163 lines
5.2 KiB
ReStructuredText
163 lines
5.2 KiB
ReStructuredText
.. currentmodule:: machine
|
|
.. _machine.I2S:
|
|
|
|
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:: 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
|
|
-------
|
|
|
|
.. 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
|
|
|
|
|