I2S (Inter-IC Sound) is a serial, synchronous communication protocol that is usually used for transmitting audio data between two digital audio devices.
{IDF_TARGET_NAME} contains {IDF_TARGET_I2S_NUM} I2S peripheral(s). These peripherals can be configured to input and output sample data via the I2S driver.
Each controller has separate rx and tx channel. That means they are able to work under different clock and slot configurations with separate GPIO pins. Note that although the internal MCLK of tx channel and rx channel are separate on a controller, the output MCLK signal can only be attached to one channel. If two different MCLK ouput is required, they must be allocated on different I2S controller.
**Public headers that need to be included in the I2S application**
-``i2s.h``: The header file of legacy I2S APIs (for apps using legacy driver).
-``i2s_std.h``: The header file that provides standard communication mode specific APIs (for apps using new driver with standard mode).
-``i2s_pdm.h``: The header file that provides PDM communication mode specific APIs (for apps using new driver with PDM mode).
-``i2s_tdm.h``: The header file that provides TDM communication mode specific APIs (for apps using new driver with TDM mode).
..note::
The legacy driver can't coexist with the new driver. Including ``i2s.h`` to use the legacy driver or the other three headers to use the new driver. The legacy driver might be removed in future.
**Public headers that have been included in the headers above**
-``i2s_types_legacy.h``: The legacy public types that only used in the legacy driver.
-``i2s_types.h``: The header file that provides public types.
-``i2s_common.h``: The header file that provides common APIs for all communication modes.
-:cpp:enumerator:`i2s_clock_src_t::I2S_CLK_SRC_APLL`: Audio PLL clock, more precise than ``I2S_CLK_SRC_PLL_160M`` in high sample rate applications. Its frequency is configurable according to the sample rate, but if APLL has been occupied by emac or other channels already, the APLL frequency is not allowed to change, the driver will try to work under this APLL frequency, if this APLL frequency can't meet the requirements of I2S, the clock configuration will fail.
Clock Terminology
^^^^^^^^^^^^^^^^^
-**sample rate**: The number of sampled data in one second per slot.
-**sclk**: Source clock frequency. It is the frequency of the clock source.
-**mclk**: Master clock frequency. ``bclk`` is generate from this clock, ``mclk`` is mostly needed in the case that requires the MCLK signal as a reference clock to synchronize BCLK and WS between I2S master role and slave role.
-**bclk**: Bit clock frequency. Every tick of this clock stands for one data bit on data pin. It means there will be 8/16/24/32 ``bclk`` ticks in one slot, because the number of ``bclk`` ticks in one slot is equal to the :cpp:member:`i2s_std_slot_config_t::slot_bit_width`.
-**lrck** / **ws**: Left/Right clock or word select clock. For non-PDM mode, its frequency is equal to the sample rate.
..note::
Normally ``mclk`` should be the multiple of ``sample rate`` and ``bclk`` at the same time. This field :cpp:member:`i2s_std_clk_config_t::mclk_multiple` means the multiple of ``mclk`` to the ``sample rate``. If ``slot_bit_width`` is set to ``I2S_SLOT_BIT_WIDTH_24BIT``, to keep ``mclk`` a multiple to the ``bclk``, :cpp:member:`i2s_std_clk_config_t::mclk_multiple` should be set to ``I2S_MCLK_MULTIPLE_384``, otherwise the ``ws`` will be inaccurate. But in the most other cases, ``I2S_MCLK_MULTIPLE_256`` should be enough.
Standard mode always has left and right two sound channels which are called 'slots'. These slots can support 8/16/24/32 bits width sample data. And the communication format for the slots mainly includes these following formats:
PDM mode for tx channel can convert PCM data into PDM format which always has left and right slots. PDM TX can only support 16 bits width sample data. PDM TX only needs CLK pin for clock signal and DOUT pin for data signal (i.e. WS and SD signal in the following figure, the BCK signal is an internal bit sampling clock, not needed between PDM devices). This mode allows user to configure the up-sampling parameters :cpp:member:`i2s_pdm_tx_clk_config_t::up_sample_fp`:cpp:member:`i2s_pdm_tx_clk_config_t::up_sample_fs`. The up-sampling rate can be calculated by ``up_sample_rate = fp / fs``, there are up-sampling modes in PDM TX:
-**Fixed Clock Frequency**: In this mode the up-sampling rate will change according to the sample rate. Setting ``fp = 960`` and ``fs = sample_rate / 100``, then the clock frequency(Fpdm) on CLK pin will be fixed to 128 * 48 KHz = 6.144 MHz, note that this frequency is not equal to the sample rate(Fpcm).
-**Fixed Up-sampling Rate**: In this mode the up-sampling rate is fixed to 2. Setting ``fp = 960`` and ``fs = 480``, then the clock frequency(Fpdm) on CLK pin will be ``128 * sample_rate``
PDM mode for rx channel can receive PDM format data and convert the data into PCM format. PDM RX can only support 16 bits width sample data. PDM RX only need WS pin for clock signal and DIN pin for data signal. This mode allows user to configure the down-sampling parameter :cpp:member:`i2s_pdm_rx_clk_config_t::dn_sample_mode`, there are two down-sampling modes in PDM RX:
TDM mode supports upto 16 slots, these slots can be enabled by :cpp:member:`i2s_tdm_slot_config_t::slot_mask`. But due to the hardware limitation, only upto 4 slots are supported while the slot is set to 32 bit-width, and 8 slots for 16 bit-width, 16 slots for 8 bit-width. The slot communication format of TDM is almost same as standard mode, but there are some small differences between them.
-**Philip Format**： Data signal have one bit shift comparing to the WS(word select) signal. And no matter how many slots are contained in one frame, the duty of WS signal will always keep 50%.
-**PCM Long Format**: Data have one bit shift and meanwhile WS signal will lasting one slot bit width for every frame. For example, if there are 4 slots enabled, then the duty of WS will be 25%, and if there are 5 slots, it will be 20%.
LCD/Camera mode are only supported on I2S0 over a parallel bus. For LCD mode, I2S0 should working at master tx mode. For camera mode, I2S0 should working at slave rx mode. These two modes are not implemented by I2S driver, please refer to :doc:`/api-reference/peripherals/lcd` for LCD implementation. For more information, see *{IDF_TARGET_NAME} Technical Reference Manual* > *I2S Controller (I2S)* > LCD Mode [`PDF <{IDF_TARGET_TRM_EN_URL}#camlcdctrl>`__].
ADC and DAC modes only exist on ESP32 and are only supported on I2S0. Actually, they are two sub-modes of LCD/Camera mode. I2S0 can be routed directly to the internal analog-to-digital converter(ADC) and digital-to-analog converter(DAC). In other words, ADC and DAC peripherals can read or write continuously via I2S0 DMA. As they are not an actual communication mode, the I2S driver does not implement them.
The public APIs are all channel level APIs, the channel handle :cpp:type:`i2s_chan_handle_t` can help user to manage the resources under a specific channel without considering the other two levels. The other two upper levels' resources are private and will be managed by the driver automatically. Users can call :cpp:func:`i2s_new_channel` to allocate a channel handle and call :cpp:func:`i2s_del_channel` to delete it.
When the power management is enabled (i.e. :ref:`CONFIG_PM_ENABLE` is on), the system will adjust or stop the source clock of I2S before going into light sleep, thus potentially changing the I2S signals and leading to transmitting or receiving invalid data.
I2S driver can prevent the system from changing or stopping the source clock by acquiring a power management lock. When the source clock is generated from APB, the lock type will be set to :cpp:enumerator:`esp_pm_lock_type_t::ESP_PM_APB_FREQ_MAX` and when the source clock is APLL (if target support APLL), it will be set to :cpp:enumerator:`esp_pm_lock_type_t::ESP_PM_NO_LIGHT_SLEEP`. Whenever user is reading or writing via I2S (i.e. calling :cpp:func:`i2s_channel_read` or :cpp:func:`i2s_channel_write`), the driver will guarantee that the power management lock is acquired. Likewise, the driver releases the lock after reading or writing finished.
The ``<mode>`` in the diagram can be replaced by corresponding I2S communication mode like ``std`` for standard two-slot mode, for other information of communication mode, please refer to :ref:`i2s-communication-mode` section.
The data transport of I2S peripheral, including sending and receiving, is realized by DMA. Before transporting data, please call :cpp:func:`i2s_channel_enable` to enable the specific channel. When the sent or received data reach the size of one DMA buffer, ``I2S_OUT_EOF`` or ``I2S_IN_SUC_EOF`` interrupt will be triggered. Note that the DMA buffer size is not equal to :cpp:member:`i2s_std_slot_config_t::dma_frame_num`, one frame here means all the sampled data in one WS circle. Therefore, ``dma_buffer_size = dma_frame_num * slot_num * slot_bit_width / 8``. For the transmit case, users can input the data by calling :cpp:func:`i2s_channel_write`. This function will help users to copy the data from the source buffer to the DMA tx buffer and wait for the transmition finished. Then it'll repeat until the sent bytes reach the given size. For the receive case, the function :cpp:func:`i2s_channel_read` will wait for receiving the message queue which contains the DMA buffer address, it will help users to copy the data from DMA rx buffer to the destination buffer.
Both :cpp:func:`i2s_channel_write` and :cpp:func:`i2s_channel_read` are blocking functions, they will keep waiting until the whole source buffer are sent or the whole destination buffer loaded, unless they exceed the max blocking time, then the error code `ESP_ERR_TIMEOUT` will return in this case. To send or receive data asynchronously, callbacks can be registered by :cpp:func:`i2s_channel_register_event_callback`, users are able to access the DMA buffer directly in the callback function instead of transmitting or receiving by the two blocking functions. However, please be aware that it is an interrupt callback, don't do complex logic, floating operation or call non-reentrant functions in the callback.
Users can initialize a channel by corresponding function (i.e. :func:`i2s_channel_init_std_mode`, :func:`i2s_channel_init_pdm_rx_mode`, :func:`i2s_channel_init_pdm_tx_mode` or :func:`i2s_channel_init_tdm_mode`), the channel will be initialized to the specific mode. If the configurations need to be updated after initialization, :cpp:func:`i2s_channel_disable` has to be called first to ensure the channel has stopped, and then calling corresponding 'reconfig' functions, like :cpp:func:`i2s_channel_reconfig_std_slot`, :cpp:func:`i2s_channel_reconfig_std_clock`, :cpp:func:`i2s_channel_reconfig_std_gpio`.
By default, the I2S interrupt will be deferred when the Cache is disabled for reasons like writing/erasing Flash. Thus the EOF interrupt will not get executed in time, which is not expected in a real-time application.
All the public I2S APIs are guaranteed to be thread safe by the driver, which means, user can call them from different RTOS tasks without protection by extra locks. Notice that I2S driver uses mutex lock to ensure the thread safety, thus these APIs are not allowed to be used in ISR.
Kconfig Options
^^^^^^^^^^^^^^^
-:ref:`CONFIG_I2S_ISR_IRAM_SAFE` controls whether the default ISR handler can work when cache is disabled, see `IRAM Safe <#iram-safe>`__ for more information.
-:ref:`CONFIG_I2S_SUPPRESS_DEPRECATE_WARN` controls whether to suppress the compiling warning message while using the legacy I2S driver.
-:ref:`CONFIG_I2S_ENABLE_DEBUG_LOG` is used to enabled the debug log output. Enable this option will increase the firmware binary size.
Different slot communication formats can be generated by following helper macros for standard mode. As described above, there are three formats in standard mode, their helper macros are:
Different slot communication formats can be generated by following helper macros for TDM mode. As described above, there are four formats in TDM mode, their helper macros are:
Full-duplex mode will register tx and rx channel in an I2S port at the same time, and they will share the BCLK and WS signal. Currently STD and TDM communication mode are able to adopt full-duplex mode in following way, but PDM full-duplex is not supported because PDM TX and RX clock are not same.
To allocate a channel handle in simplex mode, :cpp:func:`i2s_new_channel` should be called for each channel. The clock and gpio pins of TX/RX channel on {IDF_TARGET_NAME} are not separate, therefore TX and RX channel can't coexist on a same I2S port in simplex mode.
To allocate a channel in simplex mode, :cpp:func:`i2s_new_channel` should be called for each channel. The clock and gpio pins of TX/RX channel on {IDF_TARGET_NAME} are separate, they can be configured in different modes and clocks, and they are able to coexist on a same I2S port in simplex mode. So PDM duplex can be realized by registering PDM TX simplex and PDM RX simplex on a same I2S port. But in this way, PDM TX/RX might work with different clocks, take care when configuring the gpio pins and clocks.
The following example offers a use case for the simplex mode, but note that, although the internal MCLK signals for tx and rx channel are separate, the output MCLK can only be bound to one of them if they are from a same controller, if both channel initialized MCLK, it depends on which is initialized later.
For the applications that need a high frequency sample rate, sometimes the massive throughput of receiving data may cause data lost. Users can receive data lost event by registering isr callback function to receive event queue:
1. Determine the interrupt interval. Generally, when data lost happened, the interval should be the bigger the better, it can help to reduce the interrupt times, i.e., ``dma_frame_num`` should be as big as possible while the DMA buffer size won't exceed its maximum value 4092. The relationships are::
2. Determine the ``dma_desc_num``. The ``dma_desc_num`` is decided by the max time of ``i2s_channel_read`` polling cycle, all the received data are supposed to be stored between two ``i2s_channel_read``. This cycle can be measured by a timer or an outputting gpio signal. The relationship is::
3. Determine the receiving buffer size. The receiving buffer that offered by user in ``i2s_channel_read`` should be able to take all the data in all dma buffers, that means it should be bigger than the total size of all the dma buffers::
