cane of somaria gamebreaking bug, redux

wizzrobemaster discovered a bug, and posted about it on February 29th:
http://archive.is/9PDvc

sometime between May 7 and now, the thread got deleted.

i realize he had it in the wrong sub-forum, but it would have been better to simply move the topic instead, especially given it had new, valuable information.

anyway, here's the first post:

by wizzrobemaster on Mon 29 Feb 2016 - 1:06

i just discovered that if you use the cane of somaria in the entrance of room to hold down a switch and exit into world map (e.g skull woods big key entrance) when the block is still present to keep the door open, the game freezes. i tested this on the gba version and the game freezes instead of blacking out.

if this is still on the wrong subforum, let me know.  there are about 5 dedicated to hacking the game, yet i don't see a single one involving gameplay (and thus pre-bugfix bughunting on the vanilla game).

I tested this out and there is indeed a game-crash if you do this (ie place a cane of somaria block in that room of Skull woods to hold down the switch and exit). However nobody looked into this yet to fix it (will require ASM tracing to see what is happening and not many are able to do/fix this). I never knew about this bug, since you get the cane later in the game and probably wouldn't noticed this (since in practice no one will return to dungeon-3 after already finishing dungeon-6). This is probably why original authors missed this.

There are many such glitches you can do with the Cane of Somaria. It can also have several uses for a couple of speedrun categories.

Here's one use of it:

Another bug you can do with the Cane is to stand at a spot where all four beams from the block, when you destroy it, can stay on screen for a long time. Then you just spam the Y button and you can actually refill your magic. If you fill it up above the normal capacity, the magic meter will glitch out.

The reason is this ram
$0468[0x02] -   Flag that is set when trap doors are down.

So when the trap door is open it is the value 00 instead of 01. If you then leave the dungeon value 05 gets stored to $11 which makes the game crash. I think a code hijack is necessary to fix this.

This is the malcode:

Code:


$81/C579 EC 68 04    CPX $0468  [$80:0468]  A:0101 X:0001
$81/C57C F0 18      BEQ $18    [$C596]      A:0101 X:0001
$81/C57E 8E 68 04    STX $0468  [$80:0468] 


So it won't branch at BEQ $18 since the $0468 == 00

Ok the fix is the following (fastrom, no header):

Code:


lorom

org $82B7BB
JSL $8EFC70

org $8EFC70
LDA #$0F              
STA $10 ; repeat native code, closing spotlight routine
LDA #$01
STA $0468 ; reset trapdoor
RTL    



I hope this asm is ok, I am out of exercise,
here's the ips I tested and surely works (works also on PU, SePH, if needed):
(I will update the native fixes and all in asap

Ok, also updated the native zelda fixes
http://bszelda.zeldalegends.net/stuff/Con/native_zelda_fixes.zip

and the all-in patch with this fix:
http://bszelda.zeldalegends.net/stuff/Con/all-in_ips.zip

... and

i realize he had it in the wrong sub-forum, but it would have been better to simply move the topic instead, especially given it had new, valuable information.

Sorry for the deletion. I do not know who was responsible for this. Possibly because it was found by wizzrobemaster, who started getting...

i still can't believe i found this discovery. it happened when working on my open world hack. anyway thanks for acknowledging that i found it.

Hi hi hi there, long time no viddy wizzrobemaster!

I thought you were long gone and left up Zelda 3 editing for good. Without you and your endless questions this board as been forever more silent.

^^ but zelda 3 rom hacking is like a curse, you always come back for more even through you wanna leave. It never really ends!

i had no reason to return because of the backlog of so many new games. i am sure many found my absence to be more peaceful? i will continue my rom hack in the future. who knows maybe black magic will have another brief update when i go back.

Jepp, thank you
Though the fix is obviously for naught as the download number is still zero. Except people download it from the native fixes thread.

with this bug fix i can finally go back to using entrances that require the cane for weighted switches.