121 lines
4.4 KiB
XML
121 lines
4.4 KiB
XML
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<title>Software Defined Radio Interface (SDR)</title>
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<note>
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<title>Experimental</title>
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<para>This is an <link linkend="experimental"> experimental </link>
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interface and may change in the future.</para>
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</note>
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<para>
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SDR is an abbreviation of Software Defined Radio, the radio device
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which 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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</para>
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<para>
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SDR devices are accessed through character device special files named
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<filename>/dev/swradio0</filename> to <filename>/dev/swradio255</filename>
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with major number 81 and dynamically allocated minor numbers 0 to 255.
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</para>
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<section>
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<title>Querying Capabilities</title>
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<para>
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Devices supporting the SDR receiver interface set the
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<constant>V4L2_CAP_SDR_CAPTURE</constant> and
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<constant>V4L2_CAP_TUNER</constant> flag in the
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<structfield>capabilities</structfield> field of &v4l2-capability;
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returned by the &VIDIOC-QUERYCAP; ioctl. That flag means the device has an
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Analog to Digital Converter (ADC), which is a mandatory element for the SDR receiver.
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At least one of the read/write, streaming or asynchronous I/O methods must
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be supported.
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</para>
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</section>
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<section>
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<title>Supplemental Functions</title>
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<para>
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SDR devices can support <link linkend="control">controls</link>, and must
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support the <link linkend="tuner">tuner</link> ioctls. Tuner ioctls are used
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for setting the ADC sampling rate (sampling frequency) and the possible RF tuner
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frequency.
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</para>
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<para>
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The <constant>V4L2_TUNER_ADC</constant> tuner type is used for ADC tuners, and
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the <constant>V4L2_TUNER_RF</constant> tuner type is used for RF tuners. The
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tuner index of the RF tuner (if any) must always follow the ADC tuner index.
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Normally the ADC tuner is #0 and the RF tuner is #1.
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</para>
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<para>
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The &VIDIOC-S-HW-FREQ-SEEK; ioctl is not supported.
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</para>
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</section>
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<section>
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<title>Data Format Negotiation</title>
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<para>
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The SDR capture device uses the <link linkend="format">format</link> ioctls to
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select the capture format. Both the sampling resolution and the data streaming
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format are bound to that selectable format. In addition to the basic
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<link linkend="format">format</link> ioctls, the &VIDIOC-ENUM-FMT; ioctl
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must be supported as well.
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</para>
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<para>
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To use the <link linkend="format">format</link> ioctls applications set the
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<structfield>type</structfield> field of a &v4l2-format; to
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<constant>V4L2_BUF_TYPE_SDR_CAPTURE</constant> and use the &v4l2-sdr-format;
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<structfield>sdr</structfield> member of the <structfield>fmt</structfield>
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union as needed per the desired operation.
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Currently there is two fields, <structfield>pixelformat</structfield> and
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<structfield>buffersize</structfield>, of struct &v4l2-sdr-format; which are
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used. Content of the <structfield>pixelformat</structfield> is V4L2 FourCC
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code of the data format. The <structfield>buffersize</structfield> field is
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maximum buffer size in bytes required for data transfer, set by the driver in
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order to inform application.
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</para>
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<table pgwide="1" frame="none" id="v4l2-sdr-format">
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<title>struct <structname>v4l2_sdr_format</structname></title>
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<tgroup cols="3">
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&cs-str;
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<tbody valign="top">
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<row>
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<entry>__u32</entry>
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<entry><structfield>pixelformat</structfield></entry>
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<entry>
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The data format or type of compression, set by the application. This is a
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little endian <link linkend="v4l2-fourcc">four character code</link>.
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V4L2 defines SDR formats in <xref linkend="sdr-formats" />.
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</entry>
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</row>
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<row>
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<entry>__u32</entry>
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<entry><structfield>buffersize</structfield></entry>
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<entry>
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Maximum size in bytes required for data. Value is set by the driver.
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</entry>
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</row>
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<row>
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<entry>__u8</entry>
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<entry><structfield>reserved[24]</structfield></entry>
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<entry>This array is reserved for future extensions.
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Drivers and applications must set it to zero.</entry>
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</row>
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</tbody>
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</tgroup>
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</table>
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<para>
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An SDR device may support <link linkend="rw">read/write</link>
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and/or streaming (<link linkend="mmap">memory mapping</link>
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or <link linkend="userp">user pointer</link>) I/O.
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</para>
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</section>
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