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HSYNC
PIXCLK
First Active HSYNC Cycle
Cfg_fid_skew_pos 1 =
number of cyles in post window
Cfg_fid_skew_precount = number of
cyles in pre window
Post Window Programmable Up to
64 Cycles, Minimum 1
Pre Window Programmable
Up to 63 Cycles, Minimum 0
Internal Modules
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150 SPRUHI7A – December 2012 – Revised June 2016
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High-Definition Video Processing Subsystem (HDVPSS)
1.2.8.2.5.5 Vertical Sync
Vertical Sync is used to indicate lines that are in the vertical blanking interval. The VSYNC also separates
fields or frames. To be spec compliant, VSYNC should be active for a few lines at the bottom of the
picture. The exact number of vertical blanking lines at the bottom depends on the specification for the
picture format (480i, 480p, 720p, 1080i, 1080p).
Likewise, the number of vertical blanking lines at the top of the picture depends on the video format
specification corresponding to the incoming picture.
In the VIP parser, lines associated with an Active VSYNC are stored in the vertical ancillary data buffers
using the ANC VPI port to the VPDMA. Lines without an Active VSYNC are stored in the active video
Luma and Chroma-pair buffers using the Y and UV VPI ports, respectively, to the VPDMA.
When using HSYNC signaling instead of ACTVID, the VSYNC signal may be derived from an analog
source such as an NTSC/PAL decoder. In this case, VSYNC may not transition on the exact cycle as
HSYNC. Thus, the VIP Parser supports a window region around HSYNC in which VSYNC transitions will
be detected. A VSYNC transition occurring within the window is identified the same way as if VSYNC
transitioned on the same cycle as HSYNC going active.
The window is defined by a pre-window, which is determined by the cfg_fid_skew_precount register.
There is also a post-window that is defined by cfg_fid_skew_postcount. Note that although the
configuration registers are named fid_skew, they are also used for defining the VSYNC transition window.
The window region definition is shown in
Figure 1-98 .
Figure 1-98. VSYNC Pre and Post Window
The results of VSYNC behavior in the transition window are shown in Figure 1-99 . A low to high transition
in the window is equivalent to VSYNC going low to high on the active HSYNC cycle.
Likewise, a high to low transition in the window is equivalent to VSYNC going high to low on the active
HSYNC cycle.
Two transitions of VSYNC within the VSYNC window is not allow and is undefined behavior.
If VSYNC is high throughout the transition window, then the HSYNC line is in vertical blanking.
If VSYNC is low throughout the transition window, then the HSYNC line is in active video.