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Diffstat (limited to 'Documentation/DocBook/v4l/vidioc-enum-frameintervals.xml')
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diff --git a/Documentation/DocBook/v4l/vidioc-enum-frameintervals.xml b/Documentation/DocBook/v4l/vidioc-enum-frameintervals.xml new file mode 100644 index 000000000000..3c216e113a54 --- /dev/null +++ b/Documentation/DocBook/v4l/vidioc-enum-frameintervals.xml @@ -0,0 +1,270 @@ +<refentry id="vidioc-enum-frameintervals"> + + <refmeta> + <refentrytitle>ioctl VIDIOC_ENUM_FRAMEINTERVALS</refentrytitle> + &manvol; + </refmeta> + + <refnamediv> + <refname>VIDIOC_ENUM_FRAMEINTERVALS</refname> + <refpurpose>Enumerate frame intervals</refpurpose> + </refnamediv> + + <refsynopsisdiv> + <funcsynopsis> + <funcprototype> + <funcdef>int <function>ioctl</function></funcdef> + <paramdef>int <parameter>fd</parameter></paramdef> + <paramdef>int <parameter>request</parameter></paramdef> + <paramdef>struct v4l2_frmivalenum *<parameter>argp</parameter></paramdef> + </funcprototype> + </funcsynopsis> + </refsynopsisdiv> + + <refsect1> + <title>Arguments</title> + + <variablelist> + <varlistentry> + <term><parameter>fd</parameter></term> + <listitem> + <para>&fd;</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>request</parameter></term> + <listitem> + <para>VIDIOC_ENUM_FRAMEINTERVALS</para> + </listitem> + </varlistentry> + <varlistentry> + <term><parameter>argp</parameter></term> + <listitem> + <para>Pointer to a &v4l2-frmivalenum; structure that +contains a pixel format and size and receives a frame interval.</para> + </listitem> + </varlistentry> + </variablelist> + </refsect1> + + <refsect1> + <title>Description</title> + + <para>This ioctl allows applications to enumerate all frame +intervals that the device supports for the given pixel format and +frame size.</para> + <para>The supported pixel formats and frame sizes can be obtained +by using the &VIDIOC-ENUM-FMT; and &VIDIOC-ENUM-FRAMESIZES; +functions.</para> + <para>The return value and the content of the +<structfield>v4l2_frmivalenum.type</structfield> field depend on the +type of frame intervals the device supports. Here are the semantics of +the function for the different cases:</para> + <itemizedlist> + <listitem> + <para><emphasis role="bold">Discrete:</emphasis> The function +returns success if the given index value (zero-based) is valid. The +application should increase the index by one for each call until +<constant>EINVAL</constant> is returned. The `v4l2_frmivalenum.type` +field is set to `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the +union only the `discrete` member is valid.</para> + </listitem> + <listitem> + <para><emphasis role="bold">Step-wise:</emphasis> The function +returns success if the given index value is zero and +<constant>EINVAL</constant> for any other index value. The +<structfield>v4l2_frmivalenum.type</structfield> field is set to +<constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant> by the driver. Of the +union only the <structfield>stepwise</structfield> member is +valid.</para> + </listitem> + <listitem> + <para><emphasis role="bold">Continuous:</emphasis> This is a +special case of the step-wise type above. The function returns success +if the given index value is zero and <constant>EINVAL</constant> for +any other index value. The +<structfield>v4l2_frmivalenum.type</structfield> field is set to +<constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant> by the driver. Of +the union only the <structfield>stepwise</structfield> member is valid +and the <structfield>step</structfield> value is set to 1.</para> + </listitem> + </itemizedlist> + + <para>When the application calls the function with index zero, it +must check the <structfield>type</structfield> field to determine the +type of frame interval enumeration the device supports. Only for the +<constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant> type does it make +sense to increase the index value to receive more frame +intervals.</para> + <para>Note that the order in which the frame intervals are +returned has no special meaning. In particular does it not say +anything about potential default frame intervals.</para> + <para>Applications can assume that the enumeration data does not +change without any interaction from the application itself. This means +that the enumeration data is consistent if the application does not +perform any other ioctl calls while it runs the frame interval +enumeration.</para> + </refsect1> + + <refsect1> + <title>Notes</title> + + <itemizedlist> + <listitem> + <para><emphasis role="bold">Frame intervals and frame +rates:</emphasis> The V4L2 API uses frame intervals instead of frame +rates. Given the frame interval the frame rate can be computed as +follows:<screen>frame_rate = 1 / frame_interval</screen></para> + </listitem> + </itemizedlist> + + </refsect1> + + <refsect1> + <title>Structs</title> + + <para>In the structs below, <emphasis>IN</emphasis> denotes a +value that has to be filled in by the application, +<emphasis>OUT</emphasis> denotes values that the driver fills in. The +application should zero out all members except for the +<emphasis>IN</emphasis> fields.</para> + + <table pgwide="1" frame="none" id="v4l2-frmival-stepwise"> + <title>struct <structname>v4l2_frmival_stepwise</structname></title> + <tgroup cols="3"> + &cs-str; + <tbody valign="top"> + <row> + <entry>&v4l2-fract;</entry> + <entry><structfield>min</structfield></entry> + <entry>Minimum frame interval [s].</entry> + </row> + <row> + <entry>&v4l2-fract;</entry> + <entry><structfield>max</structfield></entry> + <entry>Maximum frame interval [s].</entry> + </row> + <row> + <entry>&v4l2-fract;</entry> + <entry><structfield>step</structfield></entry> + <entry>Frame interval step size [s].</entry> + </row> + </tbody> + </tgroup> + </table> + + <table pgwide="1" frame="none" id="v4l2-frmivalenum"> + <title>struct <structname>v4l2_frmivalenum</structname></title> + <tgroup cols="4"> + <colspec colname="c1" /> + <colspec colname="c2" /> + <colspec colname="c3" /> + <colspec colname="c4" /> + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>index</structfield></entry> + <entry></entry> + <entry>IN: Index of the given frame interval in the +enumeration.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>pixel_format</structfield></entry> + <entry></entry> + <entry>IN: Pixel format for which the frame intervals are +enumerated.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>width</structfield></entry> + <entry></entry> + <entry>IN: Frame width for which the frame intervals are +enumerated.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>height</structfield></entry> + <entry></entry> + <entry>IN: Frame height for which the frame intervals are +enumerated.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>type</structfield></entry> + <entry></entry> + <entry>OUT: Frame interval type the device supports.</entry> + </row> + <row> + <entry>union</entry> + <entry></entry> + <entry></entry> + <entry>OUT: Frame interval with the given index.</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-fract;</entry> + <entry><structfield>discrete</structfield></entry> + <entry>Frame interval [s].</entry> + </row> + <row> + <entry></entry> + <entry>&v4l2-frmival-stepwise;</entry> + <entry><structfield>stepwise</structfield></entry> + <entry></entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved[2]</structfield></entry> + <entry></entry> + <entry>Reserved space for future use.</entry> + </row> + </tbody> + </tgroup> + </table> + </refsect1> + + <refsect1> + <title>Enums</title> + + <table pgwide="1" frame="none" id="v4l2-frmivaltypes"> + <title>enum <structname>v4l2_frmivaltypes</structname></title> + <tgroup cols="3"> + &cs-def; + <tbody valign="top"> + <row> + <entry><constant>V4L2_FRMIVAL_TYPE_DISCRETE</constant></entry> + <entry>1</entry> + <entry>Discrete frame interval.</entry> + </row> + <row> + <entry><constant>V4L2_FRMIVAL_TYPE_CONTINUOUS</constant></entry> + <entry>2</entry> + <entry>Continuous frame interval.</entry> + </row> + <row> + <entry><constant>V4L2_FRMIVAL_TYPE_STEPWISE</constant></entry> + <entry>3</entry> + <entry>Step-wise defined frame interval.</entry> + </row> + </tbody> + </tgroup> + </table> + </refsect1> + + <refsect1> + &return-value; + + <para>See the description section above for a list of return +values that <varname>errno</varname> can have.</para> + </refsect1> + +</refentry> + +<!-- +Local Variables: +mode: sgml +sgml-parent-document: "v4l2.sgml" +indent-tabs-mode: nil +End: +--> |
