VIDIOC_G_FREQUENCY·VIDIOC_S_FREQUENCY ioctl

목적, 호출 형식과 인자

`VIDIOC_G_FREQUENCY`와 `VIDIOC_S_FREQUENCY`는 tuner 또는 modulator의 무선 주파수를 조회하거나 설정합니다. 입력 장치에는 tuner만 있고 출력 장치에는 modulator만 있습니다.

두 ioctl은 `struct v4l2_frequency`를 사용합니다. 조회는 수정 가능한 포인터를, 설정은 `const struct v4l2_frequency *argp`를 받으며 `fd`는 `open()`이 반환한 파일 디스크립터입니다.

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

.. _VIDIOC_G_FREQUENCY:

********************************************
ioctl VIDIOC_G_FREQUENCY, VIDIOC_S_FREQUENCY
********************************************

Name
====

VIDIOC_G_FREQUENCY - VIDIOC_S_FREQUENCY - Get or set tuner or modulator radio frequency

Synopsis
========

.. c:macro:: VIDIOC_G_FREQUENCY

``int ioctl(int fd, VIDIOC_G_FREQUENCY, struct v4l2_frequency *argp)``

.. c:macro:: VIDIOC_S_FREQUENCY

``int ioctl(int fd, VIDIOC_S_FREQUENCY, const struct v4l2_frequency *argp)``

Arguments
=========

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

``argp``
    Pointer to struct :c:type:`v4l2_frequency`.

현재 주파수 조회와 설정

현재 주파수를 읽으려면 `tuner`를 대상 tuner 또는 modulator 번호로 설정하고 `reserved` 배열을 0으로 만든 뒤 `VIDIOC_G_FREQUENCY`를 호출합니다. 드라이버가 현재 값을 `frequency`에 저장합니다.

주파수를 바꾸려면 `tuner`, `type`, `frequency`와 `reserved`를 초기화한 뒤 `VIDIOC_S_FREQUENCY`를 호출합니다. 요청값이 불가능하면 드라이버가 가장 가까운 가능한 주파수를 사용합니다.

S_FREQUENCY는 write-only ioctl이므로 실제로 선택된 새 주파수를 구조체에 돌려주지 않습니다. 조정된 값을 알아야 하면 설정 후 G_FREQUENCY로 다시 조회해야 합니다.

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

To get the current tuner or modulator radio frequency applications set
the ``tuner`` field of a struct
:c:type:`v4l2_frequency` to the respective tuner or
modulator number (only input devices have tuners, only output devices
have modulators), zero out the ``reserved`` array and call the
:ref:`VIDIOC_G_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this structure. The
driver stores the current frequency in the ``frequency`` field.

To change the current tuner or modulator radio frequency applications
initialize the ``tuner``, ``type`` and ``frequency`` fields, and the
``reserved`` array of a struct :c:type:`v4l2_frequency`
and call the :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` ioctl with a pointer to this
structure. When the requested frequency is not possible the driver
assumes the closest possible value. However :ref:`VIDIOC_S_FREQUENCY <VIDIOC_G_FREQUENCY>` is a
write-only ioctl, it does not return the actual new frequency.

struct v4l2_frequency

현재 지원되는 modulator는 radio modulator뿐이므로 modulator의 `type`은 `V4L2_TUNER_RADIO`입니다. 단위는 `v4l2_tuner` 또는 `v4l2_modulator.capability`를 먼저 확인해 해석해야 합니다.

.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|

.. c:type:: v4l2_frequency

.. flat-table:: struct v4l2_frequency
    :header-rows:  0
    :stub-columns: 0
    :widths:       1 1 2

    * - __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
      - ``frequency``
      - Tuning frequency in units of 62.5 kHz, or if the struct
	:c:type:`v4l2_tuner` or struct
	:c:type:`v4l2_modulator` ``capability`` flag
	``V4L2_TUNER_CAP_LOW`` is set, in units of 62.5 Hz. A 1 Hz unit is
	used when the ``capability`` flag ``V4L2_TUNER_CAP_1HZ`` is set.
    * - __u32
      - ``reserved``\ [8]
      - Reserved for future extensions. Drivers and applications must set
	the array to zero.

반환값과 오류

성공하면 0을 반환합니다. 오류가 발생하면 -1을 반환하고 `errno`를 설정하며 Generic Error Codes 장의 공통 오류도 적용됩니다.

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`` index is out of bounds or the value in the ``type``
    field is wrong.

EBUSY
    A hardware seek is in progress.