7.26. ioctl VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS

7.26.1. Name

VIDIOC_G_DV_TIMINGS - VIDIOC_S_DV_TIMINGS - VIDIOC_SUBDEV_G_DV_TIMINGS - VIDIOC_SUBDEV_S_DV_TIMINGS - Get or set DV timings for input or output

7.26.2. Synopsis

int ioctl(int fd, VIDIOC_G_DV_TIMINGS, struct v4l2_dv_timings *argp)
int ioctl(int fd, VIDIOC_S_DV_TIMINGS, struct v4l2_dv_timings *argp)
int ioctl(int fd, VIDIOC_SUBDEV_G_DV_TIMINGS, struct v4l2_dv_timings *argp)
int ioctl(int fd, VIDIOC_SUBDEV_S_DV_TIMINGS, struct v4l2_dv_timings *argp)

7.26.3. Arguments

fd

File descriptor returned by open().

argp

Pointer to struct v4l2_dv_timings.

7.26.4. Description

To set DV timings for the input or output, applications use the VIDIOC_S_DV_TIMINGS ioctl and to get the current timings, applications use the VIDIOC_G_DV_TIMINGS ioctl. The detailed timing information is filled in using the structure struct v4l2_dv_timings. These ioctls take a pointer to the struct v4l2_dv_timings structure as argument. If the ioctl is not supported or the timing values are not correct, the driver returns EINVAL error code.

Calling VIDIOC_SUBDEV_S_DV_TIMINGS on a subdev device node that has been registered in read-only mode is not allowed. An error is returned and the errno variable is set to -EPERM.

The linux/v4l2-dv-timings.h header can be used to get the timings of the formats in the CEA-861-E and VESA DMT standards. If the current input or output does not support DV timings (e.g. if ioctl VIDIOC_ENUMINPUT does not set the V4L2_IN_CAP_DV_TIMINGS flag), then ENODATA error code is returned.

7.26.5. 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.

EINVAL

This ioctl is not supported, or the VIDIOC_S_DV_TIMINGS parameter was unsuitable.

ENODATA

Digital video timings are not supported for this input or output.

EBUSY

The device is busy and therefore can not change the timings.

EPERM

VIDIOC_SUBDEV_S_DV_TIMINGS has been called on a read-only subdevice.

v4l2_bt_timings
struct v4l2_bt_timings

__u32

width

Width of the active video in pixels.

__u32

height

Height of the active video frame in lines. So for interlaced formats the height of the active video in each field is height/2.

__u32

interlaced

Progressive (V4L2_DV_PROGRESSIVE) or interlaced (V4L2_DV_INTERLACED).

__u32

polarities

This is a bit mask that defines polarities of sync signals. bit 0 (V4L2_DV_VSYNC_POS_POL) is for vertical sync polarity and bit 1 (V4L2_DV_HSYNC_POS_POL) is for horizontal sync polarity. If the bit is set (1) it is positive polarity and if is cleared (0), it is negative polarity.

__u64

pixelclock

Pixel clock in Hz. Ex. 74.25MHz->74250000

__u32

hfrontporch

Horizontal front porch in pixels

__u32

hsync

Horizontal sync length in pixels

__u32

hbackporch

Horizontal back porch in pixels

__u32

vfrontporch

Vertical front porch in lines. For interlaced formats this refers to the odd field (aka field 1).

__u32

vsync

Vertical sync length in lines. For interlaced formats this refers to the odd field (aka field 1).

__u32

vbackporch

Vertical back porch in lines. For interlaced formats this refers to the odd field (aka field 1).

__u32

il_vfrontporch

Vertical front porch in lines for the even field (aka field 2) of interlaced field formats. Must be 0 for progressive formats.

__u32

il_vsync

Vertical sync length in lines for the even field (aka field 2) of interlaced field formats. Must be 0 for progressive formats.

__u32

il_vbackporch

Vertical back porch in lines for the even field (aka field 2) of interlaced field formats. Must be 0 for progressive formats.

__u32

standards

The video standard(s) this format belongs to. This will be filled in by the driver. Applications must set this to 0. See DV BT Timing standards for a list of standards.

__u32

flags

Several flags giving more information about the format. See DV BT Timing flags for a description of the flags.

struct v4l2_fract

picture_aspect

The picture aspect if the pixels are not square. Only valid if the V4L2_DV_FL_HAS_PICTURE_ASPECT flag is set.

__u8

cea861_vic

The Video Identification Code according to the CEA-861 standard. Only valid if the V4L2_DV_FL_HAS_CEA861_VIC flag is set.

__u8

hdmi_vic

The Video Identification Code according to the HDMI standard. Only valid if the V4L2_DV_FL_HAS_HDMI_VIC flag is set.

__u8

reserved[46]

Reserved for future extensions. Drivers and applications must set the array to zero.

v4l2_dv_timings
struct v4l2_dv_timings

__u32

type

Type of DV timings as listed in DV Timing types.

union {

(anonymous)

struct v4l2_bt_timings

bt

Timings defined by BT.656/1120 specifications

__u32

reserved[32]

}

DV Timing types

Timing type

value

Description

V4L2_DV_BT_656_1120

0

BT.656/1120 timings

DV BT Timing standards

Timing standard

Description

V4L2_DV_BT_STD_CEA861

The timings follow the CEA-861 Digital TV Profile standard

V4L2_DV_BT_STD_DMT

The timings follow the VESA Discrete Monitor Timings standard

V4L2_DV_BT_STD_CVT

The timings follow the VESA Coordinated Video Timings standard

V4L2_DV_BT_STD_GTF

The timings follow the VESA Generalized Timings Formula standard

V4L2_DV_BT_STD_SDI

The timings follow the SDI Timings standard. There are no horizontal syncs/porches at all in this format. Total blanking timings must be set in hsync or vsync fields only.

DV BT Timing flags

Flag

Description

V4L2_DV_FL_REDUCED_BLANKING

CVT/GTF specific: the timings use reduced blanking (CVT) or the ‘Secondary GTF’ curve (GTF). In both cases the horizontal and/or vertical blanking intervals are reduced, allowing a higher resolution over the same bandwidth. This is a read-only flag, applications must not set this.

V4L2_DV_FL_CAN_REDUCE_FPS

CEA-861 specific: set for CEA-861 formats with a framerate that is a multiple of six. These formats can be optionally played at 1 / 1.001 speed to be compatible with 60 Hz based standards such as NTSC and PAL-M that use a framerate of 29.97 frames per second. If the transmitter can’t generate such frequencies, then the flag will also be cleared. This is a read-only flag, applications must not set this.

V4L2_DV_FL_REDUCED_FPS

CEA-861 specific: only valid for video transmitters or video receivers that have the V4L2_DV_FL_CAN_DETECT_REDUCED_FPS set. This flag is cleared otherwise. It is also only valid for formats with the V4L2_DV_FL_CAN_REDUCE_FPS flag set, for other formats the flag will be cleared by the driver.

If the application sets this flag for a transmitter, then the pixelclock used to set up the transmitter is divided by 1.001 to make it compatible with NTSC framerates. If the transmitter can’t generate such frequencies, then the flag will be cleared.

If a video receiver detects that the format uses a reduced framerate, then it will set this flag to signal this to the application.

V4L2_DV_FL_HALF_LINE

Specific to interlaced formats: if set, then the vertical frontporch of field 1 (aka the odd field) is really one half-line longer and the vertical backporch of field 2 (aka the even field) is really one half-line shorter, so each field has exactly the same number of half-lines. Whether half-lines can be detected or used depends on the hardware.

V4L2_DV_FL_IS_CE_VIDEO

If set, then this is a Consumer Electronics (CE) video format. Such formats differ from other formats (commonly called IT formats) in that if R’G’B’ encoding is used then by default the R’G’B’ values use limited range (i.e. 16-235) as opposed to full range (i.e. 0-255). All formats defined in CEA-861 except for the 640x480p59.94 format are CE formats.

V4L2_DV_FL_FIRST_FIELD_EXTRA_LINE

Some formats like SMPTE-125M have an interlaced signal with a odd total height. For these formats, if this flag is set, the first field has the extra line. Else, it is the second field.

V4L2_DV_FL_HAS_PICTURE_ASPECT

If set, then the picture_aspect field is valid. Otherwise assume that the pixels are square, so the picture aspect ratio is the same as the width to height ratio.

V4L2_DV_FL_HAS_CEA861_VIC

If set, then the cea861_vic field is valid and contains the Video Identification Code as per the CEA-861 standard.

V4L2_DV_FL_HAS_HDMI_VIC

If set, then the hdmi_vic field is valid and contains the Video Identification Code as per the HDMI standard (HDMI Vendor Specific InfoFrame).

V4L2_DV_FL_CAN_DETECT_REDUCED_FPS

CEA-861 specific: only valid for video receivers, the flag is cleared by transmitters. If set, then the hardware can detect the difference between regular framerates and framerates reduced by 1000/1001. E.g.: 60 vs 59.94 Hz, 30 vs 29.97 Hz or 24 vs 23.976 Hz.