# 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)
$device->write_block([1, 2, 3, 4]);
See the examples direcory for more information on usage with an Arduino
unit.
DESCRIPTION
Interface to read and write to I2C bus devices.
YOU SHOULD KNOW
There are particular things to know depending on connecting to certain
devices.
General
You need to have some core software installed before using the I2C bus.
The Raspberry Pi 3 already has everything pre-loaded. On a typical Unix
computer, you'd do something along these lines:
First thing you need to do is enable the I2C bus. You can do so in
raspi-config, or ensure the ram=i2c_arm directive is set to on in the
/boot/config.txt file:
ram=i2c_arm=on
Arduino
Often, the default speed of the I2C bus master is too fast for an
Arduino. If you do not get any results, try changing the spped. On a
Raspberry Pi, you do that by setting the dtparam=i2c_arm_baudrate
directive in the /boot/config.txt file:
dtparam=i2c_arm_baudrate=10000
METHODS
new($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.
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 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.
