Documentation/userspace-api/media/v4l/dev-radio.rst
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. _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.
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.
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.
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.