https://github.com/crapola/air_buster_md_fix
IPS patch for Air Buster (Sega Genesis)
https://github.com/crapola/air_buster_md_fix
romhacking sega sega-genesis sega-mega-drive
Last synced: about 2 months ago
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IPS patch for Air Buster (Sega Genesis)
- Host: GitHub
- URL: https://github.com/crapola/air_buster_md_fix
- Owner: crapola
- Created: 2023-08-02T21:56:52.000Z (over 1 year ago)
- Default Branch: master
- Last Pushed: 2023-08-04T13:25:23.000Z (over 1 year ago)
- Last Synced: 2025-01-15T10:07:05.823Z (3 months ago)
- Topics: romhacking, sega, sega-genesis, sega-mega-drive
- Language: Python
- Homepage:
- Size: 1.95 KB
- Stars: 0
- Watchers: 1
- Forks: 0
- Open Issues: 0
-
Metadata Files:
- Readme: readme.md
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README
## Air Buster Fix
This is an IPS patch for **Air Buster** / **Aero Blasters** on the Sega Genesis that fixes the freeze in stages 4 and 5.
#### Detailed description
The bug happens in low gravity sections when you press too many directions at the same time (specifically left, down and right).\
The faulty function:
````
loc_0000D26A:
SUBQ.w #4, $1A(A1)
MOVE.w D1, D2
ANDI.b #$0F, D0
ASL.w #2, D0
JMP loc_0000D27A(PC,D0.l)
; Followed by 11 jump destinations.
````
At this point, D0's lower nibble contains input information in the form:
```
direction: RLDU
bit: 3210
```
There are 11 functions to jump to, so the valid range for D0 before alignment
is (0,10).\
A value of 10 corresponds to right (8) + down (2) which is probably the highest you could get using the original hardware. A modern emulator that doesn't filter "wrong" inputs makes it easy to exceed this value and cause a crash.