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40>Video for Linux Two API Specification: Revision 0.24</TH
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70WIDTH="100%"></DIV
71><DIV
72CLASS="SECTION"
73><H1
74CLASS="SECTION"
75><A
76NAME="SLICED"
77>4.8. Sliced VBI Data Interface</A
78></H1
79><P
80>VBI stands for Vertical Blanking Interval, a gap in the
81sequence of lines of an analog video signal. During VBI no picture
82information is transmitted, allowing some time while the electron beam
83of a cathode ray tube TV returns to the top of the screen.</P
84><P
85>Sliced VBI devices use hardware to demodulate data transmitted
86in the VBI. V4L2 drivers shall <SPAN
87CLASS="emphasis"
88><I
89CLASS="EMPHASIS"
90>not</I
91></SPAN
92> do this by
93software, see also the <A
94HREF="x7013.htm"
95>raw VBI
96interface</A
97>. The data is passed as short packets of fixed size,
98covering one scan line each. The number of packets per video frame is
99variable.</P
100><P
101>Sliced VBI capture and output devices are accessed through the
102same character special files as raw VBI devices. When a driver
103supports both interfaces, the default function of a
104<TT
105CLASS="FILENAME"
106>/dev/vbi</TT
107> device is <SPAN
108CLASS="emphasis"
109><I
110CLASS="EMPHASIS"
111>raw</I
112></SPAN
113> VBI
114capturing or output, and the sliced VBI function is only available
115after calling the <A
116HREF="r10944.htm"
117><CODE
118CLASS="CONSTANT"
119>VIDIOC_S_FMT</CODE
120></A
121> ioctl as defined below. Likewise a
122<TT
123CLASS="FILENAME"
124>/dev/video</TT
125> device may support the sliced VBI API,
126however the default function here is video capturing or output.
127Different file descriptors must be used to pass raw and sliced VBI
128data simultaneously, if this is supported by the driver.</P
129><DIV
130CLASS="SECTION"
131><H2
132CLASS="SECTION"
133><A
134NAME="AEN7248"
135>4.8.1. Querying Capabilities</A
136></H2
137><P
138>Devices supporting the sliced VBI capturing or output API
139set the <CODE
140CLASS="CONSTANT"
141>V4L2_CAP_SLICED_VBI_CAPTURE</CODE
142> or
143<CODE
144CLASS="CONSTANT"
145>V4L2_CAP_SLICED_VBI_OUTPUT</CODE
146> flag respectively, in
147the <CODE
148CLASS="STRUCTFIELD"
149>capabilities</CODE
150> field of struct&nbsp;<A
151HREF="r13105.htm#V4L2-CAPABILITY"
152>v4l2_capability</A
153>
154returned by the <A
155HREF="r13105.htm"
156><CODE
157CLASS="CONSTANT"
158>VIDIOC_QUERYCAP</CODE
159></A
160> ioctl. At least one of the
161read/write, streaming or asynchronous <A
162HREF="c5742.htm"
163>I/O
164methods</A
165> must be supported. Sliced VBI devices may have a tuner
166or modulator.</P
167></DIV
168><DIV
169CLASS="SECTION"
170><H2
171CLASS="SECTION"
172><A
173NAME="AEN7258"
174>4.8.2. Supplemental Functions</A
175></H2
176><P
177>Sliced VBI devices shall support <A
178HREF="x309.htm"
179>video
180input or output</A
181> and <A
182HREF="x394.htm"
183>tuner or
184modulator</A
185> ioctls if they have these capabilities, and they may
186support <A
187HREF="x542.htm"
188>control</A
189> ioctls. The <A
190HREF="x448.htm"
191>video standard</A
192> ioctls provide information
193vital to program a sliced VBI device, therefore must be
194supported.</P
195></DIV
196><DIV
197CLASS="SECTION"
198><H2
199CLASS="SECTION"
200><A
201NAME="AEN7265"
202>4.8.3. Sliced VBI Format Negotiation</A
203></H2
204><P
205>To find out which data services are supported by the
206hardware applications can call the <A
207HREF="r12051.htm"
208><CODE
209CLASS="CONSTANT"
210>VIDIOC_G_SLICED_VBI_CAP</CODE
211></A
212> ioctl.
213All drivers implementing the sliced VBI interface must support this
214ioctl. The results may differ from those of the <A
215HREF="r10944.htm"
216><CODE
217CLASS="CONSTANT"
218>VIDIOC_S_FMT</CODE
219></A
220> ioctl
221when the number of VBI lines the hardware can capture or output per
222frame, or the number of services it can identify on a given line are
223limited. For example on PAL line 16 the hardware may be able to look
224for a VPS or Teletext signal, but not both at the same time.</P
225><P
226>To determine the currently selected services applications
227set the <CODE
228CLASS="STRUCTFIELD"
229>type </CODE
230> field of struct&nbsp;<A
231HREF="r10944.htm#V4L2-FORMAT"
232>v4l2_format</A
233> to
234<CODE
235CLASS="CONSTANT"
236> V4L2_BUF_TYPE_SLICED_VBI_CAPTURE</CODE
237> or <CODE
238CLASS="CONSTANT"
239>V4L2_BUF_TYPE_SLICED_VBI_OUTPUT</CODE
240>, and the <A
241HREF="r10944.htm"
242><CODE
243CLASS="CONSTANT"
244>VIDIOC_G_FMT</CODE
245></A
246>
247ioctl fills the <CODE
248CLASS="STRUCTFIELD"
249>fmt.sliced</CODE
250> member, a
251struct&nbsp;<A
252HREF="x7236.htm#V4L2-SLICED-VBI-FORMAT"
253>v4l2_sliced_vbi_format</A
254>.</P
255><P
256>Applications can request different parameters by
257initializing or modifying the <CODE
258CLASS="STRUCTFIELD"
259>fmt.sliced</CODE
260>
261member and calling the <A
262HREF="r10944.htm"
263><CODE
264CLASS="CONSTANT"
265>VIDIOC_S_FMT</CODE
266></A
267> ioctl with a pointer to the
268<CODE
269CLASS="STRUCTNAME"
270>v4l2_format</CODE
271> structure.</P
272><P
273>The sliced VBI API is more complicated than the raw VBI API
274because the hardware must be told which VBI service to expect on each
275scan line. Not all services may be supported by the hardware on all
276lines (this is especially true for VBI output where Teletext is often
277unsupported and other services can only be inserted in one specific
278line). In many cases, however, it is sufficient to just set the
279<CODE
280CLASS="STRUCTFIELD"
281>service_set</CODE
282> field to the required services
283and let the driver fill the <CODE
284CLASS="STRUCTFIELD"
285>service_lines</CODE
286>
287array according to hardware capabilities. Only if more precise control
288is needed should the programmer set the
289<CODE
290CLASS="STRUCTFIELD"
291>service_lines</CODE
292> array explicitly.</P
293><P
294>The <A
295HREF="r10944.htm"
296><CODE
297CLASS="CONSTANT"
298>VIDIOC_S_FMT</CODE
299></A
300> ioctl returns an <SPAN
301CLASS="ERRORCODE"
302>EINVAL</SPAN
303> error code only when the
304given parameters are ambiguous, otherwise it modifies the parameters
305according to hardware capabilities. When the driver allocates
306resources at this point, it may return an <SPAN
307CLASS="ERRORCODE"
308>EBUSY</SPAN
309> error code if the required
310resources are temporarily unavailable. Other resource allocation
311points which may return <SPAN
312CLASS="ERRORCODE"
313>EBUSY</SPAN
314> can be the
315<A
316HREF="r13817.htm"
317><CODE
318CLASS="CONSTANT"
319>VIDIOC_STREAMON</CODE
320></A
321> ioctl and the first <A
322HREF="r14264.htm"
323><CODE
324CLASS="FUNCTION"
325>read()</CODE
326></A
327>, <A
328HREF="r14496.htm"
329><CODE
330CLASS="FUNCTION"
331>write()</CODE
332></A
333> and
334<A
335HREF="r14390.htm"
336><CODE
337CLASS="FUNCTION"
338>select()</CODE
339></A
340> call.</P
341><DIV
342CLASS="TABLE"
343><A
344NAME="V4L2-SLICED-VBI-FORMAT"
345></A
346><P
347><B
348>Table 4-6. struct
349<CODE
350CLASS="STRUCTNAME"
351>v4l2_sliced_vbi_format</CODE
352></B
353></P
354><TABLE
355BORDER="0"
356FRAME="void"
357WIDTH="100%"
358CLASS="CALSTABLE"
359><COL
360WIDTH="25%"
361TITLE="C1"><COL
362WIDTH="25%"
363TITLE="C2"><COL
364WIDTH="17%"
365TITLE="C3"><COL
366WIDTH="17%"
367TITLE="C4"><COL
368WIDTH="17%"
369TITLE="C5"><TBODY
370VALIGN="TOP"
371><TR
372><TD
373>__u32</TD
374><TD
375><CODE
376CLASS="STRUCTFIELD"
377>service_set</CODE
378></TD
379><TD
380COLSPAN="3"
381><P
382>If
383<CODE
384CLASS="STRUCTFIELD"
385>service_set</CODE
386> is non-zero when passed with
387<A
388HREF="r10944.htm"
389><CODE
390CLASS="CONSTANT"
391>VIDIOC_S_FMT</CODE
392></A
393> or <A
394HREF="r10944.htm"
395><CODE
396CLASS="CONSTANT"
397>VIDIOC_TRY_FMT</CODE
398></A
399>, the
400<CODE
401CLASS="STRUCTFIELD"
402>service_lines</CODE
403> array will be filled by the
404driver according to the services specified in this field. For example,
405if <CODE
406CLASS="STRUCTFIELD"
407>service_set</CODE
408> is initialized with
409<CODE
410CLASS="CONSTANT"
411>V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625</CODE
412>, a
413driver for the cx25840 video decoder sets lines 7-22 of both
414fields<SUP
415>a</SUP
416> to <CODE
417CLASS="CONSTANT"
418>V4L2_SLICED_TELETEXT_B</CODE
419>
420and line 23 of the first field to
421<CODE
422CLASS="CONSTANT"
423>V4L2_SLICED_WSS_625</CODE
424>. If
425<CODE
426CLASS="STRUCTFIELD"
427>service_set</CODE
428> is set to zero, then the values
429of <CODE
430CLASS="STRUCTFIELD"
431>service_lines</CODE
432> will be used instead.</P
433><P
434>On return the driver sets this field to the union of all
435elements of the returned <CODE
436CLASS="STRUCTFIELD"
437>service_lines</CODE
438>
439array. It may contain less services than requested, perhaps just one,
440if the hardware cannot handle more services simultaneously. It may be
441empty (zero) if none of the requested services are supported by the
442hardware.</P
443></TD
444></TR
445><TR
446><TD
447>__u16</TD
448><TD
449><CODE
450CLASS="STRUCTFIELD"
451>service_lines</CODE
452>[2][24]</TD
453><TD
454COLSPAN="3"
455><P
456>Applications initialize this
457array with sets of data services the driver shall look for or insert
458on the respective scan line. Subject to hardware capabilities drivers
459return the requested set, a subset, which may be just a single
460service, or an empty set. When the hardware cannot handle multiple
461services on the same line the driver shall choose one. No assumptions
462can be made on which service the driver chooses.</P
463><P
464>Data
465services are defined in <A
466HREF="x7236.htm#VBI-SERVICES2"
467>Table 4-7</A
468>. Array indices
469map to ITU-R line numbers (see also <A
470HREF="x7013.htm#VBI-525"
471>Figure 4-2</A
472> and <A
473HREF="x7013.htm#VBI-625"
474>Figure 4-3</A
475>) as follows: </P
476></TD
477></TR
478><TR
479><TD
480>&nbsp;</TD
481><TD
482>&nbsp;</TD
483><TD
484>Element</TD
485><TD
486>525 line systems</TD
487><TD
488>625 line systems</TD
489></TR
490><TR
491><TD
492>&nbsp;</TD
493><TD
494>&nbsp;</TD
495><TD
496><CODE
497CLASS="STRUCTFIELD"
498>service_lines</CODE
499>[0][1]</TD
500><TD
501ALIGN="CENTER"
502>1</TD
503><TD
504ALIGN="CENTER"
505>1</TD
506></TR
507><TR
508><TD
509>&nbsp;</TD
510><TD
511>&nbsp;</TD
512><TD
513><CODE
514CLASS="STRUCTFIELD"
515>service_lines</CODE
516>[0][23]</TD
517><TD
518ALIGN="CENTER"
519>23</TD
520><TD
521ALIGN="CENTER"
522>23</TD
523></TR
524><TR
525><TD
526>&nbsp;</TD
527><TD
528>&nbsp;</TD
529><TD
530><CODE
531CLASS="STRUCTFIELD"
532>service_lines</CODE
533>[1][1]</TD
534><TD
535ALIGN="CENTER"
536>264</TD
537><TD
538ALIGN="CENTER"
539>314</TD
540></TR
541><TR
542><TD
543>&nbsp;</TD
544><TD
545>&nbsp;</TD
546><TD
547><CODE
548CLASS="STRUCTFIELD"
549>service_lines</CODE
550>[1][23]</TD
551><TD
552ALIGN="CENTER"
553>286</TD
554><TD
555ALIGN="CENTER"
556>336</TD
557></TR
558><TR
559><TD
560>&nbsp;</TD
561><TD
562>&nbsp;</TD
563><TD
564COLSPAN="3"
565>Drivers must set
566<CODE
567CLASS="STRUCTFIELD"
568>service_lines</CODE
569>[0][0] and
570<CODE
571CLASS="STRUCTFIELD"
572>service_lines</CODE
573>[1][0] to zero.</TD
574></TR
575><TR
576><TD
577>__u32</TD
578><TD
579><CODE
580CLASS="STRUCTFIELD"
581>io_size</CODE
582></TD
583><TD
584COLSPAN="3"
585>Maximum number of bytes passed by
586one <A
587HREF="r14264.htm"
588><CODE
589CLASS="FUNCTION"
590>read()</CODE
591></A
592> or <A
593HREF="r14496.htm"
594><CODE
595CLASS="FUNCTION"
596>write()</CODE
597></A
598> call, and the buffer size in bytes for
599the <A
600HREF="r12878.htm"
601><CODE
602CLASS="CONSTANT"
603>VIDIOC_QBUF</CODE
604></A
605> and <A
606HREF="r12878.htm"
607><CODE
608CLASS="CONSTANT"
609>VIDIOC_DQBUF</CODE
610></A
611> ioctl. Drivers set this field to
612the size of struct&nbsp;<A
613HREF="x7236.htm#V4L2-SLICED-VBI-DATA"
614>v4l2_sliced_vbi_data</A
615> times the number of non-zero
616elements in the returned <CODE
617CLASS="STRUCTFIELD"
618>service_lines</CODE
619>
620array (that is the number of lines potentially carrying data).</TD
621></TR
622><TR
623><TD
624>__u32</TD
625><TD
626><CODE
627CLASS="STRUCTFIELD"
628>reserved</CODE
629>[2]</TD
630><TD
631COLSPAN="3"
632>This array is reserved for future
633extensions. Applications and drivers must set it to zero.</TD
634></TR
635></TBODY
636><TR
637><TD
638COLSPAN="5"
639>Notes:<BR><A
640NAME="FTN.AEN7329"
641>a. </A
642>According to <A
643HREF="b17127.htm#ETS300706"
644>ETS&nbsp;300&nbsp;706</A
645> lines 6-22 of the
646first field and lines 5-22 of the second field may carry Teletext
647data.<BR></TD
648></TR
649></TABLE
650></DIV
651><DIV
652CLASS="TABLE"
653><A
654NAME="VBI-SERVICES2"
655></A
656><P
657><B
658>Table 4-7. Sliced VBI services</B
659></P
660><TABLE
661BORDER="0"
662FRAME="void"
663WIDTH="100%"
664CLASS="CALSTABLE"
665><COL
666WIDTH="25%"
667TITLE="C1"><COL
668WIDTH="12%"
669TITLE="C2"><COL
670WIDTH="12%"
671TITLE="C3"><COL
672WIDTH="25%"
673TITLE="C4"><COL
674WIDTH="25%"
675TITLE="C5"><THEAD
676><TR
677><TH
678>Symbol</TH
679><TH
680>Value</TH
681><TH
682>Reference</TH
683><TH
684>Lines, usually</TH
685><TH
686>Payload</TH
687></TR
688></THEAD
689><TBODY
690VALIGN="TOP"
691><TR
692><TD
693><CODE
694CLASS="CONSTANT"
695>V4L2_SLICED_TELETEXT_B</CODE
696>
697(Teletext System B)</TD
698><TD
699>0x0001</TD
700><TD
701><A
702HREF="b17127.htm#ETS300706"
703><ABBR
704CLASS="ABBREV"
705>ETS&nbsp;300&nbsp;706</ABBR
706></A
707>, <A
708HREF="b17127.htm#ITU653"
709><ABBR
710CLASS="ABBREV"
711>ITU&nbsp;BT.653</ABBR
712></A
713></TD
714><TD
715>PAL/SECAM line 7-22, 320-335 (second field 7-22)</TD
716><TD
717>Last 42 of the 45 byte Teletext packet, that is
718without clock run-in and framing code, lsb first transmitted.</TD
719></TR
720><TR
721><TD
722><CODE
723CLASS="CONSTANT"
724>V4L2_SLICED_VPS</CODE
725></TD
726><TD
727>0x0400</TD
728><TD
729><A
730HREF="b17127.htm#ETS300231"
731><ABBR
732CLASS="ABBREV"
733>ETS&nbsp;300&nbsp;231</ABBR
734></A
735></TD
736><TD
737>PAL line 16</TD
738><TD
739>Byte number 3 to 15 according to Figure 9 of
740ETS&nbsp;300&nbsp;231, lsb first transmitted.</TD
741></TR
742><TR
743><TD
744><CODE
745CLASS="CONSTANT"
746>V4L2_SLICED_CAPTION_525</CODE
747></TD
748><TD
749>0x1000</TD
750><TD
751><A
752HREF="b17127.htm#EIA608"
753><ABBR
754CLASS="ABBREV"
755>EIA&nbsp;608-B</ABBR
756></A
757></TD
758><TD
759>NTSC line 21, 284 (second field 21)</TD
760><TD
761>Two bytes in transmission order, including parity
762bit, lsb first transmitted.</TD
763></TR
764><TR
765><TD
766><CODE
767CLASS="CONSTANT"
768>V4L2_SLICED_WSS_625</CODE
769></TD
770><TD
771>0x4000</TD
772><TD
773><A
774HREF="b17127.htm#ITU1119"
775><ABBR
776CLASS="ABBREV"
777>ITU&nbsp;BT.1119</ABBR
778></A
779>, <A
780HREF="b17127.htm#EN300294"
781><ABBR
782CLASS="ABBREV"
783>EN&nbsp;300&nbsp;294</ABBR
784></A
785></TD
786><TD
787>PAL/SECAM line 23</TD
788><TD
789><PRE
790CLASS="SCREEN"
791>Byte         0                 1
792      msb         lsb  msb           lsb
793 Bit  7 6 5 4 3 2 1 0  x x 13 12 11 10 9</PRE
794></TD
795></TR
796><TR
797><TD
798><CODE
799CLASS="CONSTANT"
800>V4L2_SLICED_VBI_525</CODE
801></TD
802><TD
803>0x1000</TD
804><TD
805COLSPAN="3"
806>Set of services applicable to 525
807line systems.</TD
808></TR
809><TR
810><TD
811><CODE
812CLASS="CONSTANT"
813>V4L2_SLICED_VBI_625</CODE
814></TD
815><TD
816>0x4401</TD
817><TD
818COLSPAN="3"
819>Set of services applicable to 625
820line systems.</TD
821></TR
822></TBODY
823></TABLE
824></DIV
825><P
826>Drivers may return an <SPAN
827CLASS="ERRORCODE"
828>EINVAL</SPAN
829> error code when applications attempt to
830read or write data without prior format negotiation, after switching
831the video standard (which may invalidate the negotiated VBI
832parameters) and after switching the video input (which may change the
833video standard as a side effect). The <A
834HREF="r10944.htm"
835><CODE
836CLASS="CONSTANT"
837>VIDIOC_S_FMT</CODE
838></A
839> ioctl may return
840an <SPAN
841CLASS="ERRORCODE"
842>EBUSY</SPAN
843> error code when applications attempt to change the format while i/o is
844in progress (between a <A
845HREF="r13817.htm"
846><CODE
847CLASS="CONSTANT"
848>VIDIOC_STREAMON</CODE
849></A
850> and <A
851HREF="r13817.htm"
852><CODE
853CLASS="CONSTANT"
854>VIDIOC_STREAMOFF</CODE
855></A
856> call,
857and after the first <A
858HREF="r14264.htm"
859><CODE
860CLASS="FUNCTION"
861>read()</CODE
862></A
863> or <A
864HREF="r14496.htm"
865><CODE
866CLASS="FUNCTION"
867>write()</CODE
868></A
869> call).</P
870></DIV
871><DIV
872CLASS="SECTION"
873><H2
874CLASS="SECTION"
875><A
876NAME="AEN7483"
877>4.8.4. Reading and writing sliced VBI data</A
878></H2
879><P
880>A single <A
881HREF="r14264.htm"
882><CODE
883CLASS="FUNCTION"
884>read()</CODE
885></A
886> or <A
887HREF="r14496.htm"
888><CODE
889CLASS="FUNCTION"
890>write()</CODE
891></A
892> call must pass all data
893belonging to one video frame. That is an array of
894<CODE
895CLASS="STRUCTNAME"
896>v4l2_sliced_vbi_data</CODE
897> structures with one or
898more elements and a total size not exceeding
899<CODE
900CLASS="STRUCTFIELD"
901>io_size</CODE
902> bytes. Likewise in streaming I/O
903mode one buffer of <CODE
904CLASS="STRUCTFIELD"
905>io_size</CODE
906> bytes must
907contain data of one video frame. The <CODE
908CLASS="STRUCTFIELD"
909>id</CODE
910> of
911unused <CODE
912CLASS="STRUCTNAME"
913>v4l2_sliced_vbi_data</CODE
914> elements must be
915zero.</P
916><DIV
917CLASS="TABLE"
918><A
919NAME="V4L2-SLICED-VBI-DATA"
920></A
921><P
922><B
923>Table 4-8. struct
924<CODE
925CLASS="STRUCTNAME"
926>v4l2_sliced_vbi_data</CODE
927></B
928></P
929><TABLE
930BORDER="0"
931FRAME="void"
932WIDTH="100%"
933CLASS="CALSTABLE"
934><COL
935WIDTH="38%"
936TITLE="C1"><COL
937WIDTH="12%"
938TITLE="C2"><COL
939WIDTH="50%"
940TITLE="C3"><TBODY
941VALIGN="TOP"
942><TR
943><TD
944>__u32</TD
945><TD
946><CODE
947CLASS="STRUCTFIELD"
948>id</CODE
949></TD
950><TD
951>A flag from <A
952HREF="r12051.htm#VBI-SERVICES"
953>Table 2</A
954>
955identifying the type of data in this packet. Only a single bit must be
956set. When the <CODE
957CLASS="STRUCTFIELD"
958>id</CODE
959> of a captured packet is
960zero, the packet is empty and the contents of other fields are
961undefined. Applications shall ignore empty packets. When the
962<CODE
963CLASS="STRUCTFIELD"
964>id</CODE
965> of a packet for output is zero the
966contents of the <CODE
967CLASS="STRUCTFIELD"
968>data</CODE
969> field are undefined
970and the driver must no longer insert data on the requested
971<CODE
972CLASS="STRUCTFIELD"
973>field</CODE
974> and
975<CODE
976CLASS="STRUCTFIELD"
977>line</CODE
978>.</TD
979></TR
980><TR
981><TD
982>__u32</TD
983><TD
984><CODE
985CLASS="STRUCTFIELD"
986>field</CODE
987></TD
988><TD
989>The video field number this data has been captured
990from, or shall be inserted at. <CODE
991CLASS="CONSTANT"
992>0</CODE
993> for the first
994field, <CODE
995CLASS="CONSTANT"
996>1</CODE
997> for the second field.</TD
998></TR
999><TR
1000><TD
1001>__u32</TD
1002><TD
1003><CODE
1004CLASS="STRUCTFIELD"
1005>line</CODE
1006></TD
1007><TD
1008>The field (as opposed to frame) line number this
1009data has been captured from, or shall be inserted at. See <A
1010HREF="x7013.htm#VBI-525"
1011>Figure 4-2</A
1012> and <A
1013HREF="x7013.htm#VBI-625"
1014>Figure 4-3</A
1015> for valid
1016values. Sliced VBI capture devices can set the line number of all
1017packets to <CODE
1018CLASS="CONSTANT"
1019>0</CODE
1020> if the hardware cannot reliably
1021identify scan lines. The field number must always be valid.</TD
1022></TR
1023><TR
1024><TD
1025>__u32</TD
1026><TD
1027><CODE
1028CLASS="STRUCTFIELD"
1029>reserved</CODE
1030></TD
1031><TD
1032>This field is reserved for future extensions.
1033Applications and drivers must set it to zero.</TD
1034></TR
1035><TR
1036><TD
1037>__u8</TD
1038><TD
1039><CODE
1040CLASS="STRUCTFIELD"
1041>data</CODE
1042>[48]</TD
1043><TD
1044>The packet payload. See <A
1045HREF="r12051.htm#VBI-SERVICES"
1046>Table 2</A
1047> for the contents and number of
1048bytes passed for each data type. The contents of padding bytes at the
1049end of this array are undefined, drivers and applications shall ignore
1050them.</TD
1051></TR
1052></TBODY
1053></TABLE
1054></DIV
1055><P
1056>Packets are always passed in ascending line number order,
1057without duplicate line numbers. The <A
1058HREF="r14496.htm"
1059><CODE
1060CLASS="FUNCTION"
1061>write()</CODE
1062></A
1063> function and the
1064<A
1065HREF="r12878.htm"
1066><CODE
1067CLASS="CONSTANT"
1068>VIDIOC_QBUF</CODE
1069></A
1070> ioctl must return an <SPAN
1071CLASS="ERRORCODE"
1072>EINVAL</SPAN
1073> error code when applications violate
1074this rule. They must also return an <SPAN
1075CLASS="ERRORCODE"
1076>EINVAL</SPAN
1077> error code when applications pass an
1078incorrect field or line number, or a combination of
1079<CODE
1080CLASS="STRUCTFIELD"
1081>field</CODE
1082>, <CODE
1083CLASS="STRUCTFIELD"
1084>line</CODE
1085> and
1086<CODE
1087CLASS="STRUCTFIELD"
1088>id</CODE
1089> which has not been negotiated with the
1090<A
1091HREF="r10944.htm"
1092><CODE
1093CLASS="CONSTANT"
1094>VIDIOC_G_FMT</CODE
1095></A
1096> or <A
1097HREF="r10944.htm"
1098><CODE
1099CLASS="CONSTANT"
1100>VIDIOC_S_FMT</CODE
1101></A
1102> ioctl. When the line numbers are
1103unknown the driver must pass the packets in transmitted order. The
1104driver can insert empty packets with <CODE
1105CLASS="STRUCTFIELD"
1106>id</CODE
1107> set
1108to zero anywhere in the packet array.</P
1109><P
1110>To assure synchronization and to distinguish from frame
1111dropping, when a captured frame does not carry any of the requested
1112data services drivers must pass one or more empty packets. When an
1113application fails to pass VBI data in time for output, the driver
1114must output the last VPS and WSS packet again, and disable the output
1115of Closed Caption and Teletext data, or output data which is ignored
1116by Closed Caption and Teletext decoders.</P
1117><P
1118>A sliced VBI device may support <A
1119HREF="c5742.htm#RW"
1120>read/write</A
1121> and/or streaming (<A
1122HREF="x5791.htm"
1123>memory mapping</A
1124> and/or <A
1125HREF="x5884.htm"
1126>user
1127pointer</A
1128>) I/O. The latter bears the possibility of synchronizing
1129video and VBI data by using buffer timestamps.</P
1130></DIV
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1148HREF="x7013.htm"
1149ACCESSKEY="P"
1150>Prev</A
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1175VALIGN="top"
1176>Raw VBI Data Interface</TD
1177><TD
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1180VALIGN="top"
1181><A
1182HREF="c6488.htm"
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1184>Up</A
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1190>Teletext Interface</TD
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1196>
1197