50 lines
1.9 KiB
XML
50 lines
1.9 KiB
XML
<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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