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pifaceio 1.18

Python interface to the Raspberry Pi PiFace board

### PIFACEIO

This package provides a Python interface to the [PiFace][pifaceboard]
peripheral board for the [Raspberry Pi][rpi]. A PiFace board offers 8
digital inputs and 8 digital outputs. This package allows a Python
program to read the inputs and write the outputs on the board via the
Raspberry Pi SPI bus.

Multiple PiFace boards are supported. This pifaceio package is focussed
on simplicity and performance for polled implementations and is an
alternative to the [pifacedigitalio][] and [piface][] (now depreciated)
Python packages for the PiFace board.

Interrupts are not supported. See [pifacedigitalio][] for interrupt and
other functionality.

The pifaceio package is implemented in pure Python code using only the
Python standard library, uses no external 3rd party packages, and is
compatible with both Python versions 2 and 3.

### INSTALLATION

Install necessary packages on your Raspberry Pi for build etc:

    sudo apt-get install git python-setuptools

Get this package:

    git clone http://github.com/bulletmark/pifaceio

Install (can alternately do this as ordinary user in a virtualenv
of course):

    sudo python ./setup.py install

Set up permissions, groups, udev etc for spidev device on RPi:

    sudo ./install-spidev.sh

Note that the [pifaceio pypi package][pifaceio] is also available from
[PyPi][pypi] so alternatively you can install it using [pip][].

### USAGE

Board addresses, input pins, and output pins are always numbered from 0.

In general, you start with a once-off allocation of a PiFace board
instance at startup with:

    pf = pifaceio.PiFace()

Default is first PiFace board (0). Optionally takes an argument 0 to 7
for up to 8 PiFace board addresses. Create multiple PiFace() instances
if you want to use multiple boards in parallel.

There are also other (rarely needed) options to disable the input pull
up resistors, and to invert the input and output bit polarities. See
pifaceio.py for details.

At each poll time, e.g. every part second, read all the inputs (i.e. the
single input byte) with:

    pf.read() # returns the input byte you can use directly if you prefer

Then read and write individual pins according to your logic with:

    in_val = pf.read_pin(pin_in)
    ..
    pf.write_pin(pin_out, out_val)
    ..

Finally, write all the outputs at the end of processing (i.e. write the
single output byte) with:

    pf.write() # optionally, takes an output byte to write directly

Note that `read_pin()` is just a convenience method wrapping a bit
test around the previously read input byte from `read()` and
`write_pin()` is just a convenience method wrapping a bit set/clear
around the output byte pending it being written by `write()`. You don't
have to use `read_pin()` or `write_pin()` if you just want to read,
test/manipulate, and write the 8 bit input and/or output byte directly.
In that case you would just use `read()`, and `write()` only in your
application.

### EXAMPLES

Simple example to just reflect all PiFace 8 inputs to the 8 outputs
every 10 msec, on the default first PiFace board:

    import pifaceio, time
    pf = pifaceio.PiFace()

    while True:
        pf.write(pf.read())
        time.sleep(.01)

Same example, but do it across 4 PiFace boards:

    import pifaceio, time
    pifaces = [pifaceio.PiFace(n) for n in range(4)]

    while True:
        for pf in pifaces:
            pf.write(pf.read())
        time.sleep(.01)

Simple example to test if both input pin 0 and 1 are on at same time,
and then set output pin 7 if true:

    import pifaceio
    pf = pifaceio.PiFace()
    ...
    # Fetch inputs (i.e. single byte)
    pf.read()
    first_two_inputs_on = pf.read_pin(0) and pf.read_pin(1)

    # Now write that state to output pin 7
    pf.write_pin(7, first_two_inputs_on)

    # Do final (actual) write when all output pin states are set.
    pf.write()

Simulated "interrupt" processing example by light-weight poll every 10 msecs:

    import pifaceio, time
    pf = pifaceio.PiFace()

    def process_change():
        'On any changed inputs, read inputs and write outputs'
        pf.write_pin(7, pf.read_pin(0) and pf.read_pin(1))

        # .. etc .. do logic using pf.read_pin() and pf.write_pin()

    # Loop forever polling inputs ..
    last = None
    while True:
        data = pf.read()

        # Do processing only on change
        if last != data:
            last = data
            process_change()
            pf.write()        # note write() only writes if output changes

        time.sleep(.01)

### PIFACE PACKAGE BACKWARDS COMPATIBILITY

The following [piface][] API will work compatibly, but performance is
slightly degraded compared to reading and writing the single input and
output bytes using the canonical new pifaceio API described above.

    #import piface.pfio as pf (change this to next line)
    import pifaceio as pf

    # The following calls should be approximately compatible:
    pf.init()
    value = pf.digital_read(pin)
    pf.digital_write(pin, value)
    pf.deinit()

### UPGRADE

    cd pifaceio  # source dir, as above
    git pull
    sudo python ./setup.py install

### LICENSE

Copyright (C) 2013 Mark Blakeney. This program is distributed under the
terms of the GNU General Public License.
This program is free software: you can redistribute it and/or modify it
under the terms of the GNU General Public License as published by the
Free Software Foundation, either version 3 of the License, or any later
version.
This program is distributed in the hope that it will be useful, but
WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU General
Public License at <http://www.gnu.org/licenses/> for more details.

[rpi]: http://www.raspberrypi.org
[pifaceboard]: http://www.piface.org.uk/products/piface_digital/
[piface]: http://github.com/thomasmacpherson/piface
[pifacedigitalio]: http://github.com/piface/pifacedigitalio
[pypi]: https://pypi.python.org/pypi
[pip]: http://www.pip-installer.org/en/latest
[pifaceio]: https://pypi.python.org/pypi/pifaceio

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