Per VognsenMy recollection is that people implementing infinite smooth scrolling on the Amiga dealt with the wrap-around issue by replicating the streaming writes so that when you eventually reset the window to the opposite edge the data there is ready as an identical copy. On the NES it's usually assumed you do this via mappers in the carts (so you don't have to replicate the writes but can rely on address mirroring) but were there non-mapper-based smooth scrolling games on NES that replicated writes?
slembcke@pervognsen The addressing basically wraps around left to right and top to bottom (with some quirks on the vertical). You get enough VRAM for two screens worth of tiles, and there's just a pin that specifies if they are laid out vertically or horizontally.
That's why some games had mild glitches at the screen edges when doing 4 way scrolling. If you use the vertical layout for example, then there are no offscreen tiles to swap when scrolling left and right.