[deliverable/linux.git] / Documentation / linux_tv / media / v4l / dev-radio.rst

.. -*- 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
:ref:`v4l2_capability <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.
Commit	Line	Data
5377d91f MH	1	.. -- coding: utf-8; mode: rst --
	2
	3	.. _radio:
	4
	5	***************
	6	Radio Interface
	7	***************
	8
	9	This interface is intended for AM and FM (analog) radio receivers and
	10	transmitters.
	11
	12	Conventionally V4L2 radio devices are accessed through character device
	13	special files named ``/dev/radio`` and ``/dev/radio0`` to
	14	``/dev/radio63`` with major number 81 and minor numbers 64 to 127.
	15
	16
	17	Querying Capabilities
	18	=====================
	19
	20	Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and
	21	``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the
	22	``capabilities`` field of struct
	23	:ref:`v4l2_capability <v4l2-capability>` returned by the
7347081e	24	:ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of
5377d91f MH	25	capability flags are reserved for future extensions.
	26
	27
	28	Supplemental Functions
	29	======================
	30
	31	Radio devices can support :ref:`controls <control>`, and must support
	32	the :ref:`tuner or modulator <tuner>` ioctls.
	33
	34	They do not support the video input or output, audio input or output,
	35	video standard, cropping and scaling, compression and streaming
	36	parameter, or overlay ioctls. All other ioctls and I/O methods are
	37	reserved for future extensions.
	38
	39
	40	Programming
	41	===========
	42
	43	Radio devices may have a couple audio controls (as discussed in
	44	:ref:`control`) such as a volume control, possibly custom controls.
	45	Further all radio devices have one tuner or modulator (these are
	46	discussed in :ref:`tuner`) with index number zero to select the radio
	47	frequency and to determine if a monaural or FM stereo program is
	48	received/emitted. Drivers switch automatically between AM and FM
	49	depending on the selected frequency. The
4e03cb76 MCC	50	:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
4e03cb76 MCC	51	:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
5377d91f	52	supported frequency range.