781 lines
20 KiB
ReStructuredText
781 lines
20 KiB
ReStructuredText
|
.. -*- coding: utf-8; mode: rst -*-
|
||
|
|
||
|
.. _VIDIOC_QUERYCTRL:
|
||
|
|
||
|
*******************************************************************
|
||
|
ioctls VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL and VIDIOC_QUERYMENU
|
||
|
*******************************************************************
|
||
|
|
||
|
Name
|
||
|
====
|
||
|
|
||
|
VIDIOC_QUERYCTRL - VIDIOC_QUERY_EXT_CTRL - VIDIOC_QUERYMENU - Enumerate controls and menu control items
|
||
|
|
||
|
|
||
|
Synopsis
|
||
|
========
|
||
|
|
||
|
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_queryctrl *argp )
|
||
|
|
||
|
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_query_ext_ctrl *argp )
|
||
|
|
||
|
.. cpp:function:: int ioctl( int fd, int request, struct v4l2_querymenu *argp )
|
||
|
|
||
|
|
||
|
Arguments
|
||
|
=========
|
||
|
|
||
|
``fd``
|
||
|
File descriptor returned by :ref:`open() <func-open>`.
|
||
|
|
||
|
``request``
|
||
|
VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU
|
||
|
|
||
|
``argp``
|
||
|
|
||
|
|
||
|
Description
|
||
|
===========
|
||
|
|
||
|
To query the attributes of a control applications set the ``id`` field
|
||
|
of a struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` and call the
|
||
|
``VIDIOC_QUERYCTRL`` ioctl with a pointer to this structure. The driver
|
||
|
fills the rest of the structure or returns an ``EINVAL`` error code when the
|
||
|
``id`` is invalid.
|
||
|
|
||
|
It is possible to enumerate controls by calling ``VIDIOC_QUERYCTRL``
|
||
|
with successive ``id`` values starting from ``V4L2_CID_BASE`` up to and
|
||
|
exclusive ``V4L2_CID_LASTP1``. Drivers may return ``EINVAL`` if a control in
|
||
|
this range is not supported. Further applications can enumerate private
|
||
|
controls, which are not defined in this specification, by starting at
|
||
|
``V4L2_CID_PRIVATE_BASE`` and incrementing ``id`` until the driver
|
||
|
returns ``EINVAL``.
|
||
|
|
||
|
In both cases, when the driver sets the ``V4L2_CTRL_FLAG_DISABLED`` flag
|
||
|
in the ``flags`` field this control is permanently disabled and should
|
||
|
be ignored by the application. [1]_
|
||
|
|
||
|
When the application ORs ``id`` with ``V4L2_CTRL_FLAG_NEXT_CTRL`` the
|
||
|
driver returns the next supported non-compound control, or ``EINVAL`` if
|
||
|
there is none. In addition, the ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` flag
|
||
|
can be specified to enumerate all compound controls (i.e. controls with
|
||
|
type ≥ ``V4L2_CTRL_COMPOUND_TYPES`` and/or array control, in other words
|
||
|
controls that contain more than one value). Specify both
|
||
|
``V4L2_CTRL_FLAG_NEXT_CTRL`` and ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` in
|
||
|
order to enumerate all controls, compound or not. Drivers which do not
|
||
|
support these flags yet always return ``EINVAL``.
|
||
|
|
||
|
The ``VIDIOC_QUERY_EXT_CTRL`` ioctl was introduced in order to better
|
||
|
support controls that can use compound types, and to expose additional
|
||
|
control information that cannot be returned in struct
|
||
|
:ref:`v4l2_queryctrl <v4l2-queryctrl>` since that structure is full.
|
||
|
|
||
|
``VIDIOC_QUERY_EXT_CTRL`` is used in the same way as
|
||
|
``VIDIOC_QUERYCTRL``, except that the ``reserved`` array must be zeroed
|
||
|
as well.
|
||
|
|
||
|
Additional information is required for menu controls: the names of the
|
||
|
menu items. To query them applications set the ``id`` and ``index``
|
||
|
fields of struct :ref:`v4l2_querymenu <v4l2-querymenu>` and call the
|
||
|
``VIDIOC_QUERYMENU`` ioctl with a pointer to this structure. The driver
|
||
|
fills the rest of the structure or returns an ``EINVAL`` error code when the
|
||
|
``id`` or ``index`` is invalid. Menu items are enumerated by calling
|
||
|
``VIDIOC_QUERYMENU`` with successive ``index`` values from struct
|
||
|
:ref:`v4l2_queryctrl <v4l2-queryctrl>` ``minimum`` to ``maximum``,
|
||
|
inclusive. Note that it is possible for ``VIDIOC_QUERYMENU`` to return
|
||
|
an ``EINVAL`` error code for some indices between ``minimum`` and
|
||
|
``maximum``. In that case that particular menu item is not supported by
|
||
|
this driver. Also note that the ``minimum`` value is not necessarily 0.
|
||
|
|
||
|
See also the examples in :ref:`control`.
|
||
|
|
||
|
|
||
|
.. _v4l2-queryctrl:
|
||
|
|
||
|
.. flat-table:: struct v4l2_queryctrl
|
||
|
:header-rows: 0
|
||
|
:stub-columns: 0
|
||
|
:widths: 1 1 2
|
||
|
|
||
|
|
||
|
- .. row 1
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``id``
|
||
|
|
||
|
- Identifies the control, set by the application. See
|
||
|
:ref:`control-id` for predefined IDs. When the ID is ORed with
|
||
|
V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and
|
||
|
returns the first control with a higher ID. Drivers which do not
|
||
|
support this flag yet always return an ``EINVAL`` error code.
|
||
|
|
||
|
- .. row 2
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``type``
|
||
|
|
||
|
- Type of control, see :ref:`v4l2-ctrl-type`.
|
||
|
|
||
|
- .. row 3
|
||
|
|
||
|
- __u8
|
||
|
|
||
|
- ``name``\ [32]
|
||
|
|
||
|
- Name of the control, a NUL-terminated ASCII string. This
|
||
|
information is intended for the user.
|
||
|
|
||
|
- .. row 4
|
||
|
|
||
|
- __s32
|
||
|
|
||
|
- ``minimum``
|
||
|
|
||
|
- Minimum value, inclusive. This field gives a lower bound for the
|
||
|
control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
|
||
|
the minimum value is to be used for each possible control type.
|
||
|
Note that this a signed 32-bit value.
|
||
|
|
||
|
- .. row 5
|
||
|
|
||
|
- __s32
|
||
|
|
||
|
- ``maximum``
|
||
|
|
||
|
- Maximum value, inclusive. This field gives an upper bound for the
|
||
|
control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
|
||
|
the maximum value is to be used for each possible control type.
|
||
|
Note that this a signed 32-bit value.
|
||
|
|
||
|
- .. row 6
|
||
|
|
||
|
- __s32
|
||
|
|
||
|
- ``step``
|
||
|
|
||
|
- This field gives a step size for the control. See enum
|
||
|
:ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
|
||
|
to be used for each possible control type. Note that this an
|
||
|
unsigned 32-bit value.
|
||
|
|
||
|
Generally drivers should not scale hardware control values. It may
|
||
|
be necessary for example when the ``name`` or ``id`` imply a
|
||
|
particular unit and the hardware actually accepts only multiples
|
||
|
of said unit. If so, drivers must take care values are properly
|
||
|
rounded when scaling, such that errors will not accumulate on
|
||
|
repeated read-write cycles.
|
||
|
|
||
|
This field gives the smallest change of an integer control
|
||
|
actually affecting hardware. Often the information is needed when
|
||
|
the user can change controls by keyboard or GUI buttons, rather
|
||
|
than a slider. When for example a hardware register accepts values
|
||
|
0-511 and the driver reports 0-65535, step should be 128.
|
||
|
|
||
|
Note that although signed, the step value is supposed to be always
|
||
|
positive.
|
||
|
|
||
|
- .. row 7
|
||
|
|
||
|
- __s32
|
||
|
|
||
|
- ``default_value``
|
||
|
|
||
|
- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_BOOLEAN``,
|
||
|
``_BITMASK``, ``_MENU`` or ``_INTEGER_MENU`` control. Not valid
|
||
|
for other types of controls. Note that drivers reset controls to
|
||
|
their default value only when the driver is first loaded, never
|
||
|
afterwards.
|
||
|
|
||
|
- .. row 8
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``flags``
|
||
|
|
||
|
- Control flags, see :ref:`control-flags`.
|
||
|
|
||
|
- .. row 9
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``reserved``\ [2]
|
||
|
|
||
|
- Reserved for future extensions. Drivers must set the array to
|
||
|
zero.
|
||
|
|
||
|
|
||
|
|
||
|
.. _v4l2-query-ext-ctrl:
|
||
|
|
||
|
.. flat-table:: struct v4l2_query_ext_ctrl
|
||
|
:header-rows: 0
|
||
|
:stub-columns: 0
|
||
|
:widths: 1 1 2
|
||
|
|
||
|
|
||
|
- .. row 1
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``id``
|
||
|
|
||
|
- Identifies the control, set by the application. See
|
||
|
:ref:`control-id` for predefined IDs. When the ID is ORed with
|
||
|
``V4L2_CTRL_FLAG_NEXT_CTRL`` the driver clears the flag and
|
||
|
returns the first non-compound control with a higher ID. When the
|
||
|
ID is ORed with ``V4L2_CTRL_FLAG_NEXT_COMPOUND`` the driver clears
|
||
|
the flag and returns the first compound control with a higher ID.
|
||
|
Set both to get the first control (compound or not) with a higher
|
||
|
ID.
|
||
|
|
||
|
- .. row 2
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``type``
|
||
|
|
||
|
- Type of control, see :ref:`v4l2-ctrl-type`.
|
||
|
|
||
|
- .. row 3
|
||
|
|
||
|
- char
|
||
|
|
||
|
- ``name``\ [32]
|
||
|
|
||
|
- Name of the control, a NUL-terminated ASCII string. This
|
||
|
information is intended for the user.
|
||
|
|
||
|
- .. row 4
|
||
|
|
||
|
- __s64
|
||
|
|
||
|
- ``minimum``
|
||
|
|
||
|
- Minimum value, inclusive. This field gives a lower bound for the
|
||
|
control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
|
||
|
the minimum value is to be used for each possible control type.
|
||
|
Note that this a signed 64-bit value.
|
||
|
|
||
|
- .. row 5
|
||
|
|
||
|
- __s64
|
||
|
|
||
|
- ``maximum``
|
||
|
|
||
|
- Maximum value, inclusive. This field gives an upper bound for the
|
||
|
control. See enum :ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how
|
||
|
the maximum value is to be used for each possible control type.
|
||
|
Note that this a signed 64-bit value.
|
||
|
|
||
|
- .. row 6
|
||
|
|
||
|
- __u64
|
||
|
|
||
|
- ``step``
|
||
|
|
||
|
- This field gives a step size for the control. See enum
|
||
|
:ref:`v4l2_ctrl_type <v4l2-ctrl-type>` how the step value is
|
||
|
to be used for each possible control type. Note that this an
|
||
|
unsigned 64-bit value.
|
||
|
|
||
|
Generally drivers should not scale hardware control values. It may
|
||
|
be necessary for example when the ``name`` or ``id`` imply a
|
||
|
particular unit and the hardware actually accepts only multiples
|
||
|
of said unit. If so, drivers must take care values are properly
|
||
|
rounded when scaling, such that errors will not accumulate on
|
||
|
repeated read-write cycles.
|
||
|
|
||
|
This field gives the smallest change of an integer control
|
||
|
actually affecting hardware. Often the information is needed when
|
||
|
the user can change controls by keyboard or GUI buttons, rather
|
||
|
than a slider. When for example a hardware register accepts values
|
||
|
0-511 and the driver reports 0-65535, step should be 128.
|
||
|
|
||
|
- .. row 7
|
||
|
|
||
|
- __s64
|
||
|
|
||
|
- ``default_value``
|
||
|
|
||
|
- The default value of a ``V4L2_CTRL_TYPE_INTEGER``, ``_INTEGER64``,
|
||
|
``_BOOLEAN``, ``_BITMASK``, ``_MENU``, ``_INTEGER_MENU``, ``_U8``
|
||
|
or ``_U16`` control. Not valid for other types of controls. Note
|
||
|
that drivers reset controls to their default value only when the
|
||
|
driver is first loaded, never afterwards.
|
||
|
|
||
|
- .. row 8
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``flags``
|
||
|
|
||
|
- Control flags, see :ref:`control-flags`.
|
||
|
|
||
|
- .. row 9
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``elem_size``
|
||
|
|
||
|
- The size in bytes of a single element of the array. Given a char
|
||
|
pointer ``p`` to a 3-dimensional array you can find the position
|
||
|
of cell ``(z, y, x)`` as follows:
|
||
|
``p + ((z * dims[1] + y) * dims[0] + x) * elem_size``.
|
||
|
``elem_size`` is always valid, also when the control isn't an
|
||
|
array. For string controls ``elem_size`` is equal to
|
||
|
``maximum + 1``.
|
||
|
|
||
|
- .. row 10
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``elems``
|
||
|
|
||
|
- The number of elements in the N-dimensional array. If this control
|
||
|
is not an array, then ``elems`` is 1. The ``elems`` field can
|
||
|
never be 0.
|
||
|
|
||
|
- .. row 11
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``nr_of_dims``
|
||
|
|
||
|
- The number of dimension in the N-dimensional array. If this
|
||
|
control is not an array, then this field is 0.
|
||
|
|
||
|
- .. row 12
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``dims[V4L2_CTRL_MAX_DIMS]``
|
||
|
|
||
|
- The size of each dimension. The first ``nr_of_dims`` elements of
|
||
|
this array must be non-zero, all remaining elements must be zero.
|
||
|
|
||
|
- .. row 13
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
- ``reserved``\ [32]
|
||
|
|
||
|
- Reserved for future extensions. Applications and drivers must set
|
||
|
the array to zero.
|
||
|
|
||
|
|
||
|
|
||
|
.. _v4l2-querymenu:
|
||
|
|
||
|
.. flat-table:: struct v4l2_querymenu
|
||
|
:header-rows: 0
|
||
|
:stub-columns: 0
|
||
|
:widths: 1 1 2 1
|
||
|
|
||
|
|
||
|
- .. row 1
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
-
|
||
|
- ``id``
|
||
|
|
||
|
- Identifies the control, set by the application from the respective
|
||
|
struct :ref:`v4l2_queryctrl <v4l2-queryctrl>` ``id``.
|
||
|
|
||
|
- .. row 2
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
-
|
||
|
- ``index``
|
||
|
|
||
|
- Index of the menu item, starting at zero, set by the application.
|
||
|
|
||
|
- .. row 3
|
||
|
|
||
|
- union
|
||
|
|
||
|
-
|
||
|
-
|
||
|
-
|
||
|
|
||
|
- .. row 4
|
||
|
|
||
|
-
|
||
|
- __u8
|
||
|
|
||
|
- ``name``\ [32]
|
||
|
|
||
|
- Name of the menu item, a NUL-terminated ASCII string. This
|
||
|
information is intended for the user. This field is valid for
|
||
|
``V4L2_CTRL_FLAG_MENU`` type controls.
|
||
|
|
||
|
- .. row 5
|
||
|
|
||
|
-
|
||
|
- __s64
|
||
|
|
||
|
- ``value``
|
||
|
|
||
|
- Value of the integer menu item. This field is valid for
|
||
|
``V4L2_CTRL_FLAG_INTEGER_MENU`` type controls.
|
||
|
|
||
|
- .. row 6
|
||
|
|
||
|
- __u32
|
||
|
|
||
|
-
|
||
|
- ``reserved``
|
||
|
|
||
|
- Reserved for future extensions. Drivers must set the array to
|
||
|
zero.
|
||
|
|
||
|
|
||
|
|
||
|
.. _v4l2-ctrl-type:
|
||
|
|
||
|
.. flat-table:: enum v4l2_ctrl_type
|
||
|
:header-rows: 1
|
||
|
:stub-columns: 0
|
||
|
:widths: 30 5 5 5 55
|
||
|
|
||
|
|
||
|
- .. row 1
|
||
|
|
||
|
- Type
|
||
|
|
||
|
- ``minimum``
|
||
|
|
||
|
- ``step``
|
||
|
|
||
|
- ``maximum``
|
||
|
|
||
|
- Description
|
||
|
|
||
|
- .. row 2
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_INTEGER``
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- An integer-valued control ranging from minimum to maximum
|
||
|
inclusive. The step value indicates the increment between values.
|
||
|
|
||
|
- .. row 3
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_BOOLEAN``
|
||
|
|
||
|
- 0
|
||
|
|
||
|
- 1
|
||
|
|
||
|
- 1
|
||
|
|
||
|
- A boolean-valued control. Zero corresponds to "disabled", and one
|
||
|
means "enabled".
|
||
|
|
||
|
- .. row 4
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_MENU``
|
||
|
|
||
|
- ≥ 0
|
||
|
|
||
|
- 1
|
||
|
|
||
|
- N-1
|
||
|
|
||
|
- The control has a menu of N choices. The names of the menu items
|
||
|
can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl.
|
||
|
|
||
|
- .. row 5
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_INTEGER_MENU``
|
||
|
|
||
|
- ≥ 0
|
||
|
|
||
|
- 1
|
||
|
|
||
|
- N-1
|
||
|
|
||
|
- The control has a menu of N choices. The values of the menu items
|
||
|
can be enumerated with the ``VIDIOC_QUERYMENU`` ioctl. This is
|
||
|
similar to ``V4L2_CTRL_TYPE_MENU`` except that instead of strings,
|
||
|
the menu items are signed 64-bit integers.
|
||
|
|
||
|
- .. row 6
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_BITMASK``
|
||
|
|
||
|
- 0
|
||
|
|
||
|
- n/a
|
||
|
|
||
|
- any
|
||
|
|
||
|
- A bitmask field. The maximum value is the set of bits that can be
|
||
|
used, all other bits are to be 0. The maximum value is interpreted
|
||
|
as a __u32, allowing the use of bit 31 in the bitmask.
|
||
|
|
||
|
- .. row 7
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_BUTTON``
|
||
|
|
||
|
- 0
|
||
|
|
||
|
- 0
|
||
|
|
||
|
- 0
|
||
|
|
||
|
- A control which performs an action when set. Drivers must ignore
|
||
|
the value passed with ``VIDIOC_S_CTRL`` and return an ``EINVAL`` error
|
||
|
code on a ``VIDIOC_G_CTRL`` attempt.
|
||
|
|
||
|
- .. row 8
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_INTEGER64``
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- A 64-bit integer valued control. Minimum, maximum and step size
|
||
|
cannot be queried using ``VIDIOC_QUERYCTRL``. Only
|
||
|
``VIDIOC_QUERY_EXT_CTRL`` can retrieve the 64-bit min/max/step
|
||
|
values, they should be interpreted as n/a when using
|
||
|
``VIDIOC_QUERYCTRL``.
|
||
|
|
||
|
- .. row 9
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_STRING``
|
||
|
|
||
|
- ≥ 0
|
||
|
|
||
|
- ≥ 1
|
||
|
|
||
|
- ≥ 0
|
||
|
|
||
|
- The minimum and maximum string lengths. The step size means that
|
||
|
the string must be (minimum + N * step) characters long for N ≥ 0.
|
||
|
These lengths do not include the terminating zero, so in order to
|
||
|
pass a string of length 8 to
|
||
|
:ref:`VIDIOC_S_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you need to
|
||
|
set the ``size`` field of struct
|
||
|
:ref:`v4l2_ext_control <v4l2-ext-control>` to 9. For
|
||
|
:ref:`VIDIOC_G_EXT_CTRLS <VIDIOC_G_EXT_CTRLS>` you can set
|
||
|
the ``size`` field to ``maximum`` + 1. Which character encoding is
|
||
|
used will depend on the string control itself and should be part
|
||
|
of the control documentation.
|
||
|
|
||
|
- .. row 10
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_CTRL_CLASS``
|
||
|
|
||
|
- n/a
|
||
|
|
||
|
- n/a
|
||
|
|
||
|
- n/a
|
||
|
|
||
|
- This is not a control. When ``VIDIOC_QUERYCTRL`` is called with a
|
||
|
control ID equal to a control class code (see :ref:`ctrl-class`)
|
||
|
+ 1, the ioctl returns the name of the control class and this
|
||
|
control type. Older drivers which do not support this feature
|
||
|
return an ``EINVAL`` error code.
|
||
|
|
||
|
- .. row 11
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_U8``
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- An unsigned 8-bit valued control ranging from minimum to maximum
|
||
|
inclusive. The step value indicates the increment between values.
|
||
|
|
||
|
- .. row 12
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_U16``
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- An unsigned 16-bit valued control ranging from minimum to maximum
|
||
|
inclusive. The step value indicates the increment between values.
|
||
|
|
||
|
- .. row 13
|
||
|
|
||
|
- ``V4L2_CTRL_TYPE_U32``
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- any
|
||
|
|
||
|
- An unsigned 32-bit valued control ranging from minimum to maximum
|
||
|
inclusive. The step value indicates the increment between values.
|
||
|
|
||
|
|
||
|
|
||
|
.. _control-flags:
|
||
|
|
||
|
.. flat-table:: Control Flags
|
||
|
:header-rows: 0
|
||
|
:stub-columns: 0
|
||
|
:widths: 3 1 4
|
||
|
|
||
|
|
||
|
- .. row 1
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_DISABLED``
|
||
|
|
||
|
- 0x0001
|
||
|
|
||
|
- This control is permanently disabled and should be ignored by the
|
||
|
application. Any attempt to change the control will result in an
|
||
|
``EINVAL`` error code.
|
||
|
|
||
|
- .. row 2
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_GRABBED``
|
||
|
|
||
|
- 0x0002
|
||
|
|
||
|
- This control is temporarily unchangeable, for example because
|
||
|
another application took over control of the respective resource.
|
||
|
Such controls may be displayed specially in a user interface.
|
||
|
Attempts to change the control may result in an ``EBUSY`` error code.
|
||
|
|
||
|
- .. row 3
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_READ_ONLY``
|
||
|
|
||
|
- 0x0004
|
||
|
|
||
|
- This control is permanently readable only. Any attempt to change
|
||
|
the control will result in an ``EINVAL`` error code.
|
||
|
|
||
|
- .. row 4
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_UPDATE``
|
||
|
|
||
|
- 0x0008
|
||
|
|
||
|
- A hint that changing this control may affect the value of other
|
||
|
controls within the same control class. Applications should update
|
||
|
their user interface accordingly.
|
||
|
|
||
|
- .. row 5
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_INACTIVE``
|
||
|
|
||
|
- 0x0010
|
||
|
|
||
|
- This control is not applicable to the current configuration and
|
||
|
should be displayed accordingly in a user interface. For example
|
||
|
the flag may be set on a MPEG audio level 2 bitrate control when
|
||
|
MPEG audio encoding level 1 was selected with another control.
|
||
|
|
||
|
- .. row 6
|
||
|
|
||
|
- ``V4L2_CTRL_FLAG_SLIDER``
|
||
|
|
||
|
- 0x0020
|
||
|
|
||
|
- A hint that this control is best represented as a slider-like
|
||
|
element in a user interface.
|
||
|
|
||
|
- .. row 7
|
||
|
|
||
|
- ``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.
|
||
|
|
||
|
- .. row 8
|
||
|
|
||
|
- ``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 that setting a new
|
||
|
value for a volatile control will have no effect and no
|
||
|
``V4L2_EVENT_CTRL_CH_VALUE`` will be sent, unless the
|
||
|
``V4L2_CTRL_FLAG_EXECUTE_ON_WRITE`` flag (see below) is also set.
|
||
|
Otherwise the new value will just be ignored.
|
||
|
|
||
|
- .. row 9
|
||
|
|
||
|
- ``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
|
||
|
:ref:`v4l2_ext_control <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.
|
||
|
|
||
|
- .. row 10
|
||
|
|
||
|
- ``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.
|
||
|
|
||
|
|
||
|
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.
|
||
|
|
||
|
.. [1]
|
||
|
``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).
|