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- .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
- .. c:namespace:: V4L
- .. _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.
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