Based on kernel version 4.0. Page generated on 2015-04-14 21:23 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>