nesdev.org

> The progress is amazing. AFAICS there are only two mysteries left: Depends what you think is the goal of all of this. If the goal is to actually figure out the instruction set, there probably are some more opcodes that aren't used in the CIC code. If the goal is to figure out the algorithm used on...

> OK, so this is kind of groundbreaking and also great news for people who > would like to build small series of SNES dev carts or the likes. ;) > So, do any ROM dumps or die photographs exist of the D413A (PAL CIC)? I haven't seen any ROM dumps or die shots for those. They aren't needed though (ass...

> Thanks for taking the time to write that up. My pleasure, it was a wonderful ride. I hope this info is useful in some way. > Did you compare with the Tengen code, ala 'rosetta' style? Yes I did. The Tengen code isn't a 1-1 translation, it does some things in a different order, and it doesn't do mo...

> His second question was like yours: "Why does it use a polynomial > counter?" I told him my guess: a row of latches and an XNOR gate save > a few gates off the row of half adders that make a up a linear program > counter. Yes, it is actually only about half the area, which is worthwhile ...

I have posted an article at http://hackmii.com/2010/01/the-weird-and-wonderful-cic/ . It describes the architecture and instruction set of the CIC. I also posted disassemblies of the NES and SNES ROMs, and the source code for the disassembler (which is at http://git.infradead.org/users/segher/dis-ci...

> Did he reproduce this himself by looking at the IC chip, I couldn't get any good photos of the chip, I would love to see some. I reverse engineered this all from just the bits in the rom, and a lot of datasheet/patent archeology. Couldn't find the exact cpu fwiw. > or is this just based on my circ...

> Then please enlighten me

Hint: the fixed point of an LFSR is 0, and that is the start address here.

The correct name for this kind of thing is "polynomial counter".

> In other words, an LFSR program counter. No, it's not. > But of course, this would work only in a pure Harvard architecture, not the von Neumann architecture seen in an NES or the overall von Neumann architecture with Harvard implementation (often as a separate instruction cache) seen in modern CP...