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| | * Easy 6502 code tester https://skilldrick.github.io/easy6502/ | | * Easy 6502 code tester https://skilldrick.github.io/easy6502/ |
| | * Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate | | * Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate |
| − |
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| − | == Atari 8-bit family ==
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| − | The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.<br />
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| − |
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| − | The Atari 8-bit systems consists of the 6502 with custom hardware for graphics and sound.
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| − |
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| − | === Setting up ===
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| − | Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
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| − |
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| − | * Assembler: MADS Assembler - This assembler has nice macros for creating Binaries and SNA snapshot files out of the box. You can download it at https://mads.atari8.info/
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| − | * Emulator(s): I Found Altirra to work best for my usecase. Make sure to use the original Rev2 rom for best compatibility.
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| − |
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| − | ==== Special Memory Adresses ====
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| − | * FRAMECOUNTER_HIGH = 19
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| − | * FRAMECOUNTER_LOW = 20
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| − |
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| − | === Video display ===
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| − | Video display on the Atari 8bit systems use the ANTIC and GTIA chips. Information can be found here:
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| − | * https://en.wikipedia.org/wiki/ANTIC
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| − | * https://www.atariarchives.org/agagd/chapter1.php
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| − |
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| − | ==== Sync with frame ====
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| − | <syntaxhighlight lang="6502">
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| − | RTCLOK equ $0012
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| − | lda RTCLOK+2
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| − | waits
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| − | cmp RTCLOK+2
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| − | beq waits
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| − | </syntaxhighlight>
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| − |
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| − | Or if you don't mind trashing RTCLOK
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| − |
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| − | <syntaxhighlight lang="6502">
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| − | RTCLOK equ $0012
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| − | waits
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| − | lsr RTCLOK+2
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| − | bcc waits
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| − | </syntaxhighlight>
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| − |
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| − | Which is two bytes shorter.
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| − |
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| − | ==== Getting something on screen ====
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| − | <syntaxhighlight lang="6502">
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| − | ;fill screen with charset,(88,89)=an address
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| − | org $600; free 6th page:600-6ff
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| − | ldy #0
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| − | fl: tya
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| − | sta(88),y
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| − | iny
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| − | bne fl
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| − | jmp *
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| − | </syntaxhighlight>
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| − |
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| − | To be added soon.
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| − |
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| − | <syntaxhighlight lang="6502">
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| − | SDMCTL = $022f
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| − | HPOSP0 = $d000
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| − | SIZEP0 = $d008
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| − | GRAFP0 = $d00d
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| − | COLPM0 = $d012
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| − |
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| − | FRAMECOUNTER_HIGH = 19
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| − | FRAMECOUNTER = 20
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| − | WSYNC = $d40a
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| − | VCOUNT = $d40b
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| − |
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| − | sinewave = $0600 ; to $06ff
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| − |
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| − | org $80
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| − |
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| − | main
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| − | ; disable all graphics/colors
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| − | ldx #0
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| − | stx SDMCTL
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| − |
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| − | ldy #$7f
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| − | sty SIZEP0 ; size p0=127
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| − |
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| − | ldx #0
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| − | ldy #$3f
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| − | make_sine:
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| − | value_lo
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| − | lda #0
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| − | clc
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| − | delta_lo
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| − | adc #0
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| − | sta value_lo+1
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| − | value_hi
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| − | lda #0
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| − | delta_hi
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| − | adc #0
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| − | sta value_hi+1
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| − |
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| − | sta sinewave+$c0,x
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| − | sta sinewave+$80,y
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| − | eor #$7f
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| − | sta sinewave+$40,x
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| − | sta sinewave+$00,y
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| − |
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| − | lda delta_lo+1
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| − | adc #8
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| − | sta delta_lo+1
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| − | bcc nothing
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| − | inc delta_hi+1
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| − | nothing
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| − | inx
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| − | dey
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| − | bpl make_sine
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| − |
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| − | updateloop:
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| − | ; vblank
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| − | lda VCOUNT
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| − | bne updateloop
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| − |
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| − | ; clear graphics
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| − | sta HPOSP0
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| − | sta GRAFP0
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| − |
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| − | ldy #0
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| − | lda #47
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| − | sta COLPM0
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| − | yloop:
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| − | tya ; graphics shape = y
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| − | sta WSYNC
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| − | sta GRAFP0
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| − |
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| − | ; a = sin(frame+y)+48
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| − | tya
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| − | adc FRAMECOUNTER
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| − | tax
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| − | lda sinewave,x
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| − | adc #48
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| − | sta HPOSP0
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| − |
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| − | iny
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| − | bne yloop
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| − | jmp updateloop
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| − |
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| − | run main
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| − | </syntaxhighlight>
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| − |
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| − | === Sound ===
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| − | The Atari 8-bit use the POKEY chip to generate sound.
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| − | * https://en.wikipedia.org/wiki/POKEY
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| − |
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| − | ==== BASIC ====
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| − | <syntaxhighlight lang="6502">
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| − | ; from Analog, 1985-09,pp.25-32
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| − | *=$2000
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| − | AUDF1=$D200
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| − | AUDC1=$D201
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| − | AUDCTL=$D208
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| − | SKCTL=$D20F
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| − |
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| − | .MACRO SOUND ; voice,pitch,dist,vol;,dur
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| − | lda #%2
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| − | sta AUDF1+2*%1
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| − | lda #[[%3 * 16] | %4] ;lda #[[%3 shl 4] or %4]
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| − | sta AUDC1+2*%1
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| − | .ENDM
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| − |
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| − | lda #0
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| − | sta AUDCTL
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| − | lda #3
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| − | sta SKCTL
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| − |
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| − | SOUND 0,121,10,8
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| − |
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| − | jmp *
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| − | </syntaxhighlight>
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| − | ==== Make some noise ====
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| − | To be added soon.
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| − |
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| − | === Additional Resources ===
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| − | Sizecoding resource for the Atari 8bit are:
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| − | * Mapping the Atari https://www.atariarchives.org/mapping/
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| − | * Atari 8bit Memory map https://www.atariarchives.org/mapping/memorymap.php
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| − | * Fready's undocumented 6502 opcodes https://github.com/FreddyOffenga/6502
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| − | * Atari OS Rev2 disassembly for MADS assembler https://github.com/ilmenit/A800-OS-XL-Rev2
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| − | * Fready's github https://github.com/FreddyOffenga/
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Wanting to start sizecoding on a 6502 platform in this day and age can be tough.
The 6502 processor can be seen as the 8-bit micro ARM chip.
It has only has 3 registers (Accumulator, X and Y registers) and a handful of instructions to work with.
