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awilliam
GitHub Repository: awilliam/linux-vfio
 Path: blob/master/Documentation/DocBook/v4l/dev-radio.xml
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  <title>Radio Interface</title>

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  <para>This interface is intended for AM and FM (analog) radio

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receivers and transmitters.</para>

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  <para>Conventionally V4L2 radio devices are accessed through

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character device special files named <filename>/dev/radio</filename>

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and <filename>/dev/radio0</filename> to

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<filename>/dev/radio63</filename> with major number 81 and minor

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numbers 64 to 127.</para>

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  <section>

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    <title>Querying Capabilities</title>

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    <para>Devices supporting the radio interface set the

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<constant>V4L2_CAP_RADIO</constant> and

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<constant>V4L2_CAP_TUNER</constant> or

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<constant>V4L2_CAP_MODULATOR</constant> flag in the

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<structfield>capabilities</structfield> field of &v4l2-capability;

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returned by the &VIDIOC-QUERYCAP; ioctl. Other combinations of

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capability flags are reserved for future extensions.</para>

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  </section>

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  <section>

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    <title>Supplemental Functions</title>

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    <para>Radio devices can support <link

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linkend="control">controls</link>, and must support the <link

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linkend="tuner">tuner or modulator</link> ioctls.</para>

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    <para>They do not support the video input or output, audio input

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or output, video standard, cropping and scaling, compression and

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streaming parameter, or overlay ioctls. All other ioctls and I/O

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methods are reserved for future extensions.</para>

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  </section>

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  <section>

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    <title>Programming</title>

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    <para>Radio devices may have a couple audio controls (as discussed

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in <xref linkend="control" />) such as a volume control, possibly custom

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controls. Further all radio devices have one tuner or modulator (these are

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discussed in <xref linkend="tuner" />) with index number zero to select

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the radio frequency and to determine if a monaural or FM stereo

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program is received/emitted. Drivers switch automatically between AM and FM

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depending on the selected frequency. The &VIDIOC-G-TUNER; or

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&VIDIOC-G-MODULATOR; ioctl

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reports the supported frequency range.</para>

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  </section>

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<!--

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Local Variables:

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mode: sgml

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sgml-parent-document: "v4l2.sgml"

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indent-tabs-mode: nil

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End:

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 -->

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