167 lines
3.1 KiB
NASM
167 lines
3.1 KiB
NASM
processor 6502
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srcPointer = $b5
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dstPointer = $b7
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dstPointerEnd = $b9
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fake_current_byte = $126
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count = $128
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org $a000
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; autostart cartridge magic number
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WORD coldstart
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WORD coldstart
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BYTE #$41, #$30, #$c3, #$c2, #$cd
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coldstart SUBROUTINE
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cld
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sei
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jsr $fd8d ; initialize and test RAM
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jsr $fd52 ; restore default I/O vectors
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jsr $fdf9 ; initialize I/O registers
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jsr $e518 ; initialize hardware
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cli ; enable interrupts
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lda $0288
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sta $0294
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jsr $e45b ; initialize BASIC vector table
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jsr $e3a4 ; initialize BASIC RAM locations
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jsr $e404 ; print startup message and initialize memory pointers
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ldx #$fb ; value for stack start
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txs ; set stack pointer
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lda #$76 ; set "READY." pointer
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ldy #$c3
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jsr $cb1e ; print null terminated string
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lda #$80 ; set for control messages only
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jsr $ff90 ; control kernal messages
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.oracopio:
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jsr copycode
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.almost_ready:
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; set current BASIC line number
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lda #$ff
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sta $3a
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lda #0
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sta $3b
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; set start of variables
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lda #<($1001 + demo_end - demo_start)
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sta $2d
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lda #>($1001 + demo_end - demo_start)
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sta $2e
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jsr clear_color_ram
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; print informative message for user
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lda #<message
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ldy #>message
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jsr $cb1e ; print null terminated string
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; install fake chrin to hijack custom commands
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sei
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lda #<fake_chrin
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sta $324
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lda #>fake_chrin
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sta $325
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cli
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jmp $c483 ; BASIC
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; custom hijacked command line
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fake_input_line:
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BYTE "RUN",#$0d,#0,#0,#0
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fake_chrin SUBROUTINE
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ldy fake_current_byte
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lda fake_input_line,y
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iny
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sty fake_current_byte
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cpy #5
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bne .end_fake_chrin
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dey
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sty fake_current_byte
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.end_fake_chrin:
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clc
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rts
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clear_color_ram SUBROUTINE
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lda #$02
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ldx #$00
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.loop:
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sta $9600,x
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sta $9700,x
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dex
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bne .loop
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rts
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; This routine does a lot of unnecessary things,
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; but I added a lot of garbage things to debug it,
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; because it did not work as intended.
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; In the end, the problem was elsewhere, as usual.
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copycode SUBROUTINE
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sei
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lda #0
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sta count
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sta count + 1
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lda #<demo_start
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sta srcPointer
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lda #>demo_start
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sta srcPointer + 1
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lda #$01
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sta dstPointer
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lda #$10
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sta dstPointer + 1
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ldy #0
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copyloop:
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lda (srcPointer),y
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sta (dstPointer),y
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inc srcPointer
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bne .noinc1
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inc srcPointer + 1
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.noinc1:
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inc dstPointer
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bne .noinc2
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inc dstPointer + 1
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.noinc2:
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inc count
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bne .noinc3
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inc count + 1
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.noinc3:
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; lenght of program to copy
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lda count
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cmp #<DEMO_LEN
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bne copyloop
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lda count + 1
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cmp #>DEMO_LEN
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bne copyloop
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cli
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.finito:
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rts
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message:
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BYTE #$0d,#$0d,"PLEASE WAIT 20 SEC",#$0d,"I'M JUST",#$0d,"AN OLD COMPUTER",#$0d,#0
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; https://www.commodore.ca/manuals/funet/cbm/vic20/demos.basic/unexpanded/Stillenacht.prg
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demo_start:
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.incbin "build/demo.raw"
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demo_end:
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DEMO_LEN SET demo_end - demo_start
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ECHO DEMO_LEN
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. = $bffc
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jmp coldstart
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. = $bfff
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BYTE #$ff
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