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kfest18: flip pages

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This commit is contained in:
Vince Weaver 2018-07-19 16:48:59 -04:00
parent 2a975d56fc
commit f838c48968
1 changed files with 38 additions and 0 deletions
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38
kfest2018/raster.s
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@ -8,6 +8,8 @@ CURRENT_OFFSET = $EF
SET_GR = $C050 ; Enable graphics
FULLGR = $C052 ; Full screen, no text
PAGE0 = $C054 ; Page0
PAGE1 = $C055 ; Page1
LORES = $C056 ; Enable LORES graphics
@ -42,6 +44,7 @@ WAIT = $FCA8 ;; delay 1/2(26+27A+5A^2) us
; Clear Page1
lda #$4
sta DRAW_PAGE
lda #$00
jsr clear_gr
; draw border line
@ -118,9 +121,44 @@ loopB:
.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
display_loop:
ldy #96 ; 2
outer_loop:
ldx #25 ; 130 cycles with PAGE0 ; 2
page0_loop:
dex ; 2
bne page0_loop ; 2/3
bit PAGE0 ; 4
ldx #25 ; 130 cycles with PAGE1 ; 2
page1_loop:
dex ; 2
bne page1_loop ; 2/3
bit PAGE1 ; 4
dey ; 2
bne outer_loop ; 2/3
jmp display_loop ; 3
; We have 4550 cycles in the vblank, use them wisely
ldy CURRENT_OFFSET
ldx #0
data_loop: