53 lines
1.7 KiB
ReStructuredText
53 lines
1.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. _radio:
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***************
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Radio Interface
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***************
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This interface is intended for AM and FM (analog) radio receivers and
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transmitters.
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Conventionally V4L2 radio devices are accessed through character device
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special files named ``/dev/radio`` and ``/dev/radio0`` to
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``/dev/radio63`` with major number 81 and minor numbers 64 to 127.
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Querying Capabilities
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=====================
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Devices supporting the radio interface set the ``V4L2_CAP_RADIO`` and
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``V4L2_CAP_TUNER`` or ``V4L2_CAP_MODULATOR`` flag in the
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``capabilities`` field of struct
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:c:type:`v4l2_capability` returned by the
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:ref:`VIDIOC_QUERYCAP` ioctl. Other combinations of
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capability flags are reserved for future extensions.
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Supplemental Functions
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======================
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Radio devices can support :ref:`controls <control>`, and must support
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the :ref:`tuner or modulator <tuner>` ioctls.
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They do not support the video input or output, audio input or output,
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video standard, cropping and scaling, compression and streaming
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parameter, or overlay ioctls. All other ioctls and I/O methods are
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reserved for future extensions.
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Programming
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===========
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Radio devices may have a couple audio controls (as discussed in
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:ref:`control`) such as a volume control, possibly custom controls.
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Further all radio devices have one tuner or modulator (these are
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discussed in :ref:`tuner`) with index number zero to select the radio
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frequency and to determine if a monaural or FM stereo program is
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received/emitted. Drivers switch automatically between AM and FM
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depending on the selected frequency. The
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:ref:`VIDIOC_G_TUNER <VIDIOC_G_TUNER>` or
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:ref:`VIDIOC_G_MODULATOR <VIDIOC_G_MODULATOR>` ioctl reports the
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supported frequency range.
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