1 .. SPDX-License-Identifier: GFDL-1.1-no-invari 1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2 2
3 .. _radio: 3 .. _radio:
4 4
5 *************** 5 ***************
6 Radio Interface 6 Radio Interface
7 *************** 7 ***************
8 8
9 This interface is intended for AM and FM (anal 9 This interface is intended for AM and FM (analog) radio receivers and
10 transmitters. 10 transmitters.
11 11
12 Conventionally V4L2 radio devices are accessed 12 Conventionally V4L2 radio devices are accessed through character device
13 special files named ``/dev/radio`` and ``/dev/ 13 special files named ``/dev/radio`` and ``/dev/radio0`` to
14 ``/dev/radio63`` with major number 81 and mino 14 ``/dev/radio63`` with major number 81 and minor numbers 64 to 127.
15 15
16 16
17 Querying Capabilities 17 Querying Capabilities
18 ===================== 18 =====================
19 19
20 Devices supporting the radio interface set the 20 Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and
21 ``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` f 21 ``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the
22 ``capabilities`` field of struct 22 ``capabilities`` field of struct
23 :c:type:`v4l2_capability` returned by the 23 :c:type:`v4l2_capability` returned by the
24 :ref:`VIDIOC_QUERYCAP` ioctl. Other combinatio 24 :ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of
25 capability flags are reserved for future exten 25 capability flags are reserved for future extensions.
26 26
27 27
28 Supplemental Functions 28 Supplemental Functions
29 ====================== 29 ======================
30 30
31 Radio devices can support :ref:`controls <cont 31 Radio devices can support :ref:`controls <control>`, and must support
32 the :ref:`tuner or modulator <tuner>` ioctls. 32 the :ref:`tuner or modulator <tuner>` ioctls.
33 33
34 They do not support the video input or output, 34 They do not support the video input or output, audio input or output,
35 video standard, cropping and scaling, compress 35 video standard, cropping and scaling, compression and streaming
36 parameter, or overlay ioctls. All other ioctls 36 parameter, or overlay ioctls. All other ioctls and I/O methods are
37 reserved for future extensions. 37 reserved for future extensions.
38 38
39 39
40 Programming 40 Programming
41 =========== 41 ===========
42 42
43 Radio devices may have a couple audio controls 43 Radio devices may have a couple audio controls (as discussed in
44 :ref:`control`) such as a volume control, poss 44 :ref:`control`) such as a volume control, possibly custom controls.
45 Further all radio devices have one tuner or mo 45 Further all radio devices have one tuner or modulator (these are
46 discussed in :ref:`tuner`) with index number z 46 discussed in :ref:`tuner`) with index number zero to select the radio
47 frequency and to determine if a monaural or FM 47 frequency and to determine if a monaural or FM stereo program is
48 received/emitted. Drivers switch automatically 48 received/emitted. Drivers switch automatically between AM and FM
49 depending on the selected frequency. The 49 depending on the selected frequency. The
50 :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or 50 :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
51 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` 51 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
52 supported frequency range. 52 supported frequency range.
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