Name

VIDIOC_ENUM_FREQ_BANDS - Enumerate supported frequency bands

Synopsis

.. c:macro:: VIDIOC_ENUM_FREQ_BANDS

int ioctl(int fd, VIDIOC_ENUM_FREQ_BANDS, struct v4l2_frequency_band *argp)

Arguments

fd File descriptor returned by :c:func:open().

argp Pointer to struct :c:type:v4l2_frequency_band.

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{2.4cm}|

.. c:type:: v4l2_frequency_band

.. flat-table:: struct v4l2_frequency_band :header-rows: 0 :stub-columns: 0 :widths: 1 1 2 1 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.
* - __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
  - ``index``
  - Identifies the frequency band, set by the application.
* - __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.
* - __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.
* - __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.
* - __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.
* - __u32
  - ``reserved``\ [9]
  - Reserved for future extensions.

Applications and drivers must set the array to zero.

.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.5cm}|

.. _band-modulation:

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

* - ``V4L2_BAND_MODULATION_VSB``
  - 0x02
  - Vestigial Sideband modulation, used for analog TV.
* - ``V4L2_BAND_MODULATION_FM``
  - 0x04
  - Frequency Modulation, commonly used for analog radio.
* - ``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.