#define poke(addr,val)	.(:lda #val:sta addr:.)
#define doke(addr,val)	.(:lda #<val:sta addr:lda #>val:sta addr+1:.)
#define endIRQ pla:tay:pla:tax:pla:rti
#define ackIRQ pha:lda $d019:sta $d019:txa:pha:tya:pha

	*= $0801-2
	.word *+2	; load address
	.byt $0b,$08,$0a,$00,$9e,$32,$30,$36,$31,0,0,0 ; 10 sys2061
main:
	poke($d021,$04)
	sta 646
	lda#147
	jsr $ffd2
	poke($d021,0)
	poke($0400,1)  ;something to see
	poke($0428,2)

	jsr IRQstart
loop:
	inc $7e7  ; a nice untidy main loop to ensure instability!
	bpl loop
	jmp loop

IRQstart
	poke($dc0d,$7f)	; kill CIA irq
	sei
	poke($01,  $35)	; disable ROM
	poke($d01a,$01) ; enable VIC irq
	poke($d011,$1b) ; clear high bit of irq rasterline
	poke($d012,$32) ; last invisible line
	doke($fffe,irq1 ) ; set irq vector
	cli
	rts
	
irq1:
	ackIRQ
	poke($d020,$0f)   ; this is unstable!
	poke($d011,$1a)   ; force partial badline before screen starts
	poke($d020,$0b)   ; this is stable ^_^
	poke($d011,$1b)   ; trigger normal re-fetch of first row of chars
	poke($d012,$ff)   ; set end-of-screen irq
	doke($fffe,irq2 )
	endIRQ

irq2:
	ackIRQ
	;ensure first row of chars is already being displayed when badline forced by irq1
	poke($d011,$18)
	poke($d012,$32	)
	doke($fffe,irq1 )
	endIRQ

; ------------------------------------------------------------------------------
rasterlogo1	= $34
; ------------------------------------------------------------------------------
	.code 
	.org $07ff
; ------------------------------------------------------------------------------

; ------------------------------------------------------------------------------
; "sys" basic
; ------------------------------------------------------------------------------

	.word *+2	;loading bytes
basicstub:
	.word @nextline
	.word 2012	; line number
	.byte $9e	; sys
	.byte <(((init / 1000) .mod 10) + $30)
	.byte <(((init / 100 ) .mod 10) + $30)
	.byte <(((init / 10 ) .mod 10) + $30)
	.byte <(((init ) .mod 10) + $30)
	.byte 0		;end of line
@nextline:
	.word 0		;empty line == end basic code

init:
	lda #$00
	sta $d020
	sta $d021
	sta $3fff
; ------------------------------------------------------------------------------
;set up irq
; ------------------------------------------------------------------------------
setup:	lda #$1b
	sta $d011

	lda #rasterlogo1
	sta $d012

	ldy #$00
	sty $d015 

	sei  

	lda #$7f
	sta $dc0d 
	sta $dd0d 

	lda #$35   
	sta $01    

	lda #<irq1 
	sta $fffe 
	lda #>irq1
	sta $ffff

	lda #$01   
	sta $d01a

	lda $dc0d     
	lda $dd0d
	lda #$01
	sta $d019    

	cli        

jmp *
; ------------------------------------------------------------------------------
; Routine in interrupt
; ------------------------------------------------------------------------------
irq1:
	ldx #$08
	dex
	bne *-1

	lda $d012
	and #$07
	ora #$18
	sta $d011
	cmp $00,x
	cmp $00,x
	cmp $00

	inc $d021
	inc $d021
	inc $d021
	inc $d021
	inc $d021
	inc $d021


	ldy #$00
	sty $d021

	lda #$1b
	sta $d011

	asl $d019  

	rti