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Sonic 2 Nick Arcade disassembly

Discussion in 'Engineering & Reverse Engineering' started by drx, Dec 3, 2006.

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  1. Dec 3, 2006 #1
    drx

    drx

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    :rolleyes:
  2. Dec 3, 2006 #2
    Lath

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    Nice going DRX, let's see who the first to port over the wall crashing thing to S2 final XD

    Oh, pin please.
     
  3. Dec 3, 2006 #3
    Hivebrain

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    Nice work! I'll have a good look at this tomorrow.

    If you mean labels, I'm changing a lot of them for the next S1 disassembly.
     
  4. Dec 3, 2006 #4
    Rika Chou

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    Awesome, I will be looking though this later for sure. Thanks drx!
     
  5. Dec 3, 2006 #5
    Dracula

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    Nice work! How did you dig this up so fast? =P
     
  6. Dec 3, 2006 #6
    Weird Person

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    Nice. Very interesting!

    Code from ROM: (Vertical Blank code...)

    Code (Text):
    1.         move.l  #$C0000000,4(a1)
    2.         move.l  (a0)+,(a1)
    3.         move.l  (a0)+,(a1)
    4.         move.l  (a0)+,(a1)
    5.         move.l  (a0)+,(a1)
    6.         move.l  (a0)+,(a1)
    7.         move.l  (a0)+,(a1)
    8.         move.l  (a0)+,(a1)
    9.         move.l  (a0)+,(a1)
    10.         move.l  (a0)+,(a1)
    11.         move.l  (a0)+,(a1)
    12.         move.l  (a0)+,(a1)
    13.         move.l  (a0)+,(a1)
    14.         move.l  (a0)+,(a1)
    15.         move.l  (a0)+,(a1)
    16.         move.l  (a0)+,(a1)
    17.         move.l  (a0)+,(a1)
    18.         move.l  (a0)+,(a1)
    19.         move.l  (a0)+,(a1)
    20.         move.l  (a0)+,(a1)
    21.         move.l  (a0)+,(a1)
    22.         move.l  (a0)+,(a1)
    23.         move.l  (a0)+,(a1)
    24.         move.l  (a0)+,(a1)
    25.         move.l  (a0)+,(a1)
    26.         move.l  (a0)+,(a1)
    27.         move.l  (a0)+,(a1)
    28.         move.l  (a0)+,(a1)
    29.         move.l  (a0)+,(a1)
    30.         move.l  (a0)+,(a1)
    31.         move.l  (a0)+,(a1)
    32.         move.l  (a0)+,(a1)
    33.         move.l  (a0)+,(a1)
    Yuji Naka isn't the organized programmer I tough he was. =P
     
  7. Dec 3, 2006 #7
    StephenUK

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    Quackshot Disassembly
    Actually, that's done quite a few times in the S2 Final disassembly and is quicker to execute than looping over the same line X amount of times.
     
  8. Dec 3, 2006 #8
    Weird Person

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    I agree it's quicker, but the difference between a "dbra" loop and a lot of lines with the same instruction is desprezive, right?
     
  9. Dec 3, 2006 #9
    drx

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    :rolleyes:
    The whole wall crashing thingy is the Sonic_WallRecoil subroutine. And of course, you need to port the animation, frame and graphics.
     
  10. Dec 3, 2006 #10
    Quickman

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    Using my ninja context-fu I am predicting the content of this post, since "desprezive" did not translate.

    "I agree it's quicker, but isn't a dbra loop quicker?"

    The answer is no, a dbra loop is a lot slower in terms of processor cycles than just doing the same thing over and over the requisite number of times.
     
  11. Dec 3, 2006 #11
    Weird Person

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    Fixed.

    By the way, I hate you Quickman.
     
  12. Dec 3, 2006 #12
    drx

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    :rolleyes:
    Let me review the case:

    Using so many move.l:

    Each instruction takes 20 CPU cycles (3 read cycles, 2 write cycle). * 32 = 640 CPU cycles (96 read cycles and 64 write cycles).

    Now using dbra, the code would have to look like this:

    Code (Text):
    1.     move.w  #31,d1
    2. loop:
    3.     move.l  (a0)+,(a1)
    4.     dbra    d1,loop
    move.w #31,d1 - 8 cycles (2 read cycles, 0 write cycles)
    move.l (a0)+,(a1) - 640 cycles (96 read cycles and 64 write cycles), like above
    dbra d1,loop - 31 * branch taken timing - 310 cpu cycles (62 read cycles, 0 write cycles)
    branch not taken, counter expired - 14 cpu cycles, 3 read cycles, 0 write cycles.

    Let's sum it up:

    using dbra - 972 cpu cycles, 163 read cycles, 64 write cycles
    not using dbra - 640 CPU cycles, 96 read cycles and 64 write cycles.

    using dbra, you would waste 25% cpu cycles in total, and 70% read cycles. Remember, this is done during the VBlank - so the timing DOES count.

    Hope that clears the matter a little.
     
  13. Dec 3, 2006 #13
    Rika Chou

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    What would you recommend as the best assembeler to use for this?
     
  14. Dec 3, 2006 #14
    drx

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    :rolleyes:
    I use snams68k 2.1d. I know it's not the best one, but it works for me.

    I hear others use AS, but I haven't used it, so I can't tell you if it's good or not.

    Also, if you're using snasm68k, use this:

    snasm68k.exe -emax 0 -p -o ae- s2a.asm, s2a.bin
     
  15. Dec 3, 2006 #15
    ICEknight

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    Hm? What's this?
    Or did you mean SYZ?
     
  16. Dec 3, 2006 #16
    Quickman

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    Join the queue, please.
     
  17. Dec 3, 2006 #17
    drx

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    :rolleyes:
    Ice: I've updated the .rars, please redownload. That was an awful mistake on my part - it happened because I was thinking of something and wrote something else instead.
     
  18. Dec 3, 2006 #18
    SMTP

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    Nice description for object 10:

    Code (Text):
    1. Object 10 - Tails eating the master emerald
    =P
     
  19. Dec 3, 2006 #19
    Rika Chou

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    Ok, I will try sasm68k, cause I tried to use AS and it gave me a boatload of errors.
     
  20. Dec 3, 2006 #20
    Ambil

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    Excellent, drx. I bet this will uncover the mysteries we can't reach just by gameplay.

    A request for you, Hive. On your next release of the Sonic 1 disassembly, please name the splitted binary files so they can be directly replaced with the ones coming from a SonED2 hack. I use your disassembly for my hacking, and that would save the work of renaming files at every turn.

    Sig'd.
     
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