1 .. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later
2
3 .. _sdr:
4
5 **************************************
6 Software Defined Radio Interface (SDR)
7 **************************************
8
9 SDR is an abbreviation of Software Defined Radio, the radio device which
10 uses application software for modulation or demodulation. This interface
11 is intended for controlling and data streaming of such devices.
12
13 SDR devices are accessed through character device special files named
14 ``/dev/swradio0`` to ``/dev/swradio255`` with major number 81 and
15 dynamically allocated minor numbers 0 to 255.
16
17
18 Querying Capabilities
19 =====================
20
21 Devices supporting the SDR receiver interface set the
22 ``V4L2_CAP_SDR_CAPTURE`` and ``V4L2_CAP_TUNER`` flag in the
23 ``capabilities`` field of struct
24 :c:type:`v4l2_capability` returned by the
25 :ref:`VIDIOC_QUERYCAP` ioctl. That flag means the
26 device has an Analog to Digital Converter (ADC), which is a mandatory
27 element for the SDR receiver.
28
29 Devices supporting the SDR transmitter interface set the
30 ``V4L2_CAP_SDR_OUTPUT`` and ``V4L2_CAP_MODULATOR`` flag in the
31 ``capabilities`` field of struct
32 :c:type:`v4l2_capability` returned by the
33 :ref:`VIDIOC_QUERYCAP` ioctl. That flag means the
34 device has an Digital to Analog Converter (DAC), which is a mandatory
35 element for the SDR transmitter.
36
37 At least one of the read/write or streaming I/O methods
38 must be supported.
39
40
41 Supplemental Functions
42 ======================
43
44 SDR devices can support :ref:`controls <control>`, and must support
45 the :ref:`tuner` ioctls. Tuner ioctls are used for setting the
46 ADC/DAC sampling rate (sampling frequency) and the possible radio
47 frequency (RF).
48
49 The ``V4L2_TUNER_SDR`` tuner type is used for setting SDR device ADC/DAC
50 frequency, and the ``V4L2_TUNER_RF`` tuner type is used for setting
51 radio frequency. The tuner index of the RF tuner (if any) must always
52 follow the SDR tuner index. Normally the SDR tuner is #0 and the RF
53 tuner is #1.
54
55 The :ref:`VIDIOC_S_HW_FREQ_SEEK` ioctl is
56 not supported.
57
58
59 Data Format Negotiation
60 =======================
61
62 The SDR device uses the :ref:`format` ioctls to select the
63 capture and output format. Both the sampling resolution and the data
64 streaming format are bound to that selectable format. In addition to the
65 basic :ref:`format` ioctls, the
66 :ref:`VIDIOC_ENUM_FMT` ioctl must be supported as
67 well.
68
69 To use the :ref:`format` ioctls applications set the ``type``
70 field of a struct :c:type:`v4l2_format` to
71 ``V4L2_BUF_TYPE_SDR_CAPTURE`` or ``V4L2_BUF_TYPE_SDR_OUTPUT`` and use
72 the struct :c:type:`v4l2_sdr_format` ``sdr`` member
73 of the ``fmt`` union as needed per the desired operation. Currently
74 there are two fields, ``pixelformat`` and ``buffersize``, of
75 struct :c:type:`v4l2_sdr_format` which are used.
76 Content of the ``pixelformat`` is V4L2 FourCC code of the data format.
77 The ``buffersize`` field is maximum buffer size in bytes required for
78 data transfer, set by the driver in order to inform application.
79
80
81 .. c:type:: v4l2_sdr_format
82
83 .. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.5cm}|
84
85 .. flat-table:: struct v4l2_sdr_format
86 :header-rows: 0
87 :stub-columns: 0
88 :widths: 1 1 2
89
90 * - __u32
91 - ``pixelformat``
92 - The data format or type of compression, set by the application.
93 This is a little endian
94 :ref:`four character code <v4l2-fourcc>`. V4L2 defines SDR
95 formats in :ref:`sdr-formats`.
96 * - __u32
97 - ``buffersize``
98 - Maximum size in bytes required for data. Value is set by the
99 driver.
100 * - __u8
101 - ``reserved[24]``
102 - This array is reserved for future extensions. Drivers and
103 applications must set it to zero.
104
105
106 An SDR device may support :ref:`read/write <rw>` and/or streaming
107 (:ref:`memory mapping <mmap>` or :ref:`user pointer <userp>`) I/O.
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