dos33fsprogs/demosplash/appleII_intro.s

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2019-09-04 19:46:10 +00:00
; Display a 40x96 lo-res image
; by deater (Vince Weaver) <vince@deater.net>
appleII_intro:
;===================
; init screen
jsr TEXT
jsr HOME
bit KEYRESET
;===================
; init vars
lda #0
sta DRAW_PAGE
;=============================
; Load graphic page0
lda #<appleII_low
sta GBASL
lda #>appleII_low
sta GBASH
lda #$c
jsr load_rle_gr
lda #4
sta DRAW_PAGE
jsr gr_copy_to_current ; copy to page1
; GR part
bit PAGE1
bit LORES ; 4
bit SET_GR ; 4
bit FULLGR ; 4
jsr wait_until_keypressed
;=============================
; Load graphic page1
lda #<appleII_high
sta GBASL
lda #>appleII_high
sta GBASH
lda #$c
jsr load_rle_gr
lda #0
sta DRAW_PAGE
jsr gr_copy_to_current
; GR part
bit PAGE0
jsr wait_until_keypressed
;==============================
; setup graphics for vapor lock
;==============================
jsr vapor_lock ; 6+
; vapor lock returns with us at beginning of hsync in line
; 114 (7410 cycles), so with 5070 lines to go
; GR part
bit LORES ; 4
bit SET_GR ; 4
bit FULLGR ; 4
jsr gr_copy_to_current ; 6+ 9292
; now we have 322 left
; 322 - 12 = 310
; - 3 for jmp
; 307
; Try X=9 Y=6 cycles=307
ldy #6 ; 2
loopA: ldx #9 ; 2
loopB: dex ; 2
bne loopB ; 2nt/3
dey ; 2
bne loopA ; 2nt/3
jmp display_loop ; 3
.align $100
;================================================
; Display Loop
;================================================
; each scan line 65 cycles
; 1 cycle each byte (40cycles) + 25 for horizontal
; Total of 12480 cycles to draw screen
; Vertical blank = 4550 cycles (70 scan lines)
; Total of 17030 cycles to get back to where was
; We want to alternate between page1 and page2 every 65 cycles
; vblank = 4550 cycles to do scrolling
; 2 + 48*( (4+2+25*(2+3)) + (4+2+23*(2+3)+4+5)) + 9)
; 48*[(6+125)-1] + [(6+115+10)-1]
display_loop:
ldy #48 ; 2
outer_loop:
bit PAGE0 ; 4
ldx #25 ; 130 cycles with PAGE0 ; 2
page0_loop: ; delay 126+bit
dex ; 2
bne page0_loop ; 2/3
bit PAGE1 ; 4
ldx #23 ; 130 cycles with PAGE1 ; 2
page1_loop: ; delay 115+(7 loop)+4 (bit)+4(extra)
dex ; 2
bne page1_loop ; 2/3
nop ; 2
lda DRAW_PAGE ; 3
dey ; 2
bne outer_loop ; 2/3
;======================================================
; We have 4550 cycles in the vblank, use them wisely
;======================================================
; do_nothing should be 4550+1 -2-9 -7= 4533
jsr do_nothing ; 6
lda KEYPRESS ; 4
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bpl no_keypress2 ; 3
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jmp appleii_done
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no_keypress2:
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jmp display_loop ; 3
appleii_done:
rts
;=================================
; do nothing
;=================================
; and take 4533-6 = 4527 cycles to do it
do_nothing:
; Try X=4 Y=174 cycles=4525 R2
nop ; 2
ldy #174 ; 2
loop1:
ldx #4 ; 2
loop2:
dex ; 2
bne loop2 ; 2nt/3
dey ; 2
bne loop1 ; 2nt/3
rts ; 6