<title>Radio Interface</title> <para>This interface is intended for AM and FM (analog) radio receivers.</para> <para>Conventionally V4L2 radio devices are accessed through character device special files named <filename>/dev/radio</filename> and <filename>/dev/radio0</filename> to <filename>/dev/radio63</filename> with major number 81 and minor numbers 64 to 127.</para> <section> <title>Querying Capabilities</title> <para>Devices supporting the radio interface set the <constant>V4L2_CAP_RADIO</constant> and <constant>V4L2_CAP_TUNER</constant> flag in the <structfield>capabilities</structfield> field of &v4l2-capability; returned by the &VIDIOC-QUERYCAP; ioctl. Other combinations of capability flags are reserved for future extensions.</para> </section> <section> <title>Supplemental Functions</title> <para>Radio devices can support <link linkend="control">controls</link>, and must support the <link linkend="tuner">tuner</link> ioctls.</para> <para>They do not support the video input or output, audio input or output, video standard, cropping and scaling, compression and streaming parameter, or overlay ioctls. All other ioctls and I/O methods are reserved for future extensions.</para> </section> <section> <title>Programming</title> <para>Radio devices may have a couple audio controls (as discussed in <xref linkend="control">) such as a volume control, possibly custom controls. Further all radio devices have one tuner (these are discussed in <xref linkend="tuner">) with index number zero to select the radio frequency and to determine if a monaural or FM stereo program is received. Drivers switch automatically between AM and FM depending on the selected frequency. The &VIDIOC-G-TUNER; ioctl reports the supported frequency range.</para> </section> <!-- Local Variables: mode: sgml sgml-parent-document: "v4l2.sgml" indent-tabs-mode: nil End: -->