Documentation/userspace-api/media/v4l/vidioc-g-modulator.rst

Source file repositories/reference/linux-study-clean/Documentation/userspace-api/media/v4l/vidioc-g-modulator.rst

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Linux kernel
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Documentation/userspace-api/media/v4l/vidioc-g-modulator.rst
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.rst
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Support Tooling And Documentation
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Documentation
Inferred role
Support Tooling And Documentation: documentation
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Why This File Exists

Repository support layer: documentation, build tooling, samples, user-space helper tools, generated initramfs support, licenses, and validation utilities.

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Annotated Snippet

.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
.. c:namespace:: V4L

.. _VIDIOC_G_MODULATOR:

********************************************
ioctl VIDIOC_G_MODULATOR, VIDIOC_S_MODULATOR
********************************************

Name
====

VIDIOC_G_MODULATOR - VIDIOC_S_MODULATOR - Get or set modulator attributes

Synopsis
========

.. c:macro:: VIDIOC_G_MODULATOR

``int ioctl(int fd, VIDIOC_G_MODULATOR, struct v4l2_modulator *argp)``

.. c:macro:: VIDIOC_S_MODULATOR

``int ioctl(int fd, VIDIOC_S_MODULATOR, const struct v4l2_modulator *argp)``

Arguments
=========

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

``argp``
    Pointer to struct :c:type:`v4l2_modulator`.

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

To query the attributes of a modulator applications initialize the
``index`` field and zero out the ``reserved`` array of a struct
:c:type:`v4l2_modulator` and call the
:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl with a pointer to this structure. Drivers
fill the rest of the structure or return an ``EINVAL`` error code when the
index is out of bounds. To enumerate all modulators applications shall
begin at index zero, incrementing by one until the driver returns
EINVAL.

Modulators have two writable properties, an audio modulation set and the
radio frequency. To change the modulated audio subprograms, applications
initialize the ``index`` and ``txsubchans`` fields and the ``reserved``
array and call the :ref:`VIDIOC_S_MODULATOR <VIDIOC_G_MODULATOR>` ioctl. Drivers may choose a
different audio modulation if the request cannot be satisfied. However
this is a write-only ioctl, it does not return the actual audio
modulation selected.

:ref:`SDR <sdr>` specific modulator types are ``V4L2_TUNER_SDR`` and
``V4L2_TUNER_RF``. For SDR devices ``txsubchans`` field must be
initialized to zero. The term 'modulator' means SDR transmitter in this
context.

To change the radio frequency the
:ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl is available.

.. tabularcolumns:: |p{2.9cm}|p{2.9cm}|p{5.8cm}|p{2.9cm}|p{2.4cm}|

.. c:type:: v4l2_modulator

.. flat-table:: struct v4l2_modulator
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2 1 1

Annotation

Implementation Notes