Walking function in sonic 2

I'm trying to add a walking function to sonic 2, so that when A is held, the variable for speed is changed to a lower value to effectivly make sonic walk, and when you let go of A, the value is reset. I've already disabled A from jumping.

The only problem I have is with the joypad support for it, I've commented out my current 'solution' which got A to enable walking and up to disable it. As you can imagine, this isn't exacly the best way to go about it.

Code (Text):

1. loc_1A2B8:
2.         bsr.w   loc_1AC3E
3.         bsr.w   loc_1AA38
4.         bsr.w   loc_1AD96
5.         bsr.w   loc_1A35A
6.         bsr.w   loc_1A9D2
7.         bsr.w   loc_1A974
8.     ;cmpi.b #$40,($FFFFF603).w; check if A is pressed
9.     ;beq.s  walk
10.     ;cmpi.b #$1,($FFFFF603).w; check if up is pressed
11.     ;beq.s  run
12.         jsr sub_163AC
13.         bsr.w   loc_1E234
14.         bsr.w   loc_1AE08
15.  
16. locret_1A2DE:
17.         rts
18.  
19. walk:
20.         move.w  #$400,(Sonic_top_speed).w; new speed
21.         cmpi.w  #0,$14(a0); check sonic is moving
22.         beq.s   nwalk
23.         btst    #0,$22(a0); check direction
24.         bne.s   walkl
25.         move.w  #$300,$14(a0); right; if sonic is running, slow him down
26.         rts
27.  
28. walkl:
29.         move.w  #-$300,$14(a0); left
30.         rts
31.  
32. nwalk:
33.         rts
34.  
35. run:
36.         move.w  #$600,(Sonic_top_speed).w ; reset speed
37.     ;walkwalkwalk
38.         rts

 

Hmm, that doesn't work, sonic stays rooted to the spot.

Also, shouldn't ($FFFFF602).w be used instead?

 

Took me a while, but I got it working.

Now, sonic walks when you hold A

Code (Text):

1. loc_1A2B8:
2.         bsr.w   loc_1AC3E
3.         bsr.w   loc_1AA38
4.         bsr.w   loc_1AD96
5.         bsr.w   loc_1A35A
6.         bsr.w   loc_1A9D2
7.         bsr.w   loc_1A974
8.         btst #6,($FFFFF605).w; check if A is pressed
9.         bne.s   walk
10.         bsr.w run
11.         jsr sub_163AC
12.         bsr.w   loc_1E234
13.         bsr.w   loc_1AE08
14.  
15. locret_1A2DE:
16.         rts
17.  
18. walk:
19.         move.w  #$400,(Sonic_top_speed).w; slow him down
20.         cmpi.w  #0,$14(a0); check sonic is moving
21.         beq.s   nwalk
22.         btst    #0,$22(a0); check direction
23.         bne.s   walkl
24.         move.w  #$300,$14(a0); right
25.         rts
26.  
27. walkl:
28.         move.w  #-$300,$14(a0); left
29. nwalk:
30.         rts
31.  
32. run:
33.         btst #6,($FFFFF602).w; check if A is still held
34.         bne.s   rwalk; if so, don't reset the speed
35.         move.w  #$600,(Sonic_top_speed).w;reset speed
36. rwalk:
37.         rts
38. ; End of subroutine loc_1A26E

To disable A from jumping, replace;

Code (Text):

1. andi.b  #$70,d0

with;

Code (Text):

1. andi.b  #$30,d0

This works, because;

A = $40
B = $10
C = $20

A + B + C = $70

B + C = $30

Thanks to upthorn for that little gem.

 

Well, if sonic's speed is modified to $F00 or similar, it makes it quite hard to do certain things with precision.

I'm going to do that in my hack, so I found it useful.