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The Super FX co-processor was built into games cartridges such as Star Fox, Yoshi's Island and Doom. It was used for sprite transformations in Yoshi's Island and 3D effects in Star Fox and Doom, as well as for rendering polygons.

This was a RISC (Reduced Instruction Set Computing) processor used in addition to the SNES CPU, which implies that the chip was specialised for certain tasks. As there were fewer instructions, the chip could more easily be optimised for these instructions. What specific tasks was the Super FX designed and used for?

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    RISC doesn't stand for "Reduced Instruction Set Chip", and doesn't imply specialization. For example, SPARC and MIPS are general purpose RISC architectures. – Leo B. Feb 12 '17 at 5:14
  • @LeoB. Is this better? – wizzwizz4♦ Feb 12 '17 at 8:43
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    Somewhat. RISC processors aren't really specialized for certain tasks (unlike DSP processors you might have in mind); having a substantially simpler (but less compact) instruction set architecture, RISC processors don't need much chip real estate dedicated to instruction decoding or complex state machines; instead, more gates can be used to implement frequent instructions efficiently, e.g. 32-bit ADD/SUB in one clock cycle, and MUL in fewer than a typical CISC processor of the day. When it only has to run matrix multiplication in a tight loop, code compactness doesn't matter, and RISC wins. – Leo B. Feb 12 '17 at 9:17
  • @LeoB. if I'm not mistaken, the 6502 itself (and 65816) were also examples of RISC based architectures. Or at least the beginning foundations of RISC processors. – cbmeeks Feb 13 '17 at 15:07
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    @cbmeeks That "the first RISC μP" title today would be called a clickbait. It is totally unsubstantiated and there is no reference to it in the text. – Leo B. Feb 13 '17 at 23:19
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The main tasks were:

  • Emulation of a bitmap framebuffer for the SNES. The SNES is tile-based, which means plotting arbitrary lines, polygons etc. and filling them with color or a pattern isn't easy. The Super FX had enough RAM on the cartridge to use it as a framebuffer, and it can then DMA transfer it to the SNES video RAM.

  • Faster 16-bit math operations, including multiplication, necessary for 3D and 2D rendering. The Super FX is a custom 16-bit RISC chip running at up to 21 MHz, so it can easily outperform the main CPU on these tasks.

So it's very similar to what a GPU does in more modern graphics cards. Still, it has a pretty general instruction set, so in theory one could use it for everything.

This page has lots of detailed information on registers and the instruction set.

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    Wow, never occurred to me that this thing would provide a framebuffer like that, but it makes perfect sense! – Matt Lacey♦ Feb 14 '17 at 4:45

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