81 lines
3.0 KiB
ReStructuredText
81 lines
3.0 KiB
ReStructuredText
========
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Triggers
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========
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* struct :c:type:`iio_trigger` — industrial I/O trigger device
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* :c:func:`devm_iio_trigger_alloc` — Resource-managed iio_trigger_alloc
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* :c:func:`devm_iio_trigger_free` — Resource-managed iio_trigger_free
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* :c:func:`devm_iio_trigger_register` — Resource-managed iio_trigger_register
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* :c:func:`devm_iio_trigger_unregister` — Resource-managed
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iio_trigger_unregister
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* :c:func:`iio_trigger_validate_own_device` — Check if a trigger and IIO
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device belong to the same device
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In many situations it is useful for a driver to be able to capture data based
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on some external event (trigger) as opposed to periodically polling for data.
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An IIO trigger can be provided by a device driver that also has an IIO device
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based on hardware generated events (e.g. data ready or threshold exceeded) or
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provided by a separate driver from an independent interrupt source (e.g. GPIO
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line connected to some external system, timer interrupt or user space writing
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a specific file in sysfs). A trigger may initiate data capture for a number of
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sensors and also it may be completely unrelated to the sensor itself.
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IIO trigger sysfs interface
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===========================
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There are two locations in sysfs related to triggers:
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* :file:`/sys/bus/iio/devices/trigger{Y}/*`, this file is created once an
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IIO trigger is registered with the IIO core and corresponds to trigger
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with index Y.
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Because triggers can be very different depending on type there are few
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standard attributes that we can describe here:
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* :file:`name`, trigger name that can be later used for association with a
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device.
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* :file:`sampling_frequency`, some timer based triggers use this attribute to
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specify the frequency for trigger calls.
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* :file:`/sys/bus/iio/devices/iio:device{X}/trigger/*`, this directory is
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created once the device supports a triggered buffer. We can associate a
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trigger with our device by writing the trigger's name in the
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:file:`current_trigger` file.
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IIO trigger setup
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=================
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Let's see a simple example of how to setup a trigger to be used by a driver::
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struct iio_trigger_ops trigger_ops = {
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.set_trigger_state = sample_trigger_state,
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.validate_device = sample_validate_device,
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}
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struct iio_trigger *trig;
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/* first, allocate memory for our trigger */
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trig = iio_trigger_alloc(dev, "trig-%s-%d", name, idx);
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/* setup trigger operations field */
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trig->ops = &trigger_ops;
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/* now register the trigger with the IIO core */
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iio_trigger_register(trig);
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IIO trigger ops
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===============
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* struct :c:type:`iio_trigger_ops` — operations structure for an iio_trigger.
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Notice that a trigger has a set of operations attached:
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* :file:`set_trigger_state`, switch the trigger on/off on demand.
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* :file:`validate_device`, function to validate the device when the current
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trigger gets changed.
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More details
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============
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.. kernel-doc:: include/linux/iio/trigger.h
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.. kernel-doc:: drivers/iio/industrialio-trigger.c
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:export:
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