OLD_NTSC = 1
NTSC = 0
PAL = 2
DREAN = 3

        !to "detect.prg",cbm
	!cpu 6510

	* = $0801
	!by $0b,$08,$00,$00,$9e,$32,$30,$36,$31,$00,$00,$00
		
detect:	sei
w0:  	lda $d012
w1:  	cmp $d012
	beq w1
	bmi w0
	and #$03
	cmp #$01
	bne w2
	lda #OLD_NTSC
	bne detected ; unconditional
w2:	cmp #$03
	lda #$00
	rol
	beq detected	;ntsc

	;check for drean or pal
	ldx #$00
	lda #$10
l	inx
	cmp $d012
	bne l
	lda #PAL
	cpx #$70
	bcc detected
	;is a drean
	lda #DREAN
detected:
	tay
	lax offset,y
l2:	lda base_text,x
	beq end
	jsr $ffd2
	inx
	bne l2
end:	lda #$0d
	jmp $ffd2

base_text:
old_ntsc_text:	!text "OLD "
ntsc_text:	!text "NTSC",0
pal_text:	!text "PAL",0
drean_text:	!text "DREAN",0

offset:		
	!byte ntsc_text-base_text
	!byte old_ntsc_text-base_text
	!byte pal_text-base_text
	!byte drean_text-base_text

init:
	lda #$7f	; Disable kernal IRQ.
	sta $dc0d
	
	lda #$ff	; Start on line 255.
:	cmp $d012
	bne :-
	
@nextline:
	lda $d012	; Wait until the next line.
:	cmp $d012
	beq :-		; A contains the previous line number.
	
	bit $d011	; Are we back on line 0?
	bmi @nextline
	
	ora #$30	; A contains the LSB of the last line number:
	sta $0400	;   $05 = 262 x 64 cycle NTSC
	lda #1		;   $06 = 263 x 65 cycle NTSC
	sta $d800	;   $37 = 312 x 63 cycle PAL or 312 x 65 cycle DREAN

    // Use CIA #1 Timer B to count cycled in a frame
    lda #$ff
    sta $dc06
    sta $dc07  // Latch #$ffff to Timer B

    bit $d011
    bpl *-3    // Wait untill Raster > 256
    bit $d011
    bmi *-3    // Wait untill Raster = 0

    ldx #%00011001
    stx $dc0f  // Start Timer B (One shot mode (Timer stops automatically when underflow))

    bit $d011
    bpl *-3    // Wait untill Raster > 256
    bit $d011
    bmi *-3    // Wait untill Raster = 0

    sec
    sbc $dc07  // Hibyte number of total cycles
    and #%00000011

INIT
    SEI
    CLD
    LDX #$FF
    TXS
    LDA #$2F
    STA $00
    LDA #$35
    STA $01
;-------------------
    LDX #<NO_NMI
    LDY #>NO_NMI
    STX $0318
    STY $0319
    STX $FFFA
    STY $FFFB
    LDY #$00
    STY $DC03                           ; Port $DC01 = Input
    DEY
    STY $DC02                           ; Port $DC00 = Output
;-------------------
    LDA #$7F
    STA $DC0D
    STA $DD0D
    LDA $DC0D
    LDA $DD0D
;-------------------
    LDA #$00
    STA $DD0E                           ; Stop CIA #2 Timer A
    STA $DD04
    STA $DD05                           ; Set Timer A = 0 (NMI will trigger immediately when Timer A is restarted)
    LDA #$81
    STA $DD0D                           ; Set Timer A as NMI source
    LDA #$01
    STA $DD0E                           ; Start Timer A (triggers NMI and unless the NMI get's acked, any new NMI's will be ignored).
    LDA #$00                            ; From this point on we will not be disturbed and can commence testing.
    STA $D015                           ; No Sprites
;------------------------------------------------------------------------------
; Detect the model
;---------------------------------------
; 312 rasterlines -> 63 cycles per line PAL        => 312 * 63 = 19656 Cycles / VSYNC
; 262 rasterlines -> 64 cycles per line NTSC V1    => 262 * 64 = 16768 Cycles / VSYNC
; 263 rasterlines -> 65 cycles per line NTSC V2    => 263 * 65 = 17095 Cycles / VSYNC
; 312 rasterlines -> 65 cycles per line PAL DREAN  => 312 * 65 = 20280 Cycles / VSYNC
;------------------------------------------------------------------------------
    LDA #$FF                            ; Use CIA #1 Timer A to count cycled in a frame
    STA $DC06
    STA $DC07                           ; Latch #$ffff to Timer B
    LDY #%00011001
    LDA #$7F
WAIT_BEAM_01
    CMP $D012
    BNE WAIT_BEAM_01
    BIT $DEAD
    BIT $BEEF
    STA $D011
    STY $DC0F                           ; Start Timer B (One shot mode (Timer stops automatically when underflow)
    LDY #$00
    LDA #$1B
    STA $D011
    LDA #$7F
WAIT_BEAM_02
    CMP $D012
    BNE WAIT_BEAM_02
    BIT $DEAD
    BIT $BEEF
    STA $D011
;-------------------
    STY $DC0F
    LDX $DC06
    LDY $DC07
    STY $0400
    STX $0401
    LDA #$1B                            ; TURN BACK ON SCREEN TO SEE RESULT
    STA $D011
;-------------------
WAIT_SOME_SPACE
    LDA $DC01
    AND $DC00
    AND #$10
    BNE WAIT_SOME_SPACE
    JMP INIT
;-------------------
NO_NMI
    RTI