Walk Through Walls

[Whipon]

Hello to everyone!!!.
I tried to hack Zombies Ate My Neighbors, for the Sega Genesis, to make a Walk Through Walls code. The problem is that I don't know where to start.

I found the X and Y coordinates:
X Axys,
FF04F6,FF04F7

Y Axys,
FF04FA,FF04FB

The instruction that writes the coordinates is in $DC90

00DC90: 3D6E 00C4 002A             move.w  ($c4,A6), ($2a,A6)

I've also found the address for the first breakable plant wall (the one just above you on the first level).

First Wall,
FF5671

I tried comparing traces, one walking and another walking against a wall.
Then tried reads at diferent useless ram addresses (I searched with the character still, then walking against a wall) with no success.

I only need to know what is the basic method to make walk through walls codes, or how to make it for this game. Its the first time I attempt to make one of these codes and I'm lost in the proccess.

I'll really appreciatte any help or advice.

Thanks a lot.

Whipon.

[Pugsy]

You were within bytes of the code you needed to change as it happens, just a case of bra'ing past the jsr df78 so placing BRAs at DC3E & DCA4.

My method for this game was fairly basic...and so is my explanation (cheats only had basic testing - so may have side effects?)

trace zomb
walk left and right a bit without hitting any walls (to get enough code for later back tracing)
trace off
walk to the wall to you stop
wp ff0591,1,w (I found this address by RAM searching - it's related to the x coords, pretty much unimportant as it dropped me a mile away from the code that I needed to change as it transpired)
trace >>zomb (to continue the earlier trace)
wait a bit
move towards the wall
watchpoint hit (found the first hit didn't give me enough data so I continued the trace)
watchpoint hit again
trace off
backtraced and found "00DC42: jsr $df78.l" was being run
bra at dc3e to get pass it
Found could walk thro vertical walls but not horizontal walls
Had a quick look at code spotted another jsr $df78.l a bit later, bra'd passed that and found could walk through horizontal walls too



Zombies Ate My Neighbors (U) [c][!]
Walk Through Vertical Walls ADRA-AA38
Walk Through Horizontal Walls ADRA-AA7E

[Whipon]

Thank you very much

Thank you very much, Pugsy.
So basically, you searched for a ram address while moving freely, right?.
Then you maked a trace walking freely again, then another one walking against a wall, and then bactracked from the write ($DC90)?. I read your explanation severall times, but I think I don't understand it very well.
Thanks again for your help, I tried to do that the whole day yesterday without any luck :P.

[Pugsy]

So basically, you searched for a ram address while moving freely, right?.

Not really no, I searched earlier for a RAM location that was different whilst trying to walk then when walking in the open. Couldn't get one, so made do with what I did get. What I was trying to get was an address that I could wp to stop my trace as soon as the wall was hit....otherwise the longer you are walking into the wall before stopping a TRACE would just meant that backtracing could be a real nightmare.

Then you maked a trace walking freely again, then another one walking against a wall, and then bactracked from the write ($DC90)?. I read your explanation severall times, but I think I don't understand it very well.

No I just made a single trace file...I just stopped tracing to restart it latter into the same trace file, I then sprinkled some pixie dust on the big trace file and the addresses just popped right out

[MIR]

Ohh tell me the supplier of your Pixie dust and i will try and add it next to the hexbits in the GSHI mart : D

[Whipon]

=)

Well, thanks a lot for your help, these codes surelly rock!.