Code for https://kristerw.blogspot.com/2018/12/commodore-64-programming.html

test.asm

	;; Zero page variables
	sprite_x_idx = $03
	sprite_y_idx = $04
	sprite_skip_counter = $05
	tmp1 = $10
	irq_saved_a = $20
	irq_saved_x = $21
	irq_saved_y = $22
	irq_color_addr_lo = $22
	irq_color_addr_hi = $23

	* = $07ff

	;; File header and a BASIC program that calls the assembly code.
	!byte $01,$08 		; Load address $0801
	!byte $0c,$08		; ??? Usually end of 1st line of BASIC prog.
	!byte $0a,$00,$9e,$20,$32,$30,$36,$34,$00	; 10 SYS 2064
	!byte $00,$00		; End of program

	*= $0810
start:
	jsr init_irq
	jsr clear_screen
	jsr init_sprites

loop:
	jsr step_time

	;; Wait until the raster is below the sprites.
loop1:
	ldx $d012
	cpx #250
	bne loop1

	jsr move_sprites

	jmp loop


;;; Update sine-table indices one time step.
step_time:
	inc sprite_x_idx
	lda sprite_x_idx
	and #127
	sta sprite_x_idx

	;; Skip some updates to y to prevent the position from repeating
	;; every 64 frames.
	inc sprite_skip_counter
	ldx sprite_skip_counter
	cpx #53
	bne st1
	ldx #0
	stx sprite_skip_counter
	rts

st1:	
	inc sprite_y_idx
	lda sprite_y_idx
	and #127
	sta sprite_y_idx
	rts


;;; Update sprites x and y coordinates
move_sprites:
	ldx #0
	ldy sprite_x_idx
ms1:
	tya
	clc
	adc #5
	and #127
	sta tmp1
	and #63
	tay

	lda sine64,y
	clc
	adc #168
	ldy tmp1
	adc sine128,y
	sta $d000,x

	inx
	inx
	cpx #16
	bne ms1

	ldx #0
	ldy sprite_y_idx
ms2:
	tya
	clc
	adc #5
	and #127
	tay

	lda sine128,y
	clc
	adc #154
	sta $d001,x

	inx
	inx
	cpx #16
	bne ms2

	rts


clear_screen:
	lda #$20
cs_loop:	
	sta $0400,x
	sta $0500,x
	sta $0600,x
	sta $0700,x
        dex
        bne cs_loop
	rts


;;; Initialize sprites
;;;   https://www.c64-wiki.com/wiki/Sprite
init_sprites:
	ldx #0
	ldy #0
is1:
	lda #sprite1/64
	sta $07f8,y
	lda #0
	sta $d000,x
	sta $d001,x
	lda #1
	sta $d027,y
	inx
	inx
	iny
	cpx #16
	bne is1

	lda #0
	sta $d010
	lda #$ff
	sta $d015

	;; Initialize variables used for calculating sprite positions.
	lda #0
	sta sprite_x_idx
	sta sprite_skip_counter
	lda #40
	sta sprite_y_idx
	rts


;;; Initialize IRQ
;;;   http://codebase64.org/doku.php?id=base:introduction_to_raster_irqs 
init_irq:
	sei

	lda #$7f
	sta $dc0d
	sta $dd0d
	lda $dc0d
	lda $dd0d

	lda #1
	sta $d01a
	lda #80
	sta $d012
	lda #$1b
	sta $d011

	lda #$35
	sta $01

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

	cli

	rts


	;; Align the IRQ code to ensure the branches do no cross a page
	;; boundary (branches takes longer when crossing page boundaries,
	;; and the code below rely on branches taking 3 cycles).
	!align 255, 0

;;; Draw rasterbar1
irq1:
	;; Entering the IRQ takes 9-16 cycles (depending how long it takes to
	;; execute the current instruction. We do not need to be cycle-exact
	;; (as the first cycles are outside the screen), so assume 10 cycles.
	;; But this is sloppy... See the link below for implementing better
	;; raster routines:
	;; http://codebase64.org/doku.php?id=base:making_stable_raster_routines

	sta irq_saved_a			; 3 cycles
	stx irq_saved_x			; 3
	sty irq_saved_y			; 3

	lda #<irq2			; 2
	sta $fffe			; 4
	lda #>irq2			; 2
	sta $ffff 			; 4
	lda #100			; 2
	sta $d012 			; 4

	lda #$ff			; 2
	sta $d019			; 4

	lda #<rasterbar1		; 2
	sta irq_color_addr_lo		; 3
	lda #>rasterbar1		; 2
	sta irq_color_addr_hi 		; 3

	jmp rasterbar_irq       	; 3

;;; Second half of IRQ. Assumes the first part has taken 56 cycles.
rasterbar_irq:
	ldy #0				; 2 cycles
	lda (irq_color_addr_lo),y	; 5
	;; ---------------------------- = 63

irq1_loop2:
	sta $d020			; 4
	sta $d021			; 4

	ldx #9				; 2
irq1_loop3:
	dex				; 2 * n
	bne irq1_loop3 			; 3 * n - 1

	iny 				; 2
	lda (irq_color_addr_lo),y	; 4
	bne irq1_loop2			; 3 (2 for last iteration)
	;; ---------------------------- = 63/62

	sta $d020
	sta $d021
	
	ldy irq_saved_y
	ldx irq_saved_x
	lda irq_saved_a

        rti

;;; Draw rasterbar2
irq2:
	sta irq_saved_a
	stx irq_saved_x
	sty irq_saved_y

	lda #<irq1
	sta $fffe
	lda #>irq1
	sta $ffff
	lda #85
	sta $d012

	lda #$ff
	sta $d019

	lda #<rasterbar2
	sta irq_color_addr_lo
	lda #>rasterbar2
	sta irq_color_addr_hi

	jmp rasterbar_irq


rasterbar1:
	!byte 6, 14, 14, 6, 0

rasterbar2:
	!byte 8, 7, 7, 8, 0


sine64:
	!byte $00,$03,$06,$09,$0b,$0e,$11,$13,$15,$17,$19,$1a,$1c,$1d,$1d,$1e
	!byte $1e,$1e,$1d,$1d,$1c,$1a,$19,$17,$15,$13,$11,$0e,$0c,$09,$06,$03
	!byte $00,$fd,$fa,$f7,$f5,$f2,$ef,$ed,$eb,$e9,$e7,$e6,$e4,$e3,$e3,$e2
	!byte $e2,$e2,$e3,$e3,$e4,$e6,$e7,$e9,$eb,$ed,$ef,$f2,$f4,$f7,$fa,$fd

sine128:
	!byte $00,$01,$02,$04,$05,$06,$07,$08,$09,$0a,$0b,$0c,$0d,$0e,$0f,$10
	!byte $11,$12,$13,$13,$14,$15,$15,$16,$16,$17,$17,$17,$18,$18,$18,$18
	!byte $18,$18,$18,$18,$18,$17,$17,$17,$16,$16,$15,$15,$14,$13,$13,$12
	!byte $11,$10,$0f,$0e,$0d,$0c,$0b,$0a,$09,$08,$07,$06,$05,$04,$02,$01
	!byte $00,$ff,$fe,$fd,$fb,$fa,$f9,$f8,$f7,$f6,$f5,$f4,$f3,$f2,$f1,$f0
	!byte $ef,$ee,$ed,$ed,$ec,$eb,$eb,$ea,$ea,$e9,$e9,$e9,$e8,$e8,$e8,$e8
	!byte $e8,$e8,$e8,$e8,$e8,$e9,$e9,$e9,$ea,$ea,$eb,$eb,$ec,$ed,$ed,$ee
	!byte $ef,$f0,$f1,$f2,$f3,$f4,$f5,$f6,$f7,$f8,$f9,$fa,$fb,$fc,$fe,$ff


	!align 63, 0		; Sprites must be 64-byte aligned
sprite1:
	!byte $00,$7e,$00
	!byte $03,$ff,$c0
	!byte $07,$ff,$e0
	!byte $1f,$ff,$f8
	!byte $1f,$ff,$f8
	!byte $3f,$ff,$fc
	!byte $7f,$ff,$fe
	!byte $7f,$ff,$fe
	!byte $ff,$ff,$ff
	!byte $ff,$ff,$ff
	!byte $ff,$ff,$ff
	!byte $ff,$ff,$ff
	!byte $ff,$ff,$ff
	!byte $7f,$ff,$fe
	!byte $7f,$ff,$fe
	!byte $3f,$ff,$fc
	!byte $1f,$ff,$f8
	!byte $1f,$ff,$f8
	!byte $07,$ff,$e0
	!byte $03,$ff,$c0
	!byte $00,$7e,$00