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
|
Bitfield Utilities in C
===========================
This is a C library with functions to help encode and decode Controller Area
Network (CAN) message payloads or other bitfields.
The header files contain complete function documentation, but to get you
started, here are examples using the API:
## Bitfield Manipulation
The bitfields are stored in `uint8_t[]`.
uint8_t data[4] = {0x12, 0x34, 0x56, 0x78};
uint8_t result = get_byte(data, sizeof(data), 0);
// result = 0x12;
result = get_nibble(data, sizeof(data), 0);
// result = 0x1;
bool success = copy_bits_right_aligned(data, 4, 4, 12, result, 4)
// success == true
// result[0] == 0x2
// result[1] == 0x34
## 8 Byte Helpers
If you are dealing with 8 byte CAN messages as `uint64_t`, there are some
additional functions prefixed with `eightbyte_` that may be faster or more
useful.
### 8 Byte Decoding
uint64_t data = 0x8000000000000000;
uint64_t result = get_bit_field(data, 0, 1, false);
// result == 0x1
data = 0x0402574d555a0401;
result = get_bit_field(data, 16, 32, false);
// result = 0x574d555a;
data = 0x00000000F34DFCFF;
result = eightbyte_get_byte(data, 0, false);
//result = 0x0
result = eightbyte_get_byte(data, 4, false);
//result = 0xF3
result = eightbyte_get_nibble(data, 10, false);
//result = 0x4;
### 8 Byte Encoding
uint64_t data = 0;
fail_unless(set_bit_field(&data, 1, 0, 1));
uint64_t result = get_bit_field(data, 0, 1, false);
ck_assert_int_eq(result, 0x1);
### CAN Signal Encoding
The library supports encoding floating point CAN signals as well as booleans
into a uint64_t payload.
uint64_t payload = bitfield_encode_float(1, 1, 3, 1, 0)
// payload == 0x1000000000000000
payload = bitfield_encode_bool(true, 1, 3);
// payload == 0x1000000000000000
### CAN Signal Decoding
The library supports parsing floating point CAN signals as well as booleans.
uint64_t payload = 0xeb00000000000000;
float float_result = bitfield_parse_float(payload,
2, // starting bit
4, // width of the signal's field
1001.0, // transformation factor for the signal value
-30000.0); // transformation offset for the signal value
// float_result == -19990.0
bool bool_result = bitfield_parse_bool(payload,
0, // starting bit
1, // width of the signal's field
1.0, // transformation factor for the signal value
0); // transformation offset for the signal value
// bool_result == true
## Testing
The library includes a test suite that uses the `check` C unit test library. It
requires the unit testing library `check`.
$ make test
You can also see the test coverage if you have `lcov` installed and the
`BROWSER` environment variable set to your choice of web browsers:
$ BROWSER=google-chrome-stable make coverage
## Authors
Chris Peplin cpeplin@ford.com
## License
Copyright (c) 2013 Ford Motor Company
Licensed under the BSD license.
|
