1========
2Triggers
3========
4
5* struct :c:type:`iio_trigger` — industrial I/O trigger device
6* :c:func:`devm_iio_trigger_alloc` — Resource-managed iio_trigger_alloc
7* :c:func:`devm_iio_trigger_free` — Resource-managed iio_trigger_free
8* :c:func:`devm_iio_trigger_register` — Resource-managed iio_trigger_register
9* :c:func:`devm_iio_trigger_unregister` — Resource-managed
10  iio_trigger_unregister
11* :c:func:`iio_trigger_validate_own_device` — Check if a trigger and IIO
12  device belong to the same device
13
14In many situations it is useful for a driver to be able to capture data based
15on some external event (trigger) as opposed to periodically polling for data.
16An IIO trigger can be provided by a device driver that also has an IIO device
17based on hardware generated events (e.g. data ready or threshold exceeded) or
18provided by a separate driver from an independent interrupt source (e.g. GPIO
19line connected to some external system, timer interrupt or user space writing
20a specific file in sysfs). A trigger may initiate data capture for a number of
21sensors and also it may be completely unrelated to the sensor itself.
22
23IIO trigger sysfs interface
24===========================
25
26There are two locations in sysfs related to triggers:
27
28* :file:`/sys/bus/iio/devices/trigger{Y}/*`, this file is created once an
29  IIO trigger is registered with the IIO core and corresponds to trigger
30  with index Y.
31  Because triggers can be very different depending on type there are few
32  standard attributes that we can describe here:
33
34  * :file:`name`, trigger name that can be later used for association with a
35    device.
36  * :file:`sampling_frequency`, some timer based triggers use this attribute to
37    specify the frequency for trigger calls.
38
39* :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is
40  created once the device supports a triggered buffer. We can associate a
41  trigger with our device by writing the trigger's name in the
42  :file:`current_trigger` file.
43
44IIO trigger setup
45=================
46
47Let's see a simple example of how to setup a trigger to be used by a driver::
48
49      struct iio_trigger_ops trigger_ops = {
50          .set_trigger_state = sample_trigger_state,
51          .validate_device = sample_validate_device,
52      }
53
54      struct iio_trigger *trig;
55
56      /* first, allocate memory for our trigger */
57      trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
58
59      /* setup trigger operations field */
60      trig->ops = &trigger_ops;
61
62      /* now register the trigger with the IIO core */
63      iio_trigger_register(trig);
64
65IIO trigger ops
66===============
67
68* struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger.
69
70Notice that a trigger has a set of operations attached:
71
72* :file:`set_trigger_state`, switch the trigger on/off on demand.
73* :file:`validate_device`, function to validate the device when the current
74  trigger gets changed.
75
76More details
77============
78.. kernel-doc:: include/linux/iio/trigger.h
79.. kernel-doc:: drivers/iio/industrialio-trigger.c
80   :export:
81