In this explanation, HS means HS or VS or DE.
We first introduced “glitch filtering” to remove single bit pulses in control signals due to noise. HS in most cases is sent in every frame and one frame could get corrupted, resulting in HS changing, then the next frame would be correct and HS would change back. If HS is corrupted like this the image will be corrupted, so use glitch filtering.
There are corruption cases where this mechanism does not detect the problem, such as when an HS transition gets corrupted, HS transition is delayed by one bit because this is not detected as a glitch. Also, when we introduced HVEN on some parts glitch filtering is not applicable.
Now we have “tracking” for control signals. HS is measured and the lengths of low and high are stored. The next 3 lines are measured and if they are the same, HS tracker locks and HS is output. Now the HS will be output the same for every line, regardless of any corruption. If 3 successive lines are corrupted, the tracker will unlock and start again measuring HS. This detects a much larger range of issues and works with HVEN.