From 8d4f9d241cdbd71a882a852c6e9285de279c0f87 Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Sun, 18 Jan 2009 13:00:12 +0100 Subject: v4l2spec: add version 0.24 of the spec From: Hans Verkuil Priority: normal Signed-off-by: Hans Verkuil --- v4l2-spec/dev-sliced-vbi.sgml | 396 ++++++++++++++++++++++++++++++++++++++++++ 1 file changed, 396 insertions(+) create mode 100644 v4l2-spec/dev-sliced-vbi.sgml (limited to 'v4l2-spec/dev-sliced-vbi.sgml') diff --git a/v4l2-spec/dev-sliced-vbi.sgml b/v4l2-spec/dev-sliced-vbi.sgml new file mode 100644 index 000000000..42f6f6938 --- /dev/null +++ b/v4l2-spec/dev-sliced-vbi.sgml @@ -0,0 +1,396 @@ + Sliced VBI Data Interface + + 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. + + Sliced VBI devices use hardware to demodulate data transmitted +in the VBI. V4L2 drivers shall not do this by +software, see also the raw VBI +interface. The data is passed as short packets of fixed size, +covering one scan line each. The number of packets per video frame is +variable. + + 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 +/dev/vbi device is raw VBI +capturing or output, and the sliced VBI function is only available +after calling the &VIDIOC-S-FMT; ioctl as defined below. Likewise a +/dev/video 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. + +
+ Querying Capabilities + + Devices supporting the sliced VBI capturing or output API +set the V4L2_CAP_SLICED_VBI_CAPTURE or +V4L2_CAP_SLICED_VBI_OUTPUT flag respectively, in +the capabilities field of &v4l2-capability; +returned by the &VIDIOC-QUERYCAP; ioctl. At least one of the +read/write, streaming or asynchronous I/O +methods must be supported. Sliced VBI devices may have a tuner +or modulator. +
+ +
+ Supplemental Functions + + Sliced VBI devices shall support video +input or output and tuner or +modulator ioctls if they have these capabilities, and they may +support control ioctls. The video standard ioctls provide information +vital to program a sliced VBI device, therefore must be +supported. +
+ +
+ Sliced VBI Format Negotiation + + 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. + + To determine the currently selected services applications +set the type field of &v4l2-format; to + V4L2_BUF_TYPE_SLICED_VBI_CAPTURE or +V4L2_BUF_TYPE_SLICED_VBI_OUTPUT, and the &VIDIOC-G-FMT; +ioctl fills the fmt.sliced member, a +&v4l2-sliced-vbi-format;. + + Applications can request different parameters by +initializing or modifying the fmt.sliced +member and calling the &VIDIOC-S-FMT; ioctl with a pointer to the +v4l2_format structure. + + 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 +service_set field to the required services +and let the driver fill the service_lines +array according to hardware capabilities. Only if more precise control +is needed should the programmer set the +service_lines array explicitly. + + The &VIDIOC-S-FMT; ioctl returns an &EINVAL; only when the +given parameters are ambiguous, otherwise it 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 EBUSY can be the +&VIDIOC-STREAMON; ioctl and the first &func-read;, &func-write; and +&func-select; call. + + + struct +<structname>v4l2_sliced_vbi_format</structname> + + + + + + + + + + __u32 + service_set + If +service_set is non-zero when passed with +&VIDIOC-S-FMT; or &VIDIOC-TRY-FMT;, the +service_lines array will be filled by the +driver according to the services specified in this field. For example, +if service_set is initialized with +V4L2_SLICED_TELETEXT_B | V4L2_SLICED_WSS_625, a +driver for the cx25840 video decoder sets lines 7-22 of both +fieldsAccording to ETS 300 706 lines 6-22 of the +first field and lines 5-22 of the second field may carry Teletext +data. to V4L2_SLICED_TELETEXT_B +and line 23 of the first field to +V4L2_SLICED_WSS_625. If +service_set is set to zero, then the values +of service_lines will be used instead. +On return the driver sets this field to the union of all +elements of the returned service_lines +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. + + + __u16 + service_lines[2][24] + 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.Data +services are defined in . Array indices +map to ITU-R line numbers (see also and ) as follows: + + + + + Element + 525 line systems + 625 line systems + + + + + service_lines[0][1] + 1 + 1 + + + + + service_lines[0][23] + 23 + 23 + + + + + service_lines[1][1] + 264 + 314 + + + + + service_lines[1][23] + 286 + 336 + + + + + + Drivers must set +service_lines[0][0] and +service_lines[1][0] to zero. + + + __u32 + io_size + 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 service_lines +array (that is the number of lines potentially carrying data). + + + __u32 + reserved[2] + This array is reserved for future +extensions. Applications and drivers must set it to zero. + + + +
+ + + + Sliced VBI services + + + + + + + + + + Symbol + Value + Reference + Lines, usually + Payload + + + + + V4L2_SLICED_TELETEXT_B +(Teletext System B) + 0x0001 + , + PAL/SECAM line 7-22, 320-335 (second field 7-22) + Last 42 of the 45 byte Teletext packet, that is +without clock run-in and framing code, lsb first transmitted. + + + V4L2_SLICED_VPS + 0x0400 + + PAL line 16 + Byte number 3 to 15 according to Figure 9 of +ETS 300 231, lsb first transmitted. + + + V4L2_SLICED_CAPTION_525 + 0x1000 + + NTSC line 21, 284 (second field 21) + Two bytes in transmission order, including parity +bit, lsb first transmitted. + + + V4L2_SLICED_WSS_625 + 0x4000 + , + PAL/SECAM line 23 + +Byte 0 1 + msb lsb msb lsb + Bit 7 6 5 4 3 2 1 0 x x 13 12 11 10 9 + + + + V4L2_SLICED_VBI_525 + 0x1000 + Set of services applicable to 525 +line systems. + + + V4L2_SLICED_VBI_625 + 0x4401 + Set of services applicable to 625 +line systems. + + + +
+ + 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). +
+ +
+ Reading and writing sliced VBI data + + A single &func-read; or &func-write; call must pass all data +belonging to one video frame. That is an array of +v4l2_sliced_vbi_data structures with one or +more elements and a total size not exceeding +io_size bytes. Likewise in streaming I/O +mode one buffer of io_size bytes must +contain data of one video frame. The id of +unused v4l2_sliced_vbi_data elements must be +zero. + + + struct +<structname>v4l2_sliced_vbi_data</structname> + + &cs-def; + + + __u32 + id + A flag from +identifying the type of data in this packet. Only a single bit must be +set. When the id 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 +id of a packet for output is zero the +contents of the data field are undefined +and the driver must no longer insert data on the requested +field and +line. + + + __u32 + field + The video field number this data has been captured +from, or shall be inserted at. 0 for the first +field, 1 for the second field. + + + __u32 + line + The field (as opposed to frame) line number this +data has been captured from, or shall be inserted at. See and for valid +values. Sliced VBI capture devices can set the line number of all +packets to 0 if the hardware cannot reliably +identify scan lines. The field number must always be valid. + + + __u32 + reserved + This field is reserved for future extensions. +Applications and drivers must set it to zero. + + + __u8 + data[48] + The packet payload. See 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. + + + +
+ + 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 +field, line and +id 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 id set +to zero anywhere in the packet array. + + 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. + + A sliced VBI device may support read/write and/or streaming (memory mapping and/or user +pointer) I/O. The latter bears the possibility of synchronizing +video and VBI data by using buffer timestamps. + +
+ + -- cgit v1.2.3 From 25c9b30402a26393ce698bd1addc01b7973928e2 Mon Sep 17 00:00:00 2001 From: Hans Verkuil Date: Thu, 5 Feb 2009 08:34:00 +0100 Subject: v4l2-spec: remove ambiguous and incorrect text regarding sliced vbi. From: Hans Verkuil Thanks to Andy Walls for bringing this to my attention. Priority: normal Signed-off-by: Hans Verkuil --- v4l2-spec/dev-sliced-vbi.sgml | 3 +-- 1 file changed, 1 insertion(+), 2 deletions(-) (limited to 'v4l2-spec/dev-sliced-vbi.sgml') diff --git a/v4l2-spec/dev-sliced-vbi.sgml b/v4l2-spec/dev-sliced-vbi.sgml index 42f6f6938..5560650a6 100644 --- a/v4l2-spec/dev-sliced-vbi.sgml +++ b/v4l2-spec/dev-sliced-vbi.sgml @@ -84,8 +84,7 @@ array according to hardware capabilities. Only if more precise control is needed should the programmer set the service_lines array explicitly. - The &VIDIOC-S-FMT; ioctl returns an &EINVAL; only when the -given parameters are ambiguous, otherwise it modifies the parameters + 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 -- cgit v1.2.3