7.60. ioctl VIDIOC_SUBDEV_G_FRAME_INTERVAL, VIDIOC_SUBDEV_S_FRAME_INTERVAL

7.60.1. Name

VIDIOC_SUBDEV_G_FRAME_INTERVAL - VIDIOC_SUBDEV_S_FRAME_INTERVAL - Get or set the frame interval on a subdev pad

7.60.2. Synopsis

VIDIOC_SUBDEV_G_FRAME_INTERVAL

int ioctl(int fd, VIDIOC_SUBDEV_G_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)

VIDIOC_SUBDEV_S_FRAME_INTERVAL

int ioctl(int fd, VIDIOC_SUBDEV_S_FRAME_INTERVAL, struct v4l2_subdev_frame_interval *argp)

7.60.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_subdev_frame_interval.

7.60.4. Description

These ioctls are used to get and set the frame interval at specific subdev pads in the image pipeline. The frame interval only makes sense for sub-devices that can control the frame period on their own. This includes, for instance, image sensors and TV tuners. Sub-devices that don’t support frame intervals must not implement these ioctls.

To retrieve the current frame interval applications set the pad field of a struct v4l2_subdev_frame_interval to the desired pad number as reported by the media controller API. When they call the VIDIOC_SUBDEV_G_FRAME_INTERVAL ioctl with a pointer to this structure the driver fills the members of the interval field.

To change the current frame interval applications set both the pad field and all members of the interval field. When they call the VIDIOC_SUBDEV_S_FRAME_INTERVAL ioctl with a pointer to this structure the driver verifies the requested interval, adjusts it based on the hardware capabilities and configures the device. Upon return the struct v4l2_subdev_frame_interval contains the current frame interval as would be returned by a VIDIOC_SUBDEV_G_FRAME_INTERVAL call.

If the subdev device node has been registered in read-only mode, calls to VIDIOC_SUBDEV_S_FRAME_INTERVAL are only valid if the which field is set to V4L2_SUBDEV_FORMAT_TRY, otherwise an error is returned and the errno variable is set to -EPERM.

Drivers must not return an error solely because the requested interval doesn’t match the device capabilities. They must instead modify the interval to match what the hardware can provide. The modified interval should be as close as possible to the original request.

Changing the frame interval shall never change the format. Changing the format, on the other hand, may change the frame interval.

Sub-devices that support the frame interval ioctls should implement them on a single pad only. Their behaviour when supported on multiple pads of the same sub-device is not defined.

type v4l2_subdev_frame_interval

struct v4l2_subdev_frame_interval

__u32	pad	Pad number as reported by the media controller API.
struct v4l2_fract	interval	Period, in seconds, between consecutive video frames.
__u32	stream	Stream identifier.
__u32	which	Active or try frame interval, from enum v4l2_subdev_format_whence.
__u32	reserved[7]	Reserved for future extensions. Applications and drivers must set the array to zero.

7.60.5. 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 Generic Error Codes chapter.

EBUSY

The frame interval can’t be changed because the pad is currently busy. This can be caused, for instance, by an active video stream on the pad. The ioctl must not be retried without performing another action to fix the problem first. Only returned by VIDIOC_SUBDEV_S_FRAME_INTERVAL

EINVAL

The struct v4l2_subdev_frame_interval pad references a non-existing pad, the which field has an unsupported value, or the pad doesn’t support frame intervals.

EPERM

The VIDIOC_SUBDEV_S_FRAME_INTERVAL ioctl has been called on a read-only subdevice and the which field is set to V4L2_SUBDEV_FORMAT_ACTIVE.