How To Port the Sonic 2 Clone Driver into Sonic 2 HG Dissasembly

There are a few bugs I have noticed. One is that the spindash sound will not raise pitch. The music is not a perfect adaptation of Sonic 2's music, particularly sometimes the PSG channels sound slightly different. This is most noticable in Emerald Hill's music. Besides this, there are no problems.

If the above bugs will not bother you too badly, then you'll like using the Sonic 2 Clone Driver after working with Sonic 2's own sound driver. The Clone Driver is much easier to port music to, and in fact, Sonic 1 music can even just be bincluded into the ROM. This is because it's based on the Sonic 1 sound driver, and uses similar (if not the same) formatting.

With this out of the way, now it's time to edit the Sonic 2 HG Dissasembly!

Step 1 - getting started
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Back up your dissasembly if you haven't already.

To start, go into your sound folder, where you'll have a DAC folder, a music folder, and a PCM folder.

DELETE THEM ALL!

and then extract "Sonic 2 Clone Driver_fixed.7z" into the main folder of your dissasembly.

And then open up s2.sounddriver.asm, we're going to delete a lot of data from it.

Find zMasterPlaylist and delete the following lines:

Code (Text):

1. ; zbyte_11F5h:
2. zMasterPlaylist:
3.  
4. ; Music IDs
5. offset :=   MusicPoint2
6. ptrsize :=  2
7. idstart :=  80h
8. ; note: +20h means uncompressed, here
9. ; +40h is an (ignored) flag, possibly to force PAL mode on/off
10.  
11. zMusIDPtr_2PResult: db  id(MusPtr_2PResult) ; 92
12. zMusIDPtr_EHZ:      db  id(MusPtr_EHZ)      ; 81
13. zMusIDPtr_MCZ_2P:   db  id(MusPtr_MCZ_2P)   ; 85
14. zMusIDPtr_OOZ:      db  id(MusPtr_OOZ)      ; 8F
15. zMusIDPtr_MTZ:      db  id(MusPtr_MTZ)      ; 82
16. zMusIDPtr_HTZ:      db  id(MusPtr_HTZ)      ; 94
17. zMusIDPtr_ARZ:      db  id(MusPtr_ARZ)      ; 86
18. zMusIDPtr_CNZ_2P:   db  id(MusPtr_CNZ_2P)   ; 80
19. zMusIDPtr_CNZ:      db  id(MusPtr_CNZ)      ; 83
20. zMusIDPtr_DEZ:      db  id(MusPtr_DEZ)      ; 87
21. zMusIDPtr_MCZ:      db  id(MusPtr_MCZ)      ; 84
22. zMusIDPtr_EHZ_2P:   db  id(MusPtr_EHZ_2P)   ; 91
23. zMusIDPtr_SCZ:      db  id(MusPtr_SCZ)      ; 8E
24. zMusIDPtr_CPZ:      db  id(MusPtr_CPZ)      ; 8C
25. zMusIDPtr_WFZ:      db  id(MusPtr_WFZ)      ; 90
26. zMusIDPtr_HPZ:      db  id(MusPtr_HPZ)      ; 9B
27. zMusIDPtr_Options:  db  id(MusPtr_Options)  ; 89
28. zMusIDPtr_SpecStage:    db  id(MusPtr_SpecStage)    ; 88
29. zMusIDPtr_Boss:     db  id(MusPtr_Boss)     ; 8D
30. zMusIDPtr_EndBoss:  db  id(MusPtr_EndBoss)  ; 8B
31. zMusIDPtr_Ending:   db  id(MusPtr_Ending)   ; 8A
32. zMusIDPtr_SuperSonic:   db  id(MusPtr_SuperSonic)   ; 93
33. zMusIDPtr_Invincible:   db  id(MusPtr_Invincible)   ; 99
34. zMusIDPtr_ExtraLife:    db  id(MusPtr_ExtraLife)+20h; B5
35. zMusIDPtr_Title:    db  id(MusPtr_Title)    ; 96
36. zMusIDPtr_EndLevel: db  id(MusPtr_EndLevel) ; 97
37. zMusIDPtr_GameOver: db  id(MusPtr_GameOver)+20h ; B8
38. zMusIDPtr_Continue: db  (MusPtr_Continue-MusicPoint1)/ptrsize   ; 0
39. zMusIDPtr_Emerald:  db  id(MusPtr_Emerald)+20h  ; BA
40. zMusIDPtr_Credits:  db  id(MusPtr_Credits)+20h  ; BD
41. zMusIDPtr_Countdown:    db  id(MusPtr_Drowning)+40h ; DC
42. zMusIDPtr__End:

Then go to zDACMasterPlaylist, and delete these:

Code (Text):

1.     db  id(zDACPtr_Sample1),17h     ; 81h
2.     db  id(zDACPtr_Sample2),1       ; 82h
3.     db  id(zDACPtr_Sample3),6       ; 83h
4.     db  id(zDACPtr_Sample4),8       ; 84h
5.     db  id(zDACPtr_Sample5),1Bh     ; 85h
6.     db  id(zDACPtr_Sample6),0Ah     ; 86h
7.     db  id(zDACPtr_Sample7),1Bh     ; 87h
8.     db  id(zDACPtr_Sample5),12h     ; 88h
9.     db  id(zDACPtr_Sample5),15h     ; 89h
10.     db  id(zDACPtr_Sample5),1Ch     ; 8Ah
11.     db  id(zDACPtr_Sample5),1Dh     ; 8Bh
12.     db  id(zDACPtr_Sample6),2       ; 8Ch
13.     db  id(zDACPtr_Sample6),5       ; 8Dh
14.     db  id(zDACPtr_Sample6),8       ; 8Eh
15.     db  id(zDACPtr_Sample7),8       ; 8Fh
16.     db  id(zDACPtr_Sample7),0Bh     ; 90h
17.     db  id(zDACPtr_Sample7),12h     ; 91h

Step 2 - Deleting broken references
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Now open up s2.asm, and search for the line "; end of 'ROM'" near the end of your dissasemby.

On the empty line before it, past this:

Code (Text):

1.   include "Sonic 2 Clone Driver.asm"
2.   even

After this, search for "SoundIndex:", and delete everything for it, up to and including "SndPtr__End:"
Now there are many unused sounds, Sound20 - Sound70 in the dissasembly that will be unused. If you wish, delete those too, as they will only take space.

Once you've done that, locate "MusicPoint2:", and delete that, and everything below it it until the following line:

Code (Text):

1.     if * > soundBankStart + $8000

Leave this line and everything below it alone for the time being.

Now find the line

Code (Text):

1. ; loc_F1E8C:

Below this line is where the Sega sound is included. If we delete it, we will get errors. If we leave I, we will get errors. So what do we do? Change it!
Replace this:

Code (Text):

1. ; -------------------------------------------------------------------------------
2. ; Sega Intro Sound
3. ; 8-bit unsigned raw audio at 16Khz
4. ; -------------------------------------------------------------------------------
5. ; loc_F1E8C:
6. Snd_Sega:   BINCLUDE    "sound/PCM/SEGA.bin"
7. Snd_Sega_End:
8.  
9.     if Snd_Sega_End - Snd_Sega > $8000
10.         fatal "Sega sound must fit within $8000 bytes, but you have a $\{Snd_Sega_End-Snd_Sega} byte Sega sound."
11.     endif
12.     if Snd_Sega_End - Snd_Sega > Size_of_SEGA_sound
13.         fatal "Size_of_SEGA_sound = $\{Size_of_SEGA_sound}, but you have a $\{Snd_Sega_End-Snd_Sega} byte Sega sound."
14.     endif

With this:

Code (Text):

1. ; loc_F1E8C:
2. Snd_Sega:   rts
3. Snd_Sega_End:

Now, we need to delete the old BINCLUDEd DAC samples. Got to loc_ED100, or SndDAC_Start.
Staring at line "; loc_ED100:", delete everything down to (But not including) this chunk of code.

Code (Text):

1. ; --------------------------------------------------------------------
2. ; Nemesis compressed art (20 blocks)
3. ; Buzzer's fireball
4. ArtNem_Buzzer_Fireball: BINCLUDE    "art/nemesis/Fireball 1 (Buzzer).bin"
5. ; --------------------------------------------------------------------

That is art used in the game, so obviously we don't want that to get deleted.

Right above if, you will also see this line:

Code (Text):

1.     cnop -Size_of_DAC_samples, $8000

You need to delete that too.

Finally, search for sub_EC000, or "SoundDriverLoad", which will look like this:

Code (Text):

1. ; ---------------------------------------------------------------------------
2. ; Subroutine to load the sound driver
3. ; ---------------------------------------------------------------------------
4. ; sub_EC000:
5. SoundDriverLoad:
6.     move    sr,-(sp)
7.     movem.l d0-a6,-(sp)
8.     move    #$2700,sr
9.     lea (Z80_Bus_Request).l,a3
10.     lea (Z80_Reset).l,a2
11.     moveq   #0,d2
12.     move.w  #$100,d1
13.     move.w  d1,(a3) ; get Z80 bus
14.     move.w  d1,(a2) ; release Z80 reset (was held high by console on startup)
15. -   btst    d2,(a3)
16.     bne.s   -   ; wait until the 68000 has the bus
17.     jsr DecompressSoundDriver(pc)
18.     btst    #0,(VDP_control_port+1).l   ; check video mode
19.     sne (Z80_RAM+zPalModeByte).l    ; set if PAL
20.     move.w  d2,(a2) ; hold Z80 reset
21.     move.w  d2,(a3) ; release Z80 bus
22.     moveq   #$E6,d0
23. -   dbf d0,-    ; wait for 2,314 cycles
24.     move.w  d1,(a2) ; release Z80 reset
25.     movem.l (sp)+,d0-a6
26.     move    (sp)+,sr
27.     rts

Delete the whole thing, as it will now do nothing but cause an error.

Step 3 - Replace a bunch of stuff.
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Search for the routine VintRet (Search for "VintRet:"), and you'll have something like this:

Code (Text):

1. VintRet:
2.     addq.l  #1,(Vint_runcount).w
3.     movem.l (sp)+,d0-a6
4.     rte

Replace it with this:

Code (Text):

1. VintRet:
2.     jsr Init_Sonic1_Sound_Driver    ; init Sonic 1 sound driver
3.     addq.l  #1,(Vint_runcount).w
4.     movem.l (sp)+,d0-a6
5.     rte

Next, go to JmpTo_SoundDriverLoad, and find all of this:

Code (Text):

1. JmpTo_SoundDriverLoad
2.  
3.     nop
4.  
5.     jmp (SoundDriverLoad).l
6. ; End of function JmpTo_SoundDriverLoad
7.  
8. ; ===========================================================================
9.  
10. ; unused mostly-leftover subroutine to load the sound driver
11.  
12. ; SoundDriverLoadS1:
13.     move.w  #$100,(Z80_Bus_Request).l ; stop the Z80
14.     move.w  #$100,(Z80_Reset).l; reset the Z80
15.     lea (Z80_RAM).l,a1
16.     move.b  #$F3,(a1)+
17.     move.b  #$F3,(a1)+
18.     move.b  #$C3,(a1)+
19.     move.b  #0,(a1)+
20.     move.b  #0,(a1)+
21.     move.w  #0,(Z80_Reset).l
22.     nop
23.     nop
24.     nop
25.     nop
26.     move.w  #$100,(Z80_Reset).l ; reset the Z80
27.     move.w  #0,(Z80_Bus_Request).l ; start the Z80
28.     rts

and replace it like this:

Code (Text):

1. JmpTo_SoundDriverLoad
2.     move.w  #$100,(Z80_Bus_Request).l ; stop the Z80
3.     move.w  #$100,(Z80_Reset).l ; reset the Z80
4.     lea (Kos_Z80).l,a0
5.     lea (Z80_RAM).l,a1
6.     bsr.w   KosDec
7.     move.b  #$F3,(a1)+
8.     move.b  #$F3,(a1)+
9.     move.b  #$C3,(a1)+
10.     move.b  #0,(a1)+
11.     move.b  #0,(a1)+
12.     move.w  #0,(Z80_Reset).l
13.     nop
14.     nop
15.     nop
16.     nop
17.     move.w  #$100,(Z80_Reset).l ; reset the Z80
18.     move.w  #0,(Z80_Bus_Request).l ; start the Z80
19.     rts

Next, find PlayMusic, which should look like this this:

Code (Text):

1. ; sub_135E:
2. PlayMusic:
3.     tst.b   (Music_to_play).w
4.     bne.s   +
5.     move.b  d0,(Music_to_play).w
6.     rts
7. +
8.     move.b  d0,(Music_to_play_2).w
9.     rts
10. ; End of function PlayMusic

And replace it with this:

Code (Text):

1. ; sub_135E:
2. PlayMusic:
3. ;   tst.b   ($FFFFFFE0).w
4. ;   bne.s   +
5. ;   move.b  d0,($FFFFFFE0).w
6.     move.b  d0,($FFFFF00A).w
7.     rts
8. +
9.     move.b  d0,($FFFFF00A).w
10.     rts
11. ; End of function PlayMusic

Right beneath that should be PlaySound. Replace PlaySound with this:

Code (Text):

1. ; sub_1370
2. PlaySound:
3.     move.b  d0,($FFFFF00B).w
4.     rts
5. ; End of function PlaySound

Now we need to change PlaySoundStereo, which should be right beath PlaySound.
Replace it with this:

Code (Text):

1. ; sub_1376:
2. PlaySoundStereo:
3.     bra.s   PlayMusic   ; skip over routine (For S1 driver)
4.     move.b  d0,(SFX_to_play_2).w
5.     rts
6. ; End of function PlaySoundStereo

Now PlaySoundLocal is the next thing to edit, and again, it should be right below PlaySoundStereo.
Replace it with this:

Code (Text):

1. ; sub_137C:
2. PlaySoundLocal:
3.     tst.b   render_flags(a0)
4.     bpl.s   +
5.     move.b  d0,($FFFFF00B).w
6. +
7.     rts

Below this is the routine PauseGame. Rather than replacing that entire routine, we are simply going to find this:

Code (Text):

1. +
2.     move.w  #1,(Game_paused).w  ; freeze time
3.     move.b  #MusID_Pause,(Music_to_play).w  ; pause music

And replace it with this:

Code (Text):

1. +
2.     move.w  #1,(Game_paused).w  ; freeze time
3.     move.b  #1,($FFFFF003).w    ; pause music

Now go to Pause_Resume, which should look like this:

Code (Text):

1. ; loc_13F2:
2. Pause_Resume:
3.     move.b  #MusID_Unpause,(Music_to_play).w

Replace it with this:

Code (Text):

1. ; loc_13F2:
2. Pause_Resume:
3.     move.b  #$80,($FFFFF003).w

Now, find Pause_SlowMo, which should be this:

Code (Text):

1. ; loc_1400:
2. Pause_SlowMo:
3.     move.w  #1,(Game_paused).w
4.     move.b
5.     #MusID_Unpause,(Music_to_play).w
6.     rts

Replace it with the following:

Code (Text):

1. ; loc_1400:
2. Pause_SlowMo:
3.     move.w  #1,(Game_paused).w
4.     move.b  #1,($FFFFF003).w
5.     rts

Next, find SpecialStage_Unpause, which should be this:

Code (Text):

1. ; loc_541A:
2. SpecialStage_Unpause:
3.     move.b  #MusID_Unpause,(Music_to_play).w
4.     move.b  #8,(Vint_routine).w
5.     bra.w   WaitForVint

And replace it with this:

Code (Text):

1. ; loc_541A:
2. SpecialStage_Unpause:
3.     move.b  #1,($FFFFF003).w
4.     move.b  #8,(Vint_routine).w
5.     bra.w   WaitForVint

Finally, we're going to do something that will clean up some RAM for us later in the guide.
Do a search and replace (Usually CTRL+H) for "Underwater_palette_2". Replace all with "Underwater_palette".
I don't know why the game used two different section for underwater palettes, but I've done this change in my hack and it did no harm.

We're done with the first part of this guide! Try to build your Rom, and you'll get some errors! Fun!
Next up, we'll be fixing these errors.

Step 4 - Break it until it's fixed!
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If you look at the log, you'll see a lot of errors like this one:

> > >Sonic 2 Clone Driver.asm(42): error: unknown opcode
> > > INCBIN
> > > PSG7: incbin sound\psg7.bin

Luckily, this is a simple fix. Open up Sonic 2 Clone Driver.asm, anf find and replace (CRTL+H usually) all instances of "INCBIN" with "BINCLUDE" (Without the quotes, obviously).

Now repeat the process, replacing all intances of "@loc" with "Lloc". The HG dissasembly does not like local routines, so this converts them into normal routines to avoid errors.

Save the file, and compile the ROM again. I got 437 errors, and of course, they need to be fixed as well.

On the bright side, you can close s2.asm and Sonic 2 Clone Driver.asn, they are all fixed.

Step 5 - Strippers
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Re-Open s2.sounddriver.asm, because we need to strip it down even more.

Find zDACPtrTbl, and delete everything down to the line "idstart := 81h"

Go to "zBankSwitchToMusic:", and delete the contents of that routine.(Everything between "zBankSwitchToMusic:" and "ret"
Go to "zUpdateDAC:" and again delete everything down to "ret".

Now find this line:

Code (Text):

1. ensure1byteoffset macro maxsize

Delete everything between that and endm, but leave those two lines, otherwise you will get errors.

If you build the ROM now, you will get 393 errors, but almost all of these are duplicates or fixed just by fixing another.
Don't close s2.sounddriver.asm just yet, we'll be stripping more content from that later. Right now however, we're going to fix the bulk of these errors.

Step 6 - Identity Crisis
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Open s2.constants.asm. 393 is a lot of errors, but all it takes to fix them is a copy+paste job for you.

Find the line "; Music IDs". You'll see this:

Code (Text):

1. ; Music IDs
2. offset :=   zMasterPlaylist
3. ptrsize :=  1
4. idstart :=  $81
5. ; $80 is reserved for silence, so if you make idstart $80 or less,
6. ; you may need to insert a dummy zMusIDPtr in the $80 slot

delete everything from there down to "MusID__End = id(zMusIDPtr__End) ; A0", and paste the following where it used to be:

Code (Text):

1. ; Music IDs
2. offset :=   MusicIndex
3. ptrsize :=  1
4. idstart :=  $81
5. ; $80 is reserved for silence, so if you make idstart $80 or less,
6. ; you may need to insert a dummy zMusIDPtr in the $80 slot
7.  
8. MusID__First =          idstart
9. MusID_2PResult =    $81
10. MusID_EHZ =             $82
11. MusID_MCZ_2P =          $83
12. MusID_OOZ =             $84
13. MusID_MTZ =             $85
14. MusID_HTZ =             $86
15. MusID_ARZ =             $87
16. MusID_CNZ_2P =          $88
17. MusID_CNZ =             $89
18. MusID_DEZ =             $8A
19. MusID_MCZ =             $8B
20. MusID_EHZ_2P =          $8C
21. MusID_SCZ =             $8D
22. MusID_CPZ =             $8E
23. MusID_WFZ =             $8F
24. MusID_HPZ =             $90
25. MusID_Options =         $91
26. MusID_SpecStage =   $92
27. MusID_Boss =            $93
28. MusID_EndBoss =         $94
29. MusID_Ending =          $95
30. MusID_SuperSonic =  $96
31. MusID_Invincible =  $97
32. MusID_ExtraLife =   $98
33. MusID_Title =           $99
34. MusID_EndLevel =    $9A
35. MusID_GameOver =    $9B
36. MusID_Continue =    $9C
37. MusID_Emerald =         $9D
38. MusID_Credits =         $9E
39. MusID_Countdown =   $9F
40. MusID__End   =      $A0

The music is all fixed, now all that's left is the sound effects:

Find the line "; Sound IDs", and delete everything down to the line "; Special sound IDs". Leve the special IDs alone.

In place of the text you deleted, just paste this:

Code (Text):

1. ; Sound IDs
2. offset :=   SoundIndex
3. ptrsize :=  2
4. idstart :=  $A0
5.  
6. SndID__First = idstart
7. SndID_Jump =                    $A0             ; A0
8. SndID_Checkpoint =          $A1             ; A1
9. SndID_SpikeSwitch =         $A2             ; A2
10. SndID_Hurt =                    $A3             ; A3
11. SndID_Skidding =            $A4             ; A4
12. SndID_BlockPush =           $A5             ; A5
13. SndID_HurtBySpikes =        $A6     ; A6
14. SndID_Sparkle =             $A7
15. SndID_Beep =                $A8
16. SndID_Bwoop =               $A9
17. SndID_Splash =              $AA
18. SndID_Swish =               $AB
19. SndID_BossHit =             $AC
20. SndID_InhalingBubble =      $AD
21. SndID_ArrowFiring =         $AE
22. SndID_LavaBall =            $AE
23. SndID_Shield =              $Af
24. SndID_LaserBeam =           $B0
25. SndID_Zap =                 $B1
26. SndID_Drown =               $B2
27. SndID_FireBurn =            $B3
28. SndID_Bumper =              $B4
29. SndID_Ring =                $B5     ; B5
30. SndID_RingRight =           $B5
31. SndID_SpikesMove =          $B6
32. SndID_Rumbling =            $B7
33. SndID_Smash =               $B9
34. SndID_DoorSlam =            $BB
35. SndID_SpindashRelease =     $BC     ; BC
36. SndID_Hammer =              $BD
37. SndID_Roll =                $BE
38. SndID_ContinueJingle =      $BF
39. SndID_CasinoBonus =         $C0
40. SndID_Explosion =           $C1
41. SndID_WaterWarning =        $C2
42. SndID_EnterGiantRing =      $C3
43. SndID_BossExplosion =       $C4
44. SndID_TallyEnd =            $C5
45. SndID_RingSpill =           $C6
46. SndID_Flamethrower =        $C8
47. SndID_Bonus =               $C9
48. SndID_SpecStageEntry =      $CA
49. SndID_SlowSmash =           $CB
50. SndID_Spring =              $CC
51. SndID_Blip =                $CD
52. SndID_RingLeft =            $B5
53. SndID_Signpost =            $CF
54. SndID_CNZBossZap =          $D0
55. SndID_Signpost2P =          $D3
56. SndID_OOZLidPop =               $D4
57. SndID_SlidingSpike =        $D5
58. SndID_CNZElevator =         $D6
59. SndID_PlatformKnock =       $D7
60. SndID_BonusBumper =         $D8
61. SndID_LargeBumper =         $D9
62. SndID_Gloop =               $DA
63. SndID_PreArrowFiring =      $DB
64. SndID_Fire =                $DC
65. SndID_ArrowStick =          $DD
66. SndID_Helicopter =          $DE
67. SndID_SuperTransform =      $DF
68. SndID_SpindashRev =         $E0
69. SndID_Rumbling2 =           $E1
70. SndID_CNZLaunch =           $E2
71. SndID_Flipper =             $E3
72. SndID_HTZLiftClick =        $E4
73. SndID_Leaves =              $E5
74. SndID_MegaMackDrop =        $E6
75. SndID_DrawbridgeMove =      $E7
76. SndID_QuickDoorSlam =       $E8
77. SndID_DrawbridgeDown =      $E9
78. SndID_LaserBurst =          $EA
79. SndID_Scatter =             $EB
80. SndID_LaserFloor =          $EB
81. SndID_Teleport =            $EC
82. SndID_Error =               $ED
83. SndID_MechaSonicBuzz =      $EE
84. SndID_LargeLaser =          $EF
85. SndID_OilSlide =            $F0
86. SndID__End  =           $F7

Step 7 - I am Error
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Now we are going back to s2.sounddriver.asm.
There are 4 more errors here.
As before, we're going to solve this by simply emptying out the relavent routines. We can't just delete stuff because a few things in it are still going to be referenced.
So the first Routine to clean out is zDACAfterDur. change that and remove zloc_22A inside it so it looks like this:

Code (Text):

1. zDACAfterDur:
2.     ret

There is one more routine to empty. That routine is zloc_78E, or zBGMLoad. Starting at this line:

Code (Text):

1. zBGMLoad:

delete everything down to here:

Code (Text):

1.     ; End of DAC/FM init, begin PSG init

And there you have it! Close s2.sounddriver.asm, Build you ROM and test it!

Additional Step
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Uh-oh! if you've played up to Chemical Plant Zone Act 2, you'll notice the driver crashes on that level!

This is because of water. In Sonic 2, the underwater palettes are stored in a section of RAM that is now used by the sound driver, because it's based on Sonic 1's sound driver.
What we need to do now is relocate the water palette table in RAM, so the Sound Driver can do what it likes. I am going to assume you haven't modified the RAM allocation in your hack here, and go step by step. If you have modifying the RAM in your game, you are probably on your own.

Let's go back to s2.constants.asm, and find these lines:

Code (Text):

1. Underwater_palette_2:       ds.w palette_line_size  ; not sure what it's used for but it's only used when there's water
2. Underwater_palette_2_line2: ds.w palette_line_size
3. Underwater_palette_2_line3: ds.w palette_line_size
4. Underwater_palette_2_line4: ds.w palette_line_size
5.  
6. Underwater_palette:     ds.w palette_line_size  ; main palette for underwater parts of the screen
7. Underwater_palette_line2:   ds.w palette_line_size
8. Underwater_palette_line3:   ds.w palette_line_size
9. Underwater_palette_line4:   ds.w palette_line_size
10.  
11.                 ds.b    $500    ; $FFFFF100-$FFFFF5FF ; unused, leftover from the Sonic 1 sound driver (and used by it when you port it to Sonic 2)
12.  

The last four lines before the ds.b $500 are used by the sound driver now, in addition to the 500 that is labeled as such.

Replace all of the above lines with this:

Code (Text):

1.             ds.b  $100  ; Sonic 1 Sound Driver
2.                     ds.b    $500    ; Sonic 1 Sound Driver

After doing that, you will need to find at least $80 free bytes in RAM (besides the space we just put in)
Fortunately, there is an area of RAM that has $C0 free bytes, and that is where the four lines we lost will go. Search for this:

Code (Text):

1. CNZ_saucer_data:

And you will see this:

Code (Text):

1. CNZ_saucer_data:        ds.b    $40 ; the number of saucer bumpers in a group which have been destroyed. Used to decide when to give 500 points instead of 10
2.                 ds.b    $C0 ; $FFFFE740-$FFFFE7FF ; unused as far as I can tell
3. Ring_Positions:         ds.b    $600

Replace it with this:

Code (Text):

1. CNZ_saucer_data:        ds.b    $40 ; the number of saucer bumpers in a group which have been destroyed. Used to decide when to give 500 points instead of 10
2. Underwater_palette:     ds.w palette_line_size  ; main palette for underwater parts of the screen
3. Underwater_palette_line2:   ds.w palette_line_size
4. Underwater_palette_line3:   ds.w palette_line_size
5. Underwater_palette_line4:   ds.w palette_line_size
6.                 ds.b    $40 ; $FFFFE740-$FFFFE7FF ; unused as far as I can tell
7. Ring_Positions:         ds.b    $600

Build it, and test!

The sega sound will be glitched up, and you can fix it by following this link. Everything that needs to be fixed will be in "Sonic 2 Clone Driver.asm".
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Credits
Varion Icaria - Puto's sound driver port.
Esrael - Tweakers driver port, plus fixes for things broken in Puto's port, such as hanging on the title card. Extra thanks for fixing the Sega sound.
Puto - Fixes for underwater palette stuff, as well as special stage ring stuff, and various other fixes.
StephenUK - Hints on how to fix the underwater stuff.
drx - Hacking CulT's VDP calculator.
Tweaker - Wrote the orignal guide to port Sonic 1's sound driver into Sonic 2.
ValleyBell - lots of miscallanious help to get this to work, as well as worked on the Sonic 2 Clone Driver.
ShadowsofYesterday - Telling me the fix for the SEGA sound.
Caverns4 - I wrote this guide!



I'm posting this here because I wanted to get some input on improvements I can make, or changes I need to make before posting a How-To on the Wiki. If anyone has any suggestions or help, I would appreciate it very much. One other thing I wasnt cleared up is the credits - did I miss anyone?

 

Alright, since it's been here a while with no response, I'm working off the assumption that everything is fine, and and I have posted the guide on the Wiki here:

http://info.sonicretro.org/Port_the_Sonic_2_Clone_Sound_Driver_to_the_HG_version_of_Sonic_2

I forgot the "SCHG How-To:" prefix, so I don't know if anyone is capable of editing page titles, but I would appreciate it. I thought is was added automatically to How-to's.

Again though, if there are any other issues with this guide, feel free to let me know.

 

Thank you very much!

There is one more thing I noticed.

under the table for SCHG How-To Guide: Sonic the Hedgehog 2 (16-bit) atthe bottom of the page, my guide doesn't appear on there. It should be there under "Extending the Game". What's wrong?

 

Odd, it doesn't show for me... Does a page not show in lists for the creator or something?