How to play different songs on different acts (Sonic 1)

Everyone's hack was using different songs in different acts (think Sonic 1 Megamix and Sonic 1 Remastered, just to name two), and I wanted to add this feature to my soniNeko as well, so I searched the forums and the wiki for a guide or something. With much surprise, I found nothing. So I tried to do it by myself, and I'm happy to say that I succeeded! Yep guys, my first ASM edit all by myself! To be honest, I had to ask Puto what bhi.s does (since I didn't know if it was involved in the music process), but that's pretty much it, ASM isn't as hard as it seems!

So here is the result of my work, to use with the ASM68K version of Hivebrain's split disassembly.

STEP 1: REORGANIZE THE PLAYLISTS
In the disassembly, misc\muslist1.bin is used as the "normal playlist", while misc\muslist2.bin is used when invincibility wears off. This is redundant, not to mention gay, since those playlist are identical, but muslist1.bin has an extra byte for Final Zone + a 00 to make it even. Try to put an invincibility monitor in Final Zone, and when it's done you'll get Scrap Brain music. We don't want that. Delete muslist1.bin, and make FOUR copies of muslist2.bin, named muslist1.bin to muslist4.bin . Each of them should be 6 bytes long: 81 82 83 84 85 86. Save them in this way for now, we're going to edit them later.
Now the playlists have a different meaning: muslist1.bin contains the song played on the act 1 of each zone, muslist2.bin contains acts 2, etc. Muslist4.bin isn't really needed, but it will be handy. Keep on reading to find why.

STEP 2: CHANGE THE PLAYLISTS IN THE ASM TO REFLECT THE NEW ORGANIZATION
Go here:

Code (ASM):

1. MusicList:  incbin  misc\muslist1.bin
2.         even

And change it to:

Code (ASM):

1. MusicList1: incbin  misc\muslist1.bin
2.         even
3. MusicList2: incbin  misc\muslist2.bin
4.         even
5. MusicList3: incbin  misc\muslist3.bin
6.         even
7. MusicList4: incbin  misc\muslist4.bin
8.         even

Then go here:

Code (ASM):

1. MusicList2: incbin  misc\muslist2.bin
2.         even

And delete it. Of course I'm not talking about the one I just told you to add, there is one much below (look for "Music to play after invincibility wears off").

STEP 3: CHANGE THE CODE THAT PICKS THE SONG AT THE BEGINNING OF THE ACT
We're now going to use the act byte ($FFFFFE11) to load the correct playlist. Then we'll pick the entry from the playlist according to the zone byte ($FFFFFE10).
Go to Level_GetBgm. It should look like:

Code (ASM):

1. Level_GetBgm:
2.         tst.w   ($FFFFFFF0).w
3.         bmi.s   loc_3946
4.         moveq   #0,d0
5.         move.b  ($FFFFFE10).w,d0
6.         cmpi.w  #$103,($FFFFFE10).w ; is level SBZ3?
7.         bne.s   Level_BgmNotLZ4 ; if not, branch
8.         moveq   #5,d0       ; move 5 to d0
9.  
10. Level_BgmNotLZ4:
11.         cmpi.w  #$502,($FFFFFE10).w ; is level FZ?
12.         bne.s   Level_PlayBgm   ; if not, branch
13.         moveq   #6,d0       ; move 6 to d0
14.  
15. Level_PlayBgm:
16.         lea (MusicList).l,a1 ; load music playlist
17.         move.b  (a1,d0.w),d0    ; add d0 to a1
18.         bsr.w   PlaySound   ; play music
19.         move.b  #$34,($FFFFD080).w ; load title card object

Replace it with:

Code (ASM):

1. ; NineKode begins here - How to play different songs on different acts
2.  
3. Level_GetBgm:
4.         tst.w   ($FFFFFFF0).w
5.         bmi.w   loc_3946    ; change from bmi.s to bmi.w or you'll get an error
6.         moveq   #0,d0
7.         move.b  ($FFFFFE10).w,d0
8.  
9.         cmpi.b  #$0,($FFFFFE11).w   ; is this act 1?
10.         bne.s   Level_GetBgm2   ; if not, branch
11.         lea (MusicList1).l,a1   ; load Music Playlist for Acts 1
12.         bra.s   Level_PlayBgm   ; go to PlayBgm
13.  
14. Level_GetBgm2:
15.         cmpi.b  #$1,($FFFFFE11).w   ; is this act 2?
16.         bne.s   Level_GetBgm3   ; if not, branch
17.         lea (MusicList2).l,a1   ; load Music Playlist for Acts 2
18.         bra.s   Level_PlayBgm   ; go to PlayBgm
19.  
20. Level_GetBgm3:
21.         cmpi.b  #$2,($FFFFFE11).w   ; is this act 3?
22.         bne.s   Level_GetBgm4   ; if not, branch
23.         lea (MusicList3).l,a1   ; load Music Playlist for Acts 3
24.         bra.s   Level_PlayBgm   ; go to PlayBgm
25.  
26. Level_GetBgm4:
27.         cmpi.b  #$3,($FFFFFE11).w   ; is this act 4?
28.         bne.s   Level_PlayBgm   ; if not, branch
29.         lea (MusicList4).l,a1   ; load Music Playlist for Acts 4
30.  
31. Level_PlayBgm:
32.         move.b  (a1,d0.w),d0    ; get d0-th entry from the playlist
33.         bsr.w   PlaySound   ; play music
34.         move.b  #$34,($FFFFD080).w ; load title card object
35.  
36. ; NineKode ends here

STEP 4: CHANGE THE CODE THAT PICKS THE SONG WHEN INVINCIBILITY WEARS OFF
Remember, the check after the invincibility wears off is done in another section of the code. If you don't fix it, you'll get a wrong song. We just need to copy and paste the code used above, of course with different labels. So, go here:

Code (ASM):

1. Obj01_ChkInvin:
2.         tst.b   ($FFFFFE2D).w   ; does Sonic have invincibility?
3.         beq.s   Obj01_ChkShoes  ; if not, branch
4.         tst.w   $32(a0)     ; check time remaining for invinciblity
5.         beq.s   Obj01_ChkShoes  ; if no time remains, branch
6.         subq.w  #1,$32(a0)  ; subtract 1 from time
7.         bne.s   Obj01_ChkShoes
8.         tst.b   ($FFFFF7AA).w
9.         bne.s   Obj01_RmvInvin
10.         cmpi.w  #$C,($FFFFFE14).w
11.         bcs.s   Obj01_RmvInvin
12.         moveq   #0,d0
13.         move.b  ($FFFFFE10).w,d0
14.         cmpi.w  #$103,($FFFFFE10).w ; check if level is SBZ3
15.         bne.s   Obj01_PlayMusic
16.         moveq   #5,d0       ; play SBZ music
17.  
18. Obj01_PlayMusic:
19.         lea (MusicList2).l,a1
20.         move.b  (a1,d0.w),d0
21.         jsr (PlaySound).l   ; play normal music

And replace it with:

Code (ASM):

1. ; Second part of the NineKode. Play different music on different acts - after invincibility wears off
2.  
3. Obj01_ChkInvin:
4.         tst.b   ($FFFFFE2D).w   ; does Sonic have invincibility?
5.         beq.w   Obj01_ChkShoes  ; if not, branch    ; change to beq.w
6.         tst.w   $32(a0)     ; check time remaining for invinciblity
7.         beq.w   Obj01_ChkShoes  ; if no time remains, branch    ; change to beq.w
8.         subq.w  #1,$32(a0)  ; subtract 1 from time
9.         bne.w   Obj01_ChkShoes  ; change to bne.w
10.         tst.b   ($FFFFF7AA).w
11.         bne.w   Obj01_RmvInvin  ; change to bne.w
12.         cmpi.w  #$C,($FFFFFE14).w
13.         bcs.w   Obj01_RmvInvin  ; change to bcs.w
14.         moveq   #0,d0
15.         move.b  ($FFFFFE10).w,d0
16.  
17.         cmpi.b  #$0,($FFFFFE11).w   ; is this act 1?
18.         bne.s   Obj01_GetBgm2   ; if not, branch
19.         lea (MusicList1).l,a1   ; load Music Playlist for Acts 1
20.         bra.s   Obj01_PlayMusic ; go to PlayMusic
21.  
22. Obj01_GetBgm2:
23.         cmpi.b  #$1,($FFFFFE11).w   ; is this act 2?
24.         bne.s   Obj01_GetBgm3   ; if not, branch
25.         lea (MusicList2).l,a1   ; load Music Playlist for Acts 2
26.         bra.s   Obj01_PlayMusic ; go to PlayMusic
27.  
28. Obj01_GetBgm3:
29.         cmpi.b  #$2,($FFFFFE11).w   ; is this act 3?
30.         bne.s   Obj01_GetBgm4   ; if not, branch
31.         lea (MusicList3).l,a1   ; load Music Playlist for Acts 3
32.         bra.s   Obj01_PlayMusic ; go to PlayMusic
33.  
34. Obj01_GetBgm4:
35.         cmpi.b  #$3,($FFFFFE11).w   ; is this act 4?
36.         bne.s   Obj01_PlayMusic ; if not, branch
37.         lea (MusicList4).l,a1   ; load Music Playlist for Acts 4
38.  
39. Obj01_PlayMusic:
40.         move.b  (a1,d0.w),d0
41.         jsr (PlaySound).l   ; play normal music
42.  
43. ; NineKode ends here.

And now you're going to get the correct music even after invincibility wears off. But there is one more istance we need to change or we're going to have problems in Labyrinth Zone after the countdown...

STEP 5: CHANGE THE CODE THAT PICKS THE SONG AFTER THE COUNTDOWN
Go here:

Code (ASM):

1. ResumeMusic:                ; XREF: Obj64_Wobble; Sonic_Water; Obj0A_ReduceAir
2.         cmpi.w  #$C,($FFFFFE14).w
3.         bhi.s   loc_140AC
4.         move.w  #$82,d0     ; play LZ music
5.         cmpi.w  #$103,($FFFFFE10).w ; check if level is 0103 (SBZ3)
6.         bne.s   loc_140A6
7.         move.w  #$86,d0     ; play SBZ music
8.  
9. loc_140A6:
10.         jsr (PlaySound).l

And replace it with:

Code (ASM):

1. ResumeMusic:                ; XREF: Obj64_Wobble; Sonic_Water; Obj0A_ReduceAir
2.         cmpi.w  #$C,($FFFFFE14).w
3.  
4. ; Third section of the NineKode - Play correct music after the countdown (if you breathe)
5.  
6.         bhi.w   loc_140AC   ; change to bhi.w!
7.  
8.         cmpi.b  #$0,($FFFFFE11).w   ; is this act 1?
9.         bne.s   Air_GetBgm2 ; if not, branch
10.         lea (MusicList1).l,a1   ; load Music Playlist for Acts 1
11.         bra.s   Air_PlayMusic   ; go to PlayMusic
12.  
13. Air_GetBgm2:
14.         cmpi.b  #$1,($FFFFFE11).w   ; is this act 2?
15.         bne.s   Air_GetBgm3 ; if not, branch
16.         lea (MusicList2).l,a1   ; load Music Playlist for Acts 2
17.         bra.s   Air_PlayMusic   ; go to PlayMusic
18.  
19. Air_GetBgm3:
20.         cmpi.b  #$2,($FFFFFE11).w   ; is this act 3?
21.         bne.s   Air_GetBgm4 ; if not, branch
22.         lea (MusicList3).l,a1   ; load Music Playlist for Acts 3
23.         bra.s   Air_PlayMusic   ; go to PlayMusic
24.  
25. Air_GetBgm4:
26.         cmpi.b  #$3,($FFFFFE11).w   ; is this act 4?
27.         bne.s   Air_PlayMusic   ; if not, branch
28.         lea (MusicList4).l,a1   ; load Music Playlist for Acts 4
29.  
30. Air_PlayMusic:
31.         move.b  1(a1),d0    ; load entry $1 from the playlist
32.  
33. loc_140A6:
34.         jsr (PlaySound).l
35.  
36. ; NineKode ends here

As you see the code is always the same, recycled each and every time.
Now if you try to build your ROM you'll see that it works flawlessy! Well, you're still going to get the same songs, because of how we created the playlists, but if you change a byte in a playlist you'll see that it works.
There is only one more small fix to do to make it perfect btw...

STEP 6: FIX THE PLAYLIST ENTRIES FOR SCRAP BRAIN 3 AND FINAL ZONE
You know that Scrap Brain 3 is actually Labyrinth 4, and Final Zone is actually Scrap Brain 3. Way to confuse people.
So, hex edit playlist4.bin and change the 82 to 86. Hex edit playlist3.bin and change the 86 to 8D.
Now your ROM should sound exactly as before, except that you're given the chance to pick different songs on different acts!
Playlist4.bin is also useful if you plan to add acts 4 to other zones, so keep it, it's not a great waste of space.

STEP 7: FIND 12 MORE SONGS :P
Good luck on that. Now that I have the code working I can't find good songs D:
You might also need to know how to extend the playlist entries, but I didn't get that far yet.

For now, I'm really, really happy about this code as it's the very first time I challenge myself with 68K ASM. :D
Now comments plz.

 

There is something to say about this section (and the two equivalent ones), as I forgot to mention this the last time:

Code (ASM):

1. Level_GetBgm4:
2.         cmpi.b  #$3,($FFFFFE11).w   ; is this act 4?
3.         bne.s   Level_PlayBgm   ; if not, branch
4.         lea (MusicList4).l,a1   ; load Music Playlist for Acts 4
5.  
6. Level_PlayBgm:
7.         move.b  (a1,d0.w),d0    ; get d0-th entry from the playlist
8.         bsr.w   PlaySound   ; play music
9.         move.b  #$34,($FFFFD080).w ; load title card object

The cmpi.b and the bne.s aren't really needed, as that's the last chance anyway. I left them in my code for "artistic" reasons, but you can (and you should) definitely remove them. Especially because the day you have act 5 and that condition is true, there will be no playlist loaded and the game won't be happy about it.

 

Bah, I'm still using my code. It looks easier to me.