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     40 >Video for Linux Two API Specification: Revision 0.24</TH
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     56 >Chapter 4. Interfaces</TD
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     73 ><H1
     74 CLASS="SECTION"
     75 ><A
     76 NAME="RADIO"
     77 >4.10. Radio Interface</A
     78 ></H1
     79 ><P
     80 >This interface is intended for AM and FM (analog) radio
     81 receivers.</P
     82 ><P
     83 >Conventionally V4L2 radio devices are accessed through
     84 character device special files named <TT
     85 CLASS="FILENAME"
     86 >/dev/radio</TT
     87 >
     88 and <TT
     89 CLASS="FILENAME"
     90 >/dev/radio0</TT
     91 > to
     92 <TT
     93 CLASS="FILENAME"
     94 >/dev/radio63</TT
     95 > with major number 81 and minor
     96 numbers 64 to 127.</P
     97 ><DIV
     98 CLASS="SECTION"
     99 ><H2
    100 CLASS="SECTION"
    101 ><A
    102 NAME="AEN7585"
    103 >4.10.1. Querying Capabilities</A
    104 ></H2
    105 ><P
    106 >Devices supporting the radio interface set the
    107 <CODE
    108 CLASS="CONSTANT"
    109 >V4L2_CAP_RADIO</CODE
    110 > and
    111 <CODE
    112 CLASS="CONSTANT"
    113 >V4L2_CAP_TUNER</CODE
    114 > flag in the
    115 <CODE
    116 CLASS="STRUCTFIELD"
    117 >capabilities</CODE
    118 > field of struct&nbsp;<A
    119 HREF="r13105.htm#V4L2-CAPABILITY"
    120 >v4l2_capability</A
    121 >
    122 returned by the <A
    123 HREF="r13105.htm"
    124 ><CODE
    125 CLASS="CONSTANT"
    126 >VIDIOC_QUERYCAP</CODE
    127 ></A
    128 > ioctl. Other combinations of
    129 capability flags are reserved for future extensions.</P
    130 ></DIV
    131 ><DIV
    132 CLASS="SECTION"
    133 ><H2
    134 CLASS="SECTION"
    135 ><A
    136 NAME="AEN7594"
    137 >4.10.2. Supplemental Functions</A
    138 ></H2
    139 ><P
    140 >Radio devices can support <A
    141 HREF="x542.htm"
    142 >controls</A
    143 >, and must support the <A
    144 HREF="x394.htm"
    145 >tuner</A
    146 > ioctls.</P
    147 ><P
    148 >They do not support the video input or output, audio input
    149 or output, video standard, cropping and scaling, compression and
    150 streaming parameter, or overlay ioctls. All other ioctls and I/O
    151 methods are reserved for future extensions.</P
    152 ></DIV
    153 ><DIV
    154 CLASS="SECTION"
    155 ><H2
    156 CLASS="SECTION"
    157 ><A
    158 NAME="AEN7600"
    159 >4.10.3. Programming</A
    160 ></H2
    161 ><P
    162 >Radio devices may have a couple audio controls (as discussed
    163 in <A
    164 HREF="x542.htm"
    165 >Section 1.8</A
    166 >) such as a volume control, possibly custom
    167 controls. Further all radio devices have one tuner (these are
    168 discussed in <A
    169 HREF="x394.htm"
    170 >Section 1.6</A
    171 >) with index number zero to select
    172 the radio frequency and to determine if a monaural or FM stereo
    173 program is received. Drivers switch automatically between AM and FM
    174 depending on the selected frequency. The <A
    175 HREF="r12342.htm"
    176 ><CODE
    177 CLASS="CONSTANT"
    178 >VIDIOC_G_TUNER</CODE
    179 ></A
    180 > ioctl
    181 reports the supported frequency range.</P
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