Document V4L2 SDR interface. Cc: Hans Verkuil <hverkuil@xs4all.nl> Signed-off-by: Antti Palosaari <crope@iki.fi> Acked-by: Hans Verkuil <hans.verkuil@cisco.com> Signed-off-by: Mauro Carvalho Chehab <m.chehab@samsung.com>tirimbino
Antti Palosaari
11 years ago
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Mauro Carvalho Chehab
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<title>Software Defined Radio Interface (SDR)</title> |
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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-format-sdr; |
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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 only the <structfield>pixelformat</structfield> field of |
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&v4l2-format-sdr; is used. The content of that field is the V4L2 fourcc code |
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of the data format. |
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</para> |
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<table pgwide="1" frame="none" id="v4l2-format-sdr"> |
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<title>struct <structname>v4l2_format_sdr</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>__u8</entry> |
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<entry><structfield>reserved[28]</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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