391 lines
11 KiB
ReStructuredText
391 lines
11 KiB
ReStructuredText
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.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_DQEVENT:
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********************
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ioctl VIDIOC_DQEVENT
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********************
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Name
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====
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VIDIOC_DQEVENT - Dequeue event
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_DQEVENT, struct v4l2_event *argp )
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:name: VIDIOC_DQEVENT
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Pointer to struct :c:type:`v4l2_event`.
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Description
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===========
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Dequeue an event from a video device. No input is required for this
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ioctl. All the fields of the struct :c:type:`v4l2_event`
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structure are filled by the driver. The file handle will also receive
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exceptions which the application may get by e.g. using the select system
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call.
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.. tabularcolumns:: |p{3.0cm}|p{4.4cm}|p{2.4cm}|p{7.7cm}|
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.. c:type:: v4l2_event
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.. cssclass: longtable
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.. flat-table:: struct v4l2_event
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2 1
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* - __u32
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- ``type``
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-
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- Type of the event, see :ref:`event-type`.
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* - union
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- ``u``
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-
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-
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* -
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- struct :c:type:`v4l2_event_vsync`
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- ``vsync``
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- Event data for event ``V4L2_EVENT_VSYNC``.
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* -
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- struct :c:type:`v4l2_event_ctrl`
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- ``ctrl``
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- Event data for event ``V4L2_EVENT_CTRL``.
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* -
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- struct :c:type:`v4l2_event_frame_sync`
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- ``frame_sync``
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- Event data for event ``V4L2_EVENT_FRAME_SYNC``.
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* -
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- struct :c:type:`v4l2_event_motion_det`
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- ``motion_det``
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- Event data for event V4L2_EVENT_MOTION_DET.
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* -
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- struct :c:type:`v4l2_event_src_change`
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- ``src_change``
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- Event data for event V4L2_EVENT_SOURCE_CHANGE.
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* -
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- __u8
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- ``data``\ [64]
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- Event data. Defined by the event type. The union should be used to
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define easily accessible type for events.
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* - __u32
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- ``pending``
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-
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- Number of pending events excluding this one.
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* - __u32
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- ``sequence``
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-
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- Event sequence number. The sequence number is incremented for
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every subscribed event that takes place. If sequence numbers are
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not contiguous it means that events have been lost.
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* - struct timespec
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- ``timestamp``
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-
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- Event timestamp. The timestamp has been taken from the
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``CLOCK_MONOTONIC`` clock. To access the same clock outside V4L2,
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use :c:func:`clock_gettime`.
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* - u32
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- ``id``
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-
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- The ID associated with the event source. If the event does not
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have an associated ID (this depends on the event type), then this
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is 0.
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* - __u32
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- ``reserved``\ [8]
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-
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- Reserved for future extensions. Drivers must set the array to
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zero.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. cssclass:: longtable
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.. _event-type:
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.. flat-table:: Event Types
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_EVENT_ALL``
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- 0
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- All events. V4L2_EVENT_ALL is valid only for
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VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
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* - ``V4L2_EVENT_VSYNC``
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- 1
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- This event is triggered on the vertical sync. This event has a
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struct :c:type:`v4l2_event_vsync` associated
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with it.
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* - ``V4L2_EVENT_EOS``
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- 2
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- This event is triggered when the end of a stream is reached. This
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is typically used with MPEG decoders to report to the application
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when the last of the MPEG stream has been decoded.
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* - ``V4L2_EVENT_CTRL``
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- 3
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- This event requires that the ``id`` matches the control ID from
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which you want to receive events. This event is triggered if the
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control's value changes, if a button control is pressed or if the
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control's flags change. This event has a struct
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:c:type:`v4l2_event_ctrl` associated with it.
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This struct contains much of the same information as struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>` and struct
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:c:type:`v4l2_control`.
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If the event is generated due to a call to
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:ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` or
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:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then the
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event will *not* be sent to the file handle that called the ioctl
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function. This prevents nasty feedback loops. If you *do* want to
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get the event, then set the ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
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flag.
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This event type will ensure that no information is lost when more
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events are raised than there is room internally. In that case the
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struct :c:type:`v4l2_event_ctrl` of the
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second-oldest event is kept, but the ``changes`` field of the
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second-oldest event is ORed with the ``changes`` field of the
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oldest event.
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* - ``V4L2_EVENT_FRAME_SYNC``
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- 4
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- Triggered immediately when the reception of a frame has begun.
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This event has a struct
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:c:type:`v4l2_event_frame_sync`
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associated with it.
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If the hardware needs to be stopped in the case of a buffer
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underrun it might not be able to generate this event. In such
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cases the ``frame_sequence`` field in struct
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:c:type:`v4l2_event_frame_sync` will not
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be incremented. This causes two consecutive frame sequence numbers
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to have n times frame interval in between them.
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* - ``V4L2_EVENT_SOURCE_CHANGE``
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- 5
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- This event is triggered when a source parameter change is detected
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during runtime by the video device. It can be a runtime resolution
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change triggered by a video decoder or the format change happening
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on an input connector. This event requires that the ``id`` matches
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the input index (when used with a video device node) or the pad
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index (when used with a subdevice node) from which you want to
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receive events.
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This event has a struct
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:c:type:`v4l2_event_src_change`
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associated with it. The ``changes`` bitfield denotes what has
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changed for the subscribed pad. If multiple events occurred before
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application could dequeue them, then the changes will have the
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ORed value of all the events generated.
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* - ``V4L2_EVENT_MOTION_DET``
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- 6
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- Triggered whenever the motion detection state for one or more of
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the regions changes. This event has a struct
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:c:type:`v4l2_event_motion_det`
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associated with it.
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* - ``V4L2_EVENT_PRIVATE_START``
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- 0x08000000
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- Base event number for driver-private events.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. c:type:: v4l2_event_vsync
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.. flat-table:: struct v4l2_event_vsync
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u8
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- ``field``
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- The upcoming field. See enum :c:type:`v4l2_field`.
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.. tabularcolumns:: |p{3.5cm}|p{3.0cm}|p{1.8cm}|p{8.5cm}|
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.. c:type:: v4l2_event_ctrl
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.. flat-table:: struct v4l2_event_ctrl
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2 1
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* - __u32
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- ``changes``
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-
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- A bitmask that tells what has changed. See
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:ref:`ctrl-changes-flags`.
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* - __u32
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- ``type``
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-
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- The type of the control. See enum
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:c:type:`v4l2_ctrl_type`.
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* - union (anonymous)
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-
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-
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-
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* -
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- __s32
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- ``value``
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- The 32-bit value of the control for 32-bit control types. This is
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0 for string controls since the value of a string cannot be passed
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using :ref:`VIDIOC_DQEVENT`.
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* -
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- __s64
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- ``value64``
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- The 64-bit value of the control for 64-bit control types.
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* - __u32
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- ``flags``
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-
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- The control flags. See :ref:`control-flags`.
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* - __s32
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- ``minimum``
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-
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- The minimum value of the control. See struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>`.
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* - __s32
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- ``maximum``
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-
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- The maximum value of the control. See struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>`.
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* - __s32
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- ``step``
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-
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- The step value of the control. See struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>`.
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* - __s32
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- ``default_value``
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-
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- The default value value of the control. See struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>`.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. c:type:: v4l2_event_frame_sync
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.. flat-table:: struct v4l2_event_frame_sync
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``frame_sequence``
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- The sequence number of the frame being received.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. c:type:: v4l2_event_src_change
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.. flat-table:: struct v4l2_event_src_change
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``changes``
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- A bitmask that tells what has changed. See
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:ref:`src-changes-flags`.
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
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.. c:type:: v4l2_event_motion_det
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.. flat-table:: struct v4l2_event_motion_det
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``flags``
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- Currently only one flag is available: if
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``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` is set, then the
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``frame_sequence`` field is valid, otherwise that field should be
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ignored.
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* - __u32
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- ``frame_sequence``
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- The sequence number of the frame being received. Only valid if the
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``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` flag was set.
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* - __u32
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- ``region_mask``
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- The bitmask of the regions that reported motion. There is at least
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one region. If this field is 0, then no motion was detected at
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all. If there is no ``V4L2_CID_DETECT_MD_REGION_GRID`` control
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(see :ref:`detect-controls`) to assign a different region to
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each cell in the motion detection grid, then that all cells are
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automatically assigned to the default region 0.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _ctrl-changes-flags:
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.. flat-table:: Control Changes
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_EVENT_CTRL_CH_VALUE``
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- 0x0001
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- This control event was triggered because the value of the control
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changed. Special cases: Volatile controls do no generate this
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event; If a control has the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
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flag set, then this event is sent as well, regardless its value.
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* - ``V4L2_EVENT_CTRL_CH_FLAGS``
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- 0x0002
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- This control event was triggered because the control flags
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changed.
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* - ``V4L2_EVENT_CTRL_CH_RANGE``
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- 0x0004
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- This control event was triggered because the minimum, maximum,
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step or the default value of the control changed.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _src-changes-flags:
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.. flat-table:: Source Changes
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_EVENT_SRC_CH_RESOLUTION``
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|
- 0x0001
|
||
|
|
- This event gets triggered when a resolution change is detected at
|
||
|
|
an input. This can come from an input connector or from a video
|
||
|
|
decoder.
|
||
|
|
|
||
|
|
|
||
|
|
Return Value
|
||
|
|
============
|
||
|
|
|
||
|
|
On success 0 is returned, on error -1 and the ``errno`` variable is set
|
||
|
|
appropriately. The generic error codes are described at the
|
||
|
|
:ref:`Generic Error Codes <gen-errors>` chapter.
|