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@plutiedev.com Do you have any insight as to why Sega's setup code (ICD_BLK4.PRG) does two dummy reads of the VDP control register (`move.w (a4), d0` after the TMSS check and `tst.w ($C00004)` right after the data table)?

Reading the status register resets the internal flags the VDP uses to keep track of which part of a command is being written. This is useful if the Reset button is pressed in the middle of the 68000 writing a longword command (i.e. first word was written but VDP is still waiting for the second word)