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 51<!-- 52Local Variables: 53mode: sgml 54sgml-parent-document: "v4l2.sgml" 55indent-tabs-mode: nil 56End: 57 --> 58