DMA Masking - an alternative to modifying CHARBASE when vertically scrolling
Like with many other systems, a vertical scroll routine on the 7800 is a combination of fine-scrolling and coarse scrolling. The coarse scroll is just a straightforward change of data being displayed in each zone, so I won't talk about that. The fine scroll is where the interesting stuff happens.
The usual approach to fine-scroll upwards on the 7800 is to to decrease the height of a zone at the top of your scroll area, and correspondingly increase the height of a zone at the bottom o
I ran the test, and it's actually worse - you lose 3 cycles of DMA for sprites with graaphics that are in the hole. (in addition to the header dma, of course) Additional info is over in the 7800 Hardware Facts thread.
