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40>Video for Linux Two API Specification: Revision 0.24</TH
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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&nbsp;<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
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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
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155><H2
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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
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