adafruit_tca9548a.py

# The MIT License (MIT)
#
# Copyright (c) 2018 Carter Nelson for Adafruit Industries
#
# Permission is hereby granted, free of charge, to any person obtaining a copy
# of this software and associated documentation files (the "Software"), to deal
# in the Software without restriction, including without limitation the rights
# to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
# copies of the Software, and to permit persons to whom the Software is
# furnished to do so, subject to the following conditions:
#
# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
# IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
# FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
# AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
# LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
# OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
# THE SOFTWARE.
"""
``Adafruit_TCA9548A``
====================================================

CircuitPython driver for the TCA9548A I2C Multiplexer.

* Author(s): Carter Nelson

Implementation Notes
--------------------

**Hardware:**

* TCA9548A I2C Multiplexer: https://www.adafruit.com/product/2717

**Software and Dependencies:**

* Adafruit CircuitPython firmware for the supported boards:
  https://github.com/adafruit/circuitpython/releases
* Adafruit's Bus Device library: https://github.com/adafruit/Adafruit_CircuitPython_BusDevice
"""

# imports
from micropython import const

_DEFAULT_ADDRESS = const(0x70)

__version__ = "0.0.0-auto.0"
__repo__ = "https://github.com/adafruit/Adafruit_CircuitPython_TCA9548A.git"

class TCA9548A_Channel():
    """Helper class to represent an output channel on the TCA9548A and take care
       of the necessary I2C commands for channel switching. This class needs to
       behave like an I2CDevice."""

    def __init__(self, tca, channel):
        self.tca = tca
        self.channel_switch = bytearray([1 << channel])

    def try_lock(self):
        """Pass thru for try_lock."""
        while not self.tca.i2c.try_lock():
            pass
        self.tca.i2c.writeto(self.tca.address, self.channel_switch)
        return True

    def unlock(self):
        """Pass thru for unlock."""
        self.tca.i2c.writeto(self.tca.address, b'\x00')
        return self.tca.i2c.unlock()

    def readfrom_into(self, address, buffer, **kwargs):
        """Pass thru for readfrom_into."""
        if address == self.tca.address:
            raise ValueError("Device address must be different than TCA9548A address.")
        return self.tca.i2c.readfrom_into(address, buffer, **kwargs)

    def writeto(self, address, buffer, **kwargs):
        """Pass thru for writeto."""
        if address == self.tca.address:
            raise ValueError("Device address must be different than TCA9548A address.")
        return self.tca.i2c.writeto(address, buffer, **kwargs)

    def writeto_then_readfrom(self, address, buffer_out, buffer_in, **kwargs):
        """Pass thru for writeto_then_readfrom."""
        #In linux, at least, this is a special kernel function call
        if address == self.tca.address:
            raise ValueError("Device address must be different than TCA9548A address.")

        if hasattr(self.tca.i2c, 'writeto_then_readfrom'):
            self.tca.i2c.writeto_then_readfrom(address, buffer_out, buffer_in, **kwargs)
        else:
            self.tca.i2c.writeto(address, buffer_out,
                                 start=kwargs.get("out_start", 0),
                                 end=kwargs.get("out_end", None),
                                 stop=False)
            self.tca.i2c.readfrom_into(address, buffer_in,
                                       start=kwargs.get("in_start", 0),
                                       end=kwargs.get("in_end", None))

class TCA9548A():
    """Class which provides interface to TCA9548A I2C multiplexer."""

    def __init__(self, i2c, address=_DEFAULT_ADDRESS):
        self.i2c = i2c
        self.address = address
        self.channels = [None]*8

    def __len__(self):
        return 8

    def __getitem__(self, key):
        if not 0 <= key <= 7:
            raise IndexError("Channel must be an integer in the range: 0-7")
        if self.channels[key] is None:
            self.channels[key] = TCA9548A_Channel(self, key)
        return self.channels[key]