mirror of
https://mirrors.bfsu.edu.cn/git/linux.git
synced 2024-11-30 07:34:12 +08:00
82559ac027
All those files are under GFDL 1.1 or later, with no invariant sections. Tag them as such. Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>
60 lines
2.1 KiB
ReStructuredText
60 lines
2.1 KiB
ReStructuredText
.. Permission is granted to copy, distribute and/or modify this
|
|
.. document under the terms of the GNU Free Documentation License,
|
|
.. Version 1.1 or any later version published by the Free Software
|
|
.. Foundation, with no Invariant Sections, no Front-Cover Texts
|
|
.. and no Back-Cover Texts. A copy of the license is included at
|
|
.. Documentation/media/uapi/fdl-appendix.rst.
|
|
..
|
|
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections
|
|
|
|
.. _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.
|