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-.. Permission is granted to copy, distribute and/or modify this
-.. document under the terms of the GNU Free Documentation License,
-.. Version 1.1 or any later version published by the Free Software
-.. Foundation, with no Invariant Sections, no Front-Cover Texts
-.. and no Back-Cover Texts. A copy of the license is included at
-.. Documentation/media/uapi/fdl-appendix.rst.
-..
-.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
-
-.. _VIDIOC_DQEVENT:
-
-********************
-ioctl VIDIOC_DQEVENT
-********************
-
-Name
-====
-
-VIDIOC_DQEVENT - Dequeue event
-
-
-Synopsis
-========
-
-.. c:function:: int ioctl( int fd, VIDIOC_DQEVENT, struct v4l2_event *argp )
- :name: VIDIOC_DQEVENT
-
-
-Arguments
-=========
-
-``fd``
- File descriptor returned by :ref:`open() <func-open>`.
-
-``argp``
- Pointer to struct :c:type:`v4l2_event`.
-
-
-Description
-===========
-
-Dequeue an event from a video device. No input is required for this
-ioctl. All the fields of the struct :c:type:`v4l2_event`
-structure are filled by the driver. The file handle will also receive
-exceptions which the application may get by e.g. using the select system
-call.
-
-
-.. tabularcolumns:: |p{3.0cm}|p{4.4cm}|p{2.4cm}|p{7.7cm}|
-
-.. c:type:: v4l2_event
-
-.. cssclass: longtable
-
-.. flat-table:: struct v4l2_event
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u32
- - ``type``
- - Type of the event, see :ref:`event-type`.
- * - union {
- - ``u``
- * - struct :c:type:`v4l2_event_vsync`
- - ``vsync``
- - Event data for event ``V4L2_EVENT_VSYNC``.
- * - struct :c:type:`v4l2_event_ctrl`
- - ``ctrl``
- - Event data for event ``V4L2_EVENT_CTRL``.
- * - struct :c:type:`v4l2_event_frame_sync`
- - ``frame_sync``
- - Event data for event ``V4L2_EVENT_FRAME_SYNC``.
- * - struct :c:type:`v4l2_event_motion_det`
- - ``motion_det``
- - Event data for event V4L2_EVENT_MOTION_DET.
- * - struct :c:type:`v4l2_event_src_change`
- - ``src_change``
- - Event data for event V4L2_EVENT_SOURCE_CHANGE.
- * - __u8
- - ``data``\ [64]
- - Event data. Defined by the event type. The union should be used to
- define easily accessible type for events.
- * - }
- -
- * - __u32
- - ``pending``
- - Number of pending events excluding this one.
- * - __u32
- - ``sequence``
- - Event sequence number. The sequence number is incremented for
- every subscribed event that takes place. If sequence numbers are
- not contiguous it means that events have been lost.
- * - struct timespec
- - ``timestamp``
- - Event timestamp. The timestamp has been taken from the
- ``CLOCK_MONOTONIC`` clock. To access the same clock outside V4L2,
- use :c:func:`clock_gettime`.
- * - u32
- - ``id``
- - The ID associated with the event source. If the event does not
- have an associated ID (this depends on the event type), then this
- is 0.
- * - __u32
- - ``reserved``\ [8]
- - Reserved for future extensions. Drivers must set the array to
- zero.
-
-
-
-.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
-
-.. cssclass:: longtable
-
-.. _event-type:
-
-.. flat-table:: Event Types
- :header-rows: 0
- :stub-columns: 0
- :widths: 3 1 4
-
- * - ``V4L2_EVENT_ALL``
- - 0
- - All events. V4L2_EVENT_ALL is valid only for
- VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.
- * - ``V4L2_EVENT_VSYNC``
- - 1
- - This event is triggered on the vertical sync. This event has a
- struct :c:type:`v4l2_event_vsync` associated
- with it.
- * - ``V4L2_EVENT_EOS``
- - 2
- - This event is triggered when the end of a stream is reached. This
- is typically used with MPEG decoders to report to the application
- when the last of the MPEG stream has been decoded.
- * - ``V4L2_EVENT_CTRL``
- - 3
- - This event requires that the ``id`` matches the control ID from
- which you want to receive events. This event is triggered if the
- control's value changes, if a button control is pressed or if the
- control's flags change. This event has a struct
- :c:type:`v4l2_event_ctrl` associated with it.
- This struct contains much of the same information as struct
- :ref:`v4l2_queryctrl <v4l2-queryctrl>` and struct
- :c:type:`v4l2_control`.
-
- If the event is generated due to a call to
- :ref:`VIDIOC_S_CTRL <VIDIOC_G_CTRL>` or
- :ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>`, then the
- event will *not* be sent to the file handle that called the ioctl
- function. This prevents nasty feedback loops. If you *do* want to
- get the event, then set the ``V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK``
- flag.
-
- This event type will ensure that no information is lost when more
- events are raised than there is room internally. In that case the
- struct :c:type:`v4l2_event_ctrl` of the
- second-oldest event is kept, but the ``changes`` field of the
- second-oldest event is ORed with the ``changes`` field of the
- oldest event.
- * - ``V4L2_EVENT_FRAME_SYNC``
- - 4
- - Triggered immediately when the reception of a frame has begun.
- This event has a struct
- :c:type:`v4l2_event_frame_sync`
- associated with it.
-
- If the hardware needs to be stopped in the case of a buffer
- underrun it might not be able to generate this event. In such
- cases the ``frame_sequence`` field in struct
- :c:type:`v4l2_event_frame_sync` will not
- be incremented. This causes two consecutive frame sequence numbers
- to have n times frame interval in between them.
- * - ``V4L2_EVENT_SOURCE_CHANGE``
- - 5
- - This event is triggered when a source parameter change is detected
- during runtime by the video device. It can be a runtime resolution
- change triggered by a video decoder or the format change happening
- on an input connector. This event requires that the ``id`` matches
- the input index (when used with a video device node) or the pad
- index (when used with a subdevice node) from which you want to
- receive events.
-
- This event has a struct
- :c:type:`v4l2_event_src_change`
- associated with it. The ``changes`` bitfield denotes what has
- changed for the subscribed pad. If multiple events occurred before
- application could dequeue them, then the changes will have the
- ORed value of all the events generated.
- * - ``V4L2_EVENT_MOTION_DET``
- - 6
- - Triggered whenever the motion detection state for one or more of
- the regions changes. This event has a struct
- :c:type:`v4l2_event_motion_det`
- associated with it.
- * - ``V4L2_EVENT_PRIVATE_START``
- - 0x08000000
- - Base event number for driver-private events.
-
-
-
-.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
-
-.. c:type:: v4l2_event_vsync
-
-.. flat-table:: struct v4l2_event_vsync
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u8
- - ``field``
- - The upcoming field. See enum :c:type:`v4l2_field`.
-
-
-
-.. tabularcolumns:: |p{3.5cm}|p{3.0cm}|p{1.8cm}|p{8.5cm}|
-
-.. c:type:: v4l2_event_ctrl
-
-.. flat-table:: struct v4l2_event_ctrl
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u32
- - ``changes``
- - A bitmask that tells what has changed. See
- :ref:`ctrl-changes-flags`.
- * - __u32
- - ``type``
- - The type of the control. See enum
- :c:type:`v4l2_ctrl_type`.
- * - union {
- - (anonymous)
- * - __s32
- - ``value``
- - The 32-bit value of the control for 32-bit control types. This is
- 0 for string controls since the value of a string cannot be passed
- using :ref:`VIDIOC_DQEVENT`.
- * - __s64
- - ``value64``
- - The 64-bit value of the control for 64-bit control types.
- * - }
- -
- * - __u32
- - ``flags``
- - The control flags. See :ref:`control-flags`.
- * - __s32
- - ``minimum``
- - The minimum value of the control. See struct
- :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
- * - __s32
- - ``maximum``
- - The maximum value of the control. See struct
- :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
- * - __s32
- - ``step``
- - The step value of the control. See struct
- :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
- * - __s32
- - ``default_value``
- - The default value value of the control. See struct
- :ref:`v4l2_queryctrl <v4l2-queryctrl>`.
-
-
-
-.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
-
-.. c:type:: v4l2_event_frame_sync
-
-.. flat-table:: struct v4l2_event_frame_sync
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u32
- - ``frame_sequence``
- - The sequence number of the frame being received.
-
-
-
-.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
-
-.. c:type:: v4l2_event_src_change
-
-.. flat-table:: struct v4l2_event_src_change
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u32
- - ``changes``
- - A bitmask that tells what has changed. See
- :ref:`src-changes-flags`.
-
-
-
-.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|
-
-.. c:type:: v4l2_event_motion_det
-
-.. flat-table:: struct v4l2_event_motion_det
- :header-rows: 0
- :stub-columns: 0
- :widths: 1 1 2
-
- * - __u32
- - ``flags``
- - Currently only one flag is available: if
- ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` is set, then the
- ``frame_sequence`` field is valid, otherwise that field should be
- ignored.
- * - __u32
- - ``frame_sequence``
- - The sequence number of the frame being received. Only valid if the
- ``V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ`` flag was set.
- * - __u32
- - ``region_mask``
- - The bitmask of the regions that reported motion. There is at least
- one region. If this field is 0, then no motion was detected at
- all. If there is no ``V4L2_CID_DETECT_MD_REGION_GRID`` control
- (see :ref:`detect-controls`) to assign a different region to
- each cell in the motion detection grid, then that all cells are
- automatically assigned to the default region 0.
-
-
-
-.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
-
-.. _ctrl-changes-flags:
-
-.. flat-table:: Control Changes
- :header-rows: 0
- :stub-columns: 0
- :widths: 3 1 4
-
- * - ``V4L2_EVENT_CTRL_CH_VALUE``
- - 0x0001
- - This control event was triggered because the value of the control
- changed. Special cases: Volatile controls do no generate this
- event; If a control has the ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
- flag set, then this event is sent as well, regardless its value.
- * - ``V4L2_EVENT_CTRL_CH_FLAGS``
- - 0x0002
- - This control event was triggered because the control flags
- changed.
- * - ``V4L2_EVENT_CTRL_CH_RANGE``
- - 0x0004
- - This control event was triggered because the minimum, maximum,
- step or the default value of the control changed.
-
-
-
-.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
-
-.. _src-changes-flags:
-
-.. flat-table:: Source Changes
- :header-rows: 0
- :stub-columns: 0
- :widths: 3 1 4
-
- * - ``V4L2_EVENT_SRC_CH_RESOLUTION``
- - 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. Applications will have to query the new resolution (if
- any, the signal may also have been lost).
-
- For stateful decoders follow the guidelines in :ref:`decoder`.
- Video Capture devices have to query the new timings using
- :ref:`VIDIOC_QUERY_DV_TIMINGS` or
- :ref:`VIDIOC_QUERYSTD <VIDIOC_QUERYSTD>`.
-
- *Important*: even if the new video timings appear identical to the old
- ones, receiving this event indicates that there was an issue with the
- video signal and you must stop and restart streaming
- (:ref:`VIDIOC_STREAMOFF <VIDIOC_STREAMON>`
- followed by :ref:`VIDIOC_STREAMON <VIDIOC_STREAMON>`). The reason is
- that many Video Capture devices are not able to recover from a temporary
- loss of signal and so restarting streaming I/O is required in order for
- the hardware to synchronize to the video signal.
-
-
-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.