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Bản gốc:

ioctl VIDIOC_DQEVENT

Người dịch:

Google Translate (machine translation)

Phiên bản gốc:

8541d8f725c6

Cảnh báo

Tài liệu này được dịch tự động bằng máy và chưa được review bởi người dịch. Nội dung có thể không chính xác hoặc khó hiểu ở một số chỗ. Khi có sự khác biệt với bản gốc, bản gốc luôn là chuẩn. Bản dịch chất lượng cao (được review) được đặt trong thư mục vi_VN/.

7.8. ioctl VIDIOC_DQEVENT

7.8.1. Tên

VIDIOC_DQEVENT - Sự kiện xếp hàng

7.8.2. Tóm tắt

VIDIOC_DQEVENT

ZZ0000ZZ

7.8.3. Đối số

ZZ0001ZZ

Bộ mô tả tệp được trả về bởi ZZ0000ZZ.

ZZ0001ZZ

Con trỏ tới cấu trúc ZZ0000ZZ.

7.8.4. Sự miêu tả

Sắp xếp lại một sự kiện từ thiết bị video. Không cần đầu vào cho việc này ioctl. Tất cả các trường của cấu trúc ZZ0000ZZ cấu trúc được lấp đầy bởi người lái xe. Việc xử lý tập tin cũng sẽ nhận được các trường hợp ngoại lệ mà ứng dụng có thể nhận được, ví dụ: sử dụng hệ thống chọn lọc gọi.

type v4l2_event
struct v4l2_event

__u32

type

Type of the event, see Event Types.

union {

u

struct v4l2_event_vsync

vsync

Event data for event V4L2_EVENT_VSYNC.

struct v4l2_event_ctrl

ctrl

Event data for event V4L2_EVENT_CTRL.

struct v4l2_event_frame_sync

frame_sync

Event data for event V4L2_EVENT_FRAME_SYNC.

struct v4l2_event_motion_det

motion_det

Event data for event V4L2_EVENT_MOTION_DET.

struct v4l2_event_src_change

src_change

Event data for event V4L2_EVENT_SOURCE_CHANGE.

__u8

data[64]

Event data. Defined by the event type. The union should be used to define easily accessible type for events.

}

__u32

pending

Number of pending events excluding this one.

__u32

sequence

Event sequence number. The sequence number is incremented for every subscribed event that takes place. If sequence numbers are not contiguous it means that events have been lost.

struct timespec

timestamp

Event timestamp. The timestamp has been taken from the CLOCK_MONOTONIC clock. To access the same clock outside V4L2, use clock_gettime().

u32

id

The ID associated with the event source. If the event does not have an associated ID (this depends on the event type), then this is 0.

__u32

reserved[8]

Reserved for future extensions. Drivers must set the array to zero.
Event Types

V4L2_EVENT_ALL

0

All events. V4L2_EVENT_ALL is valid only for VIDIOC_UNSUBSCRIBE_EVENT for unsubscribing all events at once.

V4L2_EVENT_VSYNC

1

This event is triggered on the vertical sync. This event has a struct v4l2_event_vsync associated with it.

V4L2_EVENT_EOS

2

This event is triggered when the end of a stream is reached. This is typically used with MPEG decoders to report to the application when the last of the MPEG stream has been decoded.

V4L2_EVENT_CTRL

3

This event requires that the id matches the control ID from which you want to receive events. This event is triggered if the control’s value changes, if a button control is pressed or if the control’s flags change. This event has a struct v4l2_event_ctrl associated with it. This struct contains much of the same information as struct v4l2_queryctrl and struct v4l2_control.

If the event is generated due to a call to VIDIOC_S_CTRL or VIDIOC_S_EXT_CTRLS, then the event will not be sent to the file handle that called the ioctl function. This prevents nasty feedback loops. If you do want to get the event, then set the V4L2_EVENT_SUB_FL_ALLOW_FEEDBACK flag.

This event type will ensure that no information is lost when more events are raised than there is room internally. In that case the struct v4l2_event_ctrl of the second-oldest event is kept, but the changes field of the second-oldest event is ORed with the changes field of the oldest event.

V4L2_EVENT_FRAME_SYNC

4

Triggered immediately when the reception of a frame has begun. This event has a struct v4l2_event_frame_sync associated with it.

If the hardware needs to be stopped in the case of a buffer underrun it might not be able to generate this event. In such cases the frame_sequence field in struct v4l2_event_frame_sync will not be incremented. This causes two consecutive frame sequence numbers to have n times frame interval in between them.

V4L2_EVENT_SOURCE_CHANGE

5

This event is triggered when a source parameter change is detected during runtime by the video device. It can be a runtime resolution change triggered by a video decoder or the format change happening on an input connector. This event requires that the id matches the input index (when used with a video device node) or the pad index (when used with a subdevice node) from which you want to receive events.

This event has a struct v4l2_event_src_change associated with it. The changes bitfield denotes what has changed for the subscribed pad. If multiple events occurred before application could dequeue them, then the changes will have the ORed value of all the events generated.

V4L2_EVENT_MOTION_DET

6

Triggered whenever the motion detection state for one or more of the regions changes. This event has a struct v4l2_event_motion_det associated with it.

V4L2_EVENT_PRIVATE_START

0x08000000

Base event number for driver-private events.
type v4l2_event_vsync
struct v4l2_event_vsync

__u8

field

The upcoming field. See enum v4l2_field.
type v4l2_event_ctrl
struct v4l2_event_ctrl

__u32

changes

A bitmask that tells what has changed. See Control Changes.

__u32

type

The type of the control. See enum v4l2_ctrl_type.

union {

(anonymous)

__s32

value

The 32-bit value of the control for 32-bit control types. This is 0 for string controls since the value of a string cannot be passed using ioctl VIDIOC_DQEVENT.

__s64

value64

The 64-bit value of the control for 64-bit control types.

}

__u32

flags

The control flags. See Control Flags.

__s32

minimum

The minimum value of the control. See struct v4l2_queryctrl.

__s32

maximum

The maximum value of the control. See struct v4l2_queryctrl.

__s32

step

The step value of the control. See struct v4l2_queryctrl.

__s32

default_value

The default value of the control. See struct v4l2_queryctrl.
type v4l2_event_frame_sync
struct v4l2_event_frame_sync

__u32

frame_sequence

The sequence number of the frame being received.
type v4l2_event_src_change
struct v4l2_event_src_change

__u32

changes

A bitmask that tells what has changed. See Source Changes.
type v4l2_event_motion_det
struct v4l2_event_motion_det

__u32

flags

Currently only one flag is available: if V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ is set, then the frame_sequence field is valid, otherwise that field should be ignored.

__u32

frame_sequence

The sequence number of the frame being received. Only valid if the V4L2_EVENT_MD_FL_HAVE_FRAME_SEQ flag was set.

__u32

region_mask

The bitmask of the regions that reported motion. There is at least one region. If this field is 0, then no motion was detected at all. If there is no V4L2_CID_DETECT_MD_REGION_GRID control (see Detect Control Reference) to assign a different region to each cell in the motion detection grid, then that all cells are automatically assigned to the default region 0.
Control Changes

V4L2_EVENT_CTRL_CH_VALUE

0x0001

This control event was triggered because the value of the control changed. Special cases: Volatile controls do no generate this event; If a control has the V4L2_CTRL_FLAG_EXECUTE_ON_WRITE flag set, then this event is sent as well, regardless its value.

V4L2_EVENT_CTRL_CH_FLAGS

0x0002

This control event was triggered because the control flags changed.

V4L2_EVENT_CTRL_CH_RANGE

0x0004

This control event was triggered because the minimum, maximum, step or the default value of the control changed.

V4L2_EVENT_CTRL_CH_DIMENSIONS

0x0008

This control event was triggered because the dimensions of the control changed. Note that the number of dimensions remains the same.
Source Changes

V4L2_EVENT_SRC_CH_RESOLUTION

0x0001

This event gets triggered when a resolution change is detected at an input. This can come from an input connector or from a video decoder. Applications will have to query the new resolution (if any, the signal may also have been lost).

For stateful decoders follow the guidelines in Memory-to-Memory Stateful Video Decoder Interface. Video Capture devices have to query the new timings using ioctl VIDIOC_QUERY_DV_TIMINGS or VIDIOC_QUERYSTD.

Important: even if the new video timings appear identical to the old ones, receiving this event indicates that there was an issue with the video signal and you must stop and restart streaming (VIDIOC_STREAMOFF followed by VIDIOC_STREAMON). The reason is that many Video Capture devices are not able to recover from a temporary loss of signal and so restarting streaming I/O is required in order for the hardware to synchronize to the video signal.

7.8.5. Giá trị trả về

Khi thành công, trả về 0, lỗi -1 và biến ZZ0001ZZ được đặt một cách thích hợp. Các mã lỗi chung được mô tả tại Chương ZZ0000ZZ.