RPi::SPI - Communicate with devices over the Serial Peripheral Interface
    (SPI) bus on Raspberry Pi

        # channel 0 and 1 are the hardware SPI pins
        # CE0 and CE1

        my $spi = RPi::SPI->new(0);

        my $buf = [0x01, 0x02];
        my $len = 2;

        @$buf = $spi->rw($buf, $len);

        # use a GPIO pin to expand the number of SPI
        # channels. We'll bit-bang automatically. The
        # GPIO pin must connect to the CS/SS pin on the
        # IC you're using

        $spi = RPi::SPI->new(26); # GPIO 26 is the CS

    This distribution provides you the ability to communicate with devices
    attached to the channels on the Serial Peripheral Interface (SPI) bus.
    Although it was designed for the Raspberry Pi, that's not a hard
    requirement, and it should work on any Unix-type system that has support
    for SPI.

    You can use the hardware SPI pins CE0 and CE1 on the Raspberry Pi, but
    if you need more SPI slaves, we'll also automatically bit-bang the SPI
    bus using a standard GPIO pin for the Slave Select instead.

    Instantiates a new RPi::SPI instance, prepares a specific SPI bus
    channel for use, then returns the object.



    The SPI bus channel to initialize.

    Mandatory: Integer, `0' for `/dev/spidev0.0' or `1' for
    `/dev/spidev0.1'. You can also send in any number above `1'. If so,
    we'll treat it as a GPIO pin (connected to the CS/SS pin of the IC), and
    we'll bit-bang the CS automatically as to free up the onboard hardware


    Optional, Integer. The data rate to communicate on the bus using.
    Defaults to `1000000' (1MHz).

    Dies if we can't open the SPI bus.

    Writes specified data to the bus on the channel specified in `new()',
    then after completion, does a read of the bus and re-populates the write
    buffer with the freshly read data, and returns it as an array.



    Mandatory: Array reference where each element is an unsigned char
    (0-255). This array is the write buffer; the data we'll be sending to
    the SPI bus.


    Mandatory: Integer, the number of array elements in the `$buf' parameter
    sent in above.

    Return: The write buffer, after being re-populated with the read data,
    as a Perl array reference.

    Dies if we can't open the SPI bus.

    Steve Bertrand, `<steveb at>'

    Copyright 2017 Steve Bertrand.

    This program is free software; you can redistribute it and/or modify it
    under the terms of either: the GNU General Public License as published
    by the Free Software Foundation; or the Artistic License.

    See for more information.