diff options
Diffstat (limited to 'Documentation/userspace-api/media/v4l/vidioc-enum-frameintervals.rst')
| -rw-r--r-- | Documentation/userspace-api/media/v4l/vidioc-enum-frameintervals.rst | 203 |
1 files changed, 203 insertions, 0 deletions
diff --git a/Documentation/userspace-api/media/v4l/vidioc-enum-frameintervals.rst b/Documentation/userspace-api/media/v4l/vidioc-enum-frameintervals.rst new file mode 100644 index 000000000000..0e3db737371f --- /dev/null +++ b/Documentation/userspace-api/media/v4l/vidioc-enum-frameintervals.rst @@ -0,0 +1,203 @@ +.. Permission is granted to copy, distribute and/or modify this +.. document under the terms of the GNU Free Documentation License, +.. Version 1.1 or any later version published by the Free Software +.. Foundation, with no Invariant Sections, no Front-Cover Texts +.. and no Back-Cover Texts. A copy of the license is included at +.. Documentation/userspace-api/media/fdl-appendix.rst. +.. +.. TODO: replace it to GFDL-1.1-or-later WITH no-invariant-sections + +.. _VIDIOC_ENUM_FRAMEINTERVALS: + +******************************** +ioctl VIDIOC_ENUM_FRAMEINTERVALS +******************************** + +Name +==== + +VIDIOC_ENUM_FRAMEINTERVALS - Enumerate frame intervals + + +Synopsis +======== + +.. c:function:: int ioctl( int fd, VIDIOC_ENUM_FRAMEINTERVALS, struct v4l2_frmivalenum *argp ) + :name: VIDIOC_ENUM_FRAMEINTERVALS + + +Arguments +========= + +``fd`` + File descriptor returned by :ref:`open() <func-open>`. + +``argp`` + Pointer to struct :c:type:`v4l2_frmivalenum` + that contains a pixel format and size and receives a frame interval. + + +Description +=========== + +This ioctl allows applications to enumerate all frame intervals that the +device supports for the given pixel format and frame size. + +The supported pixel formats and frame sizes can be obtained by using the +:ref:`VIDIOC_ENUM_FMT` and +:ref:`VIDIOC_ENUM_FRAMESIZES` functions. + +The return value and the content of the ``v4l2_frmivalenum.type`` field +depend on the type of frame intervals the device supports. Here are the +semantics of the function for the different cases: + +- **Discrete:** The function returns success if the given index value + (zero-based) is valid. The application should increase the index by + one for each call until ``EINVAL`` is returned. The + `v4l2_frmivalenum.type` field is set to + `V4L2_FRMIVAL_TYPE_DISCRETE` by the driver. Of the union only + the `discrete` member is valid. + +- **Step-wise:** The function returns success if the given index value + is zero and ``EINVAL`` for any other index value. The + ``v4l2_frmivalenum.type`` field is set to + ``V4L2_FRMIVAL_TYPE_STEPWISE`` by the driver. Of the union only the + ``stepwise`` member is valid. + +- **Continuous:** This is a special case of the step-wise type above. + The function returns success if the given index value is zero and + ``EINVAL`` for any other index value. The ``v4l2_frmivalenum.type`` + field is set to ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` by the driver. Of + the union only the ``stepwise`` member is valid and the ``step`` + value is set to 1. + +When the application calls the function with index zero, it must check +the ``type`` field to determine the type of frame interval enumeration +the device supports. Only for the ``V4L2_FRMIVAL_TYPE_DISCRETE`` type +does it make sense to increase the index value to receive more frame +intervals. + +.. note:: + + The order in which the frame intervals are returned has no + special meaning. In particular does it not say anything about potential + default frame intervals. + +Applications can assume that the enumeration data does not change +without any interaction from the application itself. This means that the +enumeration data is consistent if the application does not perform any +other ioctl calls while it runs the frame interval enumeration. + +.. note:: + + **Frame intervals and frame rates:** The V4L2 API uses frame + intervals instead of frame rates. Given the frame interval the frame + rate can be computed as follows: + + :: + + frame_rate = 1 / frame_interval + + +Structs +======= + +In the structs below, *IN* denotes a value that has to be filled in by +the application, *OUT* denotes values that the driver fills in. The +application should zero out all members except for the *IN* fields. + + +.. c:type:: v4l2_frmival_stepwise + +.. tabularcolumns:: |p{4.4cm}|p{4.4cm}|p{8.7cm}| + +.. flat-table:: struct v4l2_frmival_stepwise + :header-rows: 0 + :stub-columns: 0 + :widths: 1 1 2 + + * - struct :c:type:`v4l2_fract` + - ``min`` + - Minimum frame interval [s]. + * - struct :c:type:`v4l2_fract` + - ``max`` + - Maximum frame interval [s]. + * - struct :c:type:`v4l2_fract` + - ``step`` + - Frame interval step size [s]. + + + +.. c:type:: v4l2_frmivalenum + +.. tabularcolumns:: |p{1.8cm}|p{4.4cm}|p{2.4cm}|p{8.9cm}| + +.. flat-table:: struct v4l2_frmivalenum + :header-rows: 0 + :stub-columns: 0 + + * - __u32 + - ``index`` + - IN: Index of the given frame interval in the enumeration. + * - __u32 + - ``pixel_format`` + - IN: Pixel format for which the frame intervals are enumerated. + * - __u32 + - ``width`` + - IN: Frame width for which the frame intervals are enumerated. + * - __u32 + - ``height`` + - IN: Frame height for which the frame intervals are enumerated. + * - __u32 + - ``type`` + - OUT: Frame interval type the device supports. + * - union { + - (anonymous) + - OUT: Frame interval with the given index. + * - struct :c:type:`v4l2_fract` + - ``discrete`` + - Frame interval [s]. + * - struct :c:type:`v4l2_frmival_stepwise` + - ``stepwise`` + - + * - } + - + - + * - __u32 + - ``reserved[2]`` + - + - Reserved space for future use. Must be zeroed by drivers and + applications. + + + +Enums +===== + + +.. c:type:: v4l2_frmivaltypes + +.. tabularcolumns:: |p{6.6cm}|p{2.2cm}|p{8.7cm}| + +.. flat-table:: enum v4l2_frmivaltypes + :header-rows: 0 + :stub-columns: 0 + :widths: 3 1 4 + + * - ``V4L2_FRMIVAL_TYPE_DISCRETE`` + - 1 + - Discrete frame interval. + * - ``V4L2_FRMIVAL_TYPE_CONTINUOUS`` + - 2 + - Continuous frame interval. + * - ``V4L2_FRMIVAL_TYPE_STEPWISE`` + - 3 + - Step-wise defined frame interval. + + +Return Value +============ + +On success 0 is returned, on error -1 and the ``errno`` variable is set +appropriately. The generic error codes are described at the +:ref:`Generic Error Codes <gen-errors>` chapter. |