1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
203
204
205
206
207
208
209
210
211
212
213
214
215
216
217
218
|
import os
import ctypes
import array
import fcntl
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),
]
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
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))
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)
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
|
