import os
import ctypes
import array
import fcntl
[docs]class I2CError(IOError):
"""Base class for I2C errors."""
pass
class _CI2CMessage(ctypes.Structure):
_fields_ = [
("addr", ctypes.c_ushort),
("flags", ctypes.c_ushort),
("len", ctypes.c_ushort),
("buf", ctypes.POINTER(ctypes.c_ubyte)),
]
class _CI2CIocTransfer(ctypes.Structure):
_fields_ = [
("msgs", ctypes.POINTER(_CI2CMessage)),
("nmsgs", ctypes.c_uint),
]
[docs]class I2C(object):
# Constants scraped from <linux/i2c-dev.h> and <linux/i2c.h>
_I2C_IOC_FUNCS = 0x705
_I2C_IOC_RDWR = 0x707
_I2C_FUNC_I2C = 0x1
_I2C_M_TEN = 0x0010
_I2C_M_RD = 0x0001
_I2C_M_STOP = 0x8000
_I2C_M_NOSTART = 0x4000
_I2C_M_REV_DIR_ADDR = 0x2000
_I2C_M_IGNORE_NAK = 0x1000
_I2C_M_NO_RD_ACK = 0x0800
_I2C_M_RECV_LEN = 0x0400
def __init__(self, devpath):
"""Instantiate an I2C object and open the i2c-dev device at the
specified path.
Args:
devpath (str): i2c-dev device path.
Returns:
I2C: I2C object.
Raises:
I2CError: if an I/O or OS error occurs.
"""
self._fd = None
self._devpath = None
self._open(devpath)
def __del__(self):
self.close()
def __enter__(self):
return self
def __exit__(self, t, value, traceback):
self.close()
def _open(self, devpath):
# Open i2c device
try:
self._fd = os.open(devpath, os.O_RDWR)
except OSError as e:
raise I2CError(e.errno, "Opening I2C device: " + e.strerror)
self._devpath = devpath
# Query supported functions
buf = array.array('I', [0])
try:
fcntl.ioctl(self._fd, I2C._I2C_IOC_FUNCS, buf, True)
except (OSError, IOError) as e:
self.close()
raise I2CError(e.errno, "Querying supported functions: " + e.strerror)
# Check that I2C_RDWR ioctl() is supported on this device
if (buf[0] & I2C._I2C_FUNC_I2C) == 0:
self.close()
raise I2CError(None, "I2C not supported on device \"{:s}\"".format(devpath))
# Methods
[docs] def transfer(self, address, messages):
"""Transfer `messages` to the specified I2C `address`. Modifies the
`messages` array with the results of any read transactions.
Args:
address (int): I2C address.
messages (list): list of I2C.Message messages.
Raises:
I2CError: if an I/O or OS error occurs.
TypeError: if `messages` type is not list.
ValueError: if `messages` length is zero, or if message data is not valid bytes.
"""
if not isinstance(messages, list):
raise TypeError("Invalid messages type, should be list of I2C.Message.")
elif len(messages) == 0:
raise ValueError("Invalid messages data, should be non-zero length.")
# Convert I2C.Message messages to _CI2CMessage messages
cmessages = (_CI2CMessage * len(messages))()
for i in range(len(messages)):
# Convert I2C.Message data to bytes
if isinstance(messages[i].data, bytes):
data = messages[i].data
elif isinstance(messages[i].data, bytearray):
data = bytes(messages[i].data)
elif isinstance(messages[i].data, list):
data = bytes(bytearray(messages[i].data))
cmessages[i].addr = address
cmessages[i].flags = messages[i].flags | (I2C._I2C_M_RD if messages[i].read else 0)
cmessages[i].len = len(data)
cmessages[i].buf = ctypes.cast(ctypes.create_string_buffer(data, len(data)), ctypes.POINTER(ctypes.c_ubyte))
# Prepare transfer structure
i2c_xfer = _CI2CIocTransfer()
i2c_xfer.nmsgs = len(cmessages)
i2c_xfer.msgs = cmessages
# Transfer
try:
fcntl.ioctl(self._fd, I2C._I2C_IOC_RDWR, i2c_xfer, False)
except (OSError, IOError) as e:
raise I2CError(e.errno, "I2C transfer: " + e.strerror)
# Update any read I2C.Message messages
for i in range(len(messages)):
if messages[i].read:
data = [cmessages[i].buf[j] for j in range(cmessages[i].len)]
# Convert read data to type used in I2C.Message messages
if isinstance(messages[i].data, list):
messages[i].data = data
elif isinstance(messages[i].data, bytearray):
messages[i].data = bytearray(data)
elif isinstance(messages[i].data, bytes):
messages[i].data = bytes(bytearray(data))
[docs] def close(self):
"""Close the i2c-dev I2C device.
Raises:
I2CError: if an I/O or OS error occurs.
"""
if self._fd is None:
return
try:
os.close(self._fd)
except OSError as e:
raise I2CError(e.errno, "Closing I2C device: " + e.strerror)
self._fd = None
# Immutable properties
@property
def fd(self):
"""Get the file descriptor of the underlying i2c-dev device.
:type: int
"""
return self._fd
@property
def devpath(self):
"""Get the device path of the underlying i2c-dev device.
:type: str
"""
return self._devpath
# String representation
def __str__(self):
return "I2C (device={:s}, fd={:d})".format(self.devpath, self.fd)
[docs] class Message:
def __init__(self, data, read=False, flags=0):
"""Instantiate an I2C Message object.
Args:
data (bytes, bytearray, list): a byte array or list of 8-bit
integers to write.
read (bool): specify this as a read message, where `data`
serves as placeholder bytes for the read.
flags (int): additional i2c-dev flags for this message.
Returns:
Message: Message object.
Raises:
TypeError: if `data`, `read`, or `flags` types are invalid.
"""
if not isinstance(data, (bytes, bytearray, list)):
raise TypeError("Invalid data type, should be bytes, bytearray, or list.")
if not isinstance(read, bool):
raise TypeError("Invalid read type, should be boolean.")
if not isinstance(flags, int):
raise TypeError("Invalid flags type, should be integer.")
self.data = data
self.read = read
self.flags = flags