Difference between revisions of "6502"

Revision as of 04:52, 6 July 2020

Introduction

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

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

The 6502 processor

The 6502 processor can be seen as the 8bit micro ARM chip. It has only has 3 registers (Accumilator, IX and IY registers) and only a handful of instructions to work with.

Registers

To be added.

Zero page

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

Atari 8bit family

The Atari XE/XL systems consists of the 6502 with custom hardware for graphics and sound.

Setting up

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 TIA chip, it has the following video modes:

To be added soon.

Getting something on screen

To be added soon.

<syntaxhightlight 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 8bit systems use the Pokey chip to generate sound. To be added soon.

Make some noise

To be added soon.

Additional Resources

Sizecoding resource for the Atari 8bit are sparse

• Fready's github (link to be added)

Atari Lynx

The Atari Lynx consists of the 6502 with custom hardware for graphics and sound.

Setting up

Setting up your development platform for the Atari Lynx:

• Assembler: -
• Emulator(s): -

Video display

To be added soon.

Getting something on screen

To be added soon.

Sound

To be added soon.

Make some noise

To be added soon.

Additional Resources

Sizecoding resource for the Atari Lynx are sparse

• 42Bastian's website (link to be added)

Commodore 64

The Commodore systems consists of the 6502 with custom hardware for graphics and sound.

Setting up

Setting up your development platform for the Commodore systems is quite easy, first get the following tools:

• Assembler: To be added
• Emulator(s): VICE is the way to go

Video display

Video display on the Commodore, it has the following video modes:

To be added soon.

Getting something on screen

To be added soon.

Sound

The Commodore 64 uses the famous SID chip to generate sound. To be added soon.

Make some noise

To be added soon.

Additional Resources

• links to be added