SA-1 is a Super Nintendo enhancement chip, commonly used to increase performance of games. Super Mario RPG: Legend of the Seven Stars and Kirby Super Star are some games that used this enhancement chip.
SA-1 are clocked at 10.74 MHz (4 times faster than SNES), or at 5.37 MHz if SNES and SA-1 tries to access the same area or if SA-1 accesses the BW-RAM (SRAM). Also SA-1 has a 2kB I-RAM inside chip that runs at 10.74 MHz to put own stack and it's the main Work RAM of SA-1. Like SNES, SA-1 uses the 65c816 architecture and has all the features that have SNES, such as DMA. Unlike other enhancement chip, SA-1 can have up to 8MB ROMs and both LoROM and HiROM. The SA-1 chip has been documented thoroughly in the SNES Developer Manual, book 2.
Because of high speed clock (10.74 MHz) and the architecture (65c816), SA-1 can be used in anything and with Character Conversion DMA, SA-1 can even rotate, scale or generate polygons. SA-1 can be used on Super Mario World, although it's not much used since the chip (and all other enhancement chip) can't access the WRAM and PPU registers that contains most of RAM Addresses of game.
- Not of all ROM can be accessed once. You need to switch certains banks to able access other parts of ROM.
- Again, the mapping of a SA-1 ROM is much different than a regular SNES game. If you don't program correctlly, you can access wrong area of ROM/RAM and thus creating crashes.
- SA-1 cannot access the WRAM and PPU registers. You must call the SNES CPU to access these addresses or use I-RAM and/or BW-RAM instead of WRAM.