mirror of https://gitee.com/openkylin/linux.git
651 lines
26 KiB
XML
651 lines
26 KiB
XML
<refentry id="vidioc-queryctrl">
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<refmeta>
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<refentrytitle>ioctl VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</refentrytitle>
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&manvol;
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</refmeta>
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<refnamediv>
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<refname>VIDIOC_QUERYCTRL</refname>
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<refname>VIDIOC_QUERY_EXT_CTRL</refname>
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<refname>VIDIOC_QUERYMENU</refname>
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<refpurpose>Enumerate controls and menu control items</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_queryctrl *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_query_ext_ctrl *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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<funcsynopsis>
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<funcprototype>
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<funcdef>int <function>ioctl</function></funcdef>
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<paramdef>int <parameter>fd</parameter></paramdef>
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<paramdef>int <parameter>request</parameter></paramdef>
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<paramdef>struct v4l2_querymenu *<parameter>argp</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Arguments</title>
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<variablelist>
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<varlistentry>
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<term><parameter>fd</parameter></term>
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<listitem>
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<para>&fd;</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>request</parameter></term>
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<listitem>
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<para>VIDIOC_QUERYCTRL, VIDIOC_QUERY_EXT_CTRL, VIDIOC_QUERYMENU</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><parameter>argp</parameter></term>
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<listitem>
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<para></para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Description</title>
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<para>To query the attributes of a control applications set the
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<structfield>id</structfield> field of a &v4l2-queryctrl; and call the
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<constant>VIDIOC_QUERYCTRL</constant> ioctl with a pointer to this
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structure. The driver fills the rest of the structure or returns an
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&EINVAL; when the <structfield>id</structfield> is invalid.</para>
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<para>It is possible to enumerate controls by calling
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<constant>VIDIOC_QUERYCTRL</constant> with successive
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<structfield>id</structfield> values starting from
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<constant>V4L2_CID_BASE</constant> up to and exclusive
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<constant>V4L2_CID_LASTP1</constant>. Drivers may return
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<errorcode>EINVAL</errorcode> if a control in this range is not
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supported. Further applications can enumerate private controls, which
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are not defined in this specification, by starting at
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<constant>V4L2_CID_PRIVATE_BASE</constant> and incrementing
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<structfield>id</structfield> until the driver returns
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<errorcode>EINVAL</errorcode>.</para>
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<para>In both cases, when the driver sets the
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<constant>V4L2_CTRL_FLAG_DISABLED</constant> flag in the
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<structfield>flags</structfield> field this control is permanently
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disabled and should be ignored by the application.<footnote>
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<para><constant>V4L2_CTRL_FLAG_DISABLED</constant> was
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intended for two purposes: Drivers can skip predefined controls not
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supported by the hardware (although returning EINVAL would do as
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well), or disable predefined and private controls after hardware
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detection without the trouble of reordering control arrays and indices
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(EINVAL cannot be used to skip private controls because it would
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prematurely end the enumeration).</para></footnote></para>
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<para>When the application ORs <structfield>id</structfield> with
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<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver returns the
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next supported non-compound control, or <errorcode>EINVAL</errorcode>
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if there is none. In addition, the <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant>
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flag can be specified to enumerate all compound controls (i.e. controls
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with type ≥ <constant>V4L2_CTRL_COMPOUND_TYPES</constant>). Specify both
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<constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> and
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<constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> in order to enumerate
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all controls, compound or not. Drivers which do not support these flags yet
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always return <errorcode>EINVAL</errorcode>.</para>
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<para>The <constant>VIDIOC_QUERY_EXT_CTRL</constant> ioctl was
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introduced in order to better support controls that can use compound
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types, and to expose additional control information that cannot be
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returned in &v4l2-queryctrl; since that structure is full.</para>
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<para><constant>VIDIOC_QUERY_EXT_CTRL</constant> is used in the
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same way as <constant>VIDIOC_QUERYCTRL</constant>, except that the
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<structfield>reserved</structfield> array must be zeroed as well.</para>
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<para>Additional information is required for menu controls: the
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names of the menu items. To query them applications set the
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<structfield>id</structfield> and <structfield>index</structfield>
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fields of &v4l2-querymenu; and call the
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<constant>VIDIOC_QUERYMENU</constant> ioctl with a pointer to this
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structure. The driver fills the rest of the structure or returns an
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&EINVAL; when the <structfield>id</structfield> or
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<structfield>index</structfield> is invalid. Menu items are enumerated
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by calling <constant>VIDIOC_QUERYMENU</constant> with successive
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<structfield>index</structfield> values from &v4l2-queryctrl;
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<structfield>minimum</structfield> to
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<structfield>maximum</structfield>, inclusive. Note that it is possible
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for <constant>VIDIOC_QUERYMENU</constant> to return an &EINVAL; for some
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indices between <structfield>minimum</structfield> and <structfield>maximum</structfield>.
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In that case that particular menu item is not supported by this driver. Also note that
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the <structfield>minimum</structfield> value is not necessarily 0.</para>
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<para>See also the examples in <xref linkend="control" />.</para>
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<table pgwide="1" frame="none" id="v4l2-queryctrl">
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<title>struct <structname>v4l2_queryctrl</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>id</structfield></entry>
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<entry>Identifies the control, set by the application. See
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<xref linkend="control-id" /> for predefined IDs. When the ID is ORed
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with V4L2_CTRL_FLAG_NEXT_CTRL the driver clears the flag and returns
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the first control with a higher ID. Drivers which do not support this
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flag yet always return an &EINVAL;.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of control, see <xref
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linkend="v4l2-ctrl-type" />.</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the control, a NUL-terminated ASCII
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string. This information is intended for the user.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>minimum</structfield></entry>
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<entry>Minimum value, inclusive. This field gives a lower
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bound for the control. See &v4l2-ctrl-type; how the minimum value is to
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be used for each possible control type. Note that this a signed 32-bit value.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>maximum</structfield></entry>
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<entry>Maximum value, inclusive. This field gives an upper
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bound for the control. See &v4l2-ctrl-type; how the maximum value is to
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be used for each possible control type. Note that this a signed 32-bit value.</entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>step</structfield></entry>
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<entry><para>This field gives a step size for the control.
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See &v4l2-ctrl-type; how the step value is to be used for each possible
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control type. Note that this an unsigned 32-bit value.
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</para><para>Generally drivers should not scale hardware
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control values. It may be necessary for example when the
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<structfield>name</structfield> or <structfield>id</structfield> imply
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a particular unit and the hardware actually accepts only multiples of
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said unit. If so, drivers must take care values are properly rounded
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when scaling, such that errors will not accumulate on repeated
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read-write cycles.</para><para>This field gives the smallest change of
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an integer control actually affecting hardware. Often the information
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is needed when the user can change controls by keyboard or GUI
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buttons, rather than a slider. When for example a hardware register
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accepts values 0-511 and the driver reports 0-65535, step should be
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128.</para><para>Note that although signed, the step value is supposed to
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be always positive.</para></entry>
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</row>
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<row>
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<entry>__s32</entry>
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<entry><structfield>default_value</structfield></entry>
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<entry>The default value of a
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<constant>V4L2_CTRL_TYPE_INTEGER</constant>,
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<constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>,
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<constant>_MENU</constant> or <constant>_INTEGER_MENU</constant> control.
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Not valid for other types of controls.
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Note that drivers reset controls to their default value only when the
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driver is first loaded, never afterwards.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Control flags, see <xref
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linkend="control-flags" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[2]</entry>
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<entry>Reserved for future extensions. Drivers must set
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the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-query-ext-ctrl">
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<title>struct <structname>v4l2_query_ext_ctrl</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>id</structfield></entry>
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<entry>Identifies the control, set by the application. See
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<xref linkend="control-id" /> for predefined IDs. When the ID is ORed
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with <constant>V4L2_CTRL_FLAG_NEXT_CTRL</constant> the driver clears the
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flag and returns the first non-compound control with a higher ID. When the
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ID is ORed with <constant>V4L2_CTRL_FLAG_NEXT_COMPOUND</constant> the driver
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clears 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 ID.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>type</structfield></entry>
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<entry>Type of control, see <xref
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linkend="v4l2-ctrl-type" />.</entry>
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</row>
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<row>
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<entry>char</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the control, a NUL-terminated ASCII
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string. This information is intended for the user.</entry>
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</row>
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<row>
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<entry>__s64</entry>
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<entry><structfield>minimum</structfield></entry>
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<entry>Minimum value, inclusive. This field gives a lower
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bound for the control. See &v4l2-ctrl-type; how the minimum value is to
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be used for each possible control type. Note that this a signed 64-bit value.</entry>
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</row>
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<row>
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<entry>__s64</entry>
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<entry><structfield>maximum</structfield></entry>
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<entry>Maximum value, inclusive. This field gives an upper
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bound for the control. See &v4l2-ctrl-type; how the maximum value is to
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be used for each possible control type. Note that this a signed 64-bit value.</entry>
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</row>
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<row>
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<entry>__u64</entry>
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<entry><structfield>step</structfield></entry>
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<entry><para>This field gives a step size for the control.
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See &v4l2-ctrl-type; how the step value is to be used for each possible
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control type. Note that this an unsigned 64-bit value.
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</para><para>Generally drivers should not scale hardware
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control values. It may be necessary for example when the
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<structfield>name</structfield> or <structfield>id</structfield> imply
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a particular unit and the hardware actually accepts only multiples of
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said unit. If so, drivers must take care values are properly rounded
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when scaling, such that errors will not accumulate on repeated
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read-write cycles.</para><para>This field gives the smallest change of
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an integer control actually affecting hardware. Often the information
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is needed when the user can change controls by keyboard or GUI
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buttons, rather than a slider. When for example a hardware register
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accepts values 0-511 and the driver reports 0-65535, step should be
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128.</para></entry>
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</row>
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<row>
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<entry>__s64</entry>
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<entry><structfield>default_value</structfield></entry>
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<entry>The default value of a
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<constant>V4L2_CTRL_TYPE_INTEGER</constant>, <constant>_INTEGER64</constant>,
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<constant>_BOOLEAN</constant>, <constant>_BITMASK</constant>,
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<constant>_MENU</constant>, <constant>_INTEGER_MENU</constant>,
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<constant>_U8</constant> or <constant>_U16</constant> control.
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Not valid for other types of controls.
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Note that drivers reset controls to their default value only when the
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driver is first loaded, never afterwards.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>flags</structfield></entry>
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<entry>Control flags, see <xref
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linkend="control-flags" />.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>elem_size</structfield></entry>
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<entry>The size in bytes of a single element of the array.
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Given a char pointer <constant>p</constant> to a 3-dimensional array you can find the
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position of cell <constant>(z, y, x)</constant> as follows:
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<constant>p + ((z * dims[1] + y) * dims[0] + x) * elem_size</constant>. <structfield>elem_size</structfield>
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is always valid, also when the control isn't an array. For string controls
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<structfield>elem_size</structfield> is equal to <structfield>maximum + 1</structfield>.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>elems</structfield></entry>
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<entry>The number of elements in the N-dimensional array. If this control
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is not an array, then <structfield>elems</structfield> is 1. The <structfield>elems</structfield>
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field can never be 0.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>nr_of_dims</structfield></entry>
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<entry>The number of dimension in the N-dimensional array. If this control
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is not an array, then this field is 0.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>dims[V4L2_CTRL_MAX_DIMS]</structfield></entry>
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<entry>The size of each dimension. The first <structfield>nr_of_dims</structfield>
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elements of this array must be non-zero, all remaining elements must be zero.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>reserved</structfield>[32]</entry>
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<entry>Reserved for future extensions. Applications and drivers
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must set the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-querymenu">
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<title>struct <structname>v4l2_querymenu</structname></title>
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<tgroup cols="4">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry></entry>
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<entry><structfield>id</structfield></entry>
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<entry>Identifies the control, set by the application
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from the respective &v4l2-queryctrl;
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<structfield>id</structfield>.</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry></entry>
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<entry><structfield>index</structfield></entry>
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<entry>Index of the menu item, starting at zero, set by
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the application.</entry>
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</row>
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<row>
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<entry>union</entry>
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<entry></entry>
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<entry></entry>
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<entry></entry>
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</row>
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<row>
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<entry></entry>
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<entry>__u8</entry>
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<entry><structfield>name</structfield>[32]</entry>
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<entry>Name of the menu item, a NUL-terminated ASCII
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string. This information is intended for the user. This field is valid
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for <constant>V4L2_CTRL_FLAG_MENU</constant> type controls.</entry>
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</row>
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<row>
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<entry></entry>
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<entry>__s64</entry>
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<entry><structfield>value</structfield></entry>
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<entry>
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Value of the integer menu item. This field is valid for
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<constant>V4L2_CTRL_FLAG_INTEGER_MENU</constant> type
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controls.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry></entry>
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<entry><structfield>reserved</structfield></entry>
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<entry>Reserved for future extensions. Drivers must set
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the array to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<table pgwide="1" frame="none" id="v4l2-ctrl-type">
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<title>enum v4l2_ctrl_type</title>
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<tgroup cols="5" align="left">
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<colspec colwidth="30*" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="5*" align="center" />
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<colspec colwidth="55*" />
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<thead>
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<row>
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<entry>Type</entry>
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<entry><structfield>minimum</structfield></entry>
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<entry><structfield>step</structfield></entry>
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<entry><structfield>maximum</structfield></entry>
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<entry>Description</entry>
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</row>
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</thead>
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<tbody valign="top">
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<row>
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<entry><constant>V4L2_CTRL_TYPE_INTEGER</constant></entry>
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<entry>any</entry>
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<entry>any</entry>
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<entry>any</entry>
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<entry>An integer-valued control ranging from minimum to
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maximum inclusive. The step value indicates the increment between
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values which are actually different on the hardware.</entry>
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</row>
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<row>
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<entry><constant>V4L2_CTRL_TYPE_BOOLEAN</constant></entry>
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<entry>0</entry>
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<entry>1</entry>
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<entry>1</entry>
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|
<entry>A boolean-valued control. Zero corresponds to
|
|
"disabled", and one means "enabled".</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_MENU</constant></entry>
|
|
<entry>≥ 0</entry>
|
|
<entry>1</entry>
|
|
<entry>N-1</entry>
|
|
<entry>The control has a menu of N choices. The names of
|
|
the menu items can be enumerated with the
|
|
<constant>VIDIOC_QUERYMENU</constant> ioctl.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_INTEGER_MENU</constant></entry>
|
|
<entry>≥ 0</entry>
|
|
<entry>1</entry>
|
|
<entry>N-1</entry>
|
|
<entry>
|
|
The control has a menu of N choices. The values of the
|
|
menu items can be enumerated with the
|
|
<constant>VIDIOC_QUERYMENU</constant> ioctl. This is
|
|
similar to <constant>V4L2_CTRL_TYPE_MENU</constant>
|
|
except that instead of strings, the menu items are
|
|
signed 64-bit integers.
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_BITMASK</constant></entry>
|
|
<entry>0</entry>
|
|
<entry>n/a</entry>
|
|
<entry>any</entry>
|
|
<entry>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.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_BUTTON</constant></entry>
|
|
<entry>0</entry>
|
|
<entry>0</entry>
|
|
<entry>0</entry>
|
|
<entry>A control which performs an action when set.
|
|
Drivers must ignore the value passed with
|
|
<constant>VIDIOC_S_CTRL</constant> and return an &EINVAL; on a
|
|
<constant>VIDIOC_G_CTRL</constant> attempt.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_INTEGER64</constant></entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>A 64-bit integer valued control. Minimum, maximum
|
|
and step size cannot be queried using <constant>VIDIOC_QUERYCTRL</constant>.
|
|
Only <constant>VIDIOC_QUERY_EXT_CTRL</constant> can retrieve the 64-bit
|
|
min/max/step values, they should be interpreted as n/a when using
|
|
<constant>VIDIOC_QUERYCTRL</constant>.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_STRING</constant></entry>
|
|
<entry>≥ 0</entry>
|
|
<entry>≥ 1</entry>
|
|
<entry>≥ 0</entry>
|
|
<entry>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 &VIDIOC-S-EXT-CTRLS; you need to set the
|
|
<structfield>size</structfield> field of &v4l2-ext-control; to 9. For &VIDIOC-G-EXT-CTRLS; you can
|
|
set the <structfield>size</structfield> field to <structfield>maximum</structfield> + 1.
|
|
Which character encoding is used will depend on the string control itself and
|
|
should be part of the control documentation.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_CTRL_CLASS</constant></entry>
|
|
<entry>n/a</entry>
|
|
<entry>n/a</entry>
|
|
<entry>n/a</entry>
|
|
<entry>This is not a control. When
|
|
<constant>VIDIOC_QUERYCTRL</constant> is called with a control ID
|
|
equal to a control class code (see <xref linkend="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;.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_U8</constant></entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>An unsigned 8-bit valued control ranging from minimum to
|
|
maximum inclusive. The step value indicates the increment between
|
|
values which are actually different on the hardware.
|
|
</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_TYPE_U16</constant></entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>any</entry>
|
|
<entry>An unsigned 16-bit valued control ranging from minimum to
|
|
maximum inclusive. The step value indicates the increment between
|
|
values which are actually different on the hardware.
|
|
</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
|
|
<table pgwide="1" frame="none" id="control-flags">
|
|
<title>Control Flags</title>
|
|
<tgroup cols="3">
|
|
&cs-def;
|
|
<tbody valign="top">
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_DISABLED</constant></entry>
|
|
<entry>0x0001</entry>
|
|
<entry>This control is permanently disabled and should be
|
|
ignored by the application. Any attempt to change the control will
|
|
result in an &EINVAL;.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_GRABBED</constant></entry>
|
|
<entry>0x0002</entry>
|
|
<entry>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;.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_READ_ONLY</constant></entry>
|
|
<entry>0x0004</entry>
|
|
<entry>This control is permanently readable only. Any
|
|
attempt to change the control will result in an &EINVAL;.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_UPDATE</constant></entry>
|
|
<entry>0x0008</entry>
|
|
<entry>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.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_INACTIVE</constant></entry>
|
|
<entry>0x0010</entry>
|
|
<entry>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.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_SLIDER</constant></entry>
|
|
<entry>0x0020</entry>
|
|
<entry>A hint that this control is best represented as a
|
|
slider-like element in a user interface.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_WRITE_ONLY</constant></entry>
|
|
<entry>0x0040</entry>
|
|
<entry>This control is permanently writable only. Any
|
|
attempt to read the control will result in an &EACCES; 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
|
|
(⪚ motor control) but no meaningful value can be returned.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_VOLATILE</constant></entry>
|
|
<entry>0x0080</entry>
|
|
<entry>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 <constant>V4L2_EVENT_CTRL_CH_VALUE</constant>
|
|
will be sent, unless the <constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant> flag
|
|
(see below) is also set. Otherwise the new value will just be ignored.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_HAS_PAYLOAD</constant></entry>
|
|
<entry>0x0100</entry>
|
|
<entry>This control has a pointer type, so its value has to be accessed
|
|
using one of the pointer fields of &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.</entry>
|
|
</row>
|
|
<row>
|
|
<entry><constant>V4L2_CTRL_FLAG_EXECUTE_ON_WRITE</constant></entry>
|
|
<entry>0x0200</entry>
|
|
<entry>The value provided to the control will be propagated to the driver
|
|
even if 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 <constant>V4L2_CTRL_TYPE_BUTTON</constant> have this flag set.</entry>
|
|
</row>
|
|
</tbody>
|
|
</tgroup>
|
|
</table>
|
|
</refsect1>
|
|
|
|
<refsect1>
|
|
&return-value;
|
|
|
|
<variablelist>
|
|
<varlistentry>
|
|
<term><errorcode>EINVAL</errorcode></term>
|
|
<listitem>
|
|
<para>The &v4l2-queryctrl; <structfield>id</structfield>
|
|
is invalid. The &v4l2-querymenu; <structfield>id</structfield> is
|
|
invalid or <structfield>index</structfield> is out of range (less than
|
|
<structfield>minimum</structfield> or greater than <structfield>maximum</structfield>)
|
|
or this particular menu item is not supported by the driver.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
<varlistentry>
|
|
<term><errorcode>EACCES</errorcode></term>
|
|
<listitem>
|
|
<para>An attempt was made to read a write-only control.</para>
|
|
</listitem>
|
|
</varlistentry>
|
|
</variablelist>
|
|
</refsect1>
|
|
</refentry>
|