* Setting R0 to 0 will cause numerous issues that stem from the fact that VLC is frozen. As HCC never reaches 1, the logic that increments VLC is never triggered.
* The logic that triggers vertical adjustment is broken if R0<2.
* If R7 is modified with the value of VLC when HCC<2, we are in blocked VSYNC. Then, the VSYNC can no longer occur on VLC=R7 until an unblocking condition is produced. Source: §16.4 "Conditions to consider" of the CRTC Compendium
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