Documentation/media/uapi/v4l/vidioc-query-dv-timings.rst

   1 .. -*- coding: utf-8; mode: rst -*-
   2
   3 .. _VIDIOC_QUERY_DV_TIMINGS:
   4
   5 *****************************
   6 ioctl VIDIOC_QUERY_DV_TIMINGS
   7 *****************************
   8
   9 Name
  10 ====
  11
  12 VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input
  13
  14
  15 Synopsis
  16 ========
  17
  18 .. c:function:: int ioctl( int fd, int request, struct v4l2_dv_timings *argp )
  19
  20
  21 Arguments
  22 =========
  23
  24 ``fd``
  25     File descriptor returned by :ref:`open() <func-open>`.
  26
  27 ``request``
  28     VIDIOC_QUERY_DV_TIMINGS, VIDIOC_SUBDEV_QUERY_DV_TIMINGS
  29
  30 ``argp``
  31
  32
  33 Description
  34 ===========
  35
  36 The hardware may be able to detect the current DV timings automatically,
  37 similar to sensing the video standard. To do so, applications call
  38 :ref:`VIDIOC_QUERY_DV_TIMINGS` with a pointer to a struct
  39 :ref:`v4l2_dv_timings <v4l2-dv-timings>`. Once the hardware detects
  40 the timings, it will fill in the timings structure.
  41
  42 .. note::
  43
  44    Drivers shall *not* switch timings automatically if new
  45    timings are detected. Instead, drivers should send the
  46    ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect
  47    that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`.
  48    The reason is that new timings usually mean different buffer sizes as
  49    well, and you cannot change buffer sizes on the fly. In general,
  50    applications that receive the Source Change event will have to call
  51    :ref:`VIDIOC_QUERY_DV_TIMINGS`, and if the detected timings are valid they
  52    will have to stop streaming, set the new timings, allocate new buffers
  53    and start streaming again.
  54
  55 If the timings could not be detected because there was no signal, then
  56 ENOLINK is returned. If a signal was detected, but it was unstable and
  57 the receiver could not lock to the signal, then ``ENOLCK`` is returned. If
  58 the receiver could lock to the signal, but the format is unsupported
  59 (e.g. because the pixelclock is out of range of the hardware
  60 capabilities), then the driver fills in whatever timings it could find
  61 and returns ``ERANGE``. In that case the application can call
  62 :ref:`VIDIOC_DV_TIMINGS_CAP` to compare the
  63 found timings with the hardware's capabilities in order to give more
  64 precise feedback to the user.
  65
  66
  67 Return Value
  68 ============
  69
  70 On success 0 is returned, on error -1 and the ``errno`` variable is set
  71 appropriately. The generic error codes are described at the
  72 :ref:`Generic Error Codes <gen-errors>` chapter.
  73
  74 ENODATA
  75     Digital video timings are not supported for this input or output.
  76
  77 ENOLINK
  78     No timings could be detected because no signal was found.
  79
  80 ENOLCK
  81     The signal was unstable and the hardware could not lock on to it.
  82
  83 ERANGE
  84     Timings were found, but they are out of range of the hardware
  85     capabilities.