.. 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/userspace-api/media/fdl-appendix.rst.
..
.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections

.. _VIDIOC_G_FREQUENCY:

********************************************
ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY
********************************************

Name
====

VIDIOC_G_FREQUENCY - VIDIOC_S_FREQUENCY - Get or set tuner or modulator radio frequency


Synopsis
========

.. c:function:: int ioctl( int fd, VIDIOC_G_FREQUENCY, struct v4l2_frequency *argp )
    :name: VIDIOC_G_FREQUENCY

.. c:function:: int ioctl( int fd, VIDIOC_S_FREQUENCY, const struct v4l2_frequency *argp )
    :name: VIDIOC_S_FREQUENCY


Arguments
=========

``fd``
    File descriptor returned by :ref:`open() <func-open>`.

``argp``
    Pointer to struct :c:type:`v4l2_frequency`.


Description
===========

To get the current tuner or modulator radio frequency applications set
the ``tuner`` field of a struct
:c:type:`v4l2_frequency` to the respective tuner or
modulator number (only input devices have tuners, only output devices
have modulators), zero out the ``reserved`` array and call the
:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this structure. The
driver stores the current frequency in the ``frequency`` field.

To change the current tuner or modulator radio frequency applications
initialize the ``tuner``, ``type`` and ``frequency`` fields, and the
``reserved`` array of a struct :c:type:`v4l2_frequency`
and call the :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this
structure. When the requested frequency is not possible the driver
assumes the closest possible value. However :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` is a
write-only ioctl, it does not return the actual new frequency.


.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}|

.. c:type:: v4l2_frequency

.. flat-table:: struct v4l2_frequency
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2

    * - __u32
      - ``tuner``
      - The tuner or modulator index number. This is the same value as in
	the struct :c:type:`v4l2_input` ``tuner`` field and
	the struct :c:type:`v4l2_tuner` ``index`` field, or
	the struct :c:type:`v4l2_output` ``modulator`` field
	and the struct :c:type:`v4l2_modulator` ``index``
	field.
    * - __u32
      - ``type``
      - The tuner type. This is the same value as in the struct
	:c:type:`v4l2_tuner` ``type`` field. The type must be
	set to ``V4L2_TUNER_RADIO`` for ``/dev/radioX`` device nodes, and
	to ``V4L2_TUNER_ANALOG_TV`` for all others. Set this field to
	``V4L2_TUNER_RADIO`` for modulators (currently only radio
	modulators are supported). See :c:type:`v4l2_tuner_type`
    * - __u32
      - ``frequency``
      - Tuning frequency in units of 62.5 kHz, or if the struct
	:c:type:`v4l2_tuner` or struct
	:c:type:`v4l2_modulator` ``capability`` flag
	``V4L2_TUNER_CAP_LOW`` is set, in units of 62.5 Hz. A 1 Hz unit is
	used when the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.
    * - __u32
      - ``reserved``\ [8]
      - Reserved for future extensions. Drivers and applications must set
	the array to zero.


Return Value
============

On success 0 is returned, on error -1 and the ``errno`` variable is set
appropriately. The generic error codes are described at the
:ref:`Generic Error Codes <gen-errors>` chapter.

EINVAL
    The ``tuner`` index is out of bounds or the value in the ``type``
    field is wrong.

EBUSY
    A hardware seek is in progress.
