Fix Rexon crash
From Sonic Retro
Revision as of 21:29, 20 December 2015 by Scarred Sun (talk | contribs) (Text replacement - "</asm>" to "</syntaxhighlight>")
(Original guide by redhotsonic)
On Hill Top Zone, it is possible to crash the game when hitting Rexon (the plesiosaur-like badnik that sits in the lava). Conflicts in the code cause it to jump to a section of code earlier than it was meant to jump to. This results in invalid opcodes being processed and an eventual crash.
Go to "loc_37454:" and you should see this:
<asm> loc_37454:
bsr.w loc_3750C subq.b #1,objoff_2A(a0) bmi.s loc_37462 bra.w JmpTo39_MarkObjGone
</syntaxhighlight>
That "branch to subroutine - loc_3750C" is what is causing the problem. It's happening too early. We need to move that command down a little bit. So change it to this:
<asm> loc_37454:
subq.b #1,objoff_2A(a0) bmi.s loc_37462 bsr.w loc_3750C ; Now moved here to fix Rexon crash bra.w JmpTo39_MarkObjGone
</syntaxhighlight>
One more, go to "loc_37488:" and you should see this:
<asm> loc_37488:
bsr.w loc_3750C moveq #$10,d0 add.w d0,x_vel(a0) subq.b #1,objoff_2A(a0) bmi.s loc_374A0 bsr.w JmpTo26_ObjectMove bra.w JmpTo39_MarkObjGone
</syntaxhighlight>
Again, "branch to subroutine - loc_3750C" is too early. So change it to this:
<asm> loc_37488:
moveq #$10,d0 add.w d0,x_vel(a0) subq.b #1,objoff_2A(a0) bmi.s loc_374A0 bsr.w loc_3750C ; Now moved here to fix Rexon crash bsr.w JmpTo26_ObjectMove bra.w JmpTo39_MarkObjGone
</syntaxhighlight>
Done! The rexon crash will no longer happen.