Difference between revisions of "6502"

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* 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
  
== Atari 8-bit family ==
+
== 6502 Based Platforms ==
The systems in this family are: Atari 400, 800, 5200, 1200XL, 600XL, 800XL, 130XE, 65XE, 800XE and XEGS.<br />
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*'''[[Atari 8Bit]]''' - Atari 8-Bit Family (Atari XL/XE, etc.)
 
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*'''[[Apple II]]''' - Apple II(e)
The Atari 8-bit systems consists of the 6502 with custom hardware for graphics and sound.
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*'''[[Commodore 64]]''' - Commodore 64
 
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*'''[[BBC Micro]]''' - Acorn BBC Micro/Master/Electron.
=== Setting up ===
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*'''[[Atari Lynx]]''' - Atari Lynx Handheld
Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
 
 
 
* 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/
 
* Emulator(s): I Found Altirra to work best for my usecase. Make sure to use the original Rev2 rom for best compatibility.
 
 
 
==== Special Memory Adresses ====
 
* FRAMECOUNTER_HIGH = 19
 
* FRAMECOUNTER_LOW  = 20
 
 
 
=== Video display ===
 
Video display on the Atari 8bit systems use the ANTIC and GTIA chips. Information can be found here:
 
* https://en.wikipedia.org/wiki/ANTIC
 
* https://www.atariarchives.org/agagd/chapter1.php
 
 
 
==== Sync with frame  ====
 
<syntaxhighlight lang="6502">
 
RTCLOK      equ $0012
 
      lda RTCLOK+2
 
waits
 
      cmp RTCLOK+2
 
      beq waits
 
</syntaxhighlight>
 
 
 
Or if you don't mind trashing RTCLOK
 
 
 
<syntaxhighlight lang="6502">
 
RTCLOK      equ $0012
 
waits
 
      lsr RTCLOK+2
 
      bcc waits
 
</syntaxhighlight>
 
 
 
Which is two bytes shorter.
 
 
 
==== Getting something on screen ====
 
<syntaxhighlight lang="6502">
 
;fill screen with charset,(88,89)=an address
 
org $600; free 6th page:600-6ff
 
ldy #0
 
fl: tya
 
sta(88),y
 
iny
 
bne fl
 
jmp *
 
</syntaxhighlight>
 
 
 
To be added soon.
 
 
 
<syntaxhighlight lang="6502">
 
SDMCTL = $022f
 
HPOSP0  = $d000
 
SIZEP0  = $d008
 
GRAFP0  = $d00d
 
COLPM0  = $d012
 
 
 
FRAMECOUNTER_HIGH = 19
 
FRAMECOUNTER = 20
 
WSYNC = $d40a
 
VCOUNT = $d40b
 
 
 
sinewave = $0600 ; to $06ff
 
 
 
org $80
 
 
 
main
 
; disable all graphics/colors
 
ldx #0
 
stx SDMCTL
 
 
 
ldy #$7f
 
sty SIZEP0 ; size p0=127
 
 
ldx #0
 
ldy #$3f
 
make_sine:
 
value_lo
 
lda #0
 
clc
 
delta_lo
 
adc #0
 
sta value_lo+1
 
value_hi
 
lda #0
 
delta_hi
 
adc #0
 
sta value_hi+1
 
 
sta sinewave+$c0,x
 
sta sinewave+$80,y
 
eor #$7f
 
sta sinewave+$40,x
 
sta sinewave+$00,y
 
 
lda delta_lo+1
 
adc #8
 
sta delta_lo+1
 
bcc nothing
 
inc delta_hi+1
 
nothing
 
inx
 
dey
 
bpl make_sine
 
 
 
updateloop:
 
; vblank
 
lda VCOUNT
 
bne updateloop
 
 
 
; clear graphics
 
sta HPOSP0
 
sta GRAFP0
 
 
 
ldy #0
 
lda #47
 
sta COLPM0
 
yloop:
 
tya          ; graphics shape = y
 
sta WSYNC
 
sta GRAFP0
 
 
 
; a = sin(frame+y)+48
 
tya
 
adc FRAMECOUNTER
 
tax
 
lda sinewave,x
 
adc #48
 
sta HPOSP0
 
               
 
                iny
 
                bne yloop
 
jmp updateloop
 
 
 
run main
 
</syntaxhighlight>
 
 
 
=== Sound ===
 
The Atari 8-bit use the POKEY chip to generate sound.
 
* https://en.wikipedia.org/wiki/POKEY
 
 
 
==== BASIC ====
 
<syntaxhighlight lang="6502">
 
; from Analog, 1985-09,pp.25-32
 
*=$2000
 
AUDF1=$D200
 
AUDC1=$D201
 
AUDCTL=$D208
 
SKCTL=$D20F
 
 
 
.MACRO SOUND ; voice,pitch,dist,vol;,dur
 
lda #%2
 
sta AUDF1+2*%1
 
    lda #[[%3 * 16] | %4] ;lda #[[%3 shl 4] or %4]
 
    sta AUDC1+2*%1
 
.ENDM
 
 
 
lda #0
 
sta AUDCTL
 
lda #3
 
sta SKCTL
 
 
 
SOUND 0,121,10,8
 
 
 
jmp *
 
</syntaxhighlight>
 
==== Make some noise ====
 
To be added soon.
 
 
 
=== Additional Resources ===
 
Sizecoding resource for the Atari 8bit are:
 
* Mapping the Atari https://www.atariarchives.org/mapping/
 
* Atari 8bit Memory map https://www.atariarchives.org/mapping/memorymap.php
 
* Fready's undocumented 6502 opcodes https://github.com/FreddyOffenga/6502
 
* Atari OS Rev2 disassembly for MADS assembler https://github.com/ilmenit/A800-OS-XL-Rev2
 
* Fready's github https://github.com/FreddyOffenga/
 

Latest revision as of 10:41, 8 April 2022

Introduction

Wanting to start sizecoding on a 6502 platform in this day and age can be tough.

6502.jpg

So here is a bit of help to get you started:

The 6502 processor

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.

Adressing modes

To be added.

Zero page

When using the 6502 for sizecoding, you'll mostly be working from zeropage

General 6502 Resources

6502 Based Platforms