.. -*- coding: utf-8; mode: rst -*-

.. _VIDIOC_ENUM_FREQ_BANDS:

****************************
ioctl VIDIOC_ENUM_FREQ_BANDS
****************************

*man VIDIOC_ENUM_FREQ_BANDS(2)*

Enumerate supported frequency bands


Synopsis
========

.. cpp:function:: int ioctl( int fd, int request, struct v4l2_frequency_band *argp )

Arguments
=========

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

``request``
    VIDIOC_ENUM_FREQ_BANDS

``argp``


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

Enumerates the frequency bands that a tuner or modulator supports. To do
this applications initialize the ``tuner``, ``type`` and ``index``
fields, and zero out the ``reserved`` array of a struct
:ref:`v4l2_frequency_band <v4l2-frequency-band>` and call the
:ref:`VIDIOC_ENUM_FREQ_BANDS` ioctl with a pointer to this structure.

This ioctl is supported if the ``V4L2_TUNER_CAP_FREQ_BANDS`` capability
of the corresponding tuner/modulator is set.


.. _v4l2-frequency-band:

.. flat-table:: struct v4l2_frequency_band
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2 1 1


    -  .. row 1

       -  __u32

       -  ``tuner``

       -  The tuner or modulator index number. This is the same value as in
          the struct :ref:`v4l2_input <v4l2-input>` ``tuner`` field and
          the struct :ref:`v4l2_tuner <v4l2-tuner>` ``index`` field, or
          the struct :ref:`v4l2_output <v4l2-output>` ``modulator`` field
          and the struct :ref:`v4l2_modulator <v4l2-modulator>` ``index``
          field.

    -  .. row 2

       -  __u32

       -  ``type``

       -  The tuner type. This is the same value as in the struct
          :ref:`v4l2_tuner <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 :ref:`v4l2-tuner-type`

    -  .. row 3

       -  __u32

       -  ``index``

       -  Identifies the frequency band, set by the application.

    -  .. row 4

       -  __u32

       -  ``capability``

       -  :cspan:`2` The tuner/modulator capability flags for this
          frequency band, see :ref:`tuner-capability`. The
          ``V4L2_TUNER_CAP_LOW`` or ``V4L2_TUNER_CAP_1HZ`` capability must
          be the same for all frequency bands of the selected
          tuner/modulator. So either all bands have that capability set, or
          none of them have that capability.

    -  .. row 5

       -  __u32

       -  ``rangelow``

       -  :cspan:`2` The lowest tunable frequency in units of 62.5 kHz, or
          if the ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units
          of 62.5 Hz, for this frequency band. A 1 Hz unit is used when the
          ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.

    -  .. row 6

       -  __u32

       -  ``rangehigh``

       -  :cspan:`2` The highest tunable frequency in units of 62.5 kHz,
          or if the ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in
          units of 62.5 Hz, for this frequency band. A 1 Hz unit is used
          when the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.

    -  .. row 7

       -  __u32

       -  ``modulation``

       -  :cspan:`2` The supported modulation systems of this frequency
          band. See :ref:`band-modulation`. Note that currently only one
          modulation system per frequency band is supported. More work will
          need to be done if multiple modulation systems are possible.
          Contact the linux-media mailing list
          (`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__)
          if you need that functionality.

    -  .. row 8

       -  __u32

       -  ``reserved``\ [9]

       -  Reserved for future extensions. Applications and drivers must set
          the array to zero.


.. _band-modulation:

.. flat-table:: Band Modulation Systems
    :header-rows:  0
    :stub-columns: 0
    :widths:       3 1 4


    -  .. row 1

       -  ``V4L2_BAND_MODULATION_VSB``

       -  0x02

       -  Vestigial Sideband modulation, used for analog TV.

    -  .. row 2

       -  ``V4L2_BAND_MODULATION_FM``

       -  0x04

       -  Frequency Modulation, commonly used for analog radio.

    -  .. row 3

       -  ``V4L2_BAND_MODULATION_AM``

       -  0x08

       -  Amplitude Modulation, commonly used for analog radio.


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`` or ``index`` is out of bounds or the ``type`` field is
    wrong.


.. ------------------------------------------------------------------------------
.. This file was automatically converted from DocBook-XML with the dbxml
.. library (https://github.com/return42/sphkerneldoc). The origin XML comes
.. from the linux kernel, refer to:
..
.. * https://github.com/torvalds/linux/tree/master/Documentation/DocBook
.. ------------------------------------------------------------------------------