; Hardware hacking screenmodes on the Amiga for PAL, NTSC, DBLPAL (VGA) etc.
; by Fabio "Maverick" Bizzetti

sync_mode=0 	; 0=pal
		; 1=ntsc
		; 2=dblpal
		; 3=dblntsc 
		; 4=1942

SetSyncMode:    lea     $dff000,a0
                move.l  #sync_mode,d0
                jmp     ([.jmptab,pc,d0.l*4])
.jmptab         dc.l    .pal
                dc.l    .ntsc
                dc.l    .dblpal
                dc.l    .dblntsc
                dc.l    .1942
.pal            move.w  #$0020,$1DC(a0)         ;BEAMCON0
                move.w  #$0038,$092(a0)         ;DDFSTRT
                move.w  #$00D8,$094(a0)         ;DDFSTOP
                move.w  #$0003,$1FC(a0)         ;FMODE
                move.w  #$4481,$08E(a0)         ;DIWSTRT
                move.w  #$0CC1,$090(a0)         ;DIWSTOP
                move.w  #$0211,$100(a0)         ;BPLCON0
                move.w  #$0000,$108(a0)         ;BPL1MOD
                move.w  #$0000,$10A(a0)         ;BPL2MOD
                bra.w   .exit
.ntsc           move.w  #$0000,$1DC(a0)         ;BEAMCON0
                move.w  #$0038,$092(a0)         ;DDFSTRT
                move.w  #$00D8,$094(a0)         ;DDFSTOP
                move.w  #$0003,$1FC(a0)         ;FMODE
                move.w  #$2C81,$08E(a0)         ;DIWSTRT
                move.w  #$F4C1,$090(a0)         ;DIWSTOP
                move.w  #$0211,$100(a0)         ;BPLCON0
                move.w  #$0000,$108(a0)         ;BPL1MOD
                move.w  #$0000,$10A(a0)         ;BPL2MOD
                bra.w   .exit
.dblpal         move.w  #$0005,$1C4(a0)         ;HBSTRT
                move.w  #$000F,$1DE(a0)         ;HSSTRT
                move.w  #$001B,$1C2(a0)         ;HSSTOP
                move.w  #$0021,$1C6(a0)         ;HBSTOP
                move.w  #$0073,$1C0(a0)         ;HTOTAL
                move.w  #$0000,$1CC(a0)         ;VBSTRT
                move.w  #$0003,$1E0(a0)         ;VSSTRT
                move.w  #$0005,$1CA(a0)         ;VSSTOP
                move.w  #$001D,$1CE(a0)         ;VBSTOP
                move.w  #$026D,$1C8(a0)         ;VTOTAL
                move.w  #$0B88,$1DC(a0)         ;BEAMCON0
                move.w  #$0018,$092(a0)         ;DDFSTRT
                move.w  #$0068,$094(a0)         ;DDFSTOP
                move.w  #$0003,$1FC(a0)         ;FMODE
                move.w  #$8046,$08E(a0)         ;DIWSTRT
                move.w  #$10E6,$090(a0)         ;DIWSTOP
                move.w  #$0200,$1E4(a0)         ;DIWHIGH
                move.w  #$8211,$100(a0)         ;BPLCON0
                move.w  #$0000,$108(a0)         ;BPL1MOD
                move.w  #$0000,$10A(a0)         ;BPL2MOD
                bra.w   .exit
.dblntsc        move.w  #$0005,$1C4(a0)         ;HBSTRT
                move.w  #$000E,$1DE(a0)         ;HSSTRT
                move.w  #$001B,$1C2(a0)         ;HSSTOP
                move.w  #$0021,$1C6(a0)         ;HBSTOP
                move.w  #$0072,$1C0(a0)         ;HTOTAL
                move.w  #$0000,$1CC(a0)         ;VBSTRT
                move.w  #$0003,$1E0(a0)         ;VSSTRT
                move.w  #$0005,$1CA(a0)         ;VSSTOP
                move.w  #$001D,$1CE(a0)         ;VBSTOP
                move.w  #$020E,$1C8(a0)         ;VTOTAL
                move.w  #$0B88,$1DC(a0)         ;BEAMCON0
                move.w  #$0018,$092(a0)         ;DDFSTRT
                move.w  #$0068,$094(a0)         ;DDFSTOP
                move.w  #$0003,$1FC(a0)         ;FMODE
                move.w  #$5046,$08E(a0)         ;DIWSTRT
                move.w  #$E0E6,$090(a0)         ;DIWSTOP
                move.w  #$0100,$1E4(a0)         ;DIWHIGH
                move.w  #$8211,$100(a0)         ;BPLCON0
                move.w  #$0000,$108(a0)         ;BPL1MOD
                move.w  #$0000,$10A(a0)         ;BPL2MOD
                bra.b   .exit
.1942           move.w  #$0005,$1C4(a0)         ;HBSTRT
                move.w  #$000F,$1DE(a0)         ;HSSTRT
                move.w  #$001B,$1C2(a0)         ;HSSTOP
                move.w  #$0021,$1C6(a0)         ;HBSTOP
                move.w  #$0072,$1C0(a0)         ;HTOTAL
                move.w  #$0000,$1CC(a0)         ;VBSTRT
                move.w  #$0005,$1E0(a0)         ;VSSTRT
                move.w  #$0001,$1CA(a0)         ;VSSTOP
                move.w  #$001D,$1CE(a0)         ;VBSTOP
                move.w  #$020E,$1C8(a0)         ;VTOTAL
                move.w  #$0B88,$1DC(a0)         ;BEAMCON0
                move.w  #$0018,$092(a0)         ;DDFSTRT
                move.w  #$0068,$094(a0)         ;DDFSTOP
                move.w  #$0003,$1FC(a0)         ;FMODE
                move.w  #$5046,$08E(a0)         ;DIWSTRT
                move.w  #$E0E6,$090(a0)         ;DIWSTOP
                move.w  #$0100,$1E4(a0)         ;DIWHIGH
                move.w  #$8211,$100(a0)         ;BPLCON0
                move.w  #$0000,$108(a0)         ;BPL1MOD
                move.w  #$0000,$10A(a0)         ;BPL2MOD
.exit           move.w  #$0082,$096(a0)         ;DMACON - disable cop/spr
                move.w  #$8300,$096(a0)         ;DMACON - enable mast/bpl
                rts