blob: 2b5b836574eb930e131e70403ceb0bd005acff4d (
plain) (
blame)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
|
.. -*- coding: utf-8; mode: rst -*-
.. _radio:
***************
Radio Interface
***************
This interface is intended for AM and FM (analog) radio receivers and
transmitters.
Conventionally V4L2 radio devices are accessed through character device
special files named ``/dev/radio`` and ``/dev/radio0`` to
``/dev/radio63`` with major number 81 and minor numbers 64 to 127.
Querying Capabilities
=====================
Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and
``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the
``capabilities`` field of struct
:c:type:`v4l2_capability` returned by the
:ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of
capability flags are reserved for future extensions.
Supplemental Functions
======================
Radio devices can support :ref:`controls <control>`, and must support
the :ref:`tuner or modulator <tuner>` ioctls.
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.
Programming
===========
Radio devices may have a couple audio controls (as discussed in
:ref:`control`) such as a volume control, possibly custom controls.
Further all radio devices have one tuner or modulator (these are
discussed in :ref:`tuner`) with index number zero to select the radio
frequency and to determine if a monaural or FM stereo program is
received/emitted. Drivers switch automatically between AM and FM
depending on the selected frequency. The
:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
supported frequency range.
|
