diff options
Diffstat (limited to 'Documentation/DocBook')
| -rw-r--r-- | Documentation/DocBook/media/v4l/common.xml | 132 |
1 files changed, 53 insertions, 79 deletions
diff --git a/Documentation/DocBook/media/v4l/common.xml b/Documentation/DocBook/media/v4l/common.xml index 5a97935e75a1..0936dd24ed3d 100644 --- a/Documentation/DocBook/media/v4l/common.xml +++ b/Documentation/DocBook/media/v4l/common.xml @@ -449,7 +449,7 @@ the tuner.</para> video inputs.</para> <para>To query and change tuner properties applications use the -&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctl, respectively. The +&VIDIOC-G-TUNER; and &VIDIOC-S-TUNER; ioctls, respectively. The &v4l2-tuner; returned by <constant>VIDIOC_G_TUNER</constant> also contains signal status information applicable when the tuner of the current video or radio input is queried. Note that @@ -514,7 +514,7 @@ standards or variations of standards. Each video input and output may support another set of standards. This set is reported by the <structfield>std</structfield> field of &v4l2-input; and &v4l2-output; returned by the &VIDIOC-ENUMINPUT; and -&VIDIOC-ENUMOUTPUT; ioctl, respectively.</para> +&VIDIOC-ENUMOUTPUT; ioctls, respectively.</para> <para>V4L2 defines one bit for each analog video standard currently in use worldwide, and sets aside bits for driver defined @@ -545,28 +545,10 @@ automatically.</para> <para>To query and select the standard used by the current video input or output applications call the &VIDIOC-G-STD; and &VIDIOC-S-STD; ioctl, respectively. The <emphasis>received</emphasis> -standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the parameter of all these ioctls is a pointer to a &v4l2-std-id; type (a standard set), <emphasis>not</emphasis> an index into the standard enumeration.<footnote> - <para>An alternative to the current scheme is to use pointers -to indices as arguments of <constant>VIDIOC_G_STD</constant> and -<constant>VIDIOC_S_STD</constant>, the &v4l2-input; and -&v4l2-output; <structfield>std</structfield> field would be a set of -indices like <structfield>audioset</structfield>.</para> - <para>Indices are consistent with the rest of the API -and identify the standard unambiguously. In the present scheme of -things an enumerated standard is looked up by &v4l2-std-id;. Now the -standards supported by the inputs of a device can overlap. Just -assume the tuner and composite input in the example above both -exist on a device. An enumeration of "PAL-B/G", "PAL-H/I" suggests -a choice which does not exist. We cannot merge or omit sets, because -applications would be unable to find the standards reported by -<constant>VIDIOC_G_STD</constant>. That leaves separate enumerations -for each input. Also selecting a standard by &v4l2-std-id; can be -ambiguous. Advantage of this method is that applications need not -identify the standard indirectly, after enumerating.</para><para>So in -summary, the lookup itself is unavoidable. The difference is only -whether the lookup is necessary to find an enumerated standard or to -switch to a standard by &v4l2-std-id;.</para> - </footnote> Drivers must implement all video standard ioctls +standard can be sensed with the &VIDIOC-QUERYSTD; ioctl. Note that the +parameter of all these ioctls is a pointer to a &v4l2-std-id; type +(a standard set), <emphasis>not</emphasis> an index into the standard +enumeration. Drivers must implement all video standard ioctls when the device has one or more video inputs or outputs.</para> <para>Special rules apply to devices such as USB cameras where the notion of video @@ -585,17 +567,10 @@ to zero and the <constant>VIDIOC_G_STD</constant>, <constant>VIDIOC_S_STD</constant>, <constant>VIDIOC_QUERYSTD</constant> and <constant>VIDIOC_ENUMSTD</constant> ioctls shall return the -&ENOTTY;.<footnote> - <para>See <xref linkend="buffer" /> for a rationale.</para> +&ENOTTY; or the &EINVAL;.</para> <para>Applications can make use of the <xref linkend="input-capabilities" /> and <xref linkend="output-capabilities"/> flags to determine whether the video standard ioctls -are available for the device.</para> - - <para>See <xref linkend="buffer" /> for a rationale. Probably -even USB cameras follow some well known video standard. It might have -been better to explicitly indicate elsewhere if a device cannot live -up to normal expectations, instead of this exception.</para> - </footnote></para> +can be used with the given input or output.</para> <example> <title>Information about the current video standard</title> @@ -604,22 +579,22 @@ up to normal expectations, instead of this exception.</para> &v4l2-std-id; std_id; &v4l2-standard; standard; -if (-1 == ioctl (fd, &VIDIOC-G-STD;, &std_id)) { +if (-1 == ioctl(fd, &VIDIOC-G-STD;, &std_id)) { /* Note when VIDIOC_ENUMSTD always returns ENOTTY this is no video device or it falls under the USB exception, and VIDIOC_G_STD returning ENOTTY is no error. */ - perror ("VIDIOC_G_STD"); - exit (EXIT_FAILURE); + perror("VIDIOC_G_STD"); + exit(EXIT_FAILURE); } -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & std_id) { - printf ("Current video standard: %s\n", standard.name); - exit (EXIT_SUCCESS); + printf("Current video standard: %s\n", standard.name); + exit(EXIT_SUCCESS); } standard.index++; @@ -629,8 +604,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { empty unless this device falls under the USB exception. */ if (errno == EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -643,26 +618,26 @@ input</title> &v4l2-input; input; &v4l2-standard; standard; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } -printf ("Current input %s supports:\n", input.name); +printf("Current input %s supports:\n", input.name); -memset (&standard, 0, sizeof (standard)); +memset(&standard, 0, sizeof(standard)); standard.index = 0; -while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { +while (0 == ioctl(fd, &VIDIOC-ENUMSTD;, &standard)) { if (standard.id & input.std) - printf ("%s\n", standard.name); + printf("%s\n", standard.name); standard.index++; } @@ -671,8 +646,8 @@ while (0 == ioctl (fd, &VIDIOC-ENUMSTD;, &standard)) { empty unless this device falls under the USB exception. */ if (errno != EINVAL || standard.index == 0) { - perror ("VIDIOC_ENUMSTD"); - exit (EXIT_FAILURE); + perror("VIDIOC_ENUMSTD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -684,21 +659,21 @@ if (errno != EINVAL || standard.index == 0) { &v4l2-input; input; &v4l2-std-id; std_id; -memset (&input, 0, sizeof (input)); +memset(&input, 0, sizeof(input)); -if (-1 == ioctl (fd, &VIDIOC-G-INPUT;, &input.index)) { - perror ("VIDIOC_G_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-G-INPUT;, &input.index)) { + perror("VIDIOC_G_INPUT"); + exit(EXIT_FAILURE); } -if (-1 == ioctl (fd, &VIDIOC-ENUMINPUT;, &input)) { - perror ("VIDIOC_ENUM_INPUT"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-ENUMINPUT;, &input)) { + perror("VIDIOC_ENUM_INPUT"); + exit(EXIT_FAILURE); } if (0 == (input.std & V4L2_STD_PAL_BG)) { - fprintf (stderr, "Oops. B/G PAL is not supported.\n"); - exit (EXIT_FAILURE); + fprintf(stderr, "Oops. B/G PAL is not supported.\n"); + exit(EXIT_FAILURE); } /* Note this is also supposed to work when only B @@ -706,9 +681,9 @@ if (0 == (input.std & V4L2_STD_PAL_BG)) { std_id = V4L2_STD_PAL_BG; -if (-1 == ioctl (fd, &VIDIOC-S-STD;, &std_id)) { - perror ("VIDIOC_S_STD"); - exit (EXIT_FAILURE); +if (-1 == ioctl(fd, &VIDIOC-S-STD;, &std_id)) { + perror("VIDIOC_S_STD"); + exit(EXIT_FAILURE); } </programlisting> </example> @@ -721,26 +696,25 @@ corresponding video timings. Today there are many more different hardware interf such as High Definition TV interfaces (HDMI), VGA, DVI connectors etc., that carry video signals and there is a need to extend the API to select the video timings for these interfaces. Since it is not possible to extend the &v4l2-std-id; due to -the limited bits available, a new set of IOCTLs was added to set/get video timings at -the input and output: </para><itemizedlist> - <listitem> - <para>DV Timings: This will allow applications to define detailed -video timings for the interface. This includes parameters such as width, height, -polarities, frontporch, backporch etc. The <filename>linux/v4l2-dv-timings.h</filename> +the limited bits available, a new set of ioctls was added to set/get video timings at +the input and output.</para> + + <para>These ioctls deal with the detailed digital video timings that define +each video format. This includes parameters such as the active video width and height, +signal polarities, frontporches, backporches, sync widths etc. The <filename>linux/v4l2-dv-timings.h</filename> header can be used to get the timings of the formats in the <xref linkend="cea861" /> and <xref linkend="vesadmt" /> standards. </para> - </listitem> - </itemizedlist> - <para>To enumerate and query the attributes of the DV timings supported by a device, + + <para>To enumerate and query the attributes of the DV timings supported by a device applications use the &VIDIOC-ENUM-DV-TIMINGS; and &VIDIOC-DV-TIMINGS-CAP; ioctls. - To set DV timings for the device, applications use the + To set DV timings for the device applications use the &VIDIOC-S-DV-TIMINGS; ioctl and to get current DV timings they use the &VIDIOC-G-DV-TIMINGS; ioctl. To detect the DV timings as seen by the video receiver applications use the &VIDIOC-QUERY-DV-TIMINGS; ioctl.</para> <para>Applications can make use of the <xref linkend="input-capabilities" /> and -<xref linkend="output-capabilities"/> flags to decide what ioctls are available to set the -video timings for the device.</para> +<xref linkend="output-capabilities"/> flags to determine whether the digital video ioctls +can be used with the given input or output.</para> </section> &sub-controls; |
