+++ /dev/null
- <title>Software Defined Radio Interface (SDR)</title>
-
- <para>
-SDR is an abbreviation of Software Defined Radio, the radio device
-which uses application software for modulation or demodulation. This interface
-is intended for controlling and data streaming of such devices.
- </para>
-
- <para>
-SDR devices are accessed through character device special files named
-<filename>/dev/swradio0</filename> to <filename>/dev/swradio255</filename>
-with major number 81 and dynamically allocated minor numbers 0 to 255.
- </para>
-
- <section>
- <title>Querying Capabilities</title>
-
- <para>
-Devices supporting the SDR receiver interface set the
-<constant>V4L2_CAP_SDR_CAPTURE</constant> and
-<constant>V4L2_CAP_TUNER</constant> flag in the
-<structfield>capabilities</structfield> field of &v4l2-capability;
-returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an
-Analog to Digital Converter (ADC), which is a mandatory element for the SDR receiver.
- </para>
- <para>
-Devices supporting the SDR transmitter interface set the
-<constant>V4L2_CAP_SDR_OUTPUT</constant> and
-<constant>V4L2_CAP_MODULATOR</constant> flag in the
-<structfield>capabilities</structfield> field of &v4l2-capability;
-returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an
-Digital to Analog Converter (DAC), which is a mandatory element for the SDR transmitter.
- </para>
- <para>
-At least one of the read/write, streaming or asynchronous I/O methods must
-be supported.
- </para>
- </section>
-
- <section>
- <title>Supplemental Functions</title>
-
- <para>
-SDR devices can support <link linkend="control">controls</link>, and must
-support the <link linkend="tuner">tuner</link> ioctls. Tuner ioctls are used
-for setting the ADC/DAC sampling rate (sampling frequency) and the possible
-radio frequency (RF).
- </para>
-
- <para>
-The <constant>V4L2_TUNER_SDR</constant> tuner type is used for setting SDR
-device ADC/DAC frequency, and the <constant>V4L2_TUNER_RF</constant>
-tuner type is used for setting radio frequency.
-The tuner index of the RF tuner (if any) must always follow the SDR tuner index.
-Normally the SDR tuner is #0 and the RF tuner is #1.
- </para>
-
- <para>
-The &VIDIOC-S-HW-FREQ-SEEK; ioctl is not supported.
- </para>
- </section>
-
- <section>
- <title>Data Format Negotiation</title>
-
- <para>
-The SDR device uses the <link linkend="format">format</link> ioctls to
-select the capture and output format. Both the sampling resolution and the data
-streaming format are bound to that selectable format. In addition to the basic
-<link linkend="format">format</link> ioctls, the &VIDIOC-ENUM-FMT; ioctl
-must be supported as well.
- </para>
-
- <para>
-To use the <link linkend="format">format</link> ioctls applications set the
-<structfield>type</structfield> field of a &v4l2-format; to
-<constant>V4L2_BUF_TYPE_SDR_CAPTURE</constant> or
-<constant>V4L2_BUF_TYPE_SDR_OUTPUT</constant> and use the &v4l2-sdr-format;
-<structfield>sdr</structfield> member of the <structfield>fmt</structfield>
-union as needed per the desired operation.
-Currently there is two fields, <structfield>pixelformat</structfield> and
-<structfield>buffersize</structfield>, of struct &v4l2-sdr-format; which are
-used. Content of the <structfield>pixelformat</structfield> is V4L2 FourCC
-code of the data format. The <structfield>buffersize</structfield> field is
-maximum buffer size in bytes required for data transfer, set by the driver in
-order to inform application.
- </para>
-
- <table pgwide="1" frame="none" id="v4l2-sdr-format">
- <title>struct <structname>v4l2_sdr_format</structname></title>
- <tgroup cols="3">
- &cs-str;
- <tbody valign="top">
- <row>
- <entry>__u32</entry>
- <entry><structfield>pixelformat</structfield></entry>
- <entry>
-The data format or type of compression, set by the application. This is a
-little endian <link linkend="v4l2-fourcc">four character code</link>.
-V4L2 defines SDR formats in <xref linkend="sdr-formats" />.
- </entry>
- </row>
- <row>
- <entry>__u32</entry>
- <entry><structfield>buffersize</structfield></entry>
- <entry>
-Maximum size in bytes required for data. Value is set by the driver.
- </entry>
- </row>
- <row>
- <entry>__u8</entry>
- <entry><structfield>reserved[24]</structfield></entry>
- <entry>This array is reserved for future extensions.
-Drivers and applications must set it to zero.</entry>
- </row>
- </tbody>
- </tgroup>
- </table>
-
- <para>
-An SDR device may support <link linkend="rw">read/write</link>
-and/or streaming (<link linkend="mmap">memory mapping</link>
-or <link linkend="userp">user pointer</link>) I/O.
- </para>
-
- </section>
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