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Based on kernel version 3.13. Page generated on 2014-01-20 22:02 EST.

1	  <title>Radio Interface</title>
2	
3	  <para>This interface is intended for AM and FM (analog) radio
4	receivers and transmitters.</para>
5	
6	  <para>Conventionally V4L2 radio devices are accessed through
7	character device special files named <filename>/dev/radio</filename>
8	and <filename>/dev/radio0</filename> to
9	<filename>/dev/radio63</filename> with major number 81 and minor
10	numbers 64 to 127.</para>
11	
12	  <section>
13	    <title>Querying Capabilities</title>
14	
15	    <para>Devices supporting the radio interface set the
16	<constant>V4L2_CAP_RADIO</constant> and
17	<constant>V4L2_CAP_TUNER</constant> or
18	<constant>V4L2_CAP_MODULATOR</constant> flag in the
19	<structfield>capabilities</structfield> field of &v4l2-capability;
20	returned by the &VIDIOC-QUERYCAP; ioctl. Other combinations of
21	capability flags are reserved for future extensions.</para>
22	  </section>
23	
24	  <section>
25	    <title>Supplemental Functions</title>
26	
27	    <para>Radio devices can support <link
28	linkend="control">controls</link>, and must support the <link
29	linkend="tuner">tuner or modulator</link> ioctls.</para>
30	
31	    <para>They do not support the video input or output, audio input
32	or output, video standard, cropping and scaling, compression and
33	streaming parameter, or overlay ioctls. All other ioctls and I/O
34	methods are reserved for future extensions.</para>
35	  </section>
36	
37	  <section>
38	    <title>Programming</title>
39	
40	    <para>Radio devices may have a couple audio controls (as discussed
41	in <xref linkend="control" />) such as a volume control, possibly custom
42	controls. Further all radio devices have one tuner or modulator (these are
43	discussed in <xref linkend="tuner" />) with index number zero to select
44	the radio frequency and to determine if a monaural or FM stereo
45	program is received/emitted. Drivers switch automatically between AM and FM
46	depending on the selected frequency. The &VIDIOC-G-TUNER; or
47	&VIDIOC-G-MODULATOR; ioctl
48	reports the supported frequency range.</para>
49	  </section>
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