i2c_device.py

# The MIT License (MIT)
#
# Copyright (c) 2016 Scott Shawcroft for Adafruit Industries
#
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# of this software and associated documentation files (the "Software"), to deal
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# furnished to do so, subject to the following conditions:
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# The above copyright notice and this permission notice shall be included in
# all copies or substantial portions of the Software.
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# 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
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# THE SOFTWARE.

"""
`adafruit_bus_device.i2c_device` - I2C Bus Device
====================================================
"""

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

class I2CDevice:
    """
    Represents a single I2C device and manages locking the bus and the device
    address.

    :param ~busio.I2C i2c: The I2C bus the device is on
    :param int device_address: The 7 bit device address

    .. note:: This class is **NOT** built into CircuitPython. See
      :ref:`here for install instructions <bus_device_installation>`.

    Example:

    .. code-block:: python

        import busio
        from board import *
        from adafruit_bus_device.i2c_device import I2CDevice

        with busio.I2C(SCL, SDA) as i2c:
            device = I2CDevice(i2c, 0x70)
            bytes_read = bytearray(4)
            with device:
                device.readinto(bytes_read)
            # A second transaction
            with device:
                device.write(bytes_read)
    """

    def __init__(self, i2c, device_address):
        """
        Try to read a byte from an address,
        if you get an OSError it means the device is not there
        """
        while not i2c.try_lock():
            pass
        try:
            i2c.writeto(device_address, b'')
        except OSError:
            # some OS's dont like writing an empty bytesting...
            # Retry by reading a byte
            try:
                result = bytearray(1)
                i2c.readfrom_into(device_address, result)
            except OSError:
                raise ValueError("No I2C device at address: %x" % device_address)
        finally:
            i2c.unlock()

        self.i2c = i2c
        self.device_address = device_address

    def readinto(self, buf, **kwargs):
        """
        Read into ``buf`` from the device. The number of bytes read will be the
        length of ``buf``.

        If ``start`` or ``end`` is provided, then the buffer will be sliced
        as if ``buf[start:end]``. This will not cause an allocation like
        ``buf[start:end]`` will so it saves memory.

        :param bytearray buffer: buffer to write into
        :param int start: Index to start writing at
        :param int end: Index to write up to but not include
        """
        self.i2c.readfrom_into(self.device_address, buf, **kwargs)

    def write(self, buf, **kwargs):
        """
        Write the bytes from ``buffer`` to the device. Transmits a stop bit if
        ``stop`` is set.

        If ``start`` or ``end`` is provided, then the buffer will be sliced
        as if ``buffer[start:end]``. This will not cause an allocation like
        ``buffer[start:end]`` will so it saves memory.

        :param bytearray buffer: buffer containing the bytes to write
        :param int start: Index to start writing from
        :param int end: Index to read up to but not include
        :param bool stop: If true, output an I2C stop condition after the buffer is written
        """
        self.i2c.writeto(self.device_address, buf, **kwargs)

#pylint: disable-msg=too-many-arguments
    def write_then_readinto(self, out_buffer, in_buffer, *,
                            out_start=0, out_end=None, in_start=0, in_end=None, stop=True):
        """
        Write the bytes from ``out_buffer`` to the device, then immediately
        reads into ``in_buffer`` from the device. The number of bytes read
        will be the length of ``in_buffer``.
        Transmits a stop bit after the write, if ``stop`` is set.

        If ``out_start`` or ``out_end`` is provided, then the output buffer
        will be sliced as if ``out_buffer[out_start:out_end]``. This will
        not cause an allocation like ``buffer[out_start:out_end]`` will so
        it saves memory.

        If ``in_start`` or ``in_end`` is provided, then the input buffer
        will be sliced as if ``in_buffer[in_start:in_end]``. This will not
        cause an allocation like ``in_buffer[in_start:in_end]`` will so
        it saves memory.

        :param bytearray out_buffer: buffer containing the bytes to write
        :param bytearray in_buffer: buffer containing the bytes to read into
        :param int out_start: Index to start writing from
        :param int out_end: Index to read up to but not include
        :param int in_start: Index to start writing at
        :param int in_end: Index to write up to but not include
        :param bool stop: If true, output an I2C stop condition after the buffer is written
        """
        if out_end is None:
            out_end = len(out_buffer)
        if in_end is None:
            in_end = len(in_buffer)
        if hasattr(self.i2c, 'writeto_then_readfrom'):
            # In linux, at least, this is a special kernel function call
            self.i2c.writeto_then_readfrom(self.device_address, out_buffer, in_buffer,
                                           out_start=out_start, out_end=out_end,
                                           in_start=in_start, in_end=in_end, stop=stop)

        else:
            # If we don't have a special implementation, we can fake it with two calls
            self.write(out_buffer, start=out_start, end=out_end, stop=stop)
            self.readinto(in_buffer, start=in_start, end=in_end)

#pylint: enable-msg=too-many-arguments

    def __enter__(self):
        while not self.i2c.try_lock():
            pass
        return self

    def __exit__(self, *exc):
        self.i2c.unlock()
        return False