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.. currentmodule:: machine

class I2S -- Inter-IC Sound bus protocol

I2S is a synchronous serial protocol used to connect digital audio devices. At the physical level, a bus consists of 3 lines: SCK, WS, SD. The I2S class supports controller operation. Peripheral operation is not supported.

The I2S class is currently available as a Technical Preview. During the preview period, feedback from users is encouraged. Based on this feedback, the I2S class API and implementation may be changed.

I2S objects can be created and initialized using:

from machine import I2S
from machine import Pin

# ESP32
sck_pin = Pin(14)   # Serial clock output
ws_pin = Pin(13)    # Word clock output
sd_pin = Pin(12)    # Serial data output

or

# PyBoards
sck_pin = Pin("Y6")   # Serial clock output
ws_pin = Pin("Y5")    # Word clock output
sd_pin = Pin("Y8")    # Serial data output

audio_out = I2S(2,
                sck=sck_pin, ws=ws_pin, sd=sd_pin,
                mode=I2S.TX,
                bits=16,
                format=I2S.MONO,
                rate=44100,
                ibuf=20000)

audio_in = I2S(2,
               sck=sck_pin, ws=ws_pin, sd=sd_pin,
               mode=I2S.RX,
               bits=32,
               format=I2S.STEREO,
               rate=22050,
               ibuf=20000)
3 modes of operation are supported:
  • blocking
  • non-blocking
  • uasyncio

blocking:

num_written = audio_out.write(buf) # blocks until buf emptied

num_read = audio_in.readinto(buf) # blocks until buf filled

non-blocking:

audio_out.irq(i2s_callback)         # i2s_callback is called when buf is emptied
num_written = audio_out.write(buf)  # returns immediately

audio_in.irq(i2s_callback)          # i2s_callback is called when buf is filled
num_read = audio_in.readinto(buf)   # returns immediately

uasyncio:

swriter = uasyncio.StreamWriter(audio_out)
swriter.write(buf)
await swriter.drain()

sreader = uasyncio.StreamReader(audio_in)
num_read = await sreader.readinto(buf)

Some codec devices like the WM8960 or SGTL5000 require separate initialization before they can operate with the I2S class. For these, separate drivers are supplied, which also offer methods for controlling volume, audio processing and other things. For these drivers see:

Constructor

Methods

.. method:: I2S.init(sck, ...)

  see Constructor for argument descriptions


.. method:: I2S.deinit()

  Deinitialize the I2S bus


.. method::  I2S.readinto(buf)

  Read audio samples into the buffer specified by ``buf``.  ``buf`` must support the buffer protocol, such as bytearray or array.
  "buf" byte ordering is little-endian.  For Stereo format, left channel sample precedes right channel sample. For Mono format,
  the left channel sample data is used.
  Returns number of bytes read


.. method::  I2S.write(buf)

  Write audio samples contained in ``buf``. ``buf`` must support the buffer protocol, such as bytearray or array.
  "buf" byte ordering is little-endian.  For Stereo format, left channel sample precedes right channel sample. For Mono format,
  the sample data is written to both the right and left channels.
  Returns number of bytes written


.. method::  I2S.irq(handler)

  Set a callback. ``handler`` is called when ``buf`` is emptied (``write`` method) or becomes full (``readinto`` method).
  Setting a callback changes the ``write`` and ``readinto`` methods to non-blocking operation.
  ``handler`` is called in the context of the MicroPython scheduler.


.. staticmethod::  I2S.shift(*, buf, bits, shift)

  bitwise shift of all samples contained in ``buf``. ``bits`` specifies sample size in bits. ``shift`` specifies the number of bits to shift each sample.
  Positive for left shift, negative for right shift.
  Typically used for volume control.  Each bit shift changes sample volume by 6dB.

Constants

.. data:: I2S.RX

   for initialising the I2S bus ``mode`` to receive


.. data:: I2S.TX

   for initialising the I2S bus ``mode`` to transmit


.. data:: I2S.STEREO

   for initialising the I2S bus ``format`` to stereo


.. data:: I2S.MONO

   for initialising the I2S bus ``format`` to mono