1  <title>Software Defined Radio Interface (SDR)</title>
2
3  <note>
4    <title>Experimental</title>
5    <para>This is an <link linkend="experimental"> experimental </link>
6    interface and may change in the future.</para>
7  </note>
8
9  <para>
10SDR is an abbreviation of Software Defined Radio, the radio device
11which uses application software for modulation or demodulation. This interface
12is intended for controlling and data streaming of such devices.
13  </para>
14
15  <para>
16SDR devices are accessed through character device special files named
17<filename>/dev/swradio0</filename> to <filename>/dev/swradio255</filename>
18with major number 81 and dynamically allocated minor numbers 0 to 255.
19  </para>
20
21  <section>
22    <title>Querying Capabilities</title>
23
24    <para>
25Devices supporting the SDR receiver interface set the
26<constant>V4L2_CAP_SDR_CAPTURE</constant> and
27<constant>V4L2_CAP_TUNER</constant> flag in the
28<structfield>capabilities</structfield> field of &v4l2-capability;
29returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an
30Analog to Digital Converter (ADC), which is a mandatory element for the SDR receiver.
31    </para>
32    <para>
33Devices supporting the SDR transmitter interface set the
34<constant>V4L2_CAP_SDR_OUTPUT</constant> and
35<constant>V4L2_CAP_MODULATOR</constant> flag in the
36<structfield>capabilities</structfield> field of &v4l2-capability;
37returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an
38Digital to Analog Converter (DAC), which is a mandatory element for the SDR transmitter.
39    </para>
40    <para>
41At least one of the read/write, streaming or asynchronous I/O methods must
42be supported.
43    </para>
44  </section>
45
46  <section>
47    <title>Supplemental Functions</title>
48
49    <para>
50SDR devices can support <link linkend="control">controls</link>, and must
51support the <link linkend="tuner">tuner</link> ioctls. Tuner ioctls are used
52for setting the ADC/DAC sampling rate (sampling frequency) and the possible
53radio frequency (RF).
54    </para>
55
56    <para>
57The <constant>V4L2_TUNER_SDR</constant> tuner type is used for setting SDR
58device ADC/DAC frequency, and the <constant>V4L2_TUNER_RF</constant>
59tuner type is used for setting radio frequency.
60The tuner index of the RF tuner (if any) must always follow the SDR tuner index.
61Normally the SDR tuner is #0 and the RF tuner is #1.
62    </para>
63
64    <para>
65The &VIDIOC-S-HW-FREQ-SEEK; ioctl is not supported.
66    </para>
67  </section>
68
69  <section>
70    <title>Data Format Negotiation</title>
71
72    <para>
73The SDR device uses the <link linkend="format">format</link> ioctls to
74select the capture and output format. Both the sampling resolution and the data
75streaming format are bound to that selectable format. In addition to the basic
76<link linkend="format">format</link> ioctls, the &VIDIOC-ENUM-FMT; ioctl
77must be supported as well.
78    </para>
79
80    <para>
81To use the <link linkend="format">format</link> ioctls applications set the
82<structfield>type</structfield> field of a &v4l2-format; to
83<constant>V4L2_BUF_TYPE_SDR_CAPTURE</constant> or
84<constant>V4L2_BUF_TYPE_SDR_OUTPUT</constant> and use the &v4l2-sdr-format;
85<structfield>sdr</structfield> member of the <structfield>fmt</structfield>
86union as needed per the desired operation.
87Currently there is two fields, <structfield>pixelformat</structfield> and
88<structfield>buffersize</structfield>, of struct &v4l2-sdr-format; which are
89used. Content of the <structfield>pixelformat</structfield> is V4L2 FourCC
90code of the data format. The <structfield>buffersize</structfield> field is
91maximum buffer size in bytes required for data transfer, set by the driver in
92order to inform application.
93    </para>
94
95    <table pgwide="1" frame="none" id="v4l2-sdr-format">
96      <title>struct <structname>v4l2_sdr_format</structname></title>
97      <tgroup cols="3">
98        &cs-str;
99        <tbody valign="top">
100          <row>
101            <entry>__u32</entry>
102            <entry><structfield>pixelformat</structfield></entry>
103            <entry>
104The data format or type of compression, set by the application. This is a
105little endian <link linkend="v4l2-fourcc">four character code</link>.
106V4L2 defines SDR formats in <xref linkend="sdr-formats" />.
107           </entry>
108          </row>
109          <row>
110            <entry>__u32</entry>
111            <entry><structfield>buffersize</structfield></entry>
112            <entry>
113Maximum size in bytes required for data. Value is set by the driver.
114           </entry>
115          </row>
116          <row>
117            <entry>__u8</entry>
118            <entry><structfield>reserved[24]</structfield></entry>
119            <entry>This array is reserved for future extensions.
120Drivers and applications must set it to zero.</entry>
121          </row>
122        </tbody>
123      </tgroup>
124    </table>
125
126    <para>
127An SDR device may support <link linkend="rw">read/write</link>
128and/or streaming (<link linkend="mmap">memory mapping</link>
129or <link linkend="userp">user pointer</link>) I/O.
130    </para>
131
132  </section>
133