68k initialization: Difference between revisions

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== Vectors ==
Vector table and header for AES/MVS roms:
<pre>
    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
</pre>
== Basic init code ==
== Basic init code ==
The initial PC value in your [[68k]] binary must be $C00402 (Init [[BIOS Calls|BIOS call]]), the initial SP value must be $10F300 (end of [[68k user RAM|user RAM]]).
The initial PC value in the [[68k]] binary must be $C00402 (Init [[BIOS Calls|BIOS call]]), the initial SP value must be $10F300 (end of the [[68k user RAM|user RAM]]).


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


<pre>
<pre>
     lea    $10F300, sp
     lea    $10F300, sp
     lea    $10F300, a7
     lea    $10F300, a7       ; Depends on assemblers...
     move.b  d0,REG_DIPSW      ; Kick the watchdog
     move.b  d0,REG_DIPSW      ; Kick the watchdog
     move.w  #7,REG_IRQACK    ; Acknowledge any pending interrupts
     move.w  #7,REG_IRQACK    ; Acknowledge any pending interrupts
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</pre>
</pre>


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.
Note that this function also clears the stack. Don't make a subroutine out of it unless you're sure that the return address won't be cleared.


Clearing sprites: make a BIOS call.
Clearing [[sprites]] and the [[fix layer]]: make [[BIOS Calls]].
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.
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.

Revision as of 20:40, 6 March 2011

Basic init code

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

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

    lea     $10F300, sp
    lea     $10F300, a7       ; Depends on assemblers...
    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 that the return address won't be cleared.

Clearing sprites and the fix layer: make BIOS Calls.

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.

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