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.. -*- coding: utf-8; mode: rst -*-
.. _VIDIOC_ENUM_FREQ_BANDS:
****************************
ioctl VIDIOC_ENUM_FREQ_BANDS
****************************
Name
====
VIDIOC_ENUM_FREQ_BANDS - 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:: 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.
.. _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.
|
