RUNNING state only and
   at first changes the interface state to STOPPING. When all TX blocks
   are transmitted the state is changed to READY.

enumerator I2S_TRIGGER_DROP

Discard the transmit / receive queue. 

   Stop the transmission / reception immediately and discard the
   contents of the respective queue. This trigger can be used in any
   state other than NOT_READY and changes the interface state to READY.

enumerator I2S_TRIGGER_PREPARE

Prepare the queues after underrun/overrun error has occurred. 

   This trigger can be used in ERROR state only and changes the
   interface state to READY.

Functions

int i2s_configure(const struct device *dev, enum i2s_dir dir, const struct i2s_config *cfg)

Configure operation of a host I2S controller.

The dir parameter specifies if Transmit (TX) or Receive (RX) direction will be configured by data provided via cfg parameter.

The function can be called in NOT_READY or READY state only. If executed successfully the function will change the interface state to READY.

If the function is called with the parameter cfg->frame_clk_freq set to 0 the interface state will be changed to NOT_READY.

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • dir – Stream direction: RX, TX, or both, as defined by I2S_DIR_*. The I2S_DIR_BOTH value may not be supported by some drivers. For those, the RX and TX streams need to be configured separately.

  • cfg – Pointer to the structure containing configuration parameters.

Return values

  • 0 – If successful.

  • -EINVAL – Invalid argument.

  • -ENOSYS – I2S_DIR_BOTH value is not supported.

static inline const struct i2s_config *i2s_config_get(const struct device *dev, enum i2s_dir dir)

Fetch configuration information of a host I2S controller.

Parameters

  • dev – Pointer to the device structure for the driver instance

  • dir – Stream direction: RX or TX as defined by I2S_DIR_*

Return values

Pointer – to the structure containing configuration parameters, or NULL if un-configured

static inline int i2s_read(const struct device *dev, void **mem_block, size_t *size)

Read data from the RX queue.

Data received by the I2S interface is stored in the RX queue consisting of memory blocks preallocated by this function from rx_mem_slab (as defined by i2s_configure). Ownership of the RX memory block is passed on to the user application which has to release it.

The data is read in chunks equal to the size of the memory block. If the interface is in READY state the number of bytes read can be smaller.

If there is no data in the RX queue the function will block waiting for the next RX memory block to fill in. This operation can timeout as defined by i2s_configure. If the timeout value is set to K_NO_WAIT the function is non-blocking.

Reading from the RX queue is possible in any state other than NOT_READY. If the interface is in the ERROR state it is still possible to read all the valid data stored in RX queue. Afterwards the function will return -EIO error.

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • mem_block – Pointer to the RX memory block containing received data.

  • size – Pointer to the variable storing the number of bytes read.

Return values

  • 0 – If successful.

  • -EIO – The interface is in NOT_READY or ERROR state and there are no more data blocks in the RX queue.

  • -EBUSY – Returned without waiting.

  • -EAGAIN – Waiting period timed out.

int i2s_buf_read(const struct device *dev, void *buf, size_t *size)

Read data from the RX queue into a provided buffer.

Data received by the I2S interface is stored in the RX queue consisting of memory blocks preallocated by this function from rx_mem_slab (as defined by i2s_configure). Calling this function removes one block from the queue which is copied into the provided buffer and then freed.

The provided buffer must be large enough to contain a full memory block of data, which is parameterized for the channel via i2s_configure().

This function is otherwise equivalent to i2s_read().

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • buf – Destination buffer for read data, which must be at least the as large as the configured memory block size for the RX channel.

  • size – Pointer to the variable storing the number of bytes read.

Return values

  • 0 – If successful.

  • -EIO – The interface is in NOT_READY or ERROR state and there are no more data blocks in the RX queue.

  • -EBUSY – Returned without waiting.

  • -EAGAIN – Waiting period timed out.

static inline int i2s_write(const struct device *dev, void *mem_block, size_t size)

Write data to the TX queue.

Data to be sent by the I2S interface is stored first in the TX queue. TX queue consists of memory blocks preallocated by the user from tx_mem_slab (as defined by i2s_configure). This function takes ownership of the memory block and will release it when all data are transmitted.

If there are no free slots in the TX queue the function will block waiting for the next TX memory block to be send and removed from the queue. This operation can timeout as defined by i2s_configure. If the timeout value is set to K_NO_WAIT the function is non-blocking.

Writing to the TX queue is only possible if the interface is in READY or RUNNING state.

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • mem_block – Pointer to the TX memory block containing data to be sent.

  • size – Number of bytes to write. This value has to be equal or smaller than the size of the memory block.

Return values

  • 0 – If successful.

  • -EIO – The interface is not in READY or RUNNING state.

  • -EBUSY – Returned without waiting.

  • -EAGAIN – Waiting period timed out.

int i2s_buf_write(const struct device *dev, void *buf, size_t size)

Write data to the TX queue from a provided buffer.

This function acquires a memory block from the I2S channel TX queue and copies the provided data buffer into it. It is otherwise equivalent to i2s_write().

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • buf – Pointer to a buffer containing the data to transmit.

  • size – Number of bytes to write. This value has to be equal or smaller than the size of the channel’s TX memory block configuration.

Return values

  • 0 – If successful.

  • -EIO – The interface is not in READY or RUNNING state.

  • -EBUSY – Returned without waiting.

  • -EAGAIN – Waiting period timed out.

  • -ENOMEM – No memory in TX slab queue.

  • -EINVAL – Size parameter larger than TX queue memory block.

int i2s_trigger(const struct device *dev, enum i2s_dir dir, enum i2s_trigger_cmd cmd)

Send a trigger command.

Parameters

  • dev – Pointer to the device structure for the driver instance.

  • dir – Stream direction: RX, TX, or both, as defined by I2S_DIR_*. The I2S_DIR_BOTH value may not be supported by some drivers. For those, triggering need to be done separately for the RX and TX streams.

  • cmd – Trigger command.

Return values

  • 0 – If successful.

  • -EINVAL – Invalid argument.

  • -EIO – The trigger cannot be executed in the current state or a DMA channel cannot be allocated.

  • -ENOMEM – RX/TX memory block not available.

  • -ENOSYS – I2S_DIR_BOTH value is not supported.

struct i2s_config
#include <i2s.h>

Interface configuration options.

Memory slab pointed to by the mem_slab field has to be defined and initialized by the user. For I2S driver to function correctly number of memory blocks in a slab has to be at least 2 per queue. Size of the memory block should be multiple of frame_size where frame_size = (channels * word_size_bytes). As an example 16 bit word will occupy 2 bytes, 24 or 32 bit word will occupy 4 bytes.

Please check Zephyr Kernel Primer for more information on memory slabs.

Remark

When I2S data format is selected parameter channels is ignored, number of words in a frame is always 2.

Param word_size

Number of bits representing one data word.

Param channels

Number of words per frame.

Param format

Data stream format as defined by I2S_FMT_* constants.

Param options

Configuration options as defined by I2S_OPT_* constants.

Param frame_clk_freq

Frame clock (WS) frequency, this is sampling rate.

Param mem_slab

memory slab to store RX/TX data.

Param block_size

Size of one RX/TX memory block (buffer) in bytes.

Param timeout

Read/Write timeout. Number of milliseconds to wait in case TX queue is full or RX queue is empty, or 0, or SYS_FOREVER_MS.