1  <title>Radio Interface</title>
2
3  <para>This interface is intended for AM and FM (analog) radio
4receivers and transmitters.</para>
5
6  <para>Conventionally V4L2 radio devices are accessed through
7character device special files named <filename>/dev/radio</filename>
8and <filename>/dev/radio0</filename> to
9<filename>/dev/radio63</filename> with major number 81 and minor
10numbers 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;
20returned by the &VIDIOC-QUERYCAP; ioctl. Other combinations of
21capability 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
28linkend="control">controls</link>, and must support the <link
29linkend="tuner">tuner or modulator</link> ioctls.</para>
30
31    <para>They do not support the video input or output, audio input
32or output, video standard, cropping and scaling, compression and
33streaming parameter, or overlay ioctls. All other ioctls and I/O
34methods 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
41in <xref linkend="control" />) such as a volume control, possibly custom
42controls. Further all radio devices have one tuner or modulator (these are
43discussed in <xref linkend="tuner" />) with index number zero to select
44the radio frequency and to determine if a monaural or FM stereo
45program is received/emitted. Drivers switch automatically between AM and FM
46depending on the selected frequency. The &VIDIOC-G-TUNER; or
47&VIDIOC-G-MODULATOR; ioctl
48reports the supported frequency range.</para>
49  </section>
50