1 =======
2 Buffers
3 =======
4
5 * struct iio_buffer — general buffer structu
6 * :c:func:`iio_validate_scan_mask_onehot` —
7 is selected
8 * :c:func:`iio_buffer_get` — Grab a referenc
9 * :c:func:`iio_buffer_put` — Release the ref
10
11 The Industrial I/O core offers a way for conti
12 trigger source. Multiple data channels can be
13 :file:`/dev/iio:device{X}` character device no
14
15 IIO buffer sysfs interface
16 ==========================
17 An IIO buffer has an associated attributes dir
18 :file:`/sys/bus/iio/devices/iio:device{X}/buff
19 existing attributes:
20
21 * :file:`length`, the total number of data sam
22 stored by the buffer.
23 * :file:`enable`, activate buffer capture.
24
25 IIO buffer setup
26 ================
27
28 The meta information associated with a channel
29 called a scan element. The important bits conf
30 exposed to userspace applications via the
31 :file:`/sys/bus/iio/devices/iio:device{X}/scan
32 directory contains attributes of the following
33
34 * :file:`enable`, used for enabling a channel.
35 is non *zero*, then a triggered capture will
36 channel.
37 * :file:`index`, the scan_index of the channel
38 * :file:`type`, description of the scan elemen
39 and hence the form in which it is read from
40 Format is [be|le]:[s|u]bits/storagebits[Xrep
41
42 * *be* or *le*, specifies big or little endi
43 * *s* or *u*, specifies if signed (2's compl
44 * *bits*, is the number of valid data bits.
45 * *storagebits*, is the number of bits (afte
46 buffer.
47 * *repeat*, specifies the number of bits/sto
48 repeat element is 0 or 1, then the repeat
49 * *shift*, if specified, is the shift that n
50 masking out unused bits.
51
52 For example, a driver for a 3-axis acceleromet
53 data is stored in two 8-bits registers as foll
54
55 7 6 5 4 3 2 1 0
56 +---+---+---+---+---+---+---+---+
57 |D3 |D2 |D1 |D0 | X | X | X | X | (LOW b
58 +---+---+---+---+---+---+---+---+
59
60 7 6 5 4 3 2 1 0
61 +---+---+---+---+---+---+---+---+
62 |D11|D10|D9 |D8 |D7 |D6 |D5 |D4 | (HIGH
63 +---+---+---+---+---+---+---+---+
64
65 will have the following scan element type for
66
67 $ cat /sys/bus/iio/devices/iio:device0/s
68 le:s12/16>>4
69
70 A user space application will interpret data s
71 two byte little endian signed data, that needs
72 masking out the 12 valid bits of data.
73
74 For implementing buffer support a driver shoul
75 fields in iio_chan_spec definition::
76
77 struct iio_chan_spec {
78 /* other members */
79 int scan_index
80 struct {
81 char sign;
82 u8 realbits;
83 u8 storagebits;
84 u8 shift;
85 u8 repeat;
86 enum iio_endian endianness;
87 } scan_type;
88 };
89
90 The driver implementing the accelerometer desc
91 following channel definition::
92
93 struct iio_chan_spec accel_channels[] = {
94 {
95 .type = IIO_ACCEL,
96 .modified = 1,
97 .channel2 = IIO_MOD_X,
98 /* other stuff here */
99 .scan_index = 0,
100 .scan_type = {
101 .sign = 's',
102 .realbits = 12,
103 .storagebits = 16,
104 .shift = 4,
105 .endianness = IIO_L
106 },
107 }
108 /* similar for Y (with channel2 = I
109 * and Z (with channel2 = IIO_MOD_Z
110 */
111 }
112
113 Here **scan_index** defines the order in which
114 inside the buffer. Channels with a lower **sca
115 channels with a higher index. Each channel nee
116 **scan_index**.
117
118 Setting **scan_index** to -1 can be used to in
119 does not support buffered capture. In this cas
120 the channel in the scan_elements directory.
121
122 More details
123 ============
124 .. kernel-doc:: include/linux/iio/buffer.h
125 .. kernel-doc:: drivers/iio/industrialio-buffe
126 :export:
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