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1 | ======== |
2 | Triggers | |
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 | ||
14 | In many situations it is useful for a driver to be able to capture data based | |
15 | on some external event (trigger) as opposed to periodically polling for data. | |
16 | An IIO trigger can be provided by a device driver that also has an IIO device | |
17 | based on hardware generated events (e.g. data ready or threshold exceeded) or | |
18 | provided by a separate driver from an independent interrupt source (e.g. GPIO | |
19 | line connected to some external system, timer interrupt or user space writing | |
20 | a specific file in sysfs). A trigger may initiate data capture for a number of | |
21 | sensors and also it may be completely unrelated to the sensor itself. | |
22 | ||
23 | IIO trigger sysfs interface | |
24 | =========================== | |
25 | ||
26 | There 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 | |
8c56eebc | 41 | trigger with our device by writing the trigger's name in the |
49b2fd6e JC |
42 | :file:`current_trigger` file. |
43 | ||
44 | IIO trigger setup | |
45 | ================= | |
46 | ||
47 | Let'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 | ||
65 | IIO trigger ops | |
66 | =============== | |
67 | ||
68 | * struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger. | |
69 | ||
70 | Notice 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 | ||
76 | More details | |
77 | ============ | |
78 | .. kernel-doc:: include/linux/iio/trigger.h | |
79 | .. kernel-doc:: drivers/iio/industrialio-trigger.c | |
80 | :export: |