0001 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
0002
0003 .. _radio:
0004
0005 ***************
0006 Radio Interface
0007 ***************
0008
0009 This interface is intended for AM and FM (analog) radio receivers and
0010 transmitters.
0011
0012 Conventionally V4L2 radio devices are accessed through character device
0013 special files named ``/dev/radio`` and ``/dev/radio0`` to
0014 ``/dev/radio63`` with major number 81 and minor numbers 64 to 127.
0015
0016
0017 Querying Capabilities
0018 =====================
0019
0020 Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and
0021 ``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the
0022 ``capabilities`` field of struct
0023 :c:type:`v4l2_capability` returned by the
0024 :ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of
0025 capability flags are reserved for future extensions.
0026
0027
0028 Supplemental Functions
0029 ======================
0030
0031 Radio devices can support :ref:`controls <control>`, and must support
0032 the :ref:`tuner or modulator <tuner>` ioctls.
0033
0034 They do not support the video input or output, audio input or output,
0035 video standard, cropping and scaling, compression and streaming
0036 parameter, or overlay ioctls. All other ioctls and I/O methods are
0037 reserved for future extensions.
0038
0039
0040 Programming
0041 ===========
0042
0043 Radio devices may have a couple audio controls (as discussed in
0044 :ref:`control`) such as a volume control, possibly custom controls.
0045 Further all radio devices have one tuner or modulator (these are
0046 discussed in :ref:`tuner`) with index number zero to select the radio
0047 frequency and to determine if a monaural or FM stereo program is
0048 received/emitted. Drivers switch automatically between AM and FM
0049 depending on the selected frequency. The
0050 :ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
0051 :ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
0052 supported frequency range.
