Fix Rexon crash
From Sonic Retro
Revision as of 09:18, 6 March 2019 by Inferno Gear (Made the guide have no subsections, due to the tutorial being the same for both Xenowhirl and Github versions of the Sonic 2 disasm.)
(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:
loc_37454: bsr.w loc_3750C subq.b #1,objoff_2A(a0) bmi.s loc_37462 bra.w JmpTo39_MarkObjGone
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:
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
One more, go to "loc_37488:" and you should see this:
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
Again, "branch to subroutine - loc_3750C" is too early. So change it to this:
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
Done! The rexon crash will no longer happen.
|Fix Rexon crash]]