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

.. _VIDIOC_ENUM_FREQ_BANDS:

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

Name
====

VIDIOC_ENUM_FREQ_BANDS - Enumerate supported frequency bands


Synopsis
========

.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FREQ_BANDS, struct v4l2_frequency_band *argp )
    :name: VIDIOC_ENUM_FREQ_BANDS


Arguments
=========

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

``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
:c:type:`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.


.. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|

.. c:type:: 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 :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.

    -  .. row 2

       -  __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 :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::

	     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 such functionality.

    -  .. row 8

       -  __u32

       -  ``reserved``\ [9]

       -  Reserved for future extensions.

	  Applications and drivers must set the array to zero.



.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|

.. _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.
