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1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later2 3.. _sdr:4 5**************************************6Software Defined Radio Interface (SDR)7**************************************8 9SDR is an abbreviation of Software Defined Radio, the radio device which10uses application software for modulation or demodulation. This interface11is intended for controlling and data streaming of such devices.12 13SDR devices are accessed through character device special files named14``/dev/swradio0`` to ``/dev/swradio255`` with major number 81 and15dynamically allocated minor numbers 0 to 255.16 17 18Querying Capabilities19=====================20 21Devices supporting the SDR receiver interface set the22``V4L2_CAP_SDR_CAPTURE`` and ``V4L2_CAP_TUNER`` flag in the23``capabilities`` field of struct24:c:type:`v4l2_capability` returned by the25:ref:`VIDIOC_QUERYCAP` ioctl. That flag means the26device has an Analog to Digital Converter (ADC), which is a mandatory27element for the SDR receiver.28 29Devices supporting the SDR transmitter interface set the30``V4L2_CAP_SDR_OUTPUT`` and ``V4L2_CAP_MODULATOR`` flag in the31``capabilities`` field of struct32:c:type:`v4l2_capability` returned by the33:ref:`VIDIOC_QUERYCAP` ioctl. That flag means the34device has an Digital to Analog Converter (DAC), which is a mandatory35element for the SDR transmitter.36 37At least one of the read/write or streaming I/O methods38must be supported.39 40 41Supplemental Functions42======================43 44SDR devices can support :ref:`controls <control>`, and must support45the :ref:`tuner` ioctls. Tuner ioctls are used for setting the46ADC/DAC sampling rate (sampling frequency) and the possible radio47frequency (RF).48 49The ``V4L2_TUNER_SDR`` tuner type is used for setting SDR device ADC/DAC50frequency, and the ``V4L2_TUNER_RF`` tuner type is used for setting51radio frequency. The tuner index of the RF tuner (if any) must always52follow the SDR tuner index. Normally the SDR tuner is #0 and the RF53tuner is #1.54 55The :ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl is56not supported.57 58 59Data Format Negotiation60=======================61 62The SDR device uses the :ref:`format` ioctls to select the63capture and output format. Both the sampling resolution and the data64streaming format are bound to that selectable format. In addition to the65basic :ref:`format` ioctls, the66:ref:`VIDIOC_ENUM_FMT` ioctl must be supported as67well.68 69To use the :ref:`format` ioctls applications set the ``type``70field of a struct :c:type:`v4l2_format` to71``V4L2_BUF_TYPE_SDR_CAPTURE`` or ``V4L2_BUF_TYPE_SDR_OUTPUT`` and use72the struct :c:type:`v4l2_sdr_format` ``sdr`` member73of the ``fmt`` union as needed per the desired operation. Currently74there are two fields, ``pixelformat`` and ``buffersize``, of75struct :c:type:`v4l2_sdr_format` which are used.76Content of the ``pixelformat`` is V4L2 FourCC code of the data format.77The ``buffersize`` field is maximum buffer size in bytes required for78data transfer, set by the driver in order to inform application.79 80 81.. c:type:: v4l2_sdr_format82 83.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|84 85.. flat-table:: struct v4l2_sdr_format86 :header-rows: 087 :stub-columns: 088 :widths: 1 1 289 90 * - __u3291 - ``pixelformat``92 - The data format or type of compression, set by the application.93 This is a little endian94 :ref:`four character code <v4l2-fourcc>`. V4L2 defines SDR95 formats in :ref:`sdr-formats`.96 * - __u3297 - ``buffersize``98 - Maximum size in bytes required for data. Value is set by the99 driver.100 * - __u8101 - ``reserved[24]``102 - This array is reserved for future extensions. Drivers and103 applications must set it to zero.104 105 106An SDR device may support :ref:`read/write <rw>` and/or streaming107(:ref:`memory mapping <mmap>` or :ref:`user pointer <userp>`) I/O.108