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)

Constructor

class machine.I2S(id, *, sck, ws, sd, mode, bits, format, rate, ibuf)

Construct an I2S object of the given id:

  • id identifies a particular I2S bus.

id is board and port specific:

  • PYBv1.0/v1.1: has one I2S bus with id=2.

  • PYBD-SFxW: has two I2S buses with id=1 and id=2.

  • ESP32: has two I2S buses with id=0 and id=1.

Keyword-only parameters that are supported on all ports:

  • sck is a pin object for the serial clock line

  • ws is a pin object for the word select line

  • sd is a pin object for the serial data line

  • mode specifies receive or transmit

  • bits specifies sample size (bits), 16 or 32

  • format specifies channel format, STEREO or MONO

  • rate specifies audio sampling rate (samples/s)

  • ibuf specifies internal buffer length (bytes)

For all ports, DMA runs continuously in the background and allows user applications to perform other operations while sample data is transfered between the internal buffer and the I2S peripheral unit. Increasing the size of the internal buffer has the potential to increase the time that user applications can perform non-I2S operations before underflow (e.g. write method) or overflow (e.g. readinto method).

Methods

I2S.init(sck, ...)

see Constructor for argument descriptions

I2S.deinit()

Deinitialize the I2S bus

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

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

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.

static 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

I2S.RX

for initialising the I2S bus mode to receive

I2S.TX

for initialising the I2S bus mode to transmit

I2S.STEREO

for initialising the I2S bus format to stereo

I2S.MONO

for initialising the I2S bus format to mono