186 lines
3.5 KiB
ArmAsm
186 lines
3.5 KiB
ArmAsm
;================================
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; Show the title screen
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; return when a key is pressed
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;================================
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title_screen:
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;===================
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; init screen
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jsr TEXT
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jsr HOME
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bit KEYRESET
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;===================
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; init vars
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lda #0
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sta DRAW_PAGE
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;=============================
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; Load graphic page0
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lda #$0c
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sta BASH
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lda #$00
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sta BASL ; load image to $c00
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lda #<spacebars_title_low
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sta GBASL
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lda #>spacebars_title_low
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sta GBASH
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jsr load_rle_gr
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lda #4
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sta DRAW_PAGE
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jsr gr_copy_to_current ; copy to page1
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; GR part
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bit PAGE1
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bit LORES ; 4
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bit SET_GR ; 4
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bit FULLGR ; 4
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;=============================
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; Load graphic page1
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lda #$0c
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sta BASH
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lda #$00
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sta BASL ; load image to $c00
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lda #<spacebars_title_high
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sta GBASL
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lda #>spacebars_title_high
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sta GBASH
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jsr load_rle_gr
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lda #0
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sta DRAW_PAGE
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; GR part
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bit PAGE0
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;==============================
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; setup graphics for vapor lock
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;==============================
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jsr vapor_lock
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; found first line of black after green, at up to line 26 on screen
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; so we want roughly 22 lines * 4 = 88*65 = 5720 + 4550 = 10270
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; - 65 (for the scanline we missed) = 10205 - 12 = 10193
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jsr gr_copy_to_current ; 6+ 9292
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; 10193 - 9298 = 895
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; Fudge factor (unknown) -30 = 865
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; GR part
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bit LORES ; 4
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bit SET_GR ; 4
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bit FULLGR ; 4
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; Try X=88 Y=2 cycles=893 R2
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nop
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ldy #2 ; 2
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loopA:
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ldx #88 ; 2
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loopB:
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dex ; 2
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bne loopB ; 2nt/3
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dey ; 2
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bne loopA ; 2nt/3
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jmp display_loop
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.align $100
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;================================================
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; Display Loop
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;================================================
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; each scan line 65 cycles
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; 1 cycle each byte (40cycles) + 25 for horizontal
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; Total of 12480 cycles to draw screen
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; Vertical blank = 4550 cycles (70 scan lines)
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; Total of 17030 cycles to get back to where was
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; We want to alternate between page1 and page2 every 65 cycles
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; vblank = 4550 cycles to do scrolling
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; 2 + 48*( (4+2+25*(2+3)) + (4+2+23*(2+3)+4+5)) + 9)
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; 48*[(6+125)-1] + [(6+115+10)-1]
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display_loop:
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ldy #96 ; 2
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outer_loop:
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bit PAGE0 ; 4
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ldx #12 ; 65 cycles with PAGE0 ; 2
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page0_loop: ; delay 61+bit
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dex ; 2
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bne page0_loop ; 2/3
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; bit(4) -1(fallthrough) + loop*5 -1(fallthrouh)+4 extra = 61
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; 5L = 55
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bit PAGE1 ; 4
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ldx #11 ; 65 cycles with PAGE1 ; 2
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;
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page1_loop: ; delay 115+(7 loop)+4 (bit)+4(extra)
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dex ; 2
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bne page1_loop ; 2/3
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dey ; 2
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bne outer_loop ; 2/3
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;======================================================
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; We have 4550 cycles in the vblank, use them wisely
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;======================================================
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; do_nothing should be 4550+1 -2-9 -7= 4533
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jsr do_nothing ; 6
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lda KEYPRESS ; 4
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bpl no_keypress ; 3
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jmp return
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no_keypress:
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jmp display_loop ; 3
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;=================================
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; do nothing
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;=================================
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; and take 4533-6 = 4527 cycles to do it
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do_nothing:
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; Try X=4 Y=174 cycles=4525 R2
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nop ; 2
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ldy #174 ; 2
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loop1:
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ldx #4 ; 2
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loop2:
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dex ; 2
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bne loop2 ; 2nt/3
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dey ; 2
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bne loop1 ; 2nt/3
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return:
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rts ; 6
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