NAME

RPi::I2C - Interface to the I2C bus

SYNOPSIS

    use RPi::I2C;

    my $device_addr = 0x04;

    my $device = RPi::I2C->new($device_addr);

    # read a single byte at the default register address

    print $device->read;

    # read a single byte at a specified register

    print $device->read_byte(0x15);

    # read a block of five bytes (register param optional, not shown)

    my @bytes = $device->read_block(5);

    # write a byte

    $device->write(255);

    # write a byte to a register location

    $device->write_byte(255, 0x0A);

    # write a block of bytes (register param left out again)

    $device->write_block([1, 2, 3, 4]);

See the examples direcory for more information on usage with an Arduino unit.

DESCRIPTION

Interface to read and write to I2C bus devices.

READ THIS FIRST

There are particular things to know depending on connecting to certain devices.

General

You need to have some core software installed before using the I2C bus. The Raspberry Pi 3 already has everything pre-loaded. On a typical Unix computer, you'd do something along these lines:

    sudo apt-get install libi2c-dev i2c-tools build-essential

To test your I2C bus:

    i2cdetect -y 1

...or on some machines:

    i2cdetect -y 0

Raspberry Pi

First thing you need to do is enable the I2C bus. You can do so in raspi-config, or ensure the ram=i2c_arm directive is set to on in the /boot/config.txt file:

    ram=i2c_arm=on

Arduino

Often, the default speed of the I2C bus master is too fast for an Arduino. If you do not get any results, try changing the speed. On a Raspberry Pi, you do that by setting the dtparam=i2c_arm_baudrate directive in the /boot/config.txt file:

    dtparam=i2c_arm_baudrate=10000

METHODS

new($addr, [$device])

Instantiates a new I2C device object ready to be read from and written to.

Parameters:

    $addr

Mandatory, Integer (in hex): The address of the device on the I2C bus (i2cdetect -y 1). eg: 0x78.

    $device

Optional, String: The name of the I2C device file. Defaults to /dev/i2c-1.

read

Performs a simple read of a single byte from the device, and returns it.

read_byte([$reg])

Same as "read", but allows you to optionally specify a specific device register to read from.

Parameters:

    $reg

Optional, Integer: The device's register to read from. eg: 0x01. Defaults to 0x0.

read_bytes($num_bytes, [$reg])

Allows you to read a specific number of bytes from a register and get the bytes returned as an array.

Parameters:

    $num_bytes

Mandatory, Integer: The number of bytes you want to read. These are contiguous starting from the $reg (if supplied, otherwise 0x00).

    $reg

Optional, Integer: The device's register to read from. eg: 0x01. Defaults to 0x0.

Return, Array: An array where each element is a byte of data. The length of this array is dictated by the $num_bytes parameter.

read_word([$reg])

Same as read_byte(), but reads two bytes (16-bit word) instead.

read_block($num_bytes, [$reg])

Reads a block of data and returns it as an array.

Parameters:

    $num_bytes

Mandatory, Integer: The number of bytes you want to read.

    $reg

Optional, Integer: The register to start reading the block of bytes from. It defaults to 0x00 if you don't send it in.

Returns an array containing each byte read per element.

write($data)

Performs a simple write of a single byte to the I2C device.

Parameters:

    $data

Mandatory, 8-bit unsigned integer: The byte to send to the device.

write_byte($data, [$reg])

Same as write(), but allows you to optionally specify a specific device register to write to.

Parameters:

    $data

Mandatory, 8-bit unsigned integer: The byte to send to the device.

    $reg

Optional, Integer: The device's register to write to. eg: 0x01. Defaults to 0x0.

write_word($data, [$reg])

Same as write_byte(), but writes two bytes (16-bit word) instead.

write_block($values, [$reg])

Writes a block of up to 32 contiguous bytes to the device. Each byte is put into an element of an array, and a reference to that array is sent in.

Parameters:

    $values

Mandatory, Array Reference: Up to 32 elements, where each element is a single byte to be written to the device.

    $reg

Optional, Integer: The register to start writing the block of bytes to. It is prudent to be sure you have enough contiguous byte blocks available, or things can be overwritten. Defaults to 0x00 if you don't send it in.

process($value, [$reg])

This method starts at the register address, writes 16 bits of data to it, then reads 16 bits of data and returns it.

Parameters:

    $value

Mandatory, 16-bit Word: The value (16 bits) that you want to write to the device.

    $reg

Optional, Integer: The device's register to write to. eg: 0x01. Defaults to 0x0.

file_error

Returns any stored IO::Handle errors since the last clearerr().

check_device($addr)

Check to see if a device is available.

Parameters:

    $addr

Mandatory, Integer: The I2C address of a device you suspect is connected. eg: 0x7c.

Return, Bool: True (1) if the device responds, False (0) if not.

UNIT TESTS

This distribution has a bare minimum of unit tests. This is because the larger encompassing distribution, RPi::WiringPi has an automated Continuous Integration suite (including a dedicated hardware platform) for testing all of the RPi:: distributions automatically.

The tests specific to this distribution use I2C communication between a Pi and an Arduino board. The files in the examples directory are the foundation of the tests that are now run, and both the examples and the real tests use the arduino.ino sketch in the examples directory as the Arduino code.

TROUBLESHOOTING

Arduino

If you are having issues communicating with an Arduino, the most likely cause is that the Raspberry Pi's I2C communicates much too fast for it.

The fix is to lower the speed of the I2C bus on the Pi. This can be done by setting the dtparam=i2c_arm_baudrate directive in the /boot/config.txt file to a lower value:

    dtparam=i2c_arm_baudrate=10000

ACKNOWLEDGEMENTS

All of the XS code was copied directly from Device::I2C, written by Slava Volkov (SVOLKOV). The module itself was brought over as well, but changed quite a bit. Thanks Slava for a great piece of work!

AUTHOR

Steve Bertrand, <steveb at cpan.org>

LICENSE AND COPYRIGHT

Copyright (C) 2017,2018 by Steve Bertrand

This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself, either Perl version 5.18.2 or, at your option, any later version of Perl 5 you may have available.

cpanm RPi::I2C

perl -MCPAN -e shell
install RPi::I2C