vidioc-query-dv-timings.rst (2881B)
1.. SPDX-License-Identifier: GFDL-1.1-no-invariants-or-later 2.. c:namespace:: V4L 3 4.. _VIDIOC_QUERY_DV_TIMINGS: 5 6***************************** 7ioctl VIDIOC_QUERY_DV_TIMINGS 8***************************** 9 10Name 11==== 12 13VIDIOC_QUERY_DV_TIMINGS - VIDIOC_SUBDEV_QUERY_DV_TIMINGS - Sense the DV preset received by the current input 14 15Synopsis 16======== 17 18.. c:macro:: VIDIOC_QUERY_DV_TIMINGS 19 20``int ioctl(int fd, VIDIOC_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 21 22.. c:macro:: VIDIOC_SUBDEV_QUERY_DV_TIMINGS 23 24``int ioctl(int fd, VIDIOC_SUBDEV_QUERY_DV_TIMINGS, struct v4l2_dv_timings *argp)`` 25 26Arguments 27========= 28 29``fd`` 30 File descriptor returned by :c:func:`open()`. 31 32``argp`` 33 Pointer to struct :c:type:`v4l2_dv_timings`. 34 35Description 36=========== 37 38The hardware may be able to detect the current DV timings automatically, 39similar to sensing the video standard. To do so, applications call 40:ref:`VIDIOC_QUERY_DV_TIMINGS` with a pointer to a struct 41:c:type:`v4l2_dv_timings`. Once the hardware detects 42the timings, it will fill in the timings structure. 43 44.. note:: 45 46 Drivers shall *not* switch timings automatically if new 47 timings are detected. Instead, drivers should send the 48 ``V4L2_EVENT_SOURCE_CHANGE`` event (if they support this) and expect 49 that userspace will take action by calling :ref:`VIDIOC_QUERY_DV_TIMINGS`. 50 The reason is that new timings usually mean different buffer sizes as 51 well, and you cannot change buffer sizes on the fly. In general, 52 applications that receive the Source Change event will have to call 53 :ref:`VIDIOC_QUERY_DV_TIMINGS`, and if the detected timings are valid they 54 will have to stop streaming, set the new timings, allocate new buffers 55 and start streaming again. 56 57If the timings could not be detected because there was no signal, then 58ENOLINK is returned. If a signal was detected, but it was unstable and 59the receiver could not lock to the signal, then ``ENOLCK`` is returned. If 60the receiver could lock to the signal, but the format is unsupported 61(e.g. because the pixelclock is out of range of the hardware 62capabilities), then the driver fills in whatever timings it could find 63and returns ``ERANGE``. In that case the application can call 64:ref:`VIDIOC_DV_TIMINGS_CAP` to compare the 65found timings with the hardware's capabilities in order to give more 66precise feedback to the user. 67 68Return Value 69============ 70 71On success 0 is returned, on error -1 and the ``errno`` variable is set 72appropriately. The generic error codes are described at the 73:ref:`Generic Error Codes <gen-errors>` chapter. 74 75ENODATA 76 Digital video timings are not supported for this input or output. 77 78ENOLINK 79 No timings could be detected because no signal was found. 80 81ENOLCK 82 The signal was unstable and the hardware could not lock on to it. 83 84ERANGE 85 Timings were found, but they are out of range of the hardware 86 capabilities.