1<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN""http://www.w3.org/TR/html4/loose.dtd"> 2<HTML 3><HEAD 4><TITLE 5>Radio Interface</TITLE 6><META 7NAME="GENERATOR" 8CONTENT="Modular DocBook HTML Stylesheet Version 1.79"><LINK 9REL="HOME" 10TITLE="Video for Linux Two API Specification" 11HREF="book1.htm"><LINK 12REL="UP" 13TITLE="Interfaces" 14HREF="c6488.htm"><LINK 15REL="PREVIOUS" 16TITLE="Teletext Interface" 17HREF="x7561.htm"><LINK 18REL="NEXT" 19TITLE="RDS Interface" 20HREF="x7607.htm"></HEAD 21><BODY 22CLASS="SECTION" 23BGCOLOR="#FFFFFF" 24TEXT="#000000" 25LINK="#0000FF" 26VLINK="#840084" 27ALINK="#0000FF" 28><DIV 29CLASS="NAVHEADER" 30><TABLE 31SUMMARY="Header navigation table" 32WIDTH="100%" 33BORDER="0" 34CELLPADDING="0" 35CELLSPACING="0" 36><TR 37><TH 38COLSPAN="3" 39ALIGN="center" 40>Video for Linux Two API Specification: Revision 0.24</TH 41></TR 42><TR 43><TD 44WIDTH="10%" 45ALIGN="left" 46VALIGN="bottom" 47><A 48HREF="x7561.htm" 49ACCESSKEY="P" 50>Prev</A 51></TD 52><TD 53WIDTH="80%" 54ALIGN="center" 55VALIGN="bottom" 56>Chapter 4. Interfaces</TD 57><TD 58WIDTH="10%" 59ALIGN="right" 60VALIGN="bottom" 61><A 62HREF="x7607.htm" 63ACCESSKEY="N" 64>Next</A 65></TD 66></TR 67></TABLE 68><HR 69ALIGN="LEFT" 70WIDTH="100%"></DIV 71><DIV 72CLASS="SECTION" 73><H1 74CLASS="SECTION" 75><A 76NAME="RADIO" 77>4.10. Radio Interface</A 78></H1 79><P 80>This interface is intended for AM and FM (analog) radio 81receivers.</P 82><P 83>Conventionally V4L2 radio devices are accessed through 84character device special files named <TT 85CLASS="FILENAME" 86>/dev/radio</TT 87> 88and <TT 89CLASS="FILENAME" 90>/dev/radio0</TT 91> to 92<TT 93CLASS="FILENAME" 94>/dev/radio63</TT 95> with major number 81 and minor 96numbers 64 to 127.</P 97><DIV 98CLASS="SECTION" 99><H2 100CLASS="SECTION" 101><A 102NAME="AEN7585" 103>4.10.1. Querying Capabilities</A 104></H2 105><P 106>Devices supporting the radio interface set the 107<CODE 108CLASS="CONSTANT" 109>V4L2_CAP_RADIO</CODE 110> and 111<CODE 112CLASS="CONSTANT" 113>V4L2_CAP_TUNER</CODE 114> flag in the 115<CODE 116CLASS="STRUCTFIELD" 117>capabilities</CODE 118> field of struct <A 119HREF="r13105.htm#V4L2-CAPABILITY" 120>v4l2_capability</A 121> 122returned by the <A 123HREF="r13105.htm" 124><CODE 125CLASS="CONSTANT" 126>VIDIOC_QUERYCAP</CODE 127></A 128> ioctl. Other combinations of 129capability flags are reserved for future extensions.</P 130></DIV 131><DIV 132CLASS="SECTION" 133><H2 134CLASS="SECTION" 135><A 136NAME="AEN7594" 137>4.10.2. Supplemental Functions</A 138></H2 139><P 140>Radio devices can support <A 141HREF="x542.htm" 142>controls</A 143>, and must support the <A 144HREF="x394.htm" 145>tuner</A 146> ioctls.</P 147><P 148>They do not support the video input or output, audio input 149or output, video standard, cropping and scaling, compression and 150streaming parameter, or overlay ioctls. All other ioctls and I/O 151methods are reserved for future extensions.</P 152></DIV 153><DIV 154CLASS="SECTION" 155><H2 156CLASS="SECTION" 157><A 158NAME="AEN7600" 159>4.10.3. Programming</A 160></H2 161><P 162>Radio devices may have a couple audio controls (as discussed 163in <A 164HREF="x542.htm" 165>Section 1.8</A 166>) such as a volume control, possibly custom 167controls. Further all radio devices have one tuner (these are 168discussed in <A 169HREF="x394.htm" 170>Section 1.6</A 171>) with index number zero to select 172the radio frequency and to determine if a monaural or FM stereo 173program is received. Drivers switch automatically between AM and FM 174depending on the selected frequency. The <A 175HREF="r12342.htm" 176><CODE 177CLASS="CONSTANT" 178>VIDIOC_G_TUNER</CODE 179></A 180> ioctl 181reports the supported frequency range.</P 182></DIV 183></DIV 184><DIV 185CLASS="NAVFOOTER" 186><HR 187ALIGN="LEFT" 188WIDTH="100%"><TABLE 189SUMMARY="Footer navigation table" 190WIDTH="100%" 191BORDER="0" 192CELLPADDING="0" 193CELLSPACING="0" 194><TR 195><TD 196WIDTH="33%" 197ALIGN="left" 198VALIGN="top" 199><A 200HREF="x7561.htm" 201ACCESSKEY="P" 202>Prev</A 203></TD 204><TD 205WIDTH="34%" 206ALIGN="center" 207VALIGN="top" 208><A 209HREF="book1.htm" 210ACCESSKEY="H" 211>Home</A 212></TD 213><TD 214WIDTH="33%" 215ALIGN="right" 216VALIGN="top" 217><A 218HREF="x7607.htm" 219ACCESSKEY="N" 220>Next</A 221></TD 222></TR 223><TR 224><TD 225WIDTH="33%" 226ALIGN="left" 227VALIGN="top" 228>Teletext Interface</TD 229><TD 230WIDTH="34%" 231ALIGN="center" 232VALIGN="top" 233><A 234HREF="c6488.htm" 235ACCESSKEY="U" 236>Up</A 237></TD 238><TD 239WIDTH="33%" 240ALIGN="right" 241VALIGN="top" 242>RDS Interface</TD 243></TR 244></TABLE 245></DIV 246></BODY 247></HTML 248> 249