VIDIOC_G_DV_TIMINGS, VIDIOC_S_DV_TIMINGS — Get or set DV timings for input or output
int ioctl( | int fd, |
| int request, | |
struct v4l2_dv_timings *argp); |
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.
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
VIDIOC_ENUMINPUT does not set the V4L2_IN_CAP_DV_TIMINGS flag), then
ENODATA error code is returned.
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.
This ioctl is not supported, or the
VIDIOC_S_DV_TIMINGS parameter was unsuitable.
Digital video timings are not supported for this input or output.
The device is busy and therefore can not change the timings.
Table A.57. 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 (0) or interlaced (1) |
| __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 Table A.60, “DV BT Timing standards” for a list of standards. |
| __u32 | flags | Several flags giving more information about the format. See Table A.61, “DV BT Timing flags” for a description of the flags. |
Table A.58. struct v4l2_dv_timings
| __u32 | type | Type of DV timings as listed in Table A.59, “DV Timing types”. | |
| union | | ||
| struct v4l2_bt_timings | bt | Timings defined by BT.656/1120 specifications | |
| __u32 | reserved[32] |
Table A.60. 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 |
Table A.61. 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, the flag is cleared by receivers. 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, 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 also be cleared. |
| 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. |