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https://github.com/sehugg/8bitworkshop.git
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193 lines
6.2 KiB
Plaintext
193 lines
6.2 KiB
Plaintext
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; Atari 8-bit sample code
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; Written by Daniel Boris (danlb_2000@yahoo.com)
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; Modified by Steven Hugg @8bitworkshop
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; Assemble with DASM
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;
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processor 6502
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include "atari.inc"
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;*************** Variable ***********************
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line equ $20 ;Current DLI line
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pm0pos equ $21 ;Current pos of P0
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;*************** Start of Code *******************
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org $a000 ;Start of cartridge area
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Start
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;************* Setup display list *******************
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ldx #$21 ;Number of bytes in list
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dlloop ;Copy display list to RAM
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lda dlist,x ;Get byte
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sta $1000,x ;Copy to RAM
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dex ;next byte
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bpl dlloop
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;************* Setup hardware registers *************
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lda #$22 ;Set color PF0
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sta COLOR0
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lda #$0F ;Set color PF1
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sta COLOR1
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lda #$84 ;Set color PF2
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sta COLOR2
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lda #$00 ;Set Display list pointer
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sta SDLSTL
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lda #$10
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sta SDLSTH
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lda #$f8 ;Set Charcter Set Base
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sta CHBAS
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lda #$22 ;Enable DMA
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sta SDMCTL
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; load display list interrupt address
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lda #<dli
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sta VDSLST
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lda #>dli
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sta VDSLST+1
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; activate display list interrupt and vertical blank interrupt
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lda #$C0
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sta NMIEN
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;************ Draw display graphics *******************
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ldy #$02 ;Draw bars on screen
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lda #$18 ;Screen memory starts at $1800
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sta $81
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lda #$00
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sta $80
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ldx #$18
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crloop5
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lda #$FF ;Bar 4 pixels wide of color 3
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sta ($80),y ;Store data
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iny
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iny ;Skip 4 pixels
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lda #$55 ;Bar 4 pixels wide of color 1
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sta ($80),y ;Store data
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iny
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iny ;Skip 4 pixels
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lda #$AA ;Bar 4 pixels wide of color 2
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sta ($80),y ;Store data
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tya
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clc
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adc #$06 ;Move pointer to next line
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tay
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dex ;Next line
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bne crloop5 ;Branch if not done
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;************* Setup Player/Missile registers ***************
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lda #$3A ;Enable DMA (single line resolution/
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sta SDMCTL ;normal background)
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lda #$20 ;Set PM base address ($200)
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sta PMBASE
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lda #$03 ;Enable players and missiles
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sta GRACTL
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lda #$16 ;Color of player 0
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sta PCOLR0
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ldy #$00
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lda #$02 ;Size of player 0
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sta SIZEP0
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lda #$01 ;Give players priority over playfield
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sta GPRIOR
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;************ Copy player data to RAM ********************************
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pmloop1
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lda pm1,y ;Get data
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sta $2430,y ;Write it into RAM
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sta $24C0,y
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iny
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cpy #$08 ;Copy 8 bytes
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bne pmloop1
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;************ Move player ********************************************
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ldx #$20 ;Starting position of player
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mvloop1
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jsr waitvb ;Wait for a vertical bank
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lda #$00 ;Reset line counter
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sta line
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stx HPOSP0 ;Set position of player
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stx pm0pos ;Save position for DLI
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inx
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cpx #$C0 ;Check for end of move
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bne mvloop1 ;If not keep moving right
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lda #$04 ;Give playfield priority player
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sta GPRIOR
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mvloop2
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jsr waitvb ;Wait for a vertical blank
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lda #$00 ;Reset line counter
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sta line
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stx HPOSP0 ;Set position of player
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stx pm0pos ;Save position for DLI
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dex
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cpx #$30 ;Check for end of move
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bne mvloop2 ;If not keep moving left
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lda #$01 ;Give player priority over playfield
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sta GPRIOR
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jmp mvloop1 ;Continue looping
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;************ Wait for vertical blank ************************
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waitvb
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lda RTCLOK+2 ;Read timer (this is incremented during VB)
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waitvb2
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cmp RTCLOK+2 ;Did it change?
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beq waitvb2 ;If not keep waiting
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rts
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;************ Display list interrupt ************************
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dli
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pha ;Save A
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inc line ;Increment the line counter
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lda line ;Past the fifth DLI?
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cmp #$05
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bne done ;If not then exit DLI
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lda pm0pos ;Get player 0 position
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eor #$FF ;Invert it
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sta HPOSP0 ;Set player 0 position
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lda #$0F ;Change player color
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sta COLPM0 ;
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; Note: Player color is changed in hardware register not the shadow
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; register so it takes effect immediatly.
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done
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pla ;Restore A
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rti ;Done
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;************* Display list data ****************************
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; starts at $1000
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dlist .byte $70,$70,$70 ;24 blank scanlines
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.byte $48,$00,$18 ;Mode 8 and Load memory scan $1800
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.byte $88,$88,$88,$88,$88,$88,$88 ;23 more line of mode 8
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.byte $88,$88,$88,$88,$88,$88,$88,$88,$88,$88,$88,$88,$88
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.byte $88,$88,$88
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.byte $41,$00,$10 ;Jump back to start at $1000
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;************* Player shape *********************************
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pm1 .byte %00111100
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.byte %01000010
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.byte %10100101
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.byte %10000001
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.byte %10100101
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.byte %10011001
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.byte %01000010
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.byte %00111100
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;************** Cart reset vector **************************
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;Cartridge footer
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org CARTCS
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.word Start ; cold start address
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.byte $00 ; 0 == cart exists
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.byte $04 ; boot cartridge
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.word Start ; start
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