Difference between revisions of "6502"

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=== The 6502 processor  ===
 
=== The 6502 processor  ===
The 6502 processor can be seen as the 8bit micro ARM chip.  
+
The 6502 processor can be seen as the 8-bit micro ARM chip.  
It has only has 3 registers (Accumilator, IX and IY registers) and only a handful of instructions to work with.
+
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 ===
 
=== Zero page ===
 
When using the 6502 for sizecoding, you'll mostly be working from zeropage
 
When using the 6502 for sizecoding, you'll mostly be working from zeropage
  
== Atari 8bit family ==
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=== General 6502 Resources ===
The Atari XE/XL systems consists of the 6502 with custom hardware for graphics and sound.
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* 6502.org http://www.6502.org/
 
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* 6502 instruction reference http://www.6502.org/tutorials/6502opcodes.html
=== Setting up ===
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* 6502 books http://retro.hansotten.nl/6502-sbc/
Setting up your development platform for the Atari 8bit systems is quite easy, first get the following tools:
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* 6502 Assembler tutorial https://dwheeler.com/6502/oneelkruns/asm1step.html
 
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* Easy 6502 code tester https://skilldrick.github.io/easy6502/
* 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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* Synthetic instructions https://wiki.nesdev.com/w/index.php/Synthetic_instructions#8-bit_rotate
* 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.
 
 
 
<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 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
 
 
 
=== Autoboot ===
 
<syntaxhighlight lang="6502">
 
*=$0326
 
        .word start             
 
        .byte $ed,$f6
 
start
 
; rest of code
 
</syntaxhighlight>
 
Will give you autoboot and more space directly. (though writing through to $0400 will load it onto the screen unless you move the pointers)
 
 
 
=== 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
 
 
 
 
 
== Apple II ==
 
The Apple II is an 8-bit home computer and one of the world's first highly successful mass-produced microcomputer products. It was designed primarily by Steve Wozniak.
 
 
 
 
 
=== Setting up ===
 
ACME 6502 cross-assembler(https://sourceforge.net/projects/acme-crossass/)
 
Apple Commander(http://applecommander.sourceforge.net) for batch compilation
 
AppleWin emulator(https://github.com/AppleWin/AppleWin/releases) -supports Mockingboard card(AY-8910+speech synthesier), HDD, Z80 card(for CP/M), mouse etc.
 
CiderPress(https://a2ciderpress.com)
 
 
 
compilation can be done as follows (master.dsk can be found with applewin)
 
acme hl.asm
 
java -jar AppleCommander-1.3.5.jar -d master.dsk hl
 
java -jar AppleCommander-1.3.5.jar -p master.dsk hl B 24576 < hl.bin
 
 
 
=== Memory Map ===
 
  0-255 $0-$FF    ZERO-PAGE SYSTEM STORAGE
 
  256-511      $100-$1FF    SYSTEM STACK
 
  512-767      $200-$2FF    KEYBOARD CHARACTER BUFFER
 
  768-975      $300-$3CF    OFTEN AVAILABLE AS FREE SPACE FOR USER PROGRAMS
 
  976-1023    $3D0-3FF    SYSTEM VECTORS
 
1024-2047    $400-$7FF    TEXT AND LO-RES GRAPHICS PAGE 1 <--- !!!
 
2048-LOMEM    $800-LOMEM  PROGRAM STORAGE
 
2048-3071    $800-$BFF    TEXT AND LO-RES GRAPHICS PAGE 2 OR FREE SPACE
 
3072-8191    $C00-$1FFF  FREE SPACE UNLESS RAM APPLESOFT IS IN USE
 
8192-16383  $2000-$3FFF  HI-RES PAGE 1 OR FREE SPACE <--- !!!
 
16384-24575  $4000-$5FFF  HI-RES PAGE 2 OR FREE SPACE
 
24576-38999  $6000-$95FF  FREE SPACE AND STRING STORAGE
 
38400-49151  $9600-$BFFF  DOS
 
49152-53247  $C000-$CFFF  I/O HARDWARE (RESERVED)
 
53248-57343  $D000-$DFFF  APPLESOFT IN LANGUAGE CARD OR ROM
 
57344-63487  $E000-$F7FF  APPLESOFT OR INTEGER BASIC IN LANGUAGE CARD OR ROM
 
63488-65535  $F800-$FFFF  SYSTEM MONITOR
 
 
 
=== Display ===
 
 
 
=== Graphics Modes ===
 
Text Mode 40x24, 80x25 - use PR#3 for switch mode
 
LoRes(https://en.wikipedia.org/wiki/Apple_II_graphics) 40x48, 16 colors
 
Hires modes:
 
https://www.xtof.info/blog/?p=768
 
https://mrob.com/pub/xapple2/colors.html
 
https://archive.org/details/HiRes_Color_Graphics_on_the_Apple_II_Computer_by_Wozniak
 
 
 
However for sizecoding, you almost never want to do direct-access to graphics for Apple II in size-coding because the Apple II graphics modes are horrible.  The only fast way to do things is with large lookup tables.  To do hires you need to divide by 7 which as you can imagine is a bit difficult to do compactly on 6502. Double-hires is even crazier on top of that.  Deater did manage a color-bar style effect in double-hires in 128B but that was doing some crazy tricks with the firmware BASIC routines, definitely not direct-access.
 
 
 
Lores and Hires can be mixed modes and full-graphics
 
The screen structure is called memory holes(https://retrocomputing.stackexchange.com/questions/2534/what-are-the-screen-holes-in-apple-ii-graphics). The GBASCALC($F847) procedure is used to calculate the address of the horizontal line : IN:reg.A=Y, out : GBASL/GBASH($26/$27)=address. See also https://www.callapple.org/uncategorized/use-of-apple-ii-color-graphics-in-assembly-language/
 
 
 
==== Sound  ====
 
To be added soon.
 
  
=== Additional Resources ===
+
== 6502 Based Platforms ==
* Deater's page on Apple II sizecoding http://www.deater.net/weave/vmwprod/demos/sizecoding.html
+
*'''[[Atari 8Bit]]''' - Atari 8-Bit Family (Atari XL/XE, etc.)
* Article on double hi-res http://www.battlestations.zone/2017/04/apple-ii-double-hi-res-from-ground-up.html
+
*'''[[Apple II]]''' - Apple II(e)
* Applesoft Hi-Res Subroutines : http://hackzapple.org/scripts_php/index.php?menu=5&mod=ASM&sub=AAL&sub2=8112&PHPSESSID=f65fabfd0cdbf56b6bdc0ddac25117c6#a2
+
*'''[[Commodore 64]]''' - Commodore 64
 +
*'''[[BBC Micro]]''' - Acorn BBC Micro/Master/Electron.
 +
*'''[[Atari Lynx]]''' - Atari Lynx Handheld

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