[Sonic 1 Github]: MSU-MD Implementation (Follow it at your own risk)

Hello! It's been a while since I made guides for this site. So it was about time to do it.

A few years ago, Sonic hacks began to appear, which included the ability to play CD quality music in the game. (Although they have been developing since the last decade)

Many still don't know how to do this, and decide to install modifications to the DAC Channel to use PCM music, which when making a larger hack rom ends up being a space inconvenience in the long term.

So if you are one of those people who want CD quality music without spending so much space on a rom without mappers for Sonic 1, this is your guide.

Quick explanation of what MSU-MD is:

MSU-MD is a driver that is installed on Sega Genesis games to enable Sega CD Mode 1. In short, it gives the game access to use the Sega CD. BUT only for music.

If you want to access more features of the Sega CD through a Sega Genesis cartridge, I recommend you look elsewhere because I won't teach you how to turn on Mode 1 completely here.

With that explained we can now move on to the guide itself:

This guide is very prone to failure so it is only recommended if you want to try and fail constantly

Installing the Driver:

You don't have to be a genius to know what to do in a first step like this
I'll also be basing this Sonic 1 mod disassembly for this guide.

Now the installation starts inside the game:
After:

Code:

ZoneCount:    equ 6    ; discrete zones are: GHZ, MZ, SYZ, LZ, SLZ, and SBZ

We will insert:

Code:

; MSU-MD vars
HW_version        EQU    $A10001                    ; hardware version in low nibble
                                            ; bit 6 is PAL (50Hz) if set, NTSC (60Hz) if clear
                                            ; region flags in bits 7 and 6:
                                            ;         USA NTSC = $80
                                            ;         Asia PAL = $C0
                                            ;         Japan NTSC = $00
                                            ;         Europe PAL = $C0
MCD_STAT:       equ $A12020                 ; 0-ready, 1-init, 2-cmd busy
MCD_CMD:        equ $A12010
MCD_ARG:        equ $A12011
MCD_CMD_CK:     equ $A1201F
v_LAST_MSU      equ $FFF60E

In EntryPoint. Right after the label we will insert this:

Code:

        btst    #$6,(HW_version).l          ; Check for PAL or NTSC, 0=60Hz, 1=50Hz
        bne.s    jmpLockout                    ; if !=0, branch to lockout
      
        jsr     MSUMD_DRV
        tst.b     d0                            ; if 1: no CD Hardware found
        bne.s    jmpLockout                    ; if no, branch to lockout
        move.w     #($1500|255),MCD_CMD        ; Set CD Volume to MAX
        addq.b     #1,MCD_CMD_CK                 ; Increment command clock
      
        bra.s   msuOK                       ; skip jmpLockout
      
jmpLockout:
        jmp     msuLockout

msuOK:

With this we would only need to include this at the end of the file:

Code:

MSUMD_DRV:  binclude  "sound\msu-drv.bin"
        even
      
msuLockout:     binclude "msuLockout.bin"
        even

Although we still have a long way to go, so let's continue.

Initialize it in Game Modes:

I'm going to remove the mentions on GM_Sega since they are not very relevant and can disable the Sega Scream

In GM_Title we should comment:

Code:

        move.b    #bgm_Title,d0
        bsr.w    PlaySound_Special    ; play title screen music

and instead put:

Code:

        jsr     msuPlayTrack_10

Later we will see how to make the game detect if there is an active Sega CD to keep the FM songs.

In Level_FadeDemo just after the label we will put this:

Code:

        jsr     msuStop

In Gm Special I commented the following:

Code:

        move.w    #bgm_SS,d0
        bsr.w    PlaySound    ; play special stage BG    music

and instead put:

Code:

        jsr     msuPlayTrack_09

In loc_47D4 I commented the following:

Code:

        move.w    #bgm_GotThrough,d0
        jsr    (PlaySound_Special).l     ; play end-of-level music

and instead put:

Code:

     jsr     msuPlayTrack_14

And finally, in GM_Ending put this after bgm_Stop:

Code:

        jsr msuStop

Don't delete the code we just mentioned yet. It will be useful later...

There are still several steps left so keep going.

Modifying the Sound Driver from the inside
This will be the shortest of the guide but still. Pay attention.

In .backupramloop Before:

Code:

        move.b    #$80,f_1up_playing(a6)

put this:

Code:

        jsr     msuStop

In .nextpsg Before:

Code:

        clr.b    f_1up_playing(a6)

put this:

Code:

        jsr     msuResume

With that, it's done. You just need to modify a few more files and the MSU-MD is ready.

Modifying more files (I want to kill myself. This guide became too long for me)
In PauseGame.asm which is located in _inc. Right in Pause_StopGame we will add this:

Code:

        jsr msuStop

In the same file only in Pause_EndMusic We will add this too:

Code:

        jsr msuResume

in GotThroughAct. Commented This:

Code:

        move.w    #bgm_GotThrough,d0
        jsr    (PlaySound_Special).l    ; play "Sonic got through" music

And Put This:

Code:

        jsr     msuPlayTrack_14

On Sonic Display Add this:

Code:

        move.b    #0,(v_shoes).w    ; This Not
        jsr     msuRestoreTrackSpeed     ; This yes

And Comment This:

Code:

        jmp    (PlaySound).l    ; run music at normal speed

Modifying Sub PlaySound
This will probably be the biggest code we will have to do. Pay close attention to what follows as it will be quite complicated in points.

First let's comment on this line:

Code:

        move.b    d0,(v_snddriver_ram+v_soundqueue0).w

Just Below That. We do this:

Code:

        jsr     findAndPlayTrack

With that we copy the modified disassembly routine just below the "rts"

Spoiler: Very large code

Code:

findAndPlayTrack:
        cmp.b   #$80,d0                 ; Stop MSU Sounds
        beq     msuStop
        cmp.b   #$81,d0                 ; Green Hill Zone
        beq     msuPlayTrack_01
        cmp.b   #$82,d0                 ; Labyrinth Zone
        beq     msuPlayTrack_02
        cmp.b   #$83,d0                 ; Marble Zone
        beq     msuPlayTrack_03
        cmp.b   #$84,d0                 ; Star Light Zone
        beq     msuPlayTrack_04
        cmp.b   #$85,d0                 ; Spring Yard Zone
        beq     msuPlayTrack_05
        cmp.b   #$86,d0                 ; Scrap Brain Zone
        beq     msuPlayTrack_06
        cmp.b   #$87,d0                 ; Invincibility
        beq     msuPlayTrack_07
        ;cmp.b   #$88,d0                 ; Extra Life
        ;beq     msuPlayTrack_08
        cmp.b   #$89,d0                 ; Special Stage
        beq     msuPlayTrack_09
        cmp.b   #$8A,d0                 ; Title Screen
        beq     msuPlayTrack_10
        cmp.b   #$8B,d0                 ; Ending
        beq     msuPlayTrack_11
        cmp.b   #$8C,d0                 ; Boss
        beq     msuPlayTrack_12
        cmp.b   #$8D,d0                 ; Final Zone
        beq     msuPlayTrack_13
        cmp.b   #$8E,d0                 ; Sonic Got Through
        beq     msuPlayTrack_14
        cmp.b   #$8F,d0                 ; Game Over
        beq     msuPlayTrack_15
        cmp.b   #$90,d0                 ; Continue Screen
        beq     msuPlayTrack_16
        cmp.b   #$91,d0                 ; Credits
        beq     msuPlayTrack_17
        cmp.b   #$92,d0                 ; Drowning
        beq     msuPlayTrack_18
        cmp.b   #$93,d0                 ; Get Emerald
        beq     msuPlayTrack_19
        ; track 20                      ; Seegaaa
 
        rts

Just after the PlaySoundSpecial routine ends and before the Unused Play Sound. We paste this:

Spoiler: Other Big Code

Code:

msuPlayTrack_01:                        ; Green Hill Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_21                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_01
      
    move.w  #($1200|1),MCD_CMD          ; send cmd: play track #1, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$81,(v_LAST_MSU)
    rts
  
msuPlayTrack_02:                        ; Labyrinth Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_22                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_02
      
    move.w  #($1200|2),MCD_CMD          ; send cmd: play track #2, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$82,(v_LAST_MSU)
    rts
  
msuPlayTrack_03:                        ; Marble Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_23                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_03
      
    move.w  #($1200|3),MCD_CMD          ; send cmd: play track #3, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$83,(v_LAST_MSU)
    rts
  
msuPlayTrack_04:                        ; Star Light Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_24                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_04
      
    move.w  #($1200|4),MCD_CMD          ; send cmd: play track #4, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$84,(v_LAST_MSU)
    rts
  
msuPlayTrack_05:                        ; Spring Yard Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_25                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_05
      
    move.w  #($1200|5),MCD_CMD          ; send cmd: play track #5, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$85,(v_LAST_MSU)
    rts
  
msuPlayTrack_06:                        ; Scrap Brain Zone
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_26                ; if yes, branch to play fast track

    tst.b   MCD_STAT
    bne.s   msuPlayTrack_06
      
    move.w  #($1200|6),MCD_CMD          ; send cmd: play track #6, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$86,(v_LAST_MSU)
    rts
  
msuPlayTrack_07:                        ; Invincibility
    tst.b    (v_shoes).w                    ; does Sonic have speed    shoes?
    bne.w    msuPlayTrack_27                ; if yes, branch to play fast track
      
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_07
      
    move.w  #($1100|7),MCD_CMD          ; send cmd: play track #7, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    ;move.b  #$87,(v_LAST_MSU)
    rts
  
msuPlayTrack_08:                        ; Extra Life
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_08
      
    move.w  #($1100|8),MCD_CMD          ; send cmd: play track #8, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_09:                        ; Special Stage
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_09
      
    move.w  #($1200|9),MCD_CMD          ; send cmd: play track #9, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    move.b  #$89,(v_LAST_MSU)
    rts
  
msuPlayTrack_10:                        ; Title Screen
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_10
      
    move.w  #($1100|10),MCD_CMD         ; send cmd: play track #10, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_11:                        ; Ending
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_11
      
    move.w  #($1100|11),MCD_CMD         ; send cmd: play track #11, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_12:                        ; Boss
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_12
      
    move.w  #($1200|12),MCD_CMD         ; send cmd: play track #12, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_13:                        ; Final Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_13
      
    move.w  #($1200|13),MCD_CMD         ; send cmd: play track #13, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_14:                        ; Sonic Got Through
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_14
      
    move.w  #($1100|14),MCD_CMD         ; send cmd: play track #14, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_15:                        ; Game Over
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_15
      
    move.w  #($1100|15),MCD_CMD         ; send cmd: play track #15, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_16:                        ; Continue Screen
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_16
      
    move.w  #($1100|16),MCD_CMD         ; send cmd: play track #16, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_17:                        ; Credits
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_17
      
    move.w  #($1100|17),MCD_CMD         ; send cmd: play track #17, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_18:                        ; Drowning
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_18
      
    move.w  #($1100|18),MCD_CMD         ; send cmd: play track #18, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_19:                        ; Get Emerald
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_19
      
    move.w  #($1100|19),MCD_CMD         ; send cmd: play track #19, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_20:                        ; SEEEGAAAAA
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_20
      
    move.w  #($1100|20),MCD_CMD         ; send cmd: play track #20, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
; ----- Fast Tracks :

msuPlayTrack_21:                        ; FAST Green Hill Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_21
      
    move.w  #($1200|21),MCD_CMD         ; send cmd: play track #1, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_22:                        ; FAST Labyrinth Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_22
      
    move.w  #($1200|22),MCD_CMD         ; send cmd: play track #2, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_23:                        ; FAST Marble Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_23
      
    move.w  #($1200|23),MCD_CMD         ; send cmd: play track #3, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_24:                        ; FAST Star Light Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_24
      
    move.w  #($1200|24),MCD_CMD         ; send cmd: play track #4, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_25:                        ; FAST Spring Yard Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_25
      
    move.w  #($1200|25),MCD_CMD         ; send cmd: play track #5, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_26:                        ; FAST Scrap Brain Zone
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_26
      
    move.w  #($1200|26),MCD_CMD         ; send cmd: play track #6, loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuPlayTrack_27:                        ; FAST Invincibility
    tst.b   MCD_STAT
    bne.s   msuPlayTrack_27

    ;move.b  #$87,(v_LAST_MSU)

    move.w  #($1100|27),MCD_CMD         ; send cmd: play track #7, no loop
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
; ----- end Tracks

msuStop:
    tst.b   MCD_STAT
    bne.s   msuStop
    move.w  #($1300|40),MCD_CMD         ; send cmd: pause track
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuResume:
    tst.b   MCD_STAT
    bne.s   msuResume
    move.w  #($1400),MCD_CMD            ; send cmd: resume track
    addq.b  #1,MCD_CMD_CK               ; Increment command clock
    rts
  
msuChangeTrackSpeed:                    ; Sonic got shoes
    move.b  (v_LAST_MSU),d0
    jsr     findAndPlayFastTrack
    rts
  
msuRestoreTrackSpeed:                   ; Sonic lost his shoes
    tst.b   (v_invinc).w                ; is Sonic invincible?
    bne.w   msuPlayTrack_07             ; if yes, play invincible music

    move.b  (v_LAST_MSU),d0
    jsr     findAndPlayTrack
    rts
  
findAndPlayFastTrack:
        cmp.b   #$80,d0                 ; Stop MSU Sounds
        beq     msuStop
        cmp.b   #$81,d0                 ; Fast: Green Hill Zone
        beq     msuPlayTrack_21
        cmp.b   #$82,d0                 ; Fast: Labyrinth Zone
        beq     msuPlayTrack_22
        cmp.b   #$83,d0                 ; Fast: Marble Zone
        beq     msuPlayTrack_23
        cmp.b   #$84,d0                 ; Fast: Star Light Zone
        beq     msuPlayTrack_24
        cmp.b   #$85,d0                 ; Fast: Spring Yard Zone
        beq     msuPlayTrack_25
        cmp.b   #$86,d0                 ; Fast: Scrap Brain Zone
        beq     msuPlayTrack_26
        cmp.b   #$87,d0                 ; Fast: Invincibility
        beq     msuPlayTrack_27
        rts

Now to make the Fast Musics load we will not go to the 2E object (the one with the monitor objects)
In Pow_ChkShoes we will comment

Code:

        jmp    (PlaySound).l        ; Speed    up the music

and just before bgm_SpeedUp we will paste:

Code:

        jsr     msuChangeTrackSpeed

If you think it is not necessary to use faster versions of the music, then you are free to not follow this small modification.

This would have finished the guide but there are still a few things left to cover so...

Second part: Remove this screen:
17/08 Edit: I've decided to remove this part for now, while I look for a way to make the code stable. Sincere apologies and better wait for a new code.

Final notes:

1. If you have the DMA Sonic. Kega fusion will a graphic bug when starting mode 1
2. Some Sounds will not play

Credits:
ArcadeTV: Creator of the Driver

 

Let's see how many errors a professional can detect in this thing...

 

It would have been better if you tried to ask around for someone to peer review the guide before publishing it, knowing that there's flaws with it that need to be addressed first, and also first learn to better understand what the code is even actually doing.

 

I decided I'd try and apply this guide (despite me not being a professional so I have no idea how much I'm qualified to be speaking here), and I had no errors reported when I attempted it (though I'm with Devon on the point that there should've been a proofread first before it was posted.)
My main complaint would be that there's no mention of adding the MSU's stop commands at the SEGA screen and Title Screen (meaning the CD audio could potentially play forever until interrupted by the title screen music), but otherwise, eh. I would've also credited krikzz as the person who made the driver rather than ArcadeTV who essentially made the base of this whole guide.