--- /dev/null
+<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;
+ </refsect1>
+
+</refentry>
Code Review / kvmfornfv.git / blobdiff