68k initialization

Vectors

Vector table and header for AES/MVS roms:

    org $0
    dc.l $0010F300	        ; Initial SP
    dc.l $00C00402	        ; Initial PC
    dc.l $00C00408,$00C0040E,$00C0040E,$0000034C       ; Bus error (2),Address error (3),Illegal Instruction (4),Divide by 0 (5)
    dc.l $0000034E,$0000034E,$00C0041A,$00C00420       ; CHK Instruction (6),TRAPV Instruction (7),Privilege Violation (8),Trace (9)
    dc.l $0000034E,$0000034E,$00C00426,$00C00426       ; Emu(10),Emu(11),Reserved,Reserved
    dc.l $00C00426,$00C0042C,$00C00426,$00C00426       ; Reserved,Reserved,Reserved,Reserved
    dc.l $00C00426,$00C00426,$00C00426,$00C00426       ; Reserved,Reserved,Reserved,Reserved
    dc.l $00C00426,$00C00426,$00C00432,VBlank          ; Reserved,Reserved,Spurious Interrupt(24)
    dc.l IRQ2,$00C00426,$00C00426,$00C00426
    dc.l $00C00426,$00C00426,$0000056E,$0000056E       ; Auto,Auto,Trap 0, Trap1...
    dc.l $0000056E,$0000056E,$0000056E,$0000056E
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF

    org $0100
    dc.b "NEO-GEO",$00

    dc.w $0052		; NGH Number in BCD (0052 is ssideki)
    dc.l $00080000      ; ?
    dc.l $00100000	; ?
    dc.w $0000

    org $0114
    dc.b $01            ; Bootscreen flag ($00 skips it)
    dc.b $1B		; First tile number of the NeoGeo logo in the C ROM
    dc.l $00000200	; Japanese config menu pointer
    dc.l $00000200	; English config menu pointer
    dc.l $00000200	; European config menu pointer

    jmp		Start
    jmp		Start   ; Not used ?
    jmp		Start   ; Not used ?
    jmp		Start   ; Not used ?

    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF,$FFFFFFFF,$FFFFFFFF
    dc.l $FFFFFFFF,$FFFFFFFF

    dc.l $00000186  	; Security code pointer ?

    org $186            ; ???
    dc.l $76004A6D,$0A146600,$003C206D,$0A043E2D
    dc.l $0A0813C0,$00300001,$32100C01,$00FF671A
    dc.l $30280002,$B02D0ACE,$66103028,$0004B02D
    dc.l $0ACF6606,$B22D0AD0,$67085088,$51CFFFD4
    dc.l $36074E75,$206D0A04,$3E2D0A08,$3210E049
    dc.l $0C0100FF,$671A3010,$B02D0ACE,$66123028
    dc.l $0002E048,$B02D0ACF,$6606B22D,$0AD06708
    dc.l $588851CF,$FFD83607
    dc.w $4e75

    org $200           ; Config menus, need to find format...
    dc.b	"0123456789ABCDEF"
    dc.l	$FFFFFFFF
    dc.w	$0364
    dc.b	$14,$13,$24,$01

Basic init code

The initial PC value in your 68k binary must be $C00402 (Init BIOS call), the initial SP value must be $10F300 (end of user RAM).

The entrypoints for your 68k code start at $000122. There's usually 4 JMP instructions there (why ?).

    lea     $10F300, sp
    lea     $10F300, a7
    move.b  d0,REG_DIPSW      ; Kick the watchdog
    move.w  #7,REG_IRQACK     ; Acknowledge any pending interrupts
    move.w  #$2700,sr         ; Disable all interrupts

See 68k interrupts and Watchdog for more informations.

Clearing user RAM:

    lea     RAMSTART,a0       ; Should be $100000
    move.l  #($F300/4)-1,d0   ; User RAM's size is $F300, and we clear longwords (4 bytes)
clram:
    clr.l   (a0)+
    dbra    d0,clram

Note that this function also clears the stack. Don't make a subroutine out of it unless you're sure of what addresses you're clearing.

Clearing sprites: make a BIOS call. Clearing fix: make a BIOS call too.

Don't forget to kick the watchdog regularly in your init code if the VBL interrupt isn't enabled or doesn't kick it itself.