=== Blocked VSYNC ===
On CRTC 0, if R7 is modified with the value of VLC VCC when HCC<2, we are in blocked VSYNC. Then, the VSYNC can no longer occur on VLCVCC=R7 until an unblocking condition is produced(VCC or R7 update). Source: §16.4 "Conditions to consider" of the CRTC Compendium
=== Ghost VSYNC ===