SNES: Sprites and backgrounds rendering

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To generate a pixel, the SNES needs to retrieve background and sprite descriptors, then get the actual color palette-index. Already the VRAM access time budget is blown up (4 x 100ns = 400ns) For each tilemap entry, the palette-index must be fetched from the referenced tile. To retrieve 4 pixels in one 16-bit read, the SNES mandates 4bpp background tile to be layout in yet another planar mode where two planes are stored in one byte. E.g.: Gorgeous raster effects where each lines of a layer is shifted differently during HBLANK as demonstrated in see Contra 3 below. Capcom PPUs, the CPS-A and CPS-B (from The Book of CP-System) The graphic pipeline relies on a massive 32-bit data bus, powered by dual-channel GFX ROMs.

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