108 lines
3.7 KiB
ReStructuredText
108 lines
3.7 KiB
ReStructuredText
.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
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.. _sdr:
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**************************************
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Software Defined Radio Interface (SDR)
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**************************************
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SDR is an abbreviation of Software Defined Radio, the radio device which
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uses application software for modulation or demodulation. This interface
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is intended for controlling and data streaming of such devices.
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SDR devices are accessed through character device special files named
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``/dev/swradio0`` to ``/dev/swradio255`` with major number 81 and
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dynamically allocated minor numbers 0 to 255.
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Querying Capabilities
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=====================
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Devices supporting the SDR receiver interface set the
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``V4L2_CAP_SDR_CAPTURE`` and ``V4L2_CAP_TUNER`` 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. That flag means the
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device has an Analog to Digital Converter (ADC), which is a mandatory
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element for the SDR receiver.
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Devices supporting the SDR transmitter interface set the
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``V4L2_CAP_SDR_OUTPUT`` and ``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. That flag means the
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device has an Digital to Analog Converter (DAC), which is a mandatory
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element for the SDR transmitter.
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At least one of the read/write, streaming or asynchronous I/O methods
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must be supported.
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Supplemental Functions
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======================
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SDR devices can support :ref:`controls <control>`, and must support
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the :ref:`tuner` ioctls. Tuner ioctls are used for setting the
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ADC/DAC sampling rate (sampling frequency) and the possible radio
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frequency (RF).
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The ``V4L2_TUNER_SDR`` tuner type is used for setting SDR device ADC/DAC
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frequency, and the ``V4L2_TUNER_RF`` tuner type is used for setting
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radio frequency. The tuner index of the RF tuner (if any) must always
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follow the SDR tuner index. Normally the SDR tuner is #0 and the RF
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tuner is #1.
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The :ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl is
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not supported.
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Data Format Negotiation
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=======================
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The SDR device uses the :ref:`format` ioctls to select the
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capture and output format. Both the sampling resolution and the data
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streaming format are bound to that selectable format. In addition to the
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basic :ref:`format` ioctls, the
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:ref:`VIDIOC_ENUM_FMT` ioctl must be supported as
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well.
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To use the :ref:`format` ioctls applications set the ``type``
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field of a struct :c:type:`v4l2_format` to
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``V4L2_BUF_TYPE_SDR_CAPTURE`` or ``V4L2_BUF_TYPE_SDR_OUTPUT`` and use
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the struct :c:type:`v4l2_sdr_format` ``sdr`` member
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of the ``fmt`` union as needed per the desired operation. Currently
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there are two fields, ``pixelformat`` and ``buffersize``, of
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struct :c:type:`v4l2_sdr_format` which are used.
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Content of the ``pixelformat`` is V4L2 FourCC code of the data format.
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The ``buffersize`` field is maximum buffer size in bytes required for
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data transfer, set by the driver in order to inform application.
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.. c:type:: v4l2_sdr_format
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.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
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.. flat-table:: struct v4l2_sdr_format
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:header-rows: 0
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:stub-columns: 0
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:widths: 1 1 2
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* - __u32
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- ``pixelformat``
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- The data format or type of compression, set by the application.
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This is a little endian
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:ref:`four character code <v4l2-fourcc>`. V4L2 defines SDR
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formats in :ref:`sdr-formats`.
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* - __u32
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- ``buffersize``
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- Maximum size in bytes required for data. Value is set by the
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driver.
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* - __u8
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- ``reserved[24]``
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- This array is reserved for future extensions. Drivers and
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applications must set it to zero.
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An SDR device may support :ref:`read/write <rw>` and/or streaming
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(:ref:`memory mapping <mmap>` or :ref:`user pointer <userp>`) I/O.
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