#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

mov #$00, $d020

.pc = $0810

	sei
	lda #$35	// switch off kernal
	sta $01
	
	ldx #$00
	stx $d015	// switch off sprites
	stx $3fff	// clear garbage gfx
	inx
	stx $d01a	// raster interrupt

	lda #$7f	// clear timers
	sta $dc0d
	sta $dd0d
	lda #$1b	// clear MSB of rasterline
	sta $d011
	lda #$33	// set triggering rasterline
	sta $d012
	ldx #<irq	// set IRQ vectors
	ldy #>irq
	stx $fffe
	sty $ffff

	lda $dc0d	// ack pending timers
	lda $dd0d
	lda #$01	// ack pending irq
	sta $d019

	cli
	jmp *		// infinite loop

irq:
	sta saveA
	stx saveX
	sty saveY
	
	ldx #$08
timeloop1:
	dex
	bne timeloop1

	nop
	nop

	lda $d012	// DMA
	and #$07
	ora #$18
	sta $d011

	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea
	bit $eaea	// jitters, change into bit $ea to stabilize

	ldy #$c0
	lda #$c8
	sty $d021
	sta $d021

	lda #$1b
	sta $d011

	asl $d019

.label saveA = * +1
	lda #$00
.label saveX = * +1
	ldx #$00
.label saveY = * +1
	ldy #$00
	rti