User:PostNES

Mapper ideas

• CHR hardware scrolling unit
  • Scrolls portions of pattern table with wrapping for hardware accelerated parallax effects
    • implementation: two CHR ROMs with alternately stored tiles (VRAM address %0AAAAA AAAcBBBB -> ROM %c, address in ROM %AAAAAAAABBBB) for parallel fetching of pixel rows

• CHR color remapping unit
  • ExGraphix-like, with each byte in ExRAM storing a color index (0-3) to be remapped to in a character, for every source color index (0-3). This would allow to conserve some palette/CHR-ROM space in some cases.
    Example:

ExRAM byte = %01010000, or 1100 in quaternary system: remap 0 to 0, 1 to 0, 2 to 1, 3 to 1

Original character:
.defchr $00000000,
        $02233200,
        $02100120,
        $03000030,
        $03333310,
        $03000030,
        $03000030,
        $03222210

Remapped:
.defchr $00000000,
        $01111100,
        $01000010,
        $01000010,
        $01111100,
        $01000010,
        $01000010,
        $01111100

• DPCM converter
  • Converts any on-cartridge audio to DPCM and returns it to CPU on sample reads so that there's audio expansion on NES!
    • DMC rate control would coarsely alter pitch if the conversion rate is constant

• DPCM hardware mixer
  • Plays back (by returning to CPU on sample read) multiple samples at different speeds