mirror of
https://github.com/KevinMidboe/python-gpiozero.git
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218 lines
7.0 KiB
ReStructuredText
218 lines
7.0 KiB
ReStructuredText
====
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Pins
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====
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.. currentmodule:: gpiozero
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As of release 1.1, the GPIO Zero library can be roughly divided into two
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things: pins and the devices that are connected to them. The majority of the
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documentation focuses on devices as pins are below the level that most users
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are concerned with. However, some users may wish to take advantage of the
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capabilities of alternative GPIO implementations or (in future) use GPIO
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extender chips. This is the purpose of the pins portion of the library.
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When you construct a device, you pass in a pin specification. This is passed to
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a pin :class:`Factory` which turns it into a :class:`Pin` implementation. The
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default factory can be queried (and changed) with ``Device.pin_factory``, i.e.
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the ``pin_factory`` attribute of the :class:`Device` class. However, all
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classes accept a ``pin_factory`` keyword argument to their constructors
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permitting the factory to be overridden on a per-device basis (the reason for
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allowing per-device factories is made apparent later in the :doc:`remote_gpio`
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chapter).
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This is illustrated in the following flow-chart:
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.. image:: images/device_pin_flowchart.*
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The default factory is constructed when GPIO Zero is first imported; if no
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default factory can be constructed (e.g. because no GPIO implementations are
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installed, or all of them fail to load for whatever reason), an
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:exc:`ImportError` will be raised.
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Changing the pin factory
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========================
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The default pin factory can be replaced by specifying a value for the
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``GPIOZERO_PIN_FACTORY`` environment variable. For example:
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.. code-block:: console
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$ GPIOZERO_PIN_FACTORY=native python
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Python 3.4.2 (default, Oct 19 2014, 13:31:11)
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[GCC 4.9.1] on linux
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import gpiozero
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>>> gpiozero.Device.pin_factory
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<gpiozero.pins.native.NativeFactory object at 0x762c26b0>
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To set the ``GPIOZERO_PIN_FACTORY`` for the rest of your session you can
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export this value:
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.. code-block:: console
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$ export GPIOZERO_PIN_FACTORY=native
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$ python
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Python 3.4.2 (default, Oct 19 2014, 13:31:11)
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[GCC 4.9.1] on linux
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import gpiozero
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>>> gpiozero.Device.pin_factory
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<gpiozero.pins.native.NativeFactory object at 0x762c26b0>
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>>> quit()
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$ python
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Python 3.4.2 (default, Oct 19 2014, 13:31:11)
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[GCC 4.9.1] on linux
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Type "help", "copyright", "credits" or "license" for more information.
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>>> import gpiozero
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>>> gpiozero.Device.pin_factory
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<gpiozero.pins.native.NativeFactory object at 0x76401330>
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If you add the ``export`` command to your :file:`~/.bashrc` file, you'll set
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the default pin factory for all future sessions too.
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The following values, and the corresponding :class:`Factory` and :class:`Pin`
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classes are listed in the table below. Factories are listed in the order that
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they are tried by default.
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+---------+-----------------------------------------------+-------------------------------------------+
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| Name | Factory class | Pin class |
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+=========+===============================================+===========================================+
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| rpigpio | :class:`gpiozero.pins.rpigpio.RPiGPIOFactory` | :class:`gpiozero.pins.rpigpio.RPiGPIOPin` |
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+---------+-----------------------------------------------+-------------------------------------------+
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| rpio | :class:`gpiozero.pins.rpio.RPIOFactory` | :class:`gpiozero.pins.rpio.RPIOPin` |
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+---------+-----------------------------------------------+-------------------------------------------+
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| pigpio | :class:`gpiozero.pins.pigpio.PiGPIOFactory` | :class:`gpiozero.pins.pigpio.PiGPIOPin` |
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+---------+-----------------------------------------------+-------------------------------------------+
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| native | :class:`gpiozero.pins.native.NativeFactory` | :class:`gpiozero.pins.native.NativePin` |
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+---------+-----------------------------------------------+-------------------------------------------+
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If you need to change the default pin factory from within a script, either set
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``Device.pin_factory`` to the new factory instance to use::
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from gpiozero.pins.native import NativeFactory
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from gpiozero import Device, LED
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Device.pin_factory = NativeFactory()
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# These will now implicitly use NativePin instead of
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# RPiGPIOPin
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led1 = LED(16)
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led2 = LED(17)
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Or use the ``pin_factory`` keyword parameter mentioned above::
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from gpiozero.pins.native import NativeFactory
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from gpiozero import LED
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my_factory = NativeFactory()
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# This will use NativePin instead of RPiGPIOPin for led1
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# but led2 will continue to use RPiGPIOPin
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led1 = LED(16, pin_factory=my_factory)
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led2 = LED(17)
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Certain factories may take default information from additional sources.
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For example, to default to creating pins with
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:class:`gpiozero.pins.pigpio.PiGPIOPin` on a remote pi called ``remote-pi``
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you can set the :envvar:`PIGPIO_ADDR` environment variable when running your
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script:
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.. code-block:: console
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$ GPIOZERO_PIN_FACTORY=pigpio PIGPIO_ADDR=remote-pi python3 my_script.py
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Like the ``GPIOZERO_PIN_FACTORY`` value, these can be exported from your
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:file:`~/.bashrc` script too.
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.. warning::
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The astute and mischievous reader may note that it is possible to mix
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strictly local pin implementations, e.g. using ``RPiGPIOPin`` for one pin,
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and ``NativePin`` for another. This is unsupported, and if it results in
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your script crashing, your components failing, or your Raspberry Pi turning
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into an actual raspberry pie, you have only yourself to blame.
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Sensible uses of multiple pin factories are given in :doc:`remote_gpio`.
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RPi.GPIO
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========
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.. autoclass:: gpiozero.pins.rpigpio.RPiGPIOFactory
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.. autoclass:: gpiozero.pins.rpigpio.RPiGPIOPin
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RPIO
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====
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.. autoclass:: gpiozero.pins.rpio.RPIOFactory
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.. autoclass:: gpiozero.pins.rpio.RPIOPin
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PiGPIO
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======
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.. autoclass:: gpiozero.pins.pigpio.PiGPIOFactory
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.. autoclass:: gpiozero.pins.pigpio.PiGPIOPin
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Native
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======
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.. autoclass:: gpiozero.pins.native.NativeFactory
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.. autoclass:: gpiozero.pins.native.NativePin
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Base classes
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============
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.. autoclass:: Factory
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:members:
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.. autoclass:: Pin
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:members:
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.. autoclass:: SPI
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:members:
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.. currentmodule:: gpiozero.pins.pi
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.. autoclass:: PiFactory
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:members:
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.. autoclass:: PiPin
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:members:
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.. currentmodule:: gpiozero.pins.local
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.. autoclass:: LocalPiFactory
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:members:
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.. autoclass:: LocalPiPin
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:members:
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Utilities
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=========
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The pins module also contains a database of information about the various
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revisions of Raspberry Pi. This is used internally to raise warnings when
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non-physical pins are used, or to raise exceptions when pull-downs are
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requested on pins with physical pull-up resistors attached. The following
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functions and classes can be used to query this database:
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.. currentmodule:: gpiozero
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.. autofunction:: pi_info
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.. autoclass:: PiBoardInfo
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.. autoclass:: HeaderInfo
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.. autoclass:: PinInfo
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