I wonder, how it is possible to have vertical scrolling in bottom part of a split screen. It is said in the docs that writes in Y scroll register only applied in the beginning of a frame and can't be changed mid-frame, and emulators acts accordingly, so you can't just change Y scroll after split.
Together with PPU_ADDR registers it is easy to get split screen with vertical scroll in the upper part and static bottom part. It does not work vice versa because of the reason mentioned above, and PPU_ADDR only allow to set vertical position at a character row, not a pixel row.
However, there are examples that it is possible to have static upper part with vertical scrolling in the bottom part, like in Ninja Gaiden 3 (vertical part of first level). Is some trick was used there to achieve the result?
Together with PPU_ADDR registers it is easy to get split screen with vertical scroll in the upper part and static bottom part. It does not work vice versa because of the reason mentioned above, and PPU_ADDR only allow to set vertical position at a character row, not a pixel row.
However, there are examples that it is possible to have static upper part with vertical scrolling in the bottom part, like in Ninja Gaiden 3 (vertical part of first level). Is some trick was used there to achieve the result?