143 строки
4.2 KiB
ReStructuredText
143 строки
4.2 KiB
ReStructuredText
.. -*- coding: utf-8; mode: rst -*-
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.. _VIDIOC_ENUM_FREQ_BANDS:
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****************************
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ioctl VIDIOC_ENUM_FREQ_BANDS
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****************************
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Name
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====
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VIDIOC_ENUM_FREQ_BANDS - Enumerate supported frequency bands
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Synopsis
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========
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.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FREQ_BANDS, struct v4l2_frequency_band *argp )
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:name: VIDIOC_ENUM_FREQ_BANDS
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Arguments
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=========
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``fd``
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File descriptor returned by :ref:`open() <func-open>`.
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``argp``
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Description
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===========
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Enumerates the frequency bands that a tuner or modulator supports. To do
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this applications initialize the ``tuner``, ``type`` and ``index``
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fields, and zero out the ``reserved`` array of a struct
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:c:type:`v4l2_frequency_band` and call the
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:ref:`VIDIOC_ENUM_FREQ_BANDS` ioctl with a pointer to this structure.
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This ioctl is supported if the ``V4L2_TUNER_CAP_FREQ_BANDS`` capability
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of the corresponding tuner/modulator is set.
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.. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{3.0cm}|
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.. c:type:: v4l2_frequency_band
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.. flat-table:: struct v4l2_frequency_band
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2 1 1
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* - __u32
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- ``tuner``
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- The tuner or modulator index number. This is the same value as in
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the struct :c:type:`v4l2_input` ``tuner`` field and
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the struct :c:type:`v4l2_tuner` ``index`` field, or
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the struct :c:type:`v4l2_output` ``modulator`` field
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and the struct :c:type:`v4l2_modulator` ``index``
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field.
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* - __u32
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- ``type``
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- The tuner type. This is the same value as in the struct
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:c:type:`v4l2_tuner` ``type`` field. The type must be
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set to ``V4L2_TUNER_RADIO`` for ``/dev/radioX`` device nodes, and
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to ``V4L2_TUNER_ANALOG_TV`` for all others. Set this field to
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``V4L2_TUNER_RADIO`` for modulators (currently only radio
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modulators are supported). See :c:type:`v4l2_tuner_type`
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* - __u32
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- ``index``
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- Identifies the frequency band, set by the application.
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* - __u32
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- ``capability``
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- :cspan:`2` The tuner/modulator capability flags for this
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frequency band, see :ref:`tuner-capability`. The
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``V4L2_TUNER_CAP_LOW`` or ``V4L2_TUNER_CAP_1HZ`` capability must
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be the same for all frequency bands of the selected
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tuner/modulator. So either all bands have that capability set, or
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none of them have that capability.
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* - __u32
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- ``rangelow``
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- :cspan:`2` The lowest tunable frequency in units of 62.5 kHz, or
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if the ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in units
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of 62.5 Hz, for this frequency band. A 1 Hz unit is used when the
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``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.
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* - __u32
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- ``rangehigh``
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- :cspan:`2` The highest tunable frequency in units of 62.5 kHz,
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or if the ``capability`` flag ``V4L2_TUNER_CAP_LOW`` is set, in
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units of 62.5 Hz, for this frequency band. A 1 Hz unit is used
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when the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.
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* - __u32
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- ``modulation``
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- :cspan:`2` The supported modulation systems of this frequency
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band. See :ref:`band-modulation`.
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.. note::
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Currently only one modulation system per frequency band
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is supported. More work will need to be done if multiple
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modulation systems are possible. Contact the linux-media
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mailing list
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(`https://linuxtv.org/lists.php <https://linuxtv.org/lists.php>`__)
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if you need such functionality.
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* - __u32
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- ``reserved``\ [9]
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- Reserved for future extensions.
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Applications and drivers must set the array to zero.
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.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}|
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.. _band-modulation:
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.. flat-table:: Band Modulation Systems
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:header-rows: 0
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:stub-columns: 0
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:widths: 3 1 4
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* - ``V4L2_BAND_MODULATION_VSB``
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- 0x02
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- Vestigial Sideband modulation, used for analog TV.
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* - ``V4L2_BAND_MODULATION_FM``
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- 0x04
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- Frequency Modulation, commonly used for analog radio.
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* - ``V4L2_BAND_MODULATION_AM``
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- 0x08
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- Amplitude Modulation, commonly used for analog radio.
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Return Value
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============
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On success 0 is returned, on error -1 and the ``errno`` variable is set
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appropriately. The generic error codes are described at the
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:ref:`Generic Error Codes <gen-errors>` chapter.
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EINVAL
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The ``tuner`` or ``index`` is out of bounds or the ``type`` field is
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wrong.
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