139 lines
3.2 KiB
ArmAsm
139 lines
3.2 KiB
ArmAsm
; lenser -- multicolor interlace viewer (self-contained)
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;
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; Shows two multicolor frames on alternating fields by flipping the VIC bank in a
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; once-per-frame raster IRQ (no cycle-exact timing needed, so it is robust).
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; Frame A lives in bank 0 (bitmap $2000, screen $0400); frame B in bank 1 (bitmap
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; $6000, screen $4400). Both use $D018=$18; only the $DD00 bank bit toggles.
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;
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; Memory layout of appended data (loads from $2000):
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; $2000 bitmap A 8000
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; $3F40 screen A 1000 (copied to $0400)
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; $4400 screen B 1000 (in place, bank 1 video matrix)
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; $6000 bitmap B 8000
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; $8000 colour RAM 1000 (copied to $D800)
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; $83E8 background 1
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;
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; assembled by viewer/assemble.py via xa
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; BASIC autostart, SYS 2061
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* = $0801
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.word basicend
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.word 10
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.byte $9e
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.byte "2061"
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.byte 0
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basicend:
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.word 0
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SRC = $fb
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DST = $fd
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start:
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sei
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; screen A $3F40 -> $0400
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lda #$40
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sta SRC
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lda #$3f
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sta SRC+1
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lda #$00
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sta DST
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lda #$04
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sta DST+1
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jsr copy1024
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; colour RAM $8000 -> $D800
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lda #$00
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sta SRC
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lda #$80
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sta SRC+1
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lda #$00
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sta DST
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lda #$d8
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sta DST+1
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jsr copy1024
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lda $83e8
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sta $d021 ; background
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lda #$00
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sta $d020 ; border black
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lda $dd00
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and #$fc
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ora #$03
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sta $dd00 ; start on VIC bank 0 (frame A)
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lda #$18
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sta $d018 ; screen $x400, bitmap $x000+$2000
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lda #$d8
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sta $d016 ; multicolor on
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lda #$3b
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sta $d011 ; bitmap mode, display on
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; frame-flip raster IRQ near the bottom border
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lda #<irq
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sta $0314
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lda #>irq
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sta $0315
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lda #$7f
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sta $dc0d
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sta $dd0d
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lda $dc0d
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lda $dd0d
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lda #$01
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sta $d01a
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lda #$fa
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sta $d012 ; line 250
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lda $d011
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and #$7f
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sta $d011
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asl $d019
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cli
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; hold the picture per the display option (our IRQ chains to the KERNAL
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; $ea31 housekeeping, so GETIN and the jiffy clock both work here).
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#include "wait.i"
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; restore text mode + KERNAL IRQ
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sei
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lda #$00
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sta $d01a ; disable raster IRQ
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lda #$81
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sta $dc0d ; re-enable CIA timer IRQ
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lda #$31
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sta $0314
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lda #$ea
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sta $0315
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lda #$1b
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sta $d011
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lda #$c8
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sta $d016
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lda #$15
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sta $d018
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lda $dd00
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ora #$03
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sta $dd00
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asl $d019
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cli
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jsr $e544 ; clear screen
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rts
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; once per frame, flip bank 0 <-> bank 1, then let the KERNAL IRQ finish
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irq:
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lda $dd00
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eor #$01
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sta $dd00
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asl $d019 ; ack raster IRQ
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jmp $ea31 ; KERNAL housekeeping (keyboard) + RTI
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copy1024:
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ldx #4
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ldy #0
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cploop:
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lda (SRC),y
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sta (DST),y
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iny
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bne cploop
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inc SRC+1
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inc DST+1
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dex
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bne cploop
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rts
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