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diff --git a/v4l2-spec/dev-sliced-vbi.sgml b/v4l2-spec/dev-sliced-vbi.sgml new file mode 100644 index 000000000..5560650a6 --- /dev/null +++ b/v4l2-spec/dev-sliced-vbi.sgml @@ -0,0 +1,395 @@ + <title>Sliced VBI Data Interface</title> + + <para>VBI stands for Vertical Blanking Interval, a gap in the +sequence of lines of an analog video signal. During VBI no picture +information is transmitted, allowing some time while the electron beam +of a cathode ray tube TV returns to the top of the screen.</para> + + <para>Sliced VBI devices use hardware to demodulate data transmitted +in the VBI. V4L2 drivers shall <emphasis>not</emphasis> do this by +software, see also the <link linkend="raw-vbi">raw VBI +interface</link>. The data is passed as short packets of fixed size, +covering one scan line each. The number of packets per video frame is +variable.</para> + + <para>Sliced VBI capture and output devices are accessed through the +same character special files as raw VBI devices. When a driver +supports both interfaces, the default function of a +<filename>/dev/vbi</filename> device is <emphasis>raw</emphasis> VBI +capturing or output, and the sliced VBI function is only available +after calling the &VIDIOC-S-FMT; ioctl as defined below. Likewise a +<filename>/dev/video</filename> device may support the sliced VBI API, +however the default function here is video capturing or output. +Different file descriptors must be used to pass raw and sliced VBI +data simultaneously, if this is supported by the driver.</para> + + <section> + <title>Querying Capabilities</title> + + <para>Devices supporting the sliced VBI capturing or output API +set the <constant>V4L2_CAP_SLICED_VBI_CAPTURE</constant> or +<constant>V4L2_CAP_SLICED_VBI_OUTPUT</constant> flag respectively, in +the <structfield>capabilities</structfield> field of &v4l2-capability; +returned by the &VIDIOC-QUERYCAP; ioctl. At least one of the +read/write, streaming or asynchronous <link linkend="io">I/O +methods</link> must be supported. Sliced VBI devices may have a tuner +or modulator.</para> + </section> + + <section> + <title>Supplemental Functions</title> + + <para>Sliced VBI devices shall support <link linkend="video">video +input or output</link> and <link linkend="tuner">tuner or +modulator</link> ioctls if they have these capabilities, and they may +support <link linkend="control">control</link> ioctls. The <link +linkend="standard">video standard</link> ioctls provide information +vital to program a sliced VBI device, therefore must be +supported.</para> + </section> + + <section> + <title>Sliced VBI Format Negotiation</title> + + <para>To find out which data services are supported by the +hardware applications can call the &VIDIOC-G-SLICED-VBI-CAP; ioctl. +All drivers implementing the sliced VBI interface must support this +ioctl. The results may differ from those of the &VIDIOC-S-FMT; ioctl +when the number of VBI lines the hardware can capture or output per +frame, or the number of services it can identify on a given line are +limited. For example on PAL line 16 the hardware may be able to look +for a VPS or Teletext signal, but not both at the same time.</para> + + <para>To determine the currently selected services applications +set the <structfield>type </structfield> field of &v4l2-format; to +<constant> V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</constant> or <constant> +V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</constant>, and the &VIDIOC-G-FMT; +ioctl fills the <structfield>fmt.sliced</structfield> member, a +&v4l2-sliced-vbi-format;.</para> + + <para>Applications can request different parameters by +initializing or modifying the <structfield>fmt.sliced</structfield> +member and calling the &VIDIOC-S-FMT; ioctl with a pointer to the +<structname>v4l2_format</structname> structure.</para> + + <para>The sliced VBI API is more complicated than the raw VBI API +because the hardware must be told which VBI service to expect on each +scan line. Not all services may be supported by the hardware on all +lines (this is especially true for VBI output where Teletext is often +unsupported and other services can only be inserted in one specific +line). In many cases, however, it is sufficient to just set the +<structfield>service_set</structfield> field to the required services +and let the driver fill the <structfield>service_lines</structfield> +array according to hardware capabilities. Only if more precise control +is needed should the programmer set the +<structfield>service_lines</structfield> array explicitly.</para> + + <para>The &VIDIOC-S-FMT; ioctl modifies the parameters +according to hardware capabilities. When the driver allocates +resources at this point, it may return an &EBUSY; if the required +resources are temporarily unavailable. Other resource allocation +points which may return <errorcode>EBUSY</errorcode> can be the +&VIDIOC-STREAMON; ioctl and the first &func-read;, &func-write; and +&func-select; call.</para> + + <table frame="none" pgwide="1" id="v4l2-sliced-vbi-format"> + <title>struct +<structname>v4l2_sliced_vbi_format</structname></title> + <tgroup cols="5"> + <colspec colname="c1" colwidth="3*"> + <colspec colname="c2" colwidth="3*"> + <colspec colname="c3" colwidth="2*"> + <colspec colname="c4" colwidth="2*"> + <colspec colname="c5" colwidth="2*"> + <spanspec namest="c3" nameend="c5" spanname="hspan"> + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>service_set</structfield></entry> + <entry spanname="hspan"><para>If +<structfield>service_set</structfield> is non-zero when passed with +&VIDIOC-S-FMT; or &VIDIOC-TRY-FMT;, the +<structfield>service_lines</structfield> array will be filled by the +driver according to the services specified in this field. For example, +if <structfield>service_set</structfield> is initialized with +<constant>V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625</constant>, a +driver for the cx25840 video decoder sets lines 7-22 of both +fields<footnote><para>According to <link +linkend="ets300706">ETS 300 706</link> lines 6-22 of the +first field and lines 5-22 of the second field may carry Teletext +data.</para></footnote> to <constant>V4L2_SLICED_TELETEXT_B</constant> +and line 23 of the first field to +<constant>V4L2_SLICED_WSS_625</constant>. If +<structfield>service_set</structfield> is set to zero, then the values +of <structfield>service_lines</structfield> will be used instead. +</para><para>On return the driver sets this field to the union of all +elements of the returned <structfield>service_lines</structfield> +array. It may contain less services than requested, perhaps just one, +if the hardware cannot handle more services simultaneously. It may be +empty (zero) if none of the requested services are supported by the +hardware.</para></entry> + </row> + <row> + <entry>__u16</entry> + <entry><structfield>service_lines</structfield>[2][24]</entry> + <entry spanname="hspan"><para>Applications initialize this +array with sets of data services the driver shall look for or insert +on the respective scan line. Subject to hardware capabilities drivers +return the requested set, a subset, which may be just a single +service, or an empty set. When the hardware cannot handle multiple +services on the same line the driver shall choose one. No assumptions +can be made on which service the driver chooses.</para><para>Data +services are defined in <xref linkend="vbi-services2">. Array indices +map to ITU-R line numbers (see also <xref linkend="vbi-525"> and <xref + linkend="vbi-625">) as follows: <!-- No nested +tables, sigh. --></para></entry> + </row> + <row> + <entry></entry> + <entry></entry> + <entry>Element</entry> + <entry>525 line systems</entry> + <entry>625 line systems</entry> + </row> + <row> + <entry></entry> + <entry></entry> + <entry><structfield>service_lines</structfield>[0][1]</entry> + <entry align="center">1</entry> + <entry align="center">1</entry> + </row> + <row> + <entry></entry> + <entry></entry> + <entry><structfield>service_lines</structfield>[0][23]</entry> + <entry align="center">23</entry> + <entry align="center">23</entry> + </row> + <row> + <entry></entry> + <entry></entry> + <entry><structfield>service_lines</structfield>[1][1]</entry> + <entry align="center">264</entry> + <entry align="center">314</entry> + </row> + <row> + <entry></entry> + <entry></entry> + <entry><structfield>service_lines</structfield>[1][23]</entry> + <entry align="center">286</entry> + <entry align="center">336</entry> + </row> + <!-- End of line numbers table. --> + <row> + <entry></entry> + <entry></entry> + <entry spanname="hspan">Drivers must set +<structfield>service_lines</structfield>[0][0] and +<structfield>service_lines</structfield>[1][0] to zero.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>io_size</structfield></entry> + <entry spanname="hspan">Maximum number of bytes passed by +one &func-read; or &func-write; call, and the buffer size in bytes for +the &VIDIOC-QBUF; and &VIDIOC-DQBUF; ioctl. Drivers set this field to +the size of &v4l2-sliced-vbi-data; times the number of non-zero +elements in the returned <structfield>service_lines</structfield> +array (that is the number of lines potentially carrying data).</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield>[2]</entry> + <entry spanname="hspan">This array is reserved for future +extensions. Applications and drivers must set it to zero.</entry> + </row> + </tbody> + </tgroup> + </table> + + <!-- See also vidioc-g-sliced-vbi-cap.sgml --> + <table frame="none" pgwide="1" id="vbi-services2"> + <title>Sliced VBI services</title> + <tgroup cols="5"> + <colspec colname="c1" colwidth="2*"> + <colspec colname="c2" colwidth="1*"> + <colspec colname="c3" colwidth="1*"> + <colspec colname="c4" colwidth="2*"> + <colspec colname="c5" colwidth="2*"> + <spanspec namest="c3" nameend="c5" spanname="rlp"> + <thead> + <row> + <entry>Symbol</entry> + <entry>Value</entry> + <entry>Reference</entry> + <entry>Lines, usually</entry> + <entry>Payload</entry> + </row> + </thead> + <tbody valign="top"> + <row> + <entry><constant>V4L2_SLICED_TELETEXT_B</constant> +(Teletext System B)</entry> + <entry>0x0001</entry> + <entry><xref linkend="ets300706">, <xref linkend="itu653"></entry> + <entry>PAL/SECAM line 7-22, 320-335 (second field 7-22)</entry> + <entry>Last 42 of the 45 byte Teletext packet, that is +without clock run-in and framing code, lsb first transmitted.</entry> + </row> + <row> + <entry><constant>V4L2_SLICED_VPS</constant></entry> + <entry>0x0400</entry> + <entry><xref linkend="ets300231"></entry> + <entry>PAL line 16</entry> + <entry>Byte number 3 to 15 according to Figure 9 of +ETS 300 231, lsb first transmitted.</entry> + </row> + <row> + <entry><constant>V4L2_SLICED_CAPTION_525</constant></entry> + <entry>0x1000</entry> + <entry><xref linkend="eia608"></entry> + <entry>NTSC line 21, 284 (second field 21)</entry> + <entry>Two bytes in transmission order, including parity +bit, lsb first transmitted.</entry> + </row> + <row> + <entry><constant>V4L2_SLICED_WSS_625</constant></entry> + <entry>0x4000</entry> + <entry><xref linkend="itu1119">, <xref linkend="en300294"></entry> + <entry>PAL/SECAM line 23</entry> + <entry><screen> +Byte 0 1 + msb lsb msb lsb + Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9 +</screen></entry> + </row> + <row> + <entry><constant>V4L2_SLICED_VBI_525</constant></entry> + <entry>0x1000</entry> + <entry spanname="rlp">Set of services applicable to 525 +line systems.</entry> + </row> + <row> + <entry><constant>V4L2_SLICED_VBI_625</constant></entry> + <entry>0x4401</entry> + <entry spanname="rlp">Set of services applicable to 625 +line systems.</entry> + </row> + </tbody> + </tgroup> + </table> + + <para>Drivers may return an &EINVAL; when applications attempt to +read or write data without prior format negotiation, after switching +the video standard (which may invalidate the negotiated VBI +parameters) and after switching the video input (which may change the +video standard as a side effect). The &VIDIOC-S-FMT; ioctl may return +an &EBUSY; when applications attempt to change the format while i/o is +in progress (between a &VIDIOC-STREAMON; and &VIDIOC-STREAMOFF; call, +and after the first &func-read; or &func-write; call).</para> + </section> + + <section> + <title>Reading and writing sliced VBI data</title> + + <para>A single &func-read; or &func-write; call must pass all data +belonging to one video frame. That is an array of +<structname>v4l2_sliced_vbi_data</structname> structures with one or +more elements and a total size not exceeding +<structfield>io_size</structfield> bytes. Likewise in streaming I/O +mode one buffer of <structfield>io_size</structfield> bytes must +contain data of one video frame. The <structfield>id</structfield> of +unused <structname>v4l2_sliced_vbi_data</structname> elements must be +zero.</para> + + <table frame="none" pgwide="1" id="v4l2-sliced-vbi-data"> + <title>struct +<structname>v4l2_sliced_vbi_data</structname></title> + <tgroup cols="3"> + &cs-def; + <tbody valign="top"> + <row> + <entry>__u32</entry> + <entry><structfield>id</structfield></entry> + <entry>A flag from <xref linkend="vbi-services"> +identifying the type of data in this packet. Only a single bit must be +set. When the <structfield>id</structfield> of a captured packet is +zero, the packet is empty and the contents of other fields are +undefined. Applications shall ignore empty packets. When the +<structfield>id</structfield> of a packet for output is zero the +contents of the <structfield>data</structfield> field are undefined +and the driver must no longer insert data on the requested +<structfield>field</structfield> and +<structfield>line</structfield>.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>field</structfield></entry> + <entry>The video field number this data has been captured +from, or shall be inserted at. <constant>0</constant> for the first +field, <constant>1</constant> for the second field.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>line</structfield></entry> + <entry>The field (as opposed to frame) line number this +data has been captured from, or shall be inserted at. See <xref + linkend="vbi-525"> and <xref linkend="vbi-625"> for valid +values. Sliced VBI capture devices can set the line number of all +packets to <constant>0</constant> if the hardware cannot reliably +identify scan lines. The field number must always be valid.</entry> + </row> + <row> + <entry>__u32</entry> + <entry><structfield>reserved</structfield></entry> + <entry>This field is reserved for future extensions. +Applications and drivers must set it to zero.</entry> + </row> + <row> + <entry>__u8</entry> + <entry><structfield>data</structfield>[48]</entry> + <entry>The packet payload. See <xref + linkend="vbi-services"> for the contents and number of +bytes passed for each data type. The contents of padding bytes at the +end of this array are undefined, drivers and applications shall ignore +them.</entry> + </row> + </tbody> + </tgroup> + </table> + + <para>Packets are always passed in ascending line number order, +without duplicate line numbers. The &func-write; function and the +&VIDIOC-QBUF; ioctl must return an &EINVAL; when applications violate +this rule. They must also return an &EINVAL; when applications pass an +incorrect field or line number, or a combination of +<structfield>field</structfield>, <structfield>line</structfield> and +<structfield>id</structfield> which has not been negotiated with the +&VIDIOC-G-FMT; or &VIDIOC-S-FMT; ioctl. When the line numbers are +unknown the driver must pass the packets in transmitted order. The +driver can insert empty packets with <structfield>id</structfield> set +to zero anywhere in the packet array.</para> + + <para>To assure synchronization and to distinguish from frame +dropping, when a captured frame does not carry any of the requested +data services drivers must pass one or more empty packets. When an +application fails to pass VBI data in time for output, the driver +must output the last VPS and WSS packet again, and disable the output +of Closed Caption and Teletext data, or output data which is ignored +by Closed Caption and Teletext decoders.</para> + + <para>A sliced VBI device may support <link +linkend="rw">read/write</link> and/or streaming (<link +linkend="mmap">memory mapping</link> and/or <link linkend="userp">user +pointer</link>) I/O. The latter bears the possibility of synchronizing +video and VBI data by using buffer timestamps.</para> + + </section> + +<!-- +Local Variables: +mode: sgml +sgml-parent-document: "v4l2.sgml" +indent-tabs-mode: nil +End: + --> |