551 lines
20 KiB
ReStructuredText
551 lines
20 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_QUERYCTRL:
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*******************************************************************
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ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
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*******************************************************************
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Name
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====
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VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items
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Synopsis
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========
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.. c:function:: int ioctl( int fd, int VIDIOC_QUERYCTRL, struct v4l2_queryctrl *argp )
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:name: VIDIOC_QUERYCTRL
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.. c:function:: int ioctl( int fd, VIDIOC_QUERY_EXT_CTRL, struct v4l2_query_ext_ctrl *argp )
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:name: VIDIOC_QUERY_EXT_CTRL
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.. c:function:: int ioctl( int fd, VIDIOC_QUERYMENU, struct v4l2_querymenu *argp )
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:name: VIDIOC_QUERYMENU
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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_queryctl`, :c:type:`v4l2_query_ext_ctrl`
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or :c:type`v4l2_querymenu` (depending on the ioctl).
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Description
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===========
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To query the attributes of a control applications set the ``id`` field
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of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the
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``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver
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fills the rest of the structure or returns an ``EINVAL`` error code when the
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``id`` is invalid.
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It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL``
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with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and
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exclusive ``V4L2_CID_LASTP1``. Drivers may return ``EINVAL`` if a control in
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this range is not supported. Further applications can enumerate private
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controls, which are not defined in this specification, by starting at
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``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver
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returns ``EINVAL``.
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In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag
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in the ``flags`` field this control is permanently disabled and should
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be ignored by the application. [#f1]_
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When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the
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driver returns the next supported non-compound control, or ``EINVAL`` if
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there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag
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can be specified to enumerate all compound controls (i.e. controls with
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type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words
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controls that contain more than one value). Specify both
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``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in
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order to enumerate all controls, compound or not. Drivers which do not
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support these flags yet always return ``EINVAL``.
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The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better
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support controls that can use compound types, and to expose additional
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control information that cannot be returned in struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full.
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``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as
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``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed
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as well.
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Additional information is required for menu controls: the names of the
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menu items. To query them applications set the ``id`` and ``index``
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fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the
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``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver
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fills the rest of the structure or returns an ``EINVAL`` error code when the
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``id`` or ``index`` is invalid. Menu items are enumerated by calling
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``VIDIOC_QUERYMENU`` with successive ``index`` values from struct
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:ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``,
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inclusive.
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.. note::
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It is possible for ``VIDIOC_QUERYMENU`` to return
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an ``EINVAL`` error code for some indices between ``minimum`` and
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``maximum``. In that case that particular menu item is not supported by
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this driver. Also note that the ``minimum`` value is not necessarily 0.
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See also the examples in :ref:`control`.
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.. tabularcolumns:: |p{1.2cm}|p{3.6cm}|p{12.7cm}|
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.. _v4l2-queryctrl:
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.. cssclass:: longtable
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.. flat-table:: struct v4l2_queryctrl
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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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- ``id``
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- Identifies the control, set by the application. See
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:ref:`control-id` for predefined IDs. When the ID is ORed with
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V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and
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returns the first control with a higher ID. Drivers which do not
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support this flag yet always return an ``EINVAL`` error code.
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* - __u32
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- ``type``
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- Type of control, see :c:type:`v4l2_ctrl_type`.
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* - __u8
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- ``name``\ [32]
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- Name of the control, a NUL-terminated ASCII string. This
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information is intended for the user.
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* - __s32
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- ``minimum``
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- Minimum value, inclusive. This field gives a lower bound for the
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control. See enum :c:type:`v4l2_ctrl_type` how
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the minimum value is to be used for each possible control type.
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Note that this a signed 32-bit value.
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* - __s32
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- ``maximum``
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- Maximum value, inclusive. This field gives an upper bound for the
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control. See enum :c:type:`v4l2_ctrl_type` how
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the maximum value is to be used for each possible control type.
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Note that this a signed 32-bit value.
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* - __s32
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- ``step``
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- This field gives a step size for the control. See enum
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:c:type:`v4l2_ctrl_type` how the step value is
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to be used for each possible control type. Note that this an
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unsigned 32-bit value.
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Generally drivers should not scale hardware control values. It may
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be necessary for example when the ``name`` or ``id`` imply a
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particular unit and the hardware actually accepts only multiples
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of said unit. If so, drivers must take care values are properly
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rounded when scaling, such that errors will not accumulate on
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repeated read-write cycles.
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This field gives the smallest change of an integer control
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actually affecting hardware. Often the information is needed when
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the user can change controls by keyboard or GUI buttons, rather
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than a slider. When for example a hardware register accepts values
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0-511 and the driver reports 0-65535, step should be 128.
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Note that although signed, the step value is supposed to be always
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positive.
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* - __s32
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- ``default_value``
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- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
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``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
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for other types of controls.
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.. note::
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Drivers reset controls to their default value only when
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the driver is first loaded, never afterwards.
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* - __u32
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- ``flags``
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- Control flags, see :ref:`control-flags`.
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* - __u32
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- ``reserved``\ [2]
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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{1.2cm}|p{5.0cm}|p{11.3cm}|
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.. _v4l2-query-ext-ctrl:
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.. cssclass:: longtable
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.. flat-table:: struct v4l2_query_ext_ctrl
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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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- ``id``
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- Identifies the control, set by the application. See
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:ref:`control-id` for predefined IDs. When the ID is ORed with
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``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and
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returns the first non-compound control with a higher ID. When the
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ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears
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the flag and returns the first compound control with a higher ID.
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Set both to get the first control (compound or not) with a higher
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ID.
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* - __u32
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- ``type``
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- Type of control, see :c:type:`v4l2_ctrl_type`.
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* - char
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- ``name``\ [32]
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- Name of the control, a NUL-terminated ASCII string. This
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information is intended for the user.
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* - __s64
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- ``minimum``
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- Minimum value, inclusive. This field gives a lower bound for the
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control. See enum :c:type:`v4l2_ctrl_type` how
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the minimum value is to be used for each possible control type.
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Note that this a signed 64-bit value.
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* - __s64
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- ``maximum``
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- Maximum value, inclusive. This field gives an upper bound for the
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control. See enum :c:type:`v4l2_ctrl_type` how
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the maximum value is to be used for each possible control type.
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Note that this a signed 64-bit value.
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* - __u64
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- ``step``
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- This field gives a step size for the control. See enum
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:c:type:`v4l2_ctrl_type` how the step value is
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to be used for each possible control type. Note that this an
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unsigned 64-bit value.
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Generally drivers should not scale hardware control values. It may
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be necessary for example when the ``name`` or ``id`` imply a
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particular unit and the hardware actually accepts only multiples
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of said unit. If so, drivers must take care values are properly
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rounded when scaling, such that errors will not accumulate on
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repeated read-write cycles.
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This field gives the smallest change of an integer control
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actually affecting hardware. Often the information is needed when
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the user can change controls by keyboard or GUI buttons, rather
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than a slider. When for example a hardware register accepts values
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0-511 and the driver reports 0-65535, step should be 128.
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* - __s64
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- ``default_value``
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- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
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``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
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or ``_U16`` control. Not valid for other types of controls.
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.. note::
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Drivers reset controls to their default value only when
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the driver is first loaded, never afterwards.
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* - __u32
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- ``flags``
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- Control flags, see :ref:`control-flags`.
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* - __u32
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- ``elem_size``
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- The size in bytes of a single element of the array. Given a char
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pointer ``p`` to a 3-dimensional array you can find the position
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of cell ``(z, y, x)`` as follows:
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``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``.
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``elem_size`` is always valid, also when the control isn't an
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array. For string controls ``elem_size`` is equal to
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``maximum + 1``.
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* - __u32
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- ``elems``
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- The number of elements in the N-dimensional array. If this control
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is not an array, then ``elems`` is 1. The ``elems`` field can
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never be 0.
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* - __u32
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- ``nr_of_dims``
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- The number of dimension in the N-dimensional array. If this
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control is not an array, then this field is 0.
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* - __u32
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- ``dims[V4L2_CTRL_MAX_DIMS]``
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- The size of each dimension. The first ``nr_of_dims`` elements of
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this array must be non-zero, all remaining elements must be zero.
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* - __u32
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- ``reserved``\ [32]
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- Reserved for future extensions. Applications and drivers must set
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the array to zero.
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.. tabularcolumns:: |p{1.2cm}|p{1.0cm}|p{1.7cm}|p{13.0cm}|
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.. _v4l2-querymenu:
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.. flat-table:: struct v4l2_querymenu
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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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-
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- ``id``
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- Identifies the control, set by the application from the respective
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struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
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* - __u32
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-
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- ``index``
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- Index of the menu item, starting at zero, set by the application.
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* - union
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-
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-
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-
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* -
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- __u8
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- ``name``\ [32]
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- Name of the menu item, a NUL-terminated ASCII string. This
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information is intended for the user. This field is valid for
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``V4L2_CTRL_TYPE_MENU`` type controls.
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* -
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- __s64
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- ``value``
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- Value of the integer menu item. This field is valid for
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``V4L2_CTRL_TYPE_INTEGER_MENU`` type controls.
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* - __u32
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-
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- ``reserved``
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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{5.8cm}|p{1.4cm}|p{1.0cm}|p{1.4cm}|p{6.9cm}|
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.. c:type:: v4l2_ctrl_type
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.. cssclass:: longtable
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.. flat-table:: enum v4l2_ctrl_type
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:header-rows: 1
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:stub-columns: 0
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:widths: 30 5 5 5 55
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* - Type
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- ``minimum``
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- ``step``
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- ``maximum``
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- Description
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* - ``V4L2_CTRL_TYPE_INTEGER``
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- any
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- any
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- any
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- An integer-valued control ranging from minimum to maximum
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inclusive. The step value indicates the increment between values.
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* - ``V4L2_CTRL_TYPE_BOOLEAN``
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- 0
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- 1
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- 1
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- A boolean-valued control. Zero corresponds to "disabled", and one
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means "enabled".
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* - ``V4L2_CTRL_TYPE_MENU``
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- ≥ 0
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- 1
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- N-1
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- The control has a menu of N choices. The names of the menu items
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can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
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* - ``V4L2_CTRL_TYPE_INTEGER_MENU``
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- ≥ 0
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- 1
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- N-1
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- The control has a menu of N choices. The values of the menu items
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can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is
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similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings,
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the menu items are signed 64-bit integers.
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* - ``V4L2_CTRL_TYPE_BITMASK``
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- 0
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- n/a
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- any
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- A bitmask field. The maximum value is the set of bits that can be
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used, all other bits are to be 0. The maximum value is interpreted
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as a __u32, allowing the use of bit 31 in the bitmask.
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* - ``V4L2_CTRL_TYPE_BUTTON``
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- 0
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- 0
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- 0
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- A control which performs an action when set. Drivers must ignore
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the value passed with ``VIDIOC_S_CTRL`` and return an ``EINVAL`` error
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code on a ``VIDIOC_G_CTRL`` attempt.
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* - ``V4L2_CTRL_TYPE_INTEGER64``
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- any
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- any
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- any
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- A 64-bit integer valued control. Minimum, maximum and step size
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cannot be queried using ``VIDIOC_QUERYCTRL``. Only
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``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step
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values, they should be interpreted as n/a when using
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``VIDIOC_QUERYCTRL``.
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* - ``V4L2_CTRL_TYPE_STRING``
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- ≥ 0
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- ≥ 1
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- ≥ 0
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- The minimum and maximum string lengths. The step size means that
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the string must be (minimum + N * step) characters long for N ≥ 0.
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These lengths do not include the terminating zero, so in order to
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pass a string of length 8 to
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:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
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set the ``size`` field of struct
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:c:type:`v4l2_ext_control` to 9. For
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:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
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the ``size`` field to ``maximum`` + 1. Which character encoding is
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used will depend on the string control itself and should be part
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of the control documentation.
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* - ``V4L2_CTRL_TYPE_CTRL_CLASS``
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- n/a
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- n/a
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- n/a
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- This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a
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control ID equal to a control class code (see :ref:`ctrl-class`)
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+ 1, the ioctl returns the name of the control class and this
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control type. Older drivers which do not support this feature
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return an ``EINVAL`` error code.
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* - ``V4L2_CTRL_TYPE_U8``
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- any
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- any
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- any
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- An unsigned 8-bit valued control ranging from minimum to maximum
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inclusive. The step value indicates the increment between values.
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* - ``V4L2_CTRL_TYPE_U16``
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- any
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- any
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- any
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- An unsigned 16-bit valued control ranging from minimum to maximum
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inclusive. The step value indicates the increment between values.
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* - ``V4L2_CTRL_TYPE_U32``
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- any
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- any
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- any
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- An unsigned 32-bit valued control ranging from minimum to maximum
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inclusive. The step value indicates the increment between values.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _control-flags:
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.. cssclass:: longtable
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.. flat-table:: Control Flags
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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_CTRL_FLAG_DISABLED``
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- 0x0001
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- This control is permanently disabled and should be ignored by the
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application. Any attempt to change the control will result in an
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``EINVAL`` error code.
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* - ``V4L2_CTRL_FLAG_GRABBED``
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- 0x0002
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- This control is temporarily unchangeable, for example because
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another application took over control of the respective resource.
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Such controls may be displayed specially in a user interface.
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Attempts to change the control may result in an ``EBUSY`` error code.
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* - ``V4L2_CTRL_FLAG_READ_ONLY``
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- 0x0004
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- This control is permanently readable only. Any attempt to change
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the control will result in an ``EINVAL`` error code.
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* - ``V4L2_CTRL_FLAG_UPDATE``
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- 0x0008
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- A hint that changing this control may affect the value of other
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controls within the same control class. Applications should update
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their user interface accordingly.
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* - ``V4L2_CTRL_FLAG_INACTIVE``
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- 0x0010
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- This control is not applicable to the current configuration and
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should be displayed accordingly in a user interface. For example
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the flag may be set on a MPEG audio level 2 bitrate control when
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MPEG audio encoding level 1 was selected with another control.
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* - ``V4L2_CTRL_FLAG_SLIDER``
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- 0x0020
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- A hint that this control is best represented as a slider-like
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element in a user interface.
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* - ``V4L2_CTRL_FLAG_WRITE_ONLY``
|
|
- 0x0040
|
|
- This control is permanently writable only. Any attempt to read the
|
|
control will result in an ``EACCES`` error code error code. This flag
|
|
is typically present for relative controls or action controls
|
|
where writing a value will cause the device to carry out a given
|
|
action (e. g. motor control) but no meaningful value can be
|
|
returned.
|
|
* - ``V4L2_CTRL_FLAG_VOLATILE``
|
|
- 0x0080
|
|
- This control is volatile, which means that the value of the
|
|
control changes continuously. A typical example would be the
|
|
current gain value if the device is in auto-gain mode. In such a
|
|
case the hardware calculates the gain value based on the lighting
|
|
conditions which can change over time.
|
|
|
|
.. note::
|
|
|
|
Setting a new value for a volatile control will be ignored
|
|
unless
|
|
:ref:`V4L2_CTRL_FLAG_EXECUTE_ON_WRITE <FLAG_EXECUTE_ON_WRITE>`
|
|
is also set.
|
|
Setting a new value for a volatile control will *never* trigger a
|
|
:ref:`V4L2_EVENT_CTRL_CH_VALUE <ctrl-changes-flags>` event.
|
|
* - ``V4L2_CTRL_FLAG_HAS_PAYLOAD``
|
|
- 0x0100
|
|
- This control has a pointer type, so its value has to be accessed
|
|
using one of the pointer fields of struct
|
|
:c:type:`v4l2_ext_control`. This flag is set
|
|
for controls that are an array, string, or have a compound type.
|
|
In all cases you have to set a pointer to memory containing the
|
|
payload of the control.
|
|
* .. _FLAG_EXECUTE_ON_WRITE:
|
|
|
|
- ``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE``
|
|
- 0x0200
|
|
- The value provided to the control will be propagated to the driver
|
|
even if it remains constant. This is required when the control
|
|
represents an action on the hardware. For example: clearing an
|
|
error flag or triggering the flash. All the controls of the type
|
|
``V4L2_CTRL_TYPE_BUTTON`` have this flag set.
|
|
* .. _FLAG_MODIFY_LAYOUT:
|
|
|
|
- ``V4L2_CTRL_FLAG_MODIFY_LAYOUT``
|
|
- 0x0400
|
|
- Changing this control value may modify the layout of the
|
|
buffer (for video devices) or the media bus format (for sub-devices).
|
|
|
|
A typical example would be the ``V4L2_CID_ROTATE`` control.
|
|
|
|
Note that typically controls with this flag will also set the
|
|
``V4L2_CTRL_FLAG_GRABBED`` flag when buffers are allocated or
|
|
streaming is in progress since most drivers do not support changing
|
|
the format in that case.
|
|
|
|
|
|
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.
|
|
|
|
EINVAL
|
|
The struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id`` is
|
|
invalid. The struct :ref:`v4l2_querymenu <v4l2-querymenu>` ``id``
|
|
is invalid or ``index`` is out of range (less than ``minimum`` or
|
|
greater than ``maximum``) or this particular menu item is not
|
|
supported by the driver.
|
|
|
|
EACCES
|
|
An attempt was made to read a write-only control.
|
|
|
|
.. [#f1]
|
|
``V4L2_CTRL_FLAG_DISABLED`` was intended for two purposes: Drivers
|
|
can skip predefined controls not supported by the hardware (although
|
|
returning ``EINVAL`` would do as well), or disable predefined and private
|
|
controls after hardware detection without the trouble of reordering
|
|
control arrays and indices (``EINVAL`` cannot be used to skip private
|
|
controls because it would prematurely end the enumeration).
|