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| >Video for Linux Two API Specification: Revision 0.24</TH |
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| >Chapter 4. Interfaces</TD |
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| >4.10. Radio Interface</A |
| ></H1 |
| ><P |
| >This interface is intended for AM and FM (analog) radio |
| receivers.</P |
| ><P |
| >Conventionally V4L2 radio devices are accessed through |
| character device special files named <TT |
| CLASS="FILENAME" |
| >/dev/radio</TT |
| > |
| and <TT |
| CLASS="FILENAME" |
| >/dev/radio0</TT |
| > to |
| <TT |
| CLASS="FILENAME" |
| >/dev/radio63</TT |
| > with major number 81 and minor |
| numbers 64 to 127.</P |
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| ><A |
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| >4.10.1. Querying Capabilities</A |
| ></H2 |
| ><P |
| >Devices supporting the radio interface set the |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_CAP_RADIO</CODE |
| > and |
| <CODE |
| CLASS="CONSTANT" |
| >V4L2_CAP_TUNER</CODE |
| > flag in the |
| <CODE |
| CLASS="STRUCTFIELD" |
| >capabilities</CODE |
| > field of struct <A |
| HREF="r13105.htm#V4L2-CAPABILITY" |
| >v4l2_capability</A |
| > |
| returned by the <A |
| HREF="r13105.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_QUERYCAP</CODE |
| ></A |
| > ioctl. Other combinations of |
| capability flags are reserved for future extensions.</P |
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| ><A |
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| >4.10.2. Supplemental Functions</A |
| ></H2 |
| ><P |
| >Radio devices can support <A |
| HREF="x542.htm" |
| >controls</A |
| >, and must support the <A |
| HREF="x394.htm" |
| >tuner</A |
| > ioctls.</P |
| ><P |
| >They do not support the video input or output, audio input |
| or output, video standard, cropping and scaling, compression and |
| streaming parameter, or overlay ioctls. All other ioctls and I/O |
| methods are reserved for future extensions.</P |
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| ><A |
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| >4.10.3. Programming</A |
| ></H2 |
| ><P |
| >Radio devices may have a couple audio controls (as discussed |
| in <A |
| HREF="x542.htm" |
| >Section 1.8</A |
| >) such as a volume control, possibly custom |
| controls. Further all radio devices have one tuner (these are |
| discussed in <A |
| HREF="x394.htm" |
| >Section 1.6</A |
| >) with index number zero to select |
| the radio frequency and to determine if a monaural or FM stereo |
| program is received. Drivers switch automatically between AM and FM |
| depending on the selected frequency. The <A |
| HREF="r12342.htm" |
| ><CODE |
| CLASS="CONSTANT" |
| >VIDIOC_G_TUNER</CODE |
| ></A |
| > ioctl |
| reports the supported frequency range.</P |
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