239 lines
5.3 KiB
ArmAsm
239 lines
5.3 KiB
ArmAsm
; This took a while to track down
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; On Apple II/II+ the horiz blanking addr are $1000 higher than on IIe
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; So on II+ were outside video area, so unlikely to be our set value
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; (unless I foolishly use $ff which some uninitialized mem is set to)
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; Lots of this color fiddling is to make sure you don't accidentally
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; get runs of colors on IIe due to the horiz blank
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; 0-5 aqua 6-12 = grey, 13 - 20 = yellow, 21-23 = aqua rainbow 14
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;
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;
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;16 0 YA
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;17 1 YA
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;18 2 YA
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;19 3 YA
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;20 4 YA
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;21 5 AA
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;22 6 AG
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;23 7 AG
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;0 8 AG
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;1 9 AG
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;2 10 AG
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;3 11 AG
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;4 12 AG
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;5 13 AY ****
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;6 14 GY RAINBOW
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;7 15 GY
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;8 16 GY
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;9 17 GY
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;10 18 GY
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;11 19 GY
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;12 20 GY
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;13 21 YA
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;14 22 YA
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;15 23 YA
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;==============================
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; setup graphics for vapor lock
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;==============================
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vapor_lock:
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; Clear Page0
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lda #$0
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sta DRAW_PAGE
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lda #$ee ; full screen white $ff
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jsr clear_gr
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lda #$dd
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ldy #40
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jsr clear_page_loop ; make bottom half yellow $dd
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lda #$aa
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ldy #24
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jsr clear_page_loop ; make middle grey2 $aa
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lda #$ee
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ldy #10
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jsr clear_page_loop ; make top half aqua $ee
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; set up a rainbow to aid in exact lock
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ldy #00
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rainbow_loop:
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tya
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sta $728+20,Y
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iny
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cpy #20
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bne rainbow_loop
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;btt:
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; jmp btt
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;=====================================================
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; attempt vapor lock
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; by reading the "floating bus" we can see most recently
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; written value of the display
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;=====================================================
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; See:
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; Have an Apple Split by Bob Bishop
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; Softalk, October 1982
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; Challenges: each scan line scans 40 bytes.
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; The blanking happens at the *beginning*
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; So 65 bytes are scanned, starting at adress of the line - 25
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; the scan takes 8 cycles, look for 4 repeats of the value
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; to avoid false positive found if the horiz blanking is mirroring
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; the line (max 3 repeats in that case)
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vapor_lock_loop:
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; first make sure we have a full line of $aa
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lda #$aa ; 2
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zxloop:
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ldx #$04 ; 2
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wiloop:
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cmp $C051 ; read the floating bus ; 4
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bne zxloop ; if not, start from scratch ; 2/3
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dex ; we were, dec ; 2
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bne wiloop ; if not 4 of them, restart ; 3/2
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; if we get here we read 4 proper pixels, 11 apart (2+4+2+2+3)
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; 0 11 22 33, clock at 34
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; 1 12 23 34, clock at 35
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; 2 13 24 35, clock at 36
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; 3 14 25 36, clock at 37
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; 4 15 26 37, clock at 38
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; 5 16 27 38, clock at 39
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; 6 17 28 39, clock at 40
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; X X X X
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; X X X X
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; X X X X
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; X X X X
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; X X X X
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; X X X X
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; X X X X
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; 0123456789012345678901234 0123456789012345678901234567890123456789
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; 1 2 1 2 3
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; hsync pixels
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; XXXXXXXXXXXXXXXXXXXXXXXXX 4444444444444444444444444444440123456789
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; now look for the color change that
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; happens at line 13*8 = 104
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lda #$dd ; 2
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zloop:
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ldx #$04 ; 2
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qloop:
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cmp $C051 ; read floating bus ; 4
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bne zloop ; 2/3
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dex ; 2
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bne qloop ; 3/2
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;============
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; 11
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; Found it!
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; if we get here we read 4 proper pixels, 11 apart (2+4+2+2+3)
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; 0 11 22 33, clock at 34
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; 1 12 23 34, clock at 35
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; 2 13 24 35, clock at 36
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; 3 14 25 36, clock at 37
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; 4 15 26 37, clock at 38
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; 5 16 27 38, clock at 39
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; 6 17 28 39, clock at 40
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;btt:
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; jmp btt
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; In theory near end of line 104
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; now skip ahead 8 lines and read from the rainbow pattern we set
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; up to find our exact location
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; delay 65 * 8 = 520
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; we back off a few to make sure we're not in the horiz blank
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; try to delay 510
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; *NOTE* sometimes we end up going one (or rarely, two??) lines too far
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; so instead try going 7 lines ahead, and if still dd then one more
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; so single step until we get a rainbow color
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; go to next line, -10
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lda #28 ; 2
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jsr delay_a ; delay 25+28 = 53
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; total delay = 55
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vl_try_again:
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lda #29 ; 2
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jsr delay_a ; delay 25+29 = 54
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; total delay = 56
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lda $C051 ; 4
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cmp #$dd ; 2
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beq vl_try_again ; 3
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; -1
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; now near end of line 112
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;lda $0 ; nop to match old code ; 3
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; nop ; nop to match old code ; 2
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lda $C051 ; 4
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;kbb:
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; jmp kbb
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; we are in theory on line $728 = 14*8 = 112
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; so 112*65 = 7280 cycles from start
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; we are actualy 25+20+A pixels in
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; 7325+A
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; Our goal is line 114 at 7410 cycles
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; 7410 - 7325 = 85
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; so kill 85-A cycles
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; -6 to do subtraction
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; -6 for rts
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; -25 for delay_a overhead
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eor #$ff ; 2
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sec ; 2
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adc #48 ; 2
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jsr delay_a ; should total 48 cycles
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done_vapor_lock:
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rts ; 6
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; Some random related work
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; Docs:
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; Lancaster
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; Bishop
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; Sather
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; Vaguely relevant but no help with the Apple II+ issue
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;
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; Eamon: Screen display and timing synchronization
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; on the Apple IIe and Apple IIgs
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;
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; Adams: Visually presented verbal stimuli by assembly
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; language on the Apple II computer.
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; Cavanagh and Anstis: Visual psychophysics on the
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; Apple II: Getting started
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